EP4687544A1

EP4687544A1 - Heater assembley with a curved surface

Info

Publication number: EP4687544A1
Application number: EP24714503.0A
Authority: EP
Inventors: Jérôme Christian COURBAT; Leander Dittmann; Ross Peter Jones
Original assignee: Philip Morris Products SA
Current assignee: Philip Morris Products SA
Priority date: 2023-03-29
Filing date: 2024-03-28
Publication date: 2026-02-11
Also published as: WO2024200743A1; JP2026513180A; CN121001595A; KR20250160220A; WO2024200743A9

Abstract

A heater assembly (300) for an aerosol-generating system, the heater assembly (300) comprising: a heating element (110) for vaporising a liquid aerosol-forming substrate; and a porous body (320) for conveying the liquid aerosol-forming substrate to the heating element (110), the porous body (320) having a liquid absorption surface (321), a heating surface (122) and at least one side surface extending from the liquid absorption surface (321) to the heating surface (122), wherein the heating element (110) is located on the heating surface (122) of the porous body (320), wherein the heating surface (122) of the porous body (120) is convex in one or both of a first transverse direction and a second transverse direction, wherein the heating surface (122) of the porous body (120) has a width (123) that is different to a width (323) of the liquid absorption surface (321) in a same transverse direction, and wherein the porous body (320) comprises a porous ceramic body or a porous glass body.

Description

HEATER ASSEMBLEY WITH A CURVED SURFACE

The present invention relates to a heater assembly for an aerosol-generating system. The invention also relates to an aerosol-generating system comprising the heater assembly.

Aerosol-generating systems that heat a liquid aerosol-forming substrate in order to generate an aerosol for delivery to a user are generally known in the prior art. These systems typically comprise an aerosol-generating device and a replaceable cartridge. The cartridge includes a liquid aerosol-forming substrate that is capable of releasing volatile compounds when heated. The cartridge typically also includes a heater for heating the liquid aerosolforming substrate. In known aerosol-generating systems, the heater comprises a resistive heating element wound around a wick that supplies liquid aerosol-forming substrate to the heating element. The aerosol-generating device or cartridge also comprises a mouthpiece. When a negative pressure is applied at the mouthpiece, an electric current is passed through the heating element causing it to be heated by resistive or Joule heating, which, in turn, heats the liquid aerosol-forming substrate supplied by the wick. This causes volatile compounds to be released from the liquid aerosol-forming substrate that cool to form an aerosol. The aerosol is then drawn into a user’s mouth via the mouthpiece.

In some other known aerosol-generating systems, the aerosol-generating system comprises a heater assembly having a resistive heating element located on a heating surface of a porous body. Liquid aerosol-forming substrate is supplied from a liquid storage portion to the heating element via the pores of the porous body by capillary action.

In such an aerosol-generating system, vaporisation of liquid aerosol-forming substrate may be limited by the size of the porous body and of the heating surface. However, there may be constraints on the size of the porous body and of the heating surface due to the shape, size and configuration of the aerosol-generating system and other components of the aerosolgenerating system. Where the porous body is relatively small, it may be difficult to generate an acceptable aerosol.

Typically, the porous body of the heater assembly has a flat heating surface. In an aerosol-generating system comprising such a heater assembly, airflow adjacent the heater assembly may be turbulent due to recirculation. This may particularly be the case of airflow adjacent to a central region of the heater assembly. Turbulent airflow adjacent the heater assembly his may result in less vapour of aerosol-forming substrate being entrained in air drawn through the aerosol-generating system. This may adversely impact the quality of the aerosol generated.

Vapour not entrained in air drawn through the aerosol-generating system may condense to form large droplets of liquid aerosol-forming substrate. Inhalation of the large droplets of liquid aerosol-forming substrate may result in an unpleasant and undesirable user experience.

Vapour not entrained in air drawn through the aerosol-generating system may condense on internal surfaces of the aerosol-generating system. Condensation within the aerosol-generating system may damage the aerosol-generating system, for example, by corroding surfaces or damaging circuitry.

It would be desirable to provide a heater assembly that improves the quality of aerosol delivered to a user. It would be desirable to provide a heater assembly that avoids or minimises damage to the aerosol-generating system.

The present disclosure relates to a heater assembly for an aerosol-generating system. The heater assembly may comprise a heating element for vaporising a liquid aerosol-forming substrate. The heater assembly may comprise a porous body for conveying the liquid aerosolforming substrate to the heating element. The porous body may be a porous body. The porous body may have a liquid absorption surface. The porous body may have a heating surface. The heating element may be located on the heating surface of the porous body. The heating surface of the porous body may be convex in one or both of a first transverse direction and a second transverse direction, the first transverse direction being orthogonal to the second transverse direction. The porous body may comprise a porous ceramic body or a porous glass body.

According to a first aspect of the invention, there is provided a heater assembly for an aerosol-generating system, the heater assembly comprising: a heating element for vaporising a liquid aerosol-forming substrate; and a porous body for conveying the liquid aerosol-forming substrate to the heating element, the porous body having a liquid absorption surface and a heating surface, wherein the heating element is located on the heating surface of the porous body, wherein the heating surface of the porous body is convex in one or both of a first transverse direction and a second transverse direction, the first transverse direction being orthogonal to the second transverse direction, and wherein the porous body comprises a porous ceramic body or a porous glass body.

The present disclosure also relates to an aerosol-generating system. The aerosolgenerating system may comprise a heater assembly as described above. The aerosolgenerating system may comprise a cartridge. The cartridge may comprise a liquid storage portion for storing a liquid aerosol-forming substrate. The aerosol-generating system may comprise an aerosol-generating device. The aerosol-generating device may comprise a power supply for supplying power to the heater assembly. The aerosol-generating device may comprise control circuitry for controlling the supply of power from the power supply to the heater assembly. The heater assembly may be component of either the cartridge or the aerosol-generating device. According to a second aspect of the invention, there is provided an aerosol-generating system comprising: a heater assembly according to the first aspect of the invention; a cartridge comprising a liquid storage portion for storing a liquid aerosol-forming substrate; and an aerosol-generating device comprising a power supply for supplying power to the heater assembly and control circuitry for controlling the supply of power from the power supply to the heater assembly, wherein the heater assembly is a component of either the cartridge or the aerosol-generating device.

As used herein, the term “liquid aerosol-forming substrate” is used to describe to a liquid substrate capable of releasing volatile compounds that can form an aerosol. Such volatile compounds may be released by heating the liquid aerosol-forming substrate.

As used herein, the term “aerosol” is used to describe a dispersion of solid particles, liquid droplets, or a combination of solid particles and liquid droplets, in a agas. The aerosol may be visible or invisible. The aerosol may include vapours of substances that are ordinarily liquid or solid at room temperature as well as solid particles, liquid droplets, or a combination of solid particles and liquid droplets.

As used herein, the term “cartridge” and “aerosol-generating cartridge” is used to describe a component that contains, or is configured to contain, a liquid aerosol-forming substrate. The cartridge interacts with an aerosol-generating device to generate an aerosol.

As used herein, the term “aerosol-generating device” is used to describe a device that interacts with a liquid aerosol-forming substrate to generate an aerosol.

As used herein, the term “heating element” is used to describe a component that generates heat and transfers heat energy to the liquid aerosol-forming substrate. It will be appreciated that the heating element may be located directly on the porous body or indirectly on the porous body. It will be appreciated that the heating element may be integrally formed with the porous body.

As used herein, the term “porous body” is used to describe a component that has a plurality of pores, at least some of which are interconnected. The porous body is configured to contain liquid within the plurality of pores. The porous body of the heater assembly in accordance with the first aspect of the invention comprises a porous ceramic body or a porous glass body. The porous body may be a porous ceramic body or a porous glass body.

As used herein, the term “porous ceramic body” is used to describe a body or plug comprising a porous ceramic, the porous ceramic having a plurality of pores. The body or plug may be formed of a porous ceramic material.

As used herein, the term “heating surface” refers to the surface of the porous body nearest to the heating element. The heating surface of the porous body may be in contact with the heating element. As used herein, the term “liquid absorption surface” refers to the surface of the porous body opposing the heating surface. In use, the liquid absorption surface may be arranged to receive liquid aerosol-forming substrate from a liquid storage portion or reservoir of liquid aerosol-forming substrate.

As used herein, the term “longitudinal axis” is used to describe the axis extending between the liquid absorption surface of the porous body and the heating surface of the porous body.

As used herein, the term “longitudinal” is used to describe the direction between the liquid absorption surface of the porous body and the heating surface of the porous body. During use of the heater assembly, liquid aerosol-forming substrate is drawn from the liquid absorptions surface of the porous body to the heating surface of the porous body substantially along the longitudinal direction.

As used herein, the term “length” is used to describe the maximum dimension of the heater assembly, a component of the heater assembly, or a part of the heater assembly in the longitudinal direction. The length of the heater assembly, a component of the heater assembly, or a part of the heater assembly may also be referred to as the height of the heater assembly, a component of the heater assembly, or a part of the heater assembly, respectively. The length of the heater assembly, a component of the heater assembly, or a part of the heater assembly may also be referred to as the thickness of the heater assembly, a component of the heater assembly, or a part of the heater assembly, respectively.

As used herein, the term “’’transverse” is used to describe a direction perpendicular to the longitudinal direction. Unless otherwise stated, references to the “cross-section” of the heater assembly, a component of the heater assembly, or a part of the heater assembly refer to the transverse cross-section.

As used herein, the term “width” denotes the maximum dimension of the heater assembly, a component of the heater assembly, or a part of the heater assembly in a transverse direction.

Heating assemblies according to the first aspect of the invention comprise a porous body having a heating surface that is convex in one or both of a first transverse direction and a second transverse direction, the first transverse being orthogonal to the second transverse direction, wherein the porous body comprises a porous ceramic body or a porous glass body. Inclusion of such a porous body may enable the surface area of the heating surface to be increased without increasing a volume of the porous body. This may increase the efficiency of the heater assembly at vaporising liquid aerosol-forming substrate, since it may enable the surface area of the heating assembly that is available for vaporising the liquid aerosol-forming substrate to be increased without increasing the volume of the porous body through which heat loss may occur via conduction. The provision of a heating surface that is convex in one or both of a first transverse direction and a second transverse direction may enable the surface area of the heating surface to be increased without increasing a width of the heating surface. This may increase the efficiency of the heater assembly at vaporising liquid aerosol-forming substrate, whilst helping to avoid the need to redesign other components of the aerosol-generating system to accommodate the porous body.

The provision of a heating surface that is convex along one or both of a first transverse direction and a second transverse direction may help to avoid or minimise recirculation of airflow adjacent the heater assembly. In particular, a heating surface that is convex may help to avoid or minimise recirculation of airflow adjacent to a central region of the heater assembly. This may reduce a level of turbulence in the airflow adjacent to the heater assembly. Reducing a level of turbulence in the airflow adjacent to the heater assembly may improve the entrainment of vapour of aerosol-forming substrate in the airflow. This may improve the quality of the aerosol generated by the aerosol-generating system.

Improving the entrainment of vapour in the airflow through the aerosol-generating system may avoid or reduce vapour condensing to form large droplets of liquid aerosol-forming substrate. This may help to avoid an unpleasant and undesirable user experience.

Improving the entrainment of vapour in the airflow through the aerosol-generating system may avoid or reduce condensation of vapour on internal surfaces of the aerosolgenerating system. This may help to avoid or minimise damage to the aerosol-generating system and may allow optimal function of the aerosol-generating system.

The heating surface of the porous body may be convex in a single transverse direction.

The heating surface of the porous body may be convex in both the first transverse direction and the second transverse direction.

The heating surface of the porous body may be convex in one or both of the first transverse direction and the second transverse direction based on the configuration of the heater assembly relative to one or more airflow pathways of the aerosol-generating system. The heater assembly may be configured to minimise a level of turbulence in the airflow adjacent to the heater assembly. For example, it may be advantageous for the heater assembly to be arranged in the aerosol-generating system such that air drawn into the aerosolgenerating system follows a curved path along at least a portion of a curved surface of the heater assembly.

Where the heating surface is convex in a single transverse direction, the porous body may be prismatic in shape. The longitudinal cross-sectional shape of the porous body may be constant along the entirety of a width of the porous body.

The porous body may comprise one or more longitudinal planes of symmetry. This may simplify assembly of the heater assembly in a cartridge or an aerosol-generating device, since the orientation in which the heater assembly is inserted into the cartridge or the aerosolgenerating device may be less important.

The porous body may comprise at least two longitudinal planes of symmetry.

The porous body may comprise a first longitudinal plane of symmetry, wherein the first transverse direction is parallel to or contained in the first longitudinal plane of symmetry. The porous body may comprise a second longitudinal plane of symmetry, wherein the second transverse direction is parallel to or contained in the second longitudinal plane of symmetry. The porous body may comprise a first longitudinal plane of symmetry and a second longitudinal plane of symmetry.

The porous body may be radially symmetric.

The heater assembly may comprise one or more longitudinal planes of symmetry, the heater assembly comprise one or more longitudinal planes of symmetry corresponding to the one or more longitudinal planes of symmetry of the porous body.

The heating surface of the porous body may have a radius of curvature of at least about 1.5 millimetres, at least about 2 millimetres, or at least about 2.5 millimetres in one or both of the first transverse direction and the second transverse direction.

The heating surface of the porous body may have a radius of curvature of less than or equal to about 10 millimetres, less than or equal to about 8 millimetres, or less than or equal to about 6 millimetres in one or both of the first transverse direction and the second transverse direction.

The heating surface of the porous body may have a radius of curvature of between about 1.5 millimetres and about 10 millimetres, between about 1.5 millimetres and about 8 millimetres, or between about 1.5 millimetres and about 6 millimetres in one or both of the first transverse direction and the second transverse direction.

The heating surface of the porous body may have a radius of curvature of between about 2 millimetres and about 10 millimetres, between about 2 millimetres and about 8 millimetres, or between about 2 millimetres and about 6 millimetres in one or both of the first transverse direction and the second transverse direction.

The heating surface of the porous body may have a radius of curvature of between about 2.5 millimetres and about 10 millimetres, between about 2.5 millimetres and about 8 millimetres, or between about 2.5 millimetres and about 6 millimetres in one or both of the first transverse direction and the second transverse direction.

The smaller the radius of curvature of the heating surface, the greater the curvature of the heating surface.

The larger the radius of curvature of the heating surface, the smaller the curvature of the heating surface. The radius of curvature of the heating surface may be selected based on a balance between a desired surface area of the heating surface and a length and a width of the heater assembly. The radius of curvature of the heating surface may be selected to achieve a desired surface area of the heating surface whilst minimising the amount of material required to form the porous body of the heater assembly. The radius of curvature of the heating surface may be selected to achieve an acceptable level of turbulence in the airflow adjacent to the heater assembly.

A radius of curvature of the heating surface in the first transverse direction may be different to a radius of curvature of the heating surface in the second transverse direction.

A radius of curvature of the heating surface of the porous body in the first transverse direction may be the same as a radius of curvature of the heating surface in the second transverse direction.

The curvature of the heating surface may vary at different positions on the heating surface. The curvature of the heating surface may vary at different positions on the heating surface along one or both of the first transverse direction and the second transverse direction.

The heating surface may be parabolic in one or both of the first transverse direction and the second transverse direction. A longitudinal cross-sectional shape of the heating surface may be parabolic.

The radius of curvature of the heating surface described herein may refer to the radius of curvature of the heating surface at an apex of the heating surface.

The heating surface may have a radius of curvature in the first transverse direction of greater than about half the width of the heating surface in the first transverse direction. The heating surface may have a radius of curvature in the first transverse direction substantially equal to about half the width of the heating surface in the first transverse direction. The heating surface may have a radius of curvature in the first transverse direction of at least about half the width of the heating surface in the first transverse direction.

The heating surface may have a radius of curvature in the second transverse direction of greater than about half the width of the heating surface in the second transverse direction. The heating surface may have a radius of curvature in the second transverse direction substantially equal to about half the width of the heating surface in the second transverse direction. The heating surface may have a radius of curvature in the second transverse direction of at least about half the width of the heating surface in the second transverse direction.

A ratio of the radius of curvature of the heating surface to the width of the heating surface in a same transverse direction may be at least about 0.5. For example, a ratio of the radius of curvature of the heating surface in the first transverse direction to the width of the heating surface in the first transverse direction may be at least about 0.5. As another example, a ratio of the radius of curvature of the heating surface in the second transverse direction to the width of the heating surface in the second transverse direction may be at least about 0.5. A ratio of the radius of curvature of the heating surface in the first transverse direction to the width of the heating surface in the first transverse direction may be at least about 0.5, and a ratio of the radius of curvature of the heating surface in the second transverse direction to the width of the heating surface in the second transverse direction may be at least about 0.5.

A ratio of the radius of curvature of the heating surface in the first transverse direction to the width of the heating surface in the first transverse direction may be at least about 0.5, at least about 0.55, or at least about 0.6.

A ratio of the radius of curvature of the heating surface in the first transverse direction to the width of the heating surface in the first transverse direction may be less than or equal to about 1.2, less than or equal to about 1 , or less than or equal to about 0.8. In some instances, a ratio of the radius of curvature of the heating surface in the first transverse direction to the width of the heating surface in the first transverse direction may be less than or equal to about 5, or less than or equal to about 2.

A ratio of the radius of curvature of the heating surface in the first transverse direction to the width of the heating surface in the first transverse direction may be between about 0.5 and about 5, between 0.5 and about 2, between about 0.5 and about 1.2, between about 0.5 and about 1 , or between about 0.5 and about 0.8.

A ratio of the radius of curvature of the heating surface in the first transverse direction to the width of the heating surface in the first transverse direction may be between about 0.55 and about 5, between 0.55 and about 2, between about 0.55 and about 1.2, between about 0.55 and about 1 , or between about 0.55 and about 0.8.

A ratio of the radius of curvature of the heating surface in the first transverse direction to the width of the heating surface in the first transverse direction may be between about 0.6 and about 5, between 0.6 and about 2, between about 0.6 and about 1.2, between about 0.6 and about 1 , or between about 0.6 and about 0.8.

The ratio of the radius of curvature of the heating surface in the first transverse direction to the width of the heating surface in the first transverse direction described above may be applicable to a ratio of the radius of curvature of the heating surface in the first transverse direction to the width of the porous body in the first transverse direction.

The ratio of the radius of curvature of the heating surface in the first transverse direction to the width of the heating surface in the first transverse direction described above may be applicable to a ratio of the radius of curvature of the heating surface in the first transverse direction to the width of the heater assembly in the first transverse direction. A ratio of the radius of curvature of the heating surface in the second transverse direction to the width of the heating surface in the second transverse direction may be at least about 0.5, at least about 0.55, or at least about 0.6.

A ratio of the radius of curvature of the heating surface in the second transverse direction to the width of the heating surface in the second transverse direction may be less than or equal to about 1 .2, less than or equal to about 1 , or less than or equal to about 0.8. In some instances, a ratio of the radius of curvature of the heating surface in the second transverse direction to the width of the heating surface in the second transverse direction may be less than or equal to about 5, or less than or equal to about 2.

A ratio of the radius of curvature of the heating surface in the second transverse direction to the width of the heating surface in the second transverse direction may be between about 0.5 and about 5, between about 0.5 and about 2, between about 0.5 and about 1.2, between about 0.5 and about 1 , or between about 0.5 and about 0.8.

A ratio of the radius of curvature of the heating surface in the second transverse direction to the width of the heating surface in the second transverse direction may be between about 0.55 and about 5, between about 0.55 and about 2, between about 0.55 and about 1 .2, between about 0.55 and about 1 , or between about 0.55 and about 0.8.

A ratio of the radius of curvature of the heating surface in the second transverse direction to the width of the heating surface in the second transverse direction may be between about 0.6 and about 5, between about 0.6 and about 2, between about 0.6 and about 1.2, between about 0.6 and about 1 , or between about 0.6 and about 0.8.

The ratio of the radius of curvature of the heating surface in the second transverse direction to the width of the heating surface in the second transverse direction described above may be applicable to a ratio of the radius of curvature of the heating surface in the second transverse direction to the width of the porous body in the second transverse direction.

The ratio of the radius of curvature of the heating surface in the second transverse direction to the width of the heating surface in the second transverse direction described above may be applicable to a ratio of the radius of curvature of the heating surface in the second transverse direction to the width of the heater assembly in the second transverse direction.

The heating surface of the porous body may have a width in the first transverse direction less than or substantially equal to the width of the porous body in the first transverse direction. The heating surface of the porous body may have a width in the first transverse direction less than or substantially equal to the width of the heater assembly in the first transverse direction.

The heating surface of the porous body may have a width in the first transverse direction substantially equal to the width of the porous body in the first transverse direction. The heating surface of the porous body may have a width in the first transverse direction substantially equal to the width of the heater assembly in the first transverse direction.

The heating surface of the porous body may have a width in the first transverse direction of at least about 2 millimetres, at least about 3 millimetres, or at least about 4 millimetres. In some instances, the heating surface of the porous body may have a width in the first transverse direction of at least about 0.5 millimetres.

The heating surface of the porous body may have a width in the first transverse direction of less than or equal to about 12 millimetres, less than or equal to about 10 millimetres, or less than or equal to about 8 millimetres.

The heating surface of the porous body may have a width in the first transverse direction of between about 0.5 millimetres and about 12 millimetres, between about 0.5 millimetres and about 10 millimetres, or between about 0.5 millimetres and about 8 millimetres.

The heating surface of the porous body may have a width in the first transverse direction of between about 2 millimetres and about 12 millimetres, between about 2 millimetres and about 10 millimetres, or between about 2 millimetres and about 8 millimetres.

The heating surface of the porous body may have a width in the first transverse direction of between about 3 millimetres and about 12 millimetres, between about 3 millimetres and about 10 millimetres, or between about 3 millimetres and about 8 millimetres.

The heating surface of the porous body may have a width in the first transverse direction of between about 4 millimetres and about 12 millimetres, between about 4 millimetres and about 10 millimetres, or between about 4 millimetres and about 8 millimetres.

As used herein, the width of the heating surface in the first transverse direction is used to describe the maximum dimension of the heating surface in the first transverse direction.

The heating surface of the porous body may have a width in the second transverse direction less than or substantially equal to the width of the porous body in the second transverse direction. The heating surface of the porous body may have a width in the second transverse direction less than or substantially equal to the width of the heater assembly in the second transverse direction.

The heating surface of the porous body may have a width in the second transverse direction substantially equal to the width of the porous body in the second transverse direction. The heating surface of the porous body may have a width in the second transverse direction substantially equal to the width of the heater assembly in the second transverse direction.

The heating surface of the porous body may have a width in the second transverse direction of at least about 2 millimetres, at least about 3 millimetres, or at least about 4 millimetres. In some instances, the heating surface of the porous body may have a width in the second transverse direction of at least 0.5 millimetres. The heating surface of the porous body may have a width in the second transverse direction of less than or equal to about 12 millimetres, less than or equal to about 10 millimetres, or less than or equal to about 8 millimetres.

The heating surface of the porous body may have a width in the second transverse direction of between about 0.5 millimetres and about 12 millimetres, between about 0.5 millimetres and about 10 millimetres, or between about 0.5 millimetres and about 8 millimetres

The heating surface of the porous body may have a width in the second transverse direction of between about 2 millimetres and about 12 millimetres, between about 2 millimetres and about 10 millimetres, or between about 2 millimetres and about 8 millimetres.

The heating surface of the porous body may have a width in the second transverse direction of between about 3 millimetres and about 12 millimetres, between about 3 millimetres and about 10 millimetres, or between about 3 millimetres and about 8 millimetres.

The heating surface of the porous body may have a width in the second transverse direction of between about 4 millimetres and about 12 millimetres, between about 4 millimetres and about 10 millimetres, or between about 4 millimetres and about 8 millimetres.

As used herein, the width of the heating surface in the second transverse direction is used to describe the maximum dimension of the heating surface in the second transverse direction.

The width of the heating surface in the first transverse direction may be different to the width of the heating surface in the second transverse direction.

The width of the heating surface in the first transverse direction may be the same as the width of the heating surface in the second transverse direction.

The heating surface of the porous body according to the first aspect of the invention is curved. Therefore, the heating surface of the porous body has a length greater than zero millimetres.

A substantially flat heating surface may have substantially negligible length. In other words, a substantially flat heating surface may have a length of about zero millimetres.

The heating surface of the porous body may have a length less than the length of the porous body.

The heating surface of the porous body may have a length of at least about 0.5 millimetres, at least about 1 millimetre, or at least about 1.5 millimetres.

The heating surface of the porous body may have a length of less than or equal to about 6 millimetres, less than or equal to about 5 millimetres, or less than or equal to about 4 millimetres.

The heating surface of the porous body may have a length of between about 0.5 millimetres and about 6 millimetres, between about 0.5 millimetres and about 5 millimetres, or between about 0.5 millimetres and about 4 millimetres. The heating surface of the porous body may have a length of between about 1 millimetre and about 6 millimetres, between about 1 millimetre and about 5 millimetres, or between about 01 millimetre and about 4 millimetres.

The heating surface of the porous body may have a length of between about 1.5 millimetres and about 6 millimetres, between about 1.5 millimetres and about 5 millimetres, or between about 1.5 millimetres and about 4 millimetres.

The length of the heating surface may be selected based on a desired curvature of the heating surface. For a given width of the heating surface, increasing the length of the heating surface may increase the curvature of the heating surface. For a given width of the heating surface, decreasing the length of the heating surface may decrease the curvature of the heating surface.

The width of the heating surface in one or both of the first transverse direction and the second transverse direction may be greater than the length of the heating surface.

The width of the heating surface in one or both of the first transverse direction and the second transverse direction may be greater than about double the length of the heating surface. The width of the heating surface in one or both of the first transverse direction and the second transverse direction may be substantially equal to double the length of the heating surface. The width of the heating surface in one or both of the first transverse direction and the second transverse direction may be at least about double the length of the heating surface. In other words, the width of the heating surface in one or both of the first transverse direction and the second transverse direction may be greater than or equal to about double the length of the heating surface.

The width of the heating surface in one or both of the first transverse direction and the second transverse direction may be greater than the length of the heating surface by at least about 1 millimetre, at least about 2 millimetres, or at least about 3 millimetres.

The width of the heating surface in one or both of the first transverse direction and the second transverse direction may be greater than the length of the heating surface by less than or equal to about 7 millimetres, less than or equal to about 6 millimetres, or less than or equal to about 5 millimetres.

The width of the heating surface in one or both of the first transverse direction and the second transverse direction may be greater than the length of the heating surface by between about 1 millimetre and about ? millimetres, between about 1 millimetre and about 6 millimetres, or between about 1 millimetre and about 5 millimetres.

The width of the heating surface in one or both of the first transverse direction and the second transverse direction may be greater than the length of the heating surface by between about 2 millimetres and about 7 millimetres, between about 2 millimetres and about 6 millimetres, or between about 2 millimetres and about 5 millimetres. The width of the heating surface in one or both of the first transverse direction and the second transverse direction may be greater than the length of the heating surface by between about 3 millimetres and about 7 millimetres, between about 3 millimetres and about 6 millimetres, or between about 3 millimetres and about 5 millimetres.

A ratio of the length of the heating surface to the width of the heating surface in one or both of the first transverse direction and the second transverse direction may be at least about 0.02, at least about 0.05, at least about 0.1 , at least about 0.15, or at least about 0.2.

A ratio of the length of the heating surface to the width of the heating surface in one or both of the first transverse direction and the second transverse direction may be less than or equal to about 0.5, less than or equal to about 0.45, or less than or equal to about 0.4.

A ratio of the length of the heating surface to the width of the heating surface in one or both of the first transverse direction and the second transverse direction may be between about 0.02 and about 0.5, between about 0.02 and about 0.45, or between about 0.02 and about 0.4.

A ratio of the length of the heating surface to the width of the heating surface in one or both of the first transverse direction and the second transverse direction may be between about 0.05 and about 0.5, between about 0.05 and about 0.45, or between about 0.05 and about 0.4.

A ratio of the length of the heating surface to the width of the heating surface in one or both of the first transverse direction and the second transverse direction may be between about 0.1 and about 0.5, between about 0.1 and about 0.45, or between about 0.1 and about 0.4.

A ratio of the length of the heating surface to the width of the heating surface in one or both of the first transverse direction and the second transverse direction may be between about 0.15 and about 0.5, between about 0.15 and about 0.45, or between about 0.15 and about 0.4.

A ratio of the length of the heating surface to the width of the heating surface in one or both of the first transverse direction and the second transverse direction may be between about 0.2 and about 0.5, between about 0.2 and about 0.45, or between about 0.2 and about 0.4.

For example, a ratio of the length of the heating surface to the width of the heating surface in one or both of the first transverse direction and the second transverse direction may be about 0.33. In other words, the length of the heating surface may be about a third of the width of the heating surface in one or both of the first transverse direction and the second transverse direction.

The ratio of the length of the heating surface to the width of the heating surface in one or both of the first transverse direction and the second transverse direction may be selected based on a desired curvature of the heating surface. Increasing the ratio of the length of the heating surface to the width of the heating surface in a transverse direction may increase the curvature of the heating surface in that transverse direction. Decreasing the ratio of the length of the heating surface to the width of the heating surface in a transverse direction may decrease the curvature of the heating surface in that transverse direction.

A ratio of the length of the heating surface to the length of the porous body may be at least about 0.05, at least about 0.1 , or at least about 0.15.

A ratio of the length of the heating surface to the length of the porous body may be less than or equal to about 0.45, less than or equal to about 0.4, or less than or equal to about 0.35.

A ratio of the length of the heating surface to the length of the porous body may be between about 0.05 and about 0.45, between about 0.05 and about 0.4, or between about 0.05 and about 0.35.

A ratio of the length of the heating surface to the length of the porous body may be between about 0.1 and about 0.45, between about 0.1 and about 0.4, or between about 0.1 and about 0.35.

A ratio of the length of the heating surface to the length of the porous body may be between about 0.15 and about 0.45, between about 0.15 and about 0.4, or between about 0.15 and about 0.35.

A ratio of the length of the heating surface to the length of the porous body described above may be applicable to a ratio of the length of the heating surface of the porous body to the length of the heater assembly.

The heating surface of the porous body may have a surface area of at least about 1 square millimetre, at least about 3 square millimetres, or at least about 5 square millimetres.

The heating surface of the porous body may have a surface area of less than or equal to about 50 square millimetres, less than or equal to about 45 square millimetres, or less than or equal to about 40 square millimetres.

The heating surface of the porous body may have a surface area of between about 1 square millimetre and about 50 square millimetres, or between about 1 square millimetre and about 45 square millimetres, or between about 1 square millimetre and about 40 square millimetres.

The heating surface of the porous body may have a surface area of between about 3 square millimetres and about 50 square millimetres, or between about 3 square millimetres and about 45 square millimetres, or between about 3 square millimetres and about 40 square millimetres.

The heating surface of the porous body may have a surface area of between about 5 square millimetres and about 50 square millimetres, or between about 5 square millimetres and about 45 square millimetres, or between about 5 square millimetres and about 40 square millimetres.

As used herein, the surface area of the heating surface does not take into account the porosity of the heating surface.

The surface area of the heating surface of the porous body may be selected to generate an aerosol with acceptable quality whilst conforming to the constraints on the size of the porous body.

The heating surface of the porous body may have a surface area greater than the square of the width of the heating surface in one or both of the first transverse direction and the second transverse direction.

The heating surface of the porous body may have a surface area greater than the square of the width of the heating surface in one or both of the first transverse direction and the second transverse direction by at least about 10 percent, at least about 15 percent, or at least about 20 percent.

The heating surface of the porous body may have a surface area greater than the square of the width of the heating surface in one or both of the first transverse direction and the second transverse direction by less than or equal to about 55 percent, less than or equal to about 45 percent, or less than or equal to about 35 percent.

The heating surface of the porous body may have a surface area greater than the square of the width of the heating surface in one or both of the first transverse direction and the second transverse direction by between about 10 percent and about 55 percent, between about 10 percent and about 45 percent, or between about 10 percent and about 35 percent.

The heating surface of the porous body may have a surface area greater than the square of the width of the heating surface in one or both of the first transverse direction and the second transverse direction by between about 15 percent and about 55 percent, between about 15 percent and about 45 percent, or between about 15 percent and about 35 percent.

The heating surface of the porous body may have a surface area greater than the square of the width of the heating surface in one or both of the first transverse direction and the second transverse direction by between about 25 percent and about 55 percent, between about 25 percent and about 45 percent, or between about 25 percent and about 35 percent.

The relationship between the surface area of the heating surface and the width of the heating surface in one or both of the first transverse direction and the second transverse direction may be selected based on a desired available area for heating of the liquid aerosolforming substrate and a curvature of the heating surface of the porous body. For a given width of the heating surface of the porous body, increasing the surface area of the heating surface may increase a curvature of the heating surface. For a given width of the heating surface of the porous body, decreasing the surface area of the heating surface may decrease a curvature of the heating surface.

The porous body may have a width of at least about 2 millimetres, at least about 3 millimetres, or at least about 4 millimetres in one or both of the first transverse direction and the second transverse direction. In some instances, the porous body may have a width of at least about 0.5 millimetres in one or both of the first transverse direction and the second transverse direction.

The porous body may have a width of less than or equal to about 12 millimetres, less than or equal to about 10 millimetres, or less than or equal to about 8 millimetres in one or both of the first transverse direction and the second transverse direction.

The porous body may have a width of between about 0.5 millimetres and about 12 millimetres, between about 0.5 millimetres and about 10 millimetres, or between about 0.5 millimetres and about 8 millimetres in one or both of the first transverse direction and the second transverse direction.

The porous body may have a width of between about 2 millimetres and about 12 millimetres, between about 2 millimetres and about 10 millimetres, or between about 2 millimetres and about 8 millimetres in one or both of the first transverse direction and the second transverse direction.

The porous body may have a width of between about 3 millimetres and about 12 millimetres, between about 3 millimetres and about 10 millimetres, or between about 3 millimetres and about 8 millimetres in one or both of the first transverse direction and the second transverse direction.

The porous body may have a width of between about 4 millimetres and about 12 millimetres, between about 4 millimetres and about 10 millimetres, or between about 4 millimetres and about 8 millimetres in one or both of the first transverse direction and the second transverse direction.

The width of the porous body in one or both of the first transverse direction and the second transverse direction may vary along the length of the porous body. As described further below, the porous body may have a shape that tapers, for example, from the liquid absorption surface of the porous body towards the heating surface of the porous body, or from the heating surface of the porous body towards the liquid absorption surface.

The porous body may have a length of at least about 1 millimetre, at least about 3 millimetres, or at least about 4 millimetres.

The porous body may have a length of less than or equal to about 10 millimetres, less than or equal to about 9 millimetres, or less than or equal to about 8 millimetres. The porous body may have a length of between about 1 millimetre and about 10 millimetres, between about 1 millimetre and about 9 millimetres, or between about 1 millimetre and about 8 millimetres.

The porous body may have a length of between about 3 millimetres and about 10 millimetres, between about 3 millimetres and about 9 millimetres, or between about 3 millimetres and about 8 millimetres.

The porous body may have a length of between about 4 millimetres and about 10 millimetres, between about 4 millimetres and about 9 millimetres, or between about 4 millimetres and about 8 millimetres.

The heater assembly may have a width of at least about 2 millimetres, at least about 3 millimetres, or at least about 4 millimetres in one or both of the first transverse direction and the second transverse direction. In some instances, the heating assembly may have a width of at least about 0.5 millimetres in one or both of the first transverse direction and the second transverse direction.

The heater assembly may have a width of less than or equal to about 12 millimetres, less than or equal to about 10 millimetres, or less than or equal to about 8 millimetres in one or both of the first transverse direction and the second transverse direction.

The heater assembly may have a width of between about 0.5 millimetres and about 12 millimetres, between about 0.5 millimetres and about 10 millimetres, or between about 0.5 millimetres and about 8 millimetres in one or both of the first transverse direction and the second transverse direction.

The heater assembly may have a width of between about 2 millimetres and about 12 millimetres, between about 2 millimetres and about 10 millimetres, or between about 2 millimetres and about 8 millimetres in one or both of the first transverse direction and the second transverse direction.

The heater assembly may have a width of between about 3 millimetres and about 12 millimetres, between about 3 millimetres and about 10 millimetres, or between about 3 millimetres and about 8 millimetres in one or both of the first transverse direction and the second transverse direction.

The heater assembly may have a width of between about 4 millimetres and about 12 millimetres, between about 4 millimetres and about 10 millimetres, or between about 4 millimetres and about 8 millimetres in one or both of the first transverse direction and the second transverse direction.

The heater assembly may have a length of at least about 1 millimetre, at least about 3 millimetres, or at least about 4 millimetres.

The heater assembly may have a length of less than or equal to about 10 millimetres, less than or equal to about 9 millimetres, or less than or equal to about 8 millimetres. The heater assembly may have a length of between about 1 millimetre and about 10 millimetres, between about 1 millimetre and about 9 millimetres, or between about 1 millimetre and about 8 millimetres.

The heater assembly may have a length of between about 3 millimetres and about 10 millimetres, between about 3 millimetres and about 9 millimetres, or between about 3 millimetres and about 8 millimetres.

The heater assembly may have a length of between about 4 millimetres and about 10 millimetres, between about 4 millimetres and about 9 millimetres, or between about 4 millimetres and about 8 millimetres.

The liquid absorption surface body may be substantially flat.

The porous body may comprise at least one longitudinal surface extending from the liquid absorption surface to the heating surface. As used herein, the longitudinal surface may also be referred to as a side surface or a side wall.

The at least one side surface of the porous body may be substantially orthogonal to the liquid absorption surface. Each of the side surfaces of the porous body may be substantially orthogonal to the liquid absorption surface.

The liquid absorption surface of the porous body may have an area that is different to an area of the heating surface of the porous body. As used herein, the area of the liquid absorption surface may also be referred to as the surface area of the liquid absorption surface. As used herein, the area of the heating surface may also be referred to as the surface area of the heating surface.

A heater assembly having a heating surface with the same area as the liquid absorption surface may be inefficient due to heat generated by the heater not being used to vaporise an aerosol-forming substrate. An inefficient heater assembly provides a reduced throughput of aerosol.

Advantageously, providing a porous body in which the heating surface and the liquid absorption surface have different areas may improve the throughput of aerosol that can be generated by the heater assembly compared to a heater assembly in which the heating surface has the same area as the liquid absorption surface.

For example, in a heater assembly in which the area of the heating surface of the porous body is less than the area of the liquid absorption surface of the porous body, heat flow from the heating element towards the liquid absorption surface and then to the liquid storage portion by conduction may be reduced. The relatively smaller heating surface provides a small heat transfer area through which the transfer heat, by conduction, from the heating element to the porous body, and towards the liquid absorption surface.

Decreasing heat loss from the heating element to the bulk of the porous body may consequently increase heating efficiency because more of the heat energy provided by the heating element may be used to vaporise the aerosol-forming substrate. Consequently, the porous body having a shape such that the heating surface has a smaller area than the liquid absorption surface may increase the throughput of aerosol generated by the heater assembly.

For example, in a heater assembly in which the area of the liquid absorption surface of the porous body is less than the area of the heating surface of the porous body, the smaller area of the liquid absorption surface may cause a reduction in heat flow through the aerosolforming substrate from the heating element to the liquid absorption surface via heat conduction.

Reducing heat flow from the heating surface to the liquid absorption surface may consequently increase heating efficiency because more of the heat energy provided by the heating element may be used to vaporise the liquid aerosol-forming substrate. Consequently, the porous body having a shape such that the liquid absorption surface has a smaller area than the heating surface may provide for increased heating efficiency, which may increase the throughput of aerosol generated by the heater assembly.

Increasing heating efficiency may reduce power consumption during use of the heater assembly.

The area of the heating surface of the porous body may be less than the area of the liquid absorption surface of the porous body. The area of the liquid absorption surface of the porous body may be greater than the area of the heating surface of the porous body.

Advantageously, when the porous body has a shape such that the heating surface has a smaller area than the liquid absorption surface, heat flow from the heating element towards the liquid absorption surface and then to the liquid storage portion by conduction may be reduced. The relatively smaller heating surface provides a small heat transfer area through which the transfer heat, by conduction, from the heating element to the porous body, and towards the liquid absorption surface.

Advantageously, the porous body having a shape such that the heating surface has a smaller area than the liquid absorption surface may reduce the area of the heating surface that is not close enough to the heating element to allow aerosol-forming substrate being conveyed to the heating surface to be vaporised. In other words, the size and shape of the heating surface may more closely match with the size and shape of the heating element. Consequently, more of the liquid aerosol-forming substrate may be conveyed from the liquid absorption surface to an area of the heating surface that is near to the heating element, which may result in more of the liquid aerosol-forming substrate at the heating surface being vaporised. More liquid aerosol-forming substrate being vaporised may increase the throughput of aerosol generated by the heater assembly. Further, this arrangement may allow for the power density at the heating surface to be maximised, which also improves heating efficiency.

Advantageously, the liquid absorption surface having a larger area than the heating surface may allow the liquid absorption surface to receive a larger volume of liquid aerosolsubstrate from a liquid storage portion. As a consequence of the relatively smaller area of the heating surface, as the liquid aerosol-forming substrate is conveyed through the porous body and towards the heating surface, the flow rate of the liquid aerosol-forming substrate to the heating element may be higher than with a typical heater assembly. A higher flow rate of liquid aerosol-forming substrate at the heating element may increase the throughput of aerosol generated by the heater assembly.

The area of the heating surface of the porous body may be greater than the area of the liquid absorption surface of the porous body. The area of the liquid absorption surface of the porous body may be less than the area of the heating surface of the porous body.

Advantageously, when the porous body has a shape such that the liquid absorption surface has a smaller area than the heating surface, the smaller area of the liquid absorption surface may cause a reduction in heat flow through the aerosol-forming substrate from the heating element to the liquid absorption surface via heat conduction. Reducing heat flow from the heating surface to the liquid absorption surface may consequently increase thermal efficiency because more of the heat energy provided by the heating element may be used to vaporise the liquid aerosol-forming substrate. Consequently, the porous body having a shape such that the liquid absorption surface has a smaller area than the heating surface may provide for increased heating efficiency, which may increase the throughput of aerosol generated by the heater assembly.

Advantageously, the porous body having a shape such that the liquid absorption surface has a smaller area than the heating surface may reduce the area of the heating surface that is not close enough to the heating element to allow aerosol-forming substrate being conveyed to the heating surface to be vaporised. In other words, the size and shape of the heating surface may more closely match with the size and shape of the heating element. Consequently, more of the liquid aerosol-forming substrate being may be conveyed from the liquid absorption surface and to an area of the heating surface that is near to the heating element, which may result in more of the liquid aerosol-forming substrate at the heating surface being vaporised. More liquid aerosol-forming substrate being vaporised may increase the throughput of aerosol generated by the heater assembly.

The heating surface of the porous body may have a width that is different to a width of the liquid absorption surface of the porous body in a same transverse direction. For example, the heating surface of the porous body may have a width in the first transverse direction that is different to a width of the liquid absorption surface of the porous body in the first transverse direction. The heating surface of the porous body may have a width in the second transverse direction that is different to the width of the liquid absorption surface of the porous body in the second transverse direction. The heating surface of the porous body may have a width in the first transverse direction that is different to a width of the liquid absorption surface of the porous body in the first transverse direction, and the heating surface of the porous body may have a width in the second transverse direction that is different to the width of the liquid absorption surface of the porous body in the second transverse direction.

Where the width of the heating surface of the porous body is different to the width of the liquid absorption surface of the porous body in a same transverse direction, the flow of liquid aerosol-forming substrate to different regions of the heating surface of the porous body may vary. For example, the flow path of liquid aerosol-forming substrate to an edge of the heating surface of the porous body may be longer than the flow path of liquid aerosol-forming substrate to a central region of the heating surface.

The combination of a heating surface of the porous body being convex and the width of the heating surface of the porous body being different to the width of the liquid absorption surface of the porous body in a same transverse direction may reduce any difference in the flow path of liquid aerosol-forming substrate to different regions of the heating surface of the porous body. This may advantageously help to facilitate uniform release of volatile compounds from the liquid aerosol-forming substrate across the heating surface of the porous body. A more uniform release of volatile compounds across the heating surface of the porous body may advantageously result in a more homogenous aerosol being generated.

The width of the heating surface of the porous body may be less than the width of the liquid absorption surface of the porous body in a same transverse direction.

The heating surface of the porous body may have a width in the first transverse direction that is less than the width of the liquid absorption surface of the porous body in the first transverse direction. The heating surface of the porous body may have a width in the second transverse direction that is less than the width of the liquid absorption surface of the porous body in the second transverse direction. The heating surface of the porous body may have a width in the first transverse direction that is less than the width of the liquid absorption surface of the porous body in the first transverse direction, and the heating surface of the porous body may have a width in the second transverse direction that is less than the width of the liquid absorption surface of the porous body in the second transverse direction.

The width of the heating surface of the porous body may be greater than the width of the liquid absorption surface of the porous body in a same transverse direction. The heating surface of the porous body may have a width in the first transverse direction that is greater than the width of the liquid absorption surface of the porous body in the first transverse direction. The heating surface of the porous body may have a width in the second transverse direction that is greater than the width of the liquid absorption surface of the porous body in the second transverse direction. The heating surface of the porous body may have a width in the first transverse direction that is greater than the width of the liquid absorption surface of the porous body in the first transverse direction, and the heating surface of the porous body may have a width in the second transverse direction that is greater than the width of the liquid absorption surface of the porous body in the second transverse direction.

The porous body may have a shape that tapers along at least a part of the length of the porous body. The porous body may have a shape that tapers along the entire length of the porous body.

The flow of liquid aerosol-forming substrate to different regions of the heating surface of the porous body may vary in a porous body having a shape that tapers along at least a part of the length of the porous body. For example, the flow path of liquid aerosol-forming substrate to an edge of the heating surface of the porous body may be longer than the flow path of liquid aerosol-forming substrate to a central region of the heating surface.

The combination of a heating surface of the porous body being convex and a porous body having a shape that tapers along at least a part of the length of the porous body may reduce any difference in the flow path of liquid aerosol-forming substrate to different regions of the heating surface of the porous body. This may advantageously help to facilitate uniform release of volatile compounds from the liquid aerosol-forming substrate across the heating surface of the porous body. A more uniform release of volatile compounds across the heating surface of the porous body may advantageously result in a more homogenous aerosol being generated.

The porous body may comprise a shape that tapers from the liquid absorption surface of the porous body towards the heating surface of the porous body. The porous body may comprise a shape that tapers from the liquid absorption surface of the porous body to the heating surface of the porous body.

The porous body may comprise a shape that tapers from the heating surface of the porous body towards the liquid absorption surface of the porous body. The porous body may comprise a shape that tapers from the heating surface of the porous body to the liquid absorption surface of the porous body.

The porous body comprises porous ceramic body or a porous glass body. In other words, the porous body may be a body comprising a porous ceramic, the porous ceramic having a plurality of pores, wherein at least some of the plurality of pores are interconnected. The porous body may be a body comprising a porous glass, the porous glass having a plurality of pores, wherein at least some of the plurality of pores are interconnected. The porous body may have been manufactured by sintering. The porous body may have been manufactured by directly sintering a ceramic powder, to form a porous body having pores between interconnected powder particles. The porous body may have been manufactured by using a sacrificial material within a ceramic powder, the sacrificial material being used as a spacer to form pores. The sacrificial material may have been burnt off during sintering.

The porous body may advantageously be thermally stable at temperatures at which the heater assembly typically operate. The porous body may advantageously have a thermal decomposition temperature that is significantly higher than that of a conventional wick. This may help to reduce the risk of unwanted by-products being produced during use of the heater assembly.

The porous body may comprise any suitable inert ceramic or bio-compatible ceramic. Examples of suitable ceramics are ceramics comprising aluminium oxides, zirconium oxides, silicon oxides, calcium silicates and calcium phosphate including hydroxyapatite. The porous body may comprise a porous ceramic comprising one or more of: AI2O3, ZrC>2, Ca2SiOs, Sisl^ , SiC, TisAIC2, BN, AIN, SiC>2, MgO, mica, diatomite, silicates, silicides, borides, and glass. The porous body may comprise a ceramic comprising one or more of: AI2O3, ZrC>2, SiC>2 and Ca2SiC>3. Preferably, the porous body comprises a ceramic comprising one or both of SiC>2 and Ca₂SiC>3.

The porous body may be substantially incompressible. The porous body may be incompressible.

The porous body may have a porosity of between about 30 percent and about 70 percent.

The average pore size of the porous body may vary between the liquid absorption surface and the heating surface.

The provision of a porous body which includes a variation of pore size between the liquid absorption surface and the heating surface may advantageously help to control the transport of liquid aerosol-forming substrate from a reservoir of liquid aerosol-forming substrate to the heating element. Specifically, the variation of pore size between the liquid absorption surface and the heating surface may allow the porous body to provide a consistent supply of aerosol-forming substrate to the heating surface. This may advantageously avoid undesirable “dry heating”. In addition, the porous body of the present invention may also advantageously prevent leakage of liquid aerosol-forming substrate from the heating surface of the porous body.

The average pore size of the porous body may vary in any way between the liquid absorption surface and the heating surface. The average pore size may vary from relatively larger pores at the liquid absorption surface to relatively smaller pores at the heating surface. The porous body may have a heating end and a liquid absorption end, the heating surface being disposed at the heating end, and the liquid absorption surface being disposed at the liquid absorption end. The porous body may have a first average pore size at the liquid absorption end, and a second average pore size at the heating end, first average pore size being greater than the second average pore size.

The provision of a porous body having a larger average pore size at the liquid absorption end, and a smaller average pore size at a heating end may particularly facilitate efficient transfer of liquid aerosol-forming substrate from the liquid absorption end of the porous body to the heating end of the porous body without allowing leakage. In particular, the inventors of the present invention have identified that liquid aerosol-forming substrate is transferred from the liquid absorption end of the porous body to the heating end of the porous body by capillary action. How rapidly the liquid aerosol-forming substrate moves through the porous body depends on a number of factors including, but not limited to, the geometry of the pores, the surface tension between the liquid aerosol-forming substrate and the porous body, the viscosity of the liquid aerosol-forming substrate, and the surface tension of the liquid aerosol-forming substrate. The inventors of the present invention have identified the need to balance these factors to provide efficient transfer of liquid aerosol-forming substrate to the heating surface of the porous body while preventing leakage of the liquid aerosol-forming substrate.

Firstly, in order to provide an efficient capillary flow of liquid through the porous body, the capillary pressure must overcome the viscous drag pressure. Secondly, to prevent leakage, inertial forces must not overcome the capillary pressure. These two requirements are realised by providing a porous body with larger pores at the liquid absorption end and smaller pores at the heating end.

In particular, the inventors of the present invention have realised that the viscosity of the liquid aerosol-forming substrate varies with temperature. In particular, the viscosity of the liquid aerosol-forming substrate decreases as its temperature increases. As a result, as the liquid aerosol-forming substrate moves through the porous body from the liquid absorption surface to the heating surface, the viscosity of the liquid aerosol-forming substrate decreases. Since the liquid aerosol-forming substrate is transported through the porous body by capillary forces, the capillary force needs to overcome the viscous drag of the liquid. The viscous drag decreases as viscosity decreases. As a result, the capillary force needed to move the liquid aerosol-forming substrate can decrease towards the heating surface of the porous body while still maintaining the same flow rate. Consequently, the average pore size of the porous body can decrease towards the heating surface without reducing the flow of liquid aerosol-forming substrate through the porous body. The heating element may be an electrical heating element. For example, the heating element may be a resistive heating element. The heating element may have any suitable shape or form. Examples of suitable shapes and forms of the heating element include but are not limited to a band, a strip, a filament, a wire, a mesh, a spiral coil, fibres or a fabric.

The heating element may comprise a mesh. The heating element may comprise an array of filaments forming a mesh. As used herein, the term “mesh” encompasses grids and arrays of filaments having spaces therebetween. The term “mesh” also includes woven and non-woven fabrics.

The filaments may be formed by etching a sheet material, such as a foil. This may be particularly advantageous when the heater assembly comprises an array of parallel filaments. Where the heating element comprises a mesh or fabric of filaments, the filaments may be individually formed and knitted together.

The heating element may comprise an electrically resistive heating element. The heating element may be formed from any suitable electrically conductive material. Suitable materials include but are not limited to: semiconductors such as doped ceramics, electrically conductive ceramics (such as, for example, molybdenum disilicide), carbon, graphite, metals, metal alloys and composite materials made of a ceramic material and a metallic material. Such composite materials may comprise doped or undoped ceramics. Examples of suitable doped ceramics include doped silicon carbides. Examples of suitable metals include titanium, zirconium, tantalum and metals from the platinum group. Examples of suitable metal alloys include stainless steel, constantan, nickel-, cobalt-, chromium-, aluminium-, titanium-, zirconium-, hafnium-, niobium-, molybdenum-, tantalum-, tungsten-, tin-, gallium-, manganese- and iron-containing alloys, and super-alloys based on nickel, iron, cobalt, stainless steel, Timetai®, iron-aluminium based alloys and iron-manganese-aluminium based alloys. Timetai® is a registered trade mark of Titanium Metals Corporation. The heating element may be made from stainless steel, for example, a 300 series stainless steel such as AISI 304, 316, 304L, 316L. In a preferred example, the electrical heating element may comprise one of more of NiCr and TiZr.

Additionally, the heating element may comprise combinations of the above materials. A combination of materials may be used to improve the control of the resistance of the heating element. For example, materials with a high intrinsic resistance may be combined with materials with a low intrinsic resistance. This may be advantageous if one of the materials is more beneficial from other perspectives, for example price, machinability or other physical and chemical parameters. Advantageously, high resistivity heating allow more efficient use of battery energy.

The electrical heating element may be formed from an electrically conductive material deposited onto the heating surface of the porous body. As used herein, the term “electrically conductive material” denotes a material having a resistivity of 1x1 O'² Qm, or less. As used herein, the term “deposited” means applied as a layer or coating by a physical or chemical process, for example in the form of a liquid, plasma or vapour which subsequently condenses or aggregates to form the electrical heating element, rather than simply being laid on or fixed to the porous body as a solid, pre-formed component.

The electrical heating element may be deposited directly onto the heating surface of the porous body. In other words, the electrically conductive material that forms the electrical heating element is deposited onto the heating surface of the porous body such that the electrical heating element is in direct contact with the heating surface of the porous body.

In some examples, the electrically conductive material of the electrical heating element may be at least partially diffused into the heating surface of the porous body. As used herein, the term “diffused into the porous outer surface” means that the electrically conductive material is interspersed with the material of the heating surface of the porous body at the interface between the electrically conductive material and the porous body, for example, by extending into the pores of the porous outer surface. This arrangement may help to secure the electrical heating element to the porous body and increase contact between the electrical heating element and the porous body to improve heating of the liquid aerosol-forming substrate and aerosol delivery.

The electrically conductive material from which the electrical heating element is formed may be deposited onto the heating surface of the porous body in any suitable manner. For example, the electrically conductive material may be deposited onto the heating surface of the porous body as a liquid using a dispensing pipette or syringe, or using a fine- tipped transferring device such as a needle.

The heating element may comprise a printable electrically conductive material printed on the heating surface of the porous body. The printable electrically conductive material may be printed on the heating surface of the porous body using any suitable known printing techniques, such as one or more of screen-printing, gravure printing, flex-printing, inkjet printing. Such printing processes may be particularly applicable for high speed production processes.

The electrically conductive material, from which the electrical heating element is formed, may be deposited onto the heating surface of the porous body by one or more vacuum deposition processes, such as evaporation deposition and sputtering.

The heating element may be formed from any suitable electrically conductive material. The electrically conductive material may comprise one or more of a metal, an electrically conductive polymer and an electrically conductive ceramic.

Suitable electrically conductive metals include, but are not limited to, aluminium, silver, nickel, gold, platinum, copper, tungsten, and alloys thereof. The electrically conductive material may comprise a metal powder suspended in a glue, such as an epoxy resin. In one embodiment, the electrically conductive material comprises silver-loaded epoxy.

Suitable electrically conductive polymers include, but are not limited to, PEDOT (poly(3,4-ethylenedioxythiophene)), PSS (poly(p-phenylene sulfide)), PEDOT: PSS (mixture of both PEDOT and PSS), PANI (polyanilines), PPY (poly(pyrrole)s), PPV (Poly(p-phenylene vinylene)), or any combination thereof.

Suitable electrically conductive ceramics include ITO (Indium Tin Oxide), SLT (lanthanum-doped strontium titanate), SYT (yttrium-doped strontium titanate), or any combination thereof.

The electrically conductive material may further comprise one or more additives selected from a group consisting of: solvents; curing agents; adhesion promoters; surfactants; viscosity reduction agents; and aggregation inhibitors. Such additives may be used, for example, to aid deposition of the electrically conductive material on the heating surface of the porous body, to increase the amount by which the electrically conductive material diffuses into the heating surface of the porous body, to reduce the time required for the electrically conductive material to set, to increase the level of adhesion between the electrically conductive material and the porous body, or to reduce the amount of aggregation of suspended particles, such as metal particles or powder, in the electrically conductive material prior to application onto the heating surface of the porous body.

The heating element may comprise a plurality of tracks or track portions arranged electrically in parallel. The heating element resistance at room temperature may be between 0.5 Ohms and 1.5 Ohms, preferably between 0.7 Ohms and 1.3 Ohms, and more preferably 1 Ohm. The resistance of the heating element may be matched to requirements of control electronics.

At least two of the electrically parallel heating tracks may have similar resistances to each other, or have the same resistance as each other. Preferably, all of the electrically parallel heating tracks are of similar or of the same resistance as each other. The heating tracks arranged electrically in parallel may have different resistances, which is particularly beneficial in a heater assembly where it is advantageous for zones of the heating element to generate different power levels. This could be the case, for example, to compensate for higher thermal losses in an outer part of the heating element. As such, heating tracks on an exterior or outer part of the heating element may be designed to have a lower resistance (which can generate more heat) than heating tracks in the centre of the heating element.

The heating element may comprise a plurality of tracks or track portions. The plurality of tracks or track portions may be arranged electrically in parallel. By being arranged electrically in parallel, current flow is split into separate parallel flow paths, the separate parallel flow paths being subsequently re-combined. The heating element may comprise a first connecting pad and a second connecting pad. The first or second connecting pads (or first and second connecting pads) may be configured to allow connection to an external circuit. An aperture or plurality of apertures in the heating element may separate each track or track portion. The heating element may comprise at least one diverging portion, in which current is split from the first connecting pad into track portions. The track portions define electrically parallel paths. The heating element may comprise a converging portion. In the converging portion, current is combined from track portions which define electrically parallel paths, into the second connecting pad.

Various different arrangements are possible of tracks or track portions arranged electrically in parallel. The heating element may comprise two, three, four or more track portions which define electrically parallel paths.

By having tracks or track portions arranged electrically in parallel, if one track portion is defective, current can be redistributed and can still flow through the heating element, i.e. the electrical connection between the first connecting pad and the second connecting pad is not broken. In contrast, in a simple serpentine heater defining a single electrical path between the first connecting pad and the second connecting pad, if a part of the serpentine heating element is broken or contains a defect, this can cause an increase in local resistance, causing increased power dissipation, which in turn increases the resistance until breakage.

The inventors have also identified that the electrically parallel tracks or track portions have a surprising additional advantage. In such an arrangement, in case of breakage of one track portion, the heating element will still operate and can, for an initial transitory period, operate in an advantageous way because the breakage of one track or track portion would result in a higher energy density on the remaining tracks or track portions. In such a case, the same power would still be provided but over a smaller area, so throughput of the aerosolgenerating substrate is increased. Such a breakage causing an increase in current on unbroken tracks or track portions can eventually affect the user’s experience. This can be mitigated for by a mechanism to alert the user about possible future below optimal performance of the heater assembly. Electrically parallel tracks have the advantage of increasing the number of puffs before full failure of the heater, and potentially increasing the heater lifetime up to the lifetime of the device.

The heating element may comprise a plurality of tracks or track portions defining a path having at least one bend, the inner edge of the bend being curved.

The inner edge of the bend being curved has the advantage of guiding current to flow in a more evenly distributed way around the at least one bend. This reduces a current concentration which in turn limits hot spot creation.

The heating element may comprise a plurality of tracks or track portions having a gradient of electrical resistivity perpendicular to current flow in a corner or corners, such that the electrical resistivity is higher at an inner part of the corner and lower at an outer part of the corner. Such a gradient is beneficial to counterbalance localized high current density and reduce hot spot creation.

The heating element may comprise a plurality of tracks or track portions arranged with a distance between at least two of the plurality of tracks or track portions in the range 200 to 300 micrometres.

All of the tracks or track portions may be spaced apart from at least one other track portion by 200 to 300 micrometres. This has the advantage of providing a particularly efficient heater assembly, in which an aerosol-forming substrate is efficiently vaporised.

The heating element is located on the heating surface of the porous body. As used herein, the heating element being located on the porous body does not exclude the heater assembly comprising one or more components located between the heating element and the heating surface of the porous body.

The heater assembly may comprise one or more components located between the heating element and the porous body. As described further below, the heater assembly may comprise a thermally insulating layer located between the porous body and the heating element.

The heating element may be located directly on the heating surface of the porous body. There may be no component of the heater assembly located between the porous body and the heating element. The heating element may be in contact with the heating surface of the porous body.

The heating element may extend across at least the majority of the heating surface of the porous body. The heating element may extend across substantially all of the heating surface of the porous body.

At least the majority of the heating element may be in contact with the heating surface of the porous body. The entirety of the heating element may be in contact with the heating surface of the porous body.

The heating element may be convex in one or both of the first transverse direction and the second transverse direction.

The curvature of the heating element in the first transverse direction may be substantially the same as the curvature of the heating surface of the porous body in the first transverse direction. The curvature of the heating element in the second transverse direction may be substantially the same as the curvature of the heating surface of the porous body in the second transverse direction. The curvature of the heating element in both the first transverse direction and the second transverse direction may be substantially the same as the curvature of the heating surface of the porous body in both the first transverse direction and the second transverse direction, respectively. The features relating to the curvature of the heating surface of the porous body described above may be applicable to the curvature of the heating element.

The features relating to the dimensions of the heating surface of the porous body described may be applicable to the dimensions of the heating element.

In particular, the radius of curvature, the relationship between the radius of curvature and the width, the width, the length, the relationship between the width and the length, the surface area, and the relationship between the surface area and the width of the heating surface of the porous body described above may be applicable to the relationship between the radius of curvature and the width, the width, the length, the relationship between the width and length, the surface area, and the relationship between the surface area of the width of the heating element, respectively. The relationship between the length of the heating surface of the porous body to the length of the porous body described above may be applicable to the relationship between the length of the heating element to the length of the porous body.

The porous body and heating element may be formed as two separate parts assembled together.

The heating element may be bonded to the heating surface of the porous body. An advantage of providing a heater assembly in which a heating element is bonded to a heating surface of a porous ceramic body is that a robust and reliable connection can be established between the heating element and the porous ceramic body. This may advantageously help to improve the transfer of heat between the heating element and the porous ceramic body.

Alternatively, the heating element and the porous body may be integrally formed. The provision of the heating element being integrally formed with the porous body may advantageously provide a more robust and reliable connection between the heating element and the porous body. This may advantageously help to improve the transfer of heat between the heating element and the porous body.

Forming the heating element integrally with the porous body may also advantageously provide a heating element which is easier to reliably manufacture, thus resulting in a more energy efficient heating element capable of generating a more consistent aerosol. This, in turn, may provide a user of the aerosol-generating system with an improved and more enjoyable experience. Such an arrangement may also help to reduce the likelihood of a user experiencing dry heating or a dry puff.

An advantage of forming the heating element integrally with the porous body is that it helps to alleviate the problems of manufacturing tolerances encountered with wick and coil heaters and other arrangements in which a heating element is detached from a liquid transport element. The dimensions and arrangement of the heating element relative to the porous body are also fixed, which helps to produce a more consistent aerosol. This is because the heating element is fixed to the porous body, which helps to supply liquid aerosol-forming substrate to the heating element. This also helps to prevent unwanted loss of heat, which helps to improve energy efficiency.

By forming the heating element integrally with the porous body, the resulting aerosolgenerating system may benefit from reduced material requirements. This is because the need for intermediate components which fix the heating element relative to the porous body can be reduced or eliminated entirely. The material savings can result in cost savings of the overall aerosol-generating system. An additional advantage of the reduced material requirements in the overall aerosol-generating system is the provision of a more sustainable and environmentally friendly solution.

Since the heating element is integrally formed with the porous body, the heating surface of the porous body may not be a clearly defined surface. The porous body and the heating element may be made from a single monolithic portion of porous material. Where this is the case, the heating element may be a portion of the porous material which has been configured to generate heat. As described in more detail below, this may be achieved by, for example, doping a portion of the porous material or diffusing electrically conductive material into the porous material. Accordingly, the heating surface of the porous body may represent the interface between the portion of the porous material which is configured to transport liquid aerosol-forming substrate, and a portion of the porous material which is configured to generate heat. Depending on how the heating element is formed, the heating surface of the porous body may be a gradual interface between the portion of the porous material which is configured to transport liquid aerosol-forming substrate, and a portion of the porous material which is configured to generate heat.

The heating element may be a doped portion of the porous body.

The porous body may be doped such that the portion of the porous body which acts as the heating element is electrically conductive. Doping the porous body may be advantageous in that it avoids altering the porosity of the porous body. This may be preferable to other known techniques of forming a heating element, which involve depositing the heating element by thin film or thick film techniques, which can reduce the properties of the porous body, in particular the porosity. The thickness of the doped portion may be increased where the cross sectional area of the heating element is smaller or where the heating resistance required is higher. The dopant used to dope the porous body may be an n-type dopant or a p- type dopant. The dopant may be any one of, but not limited to, nitrogen, phosphorous, aluminium or boron. The interface between the heating element and the porous body may comprise a portion of partially doped porous material.

The heater assembly may comprise a thermally insulating layer. The thermally insulating layer may have a lower thermal conductivity than the porous body. The thermally insulating layer may be disposed between the porous body and the heating element. The thermally insulating layer may be in contact with one or both of the porous body and the heating element. The thermally insulating layer may be configured to reduce heat transfer from the heating element to the porous body.

For example, the heater assembly may comprise a thermally insulating layer having a lower thermal conductivity than the porous body, the thermally insulating layer being disposed between and being in contact with each of the porous body and the heating element, and the thermally insulating layer being configured to reduce heat transfer from the heating element to the porous body

With a thermally insulating layer, heat losses from the heating element to the porous body, and to liquid within the porous body, may be reduced. This may provide a more efficient heater assembly in which the amount of use and number of uses of the device by a user can be increased, before the device power supply, such as a battery, is depleted. The inventors have estimated that in a known device, approximately one third of energy from the heating element may be lost through conduction in the porous body and liquid in the porous body. The remaining two thirds are used to generate an aerosol by heating a liquid aerosol-forming substrate. With a thermally insulating layer, these energy losses may be reduced. Specifically, the thermally insulting layer may reduce heat propagation or conduction from the heating element towards or through the porous body. This reduction in conduction can concentrate heat to a heating surface of the porous body, minimising heat dissipation and increasing heating efficiency of the heater assembly.

As used herein, the term “thermally insulating” refers to a property in which heat transfer is reduced or restricted. A more thermally insulating component will transfer less heat, via conduction, convection or radiation, than a more thermally insulating component.

The thermally insulating layer may comprise a thermally insulating material. The thermally insulating material may have a lower thermal conductivity than the porous body. The thermally insulating material may have a higher porosity than the porous body. This has the advantage of providing a thermally insulating layer which is particularly effective at reducing energy losses, while being easy to manufacture.

The thermally insulating layer may comprise a material having a thermal conductivity of less than 40 Watts per metre-Kelvin. This has the advantage of providing a thermally insulating layer which is effective at reducing energy losses through the porous body. The thermally insulating layer may comprise a material having a thermal conductivity of less than 10 Watts per metre-Kelvin. This has the advantage of providing a thermally insulating layer which is particularly effective at reducing energy losses through the porous body.

The thermally insulating layer may extend entirely between the porous body and the heating element. This has the advantage of more effectively providing a barrier between the heating element and the porous body, and as such is particularly effective at reducing energy losses through the porous body.

The thermally insulating layer may comprise one or more of: alumina, zirconia, zirconia with magnesium oxide, glass ceramic, quartz, a porous polymer. The porous polymer may be polyimide.

The thermally insulating layer may comprise alumina having a thermal conductivity of 20 - 40 Watts per metre-Kelvin. The thermally insulating layer may comprise a material having a thermal conductivity of less than 10 Watts per metre-Kelvin, such as zirconia with or without magnesium oxide, glass ceramics, quartz. Use of alumina, zirconia with or without magnesium oxide, glass ceramics, quartz, is advantageous, as these materials are compatible with a manufacturing process involving sintering, and as such a heater assembly having a thermally insulating layer of one of these materials is more easily manufactured.

The thermally insulating layer may have a thickness of between 0.1 mm and 2 mm. A thermally insulating layer with such a thickness is particularly suited to reducing energy losses from the heating element to the porous body. Preferably, the thermally insulating layer has a thickness of between 0.5 mm and 1.5 mm. A thermally insulating layer with such a thickness is further suited to reducing energy losses from the heating element to the porous body.

The thermally insulating layer may be convex in one or both of the first transverse direction and the second transverse direction.

The curvature of the thermally insulating layer in the first transverse direction may be substantially the same as the curvature of the heating surface of the porous body in the first transverse direction. The curvature of the thermally insulating layer in the second transverse direction may be substantially the same as the curvature of the heating surface of the porous body in the second transverse direction. The curvature of the thermally insulating layer in both the first transverse direction and the second transverse direction may be substantially the same as the curvature of the heating surface of the porous body in both the first transverse direction and the second transverse direction, respectively.

The heater assembly may comprise first and second electrical contacts connected to the heating element. Each electrical contact may be located at opposite sides or ends of the heating surface of the porous body. The heating element may extend between the electrical contacts. The heating element may form an electrical connection therebetween.

The electrical contacts may be formed from any suitable material. Examples of suitable materials for the electrical contacts include but are not limited to copper, zinc, silver, and gold.

The first and second electrical contacts may be formed from an electrically conductive material deposited directly onto the heating surface of the porous body. The heating element may extend between the electrical contacts in a wave-like or serpentine manner. This may help to increase the length of the heating element between the electrical contacts that is in contact with the heating surface, which may help to improve heating of the liquid aerosol-forming substrate.

According to a second aspect of the invention, there is provided an aerosol-generating system comprising: a heater assembly according to the first aspect of the invention; a cartridge comprising a liquid storage portion for storing a liquid aerosol-forming substrate; and an aerosol-generating device comprising a power supply for supplying power to the heater assembly and control circuitry for controlling the supply of power from the power supply to the heater assembly, wherein the heater assembly is a component of either the cartridge or the aerosol-generating device.

The heating element of the heater assembly may be for vaporising a liquid aerosolforming substrate stored in the liquid storage portion of the cartridge.

The heater assembly may be a component of the cartridge. Accordingly, the aerosolgenerating system may comprise: a cartridge comprising a liquid storage portion for storing a liquid aerosol-forming substrate and a heater assembly according to the first aspect of the invention; and an aerosol-generating device comprising a power supply for supplying power to the heater assembly and control circuitry for controlling the supply of power from the power supply to the heater assembly.

The heater assembly may be a component of the device. Accordingly, the aerosolgenerating system may comprise: a cartridge comprising a liquid storage portion for storing a liquid aerosol-forming substrate; and an aerosol-generating device comprising a heater assembly according to the first aspect of the invention, a power supply for supplying power to the heater assembly, and control circuitry for controlling the supply of power from the power supply to the heater assembly.

The cartridge may be a replaceable cartridge. The cartridge may be removably couplable to the aerosol-generating device.

The cartridge may have a connection end configured to couple the cartridge to the aerosol-generating device. The connection end of the cartridge may be configured to removably couple the cartridge to the aerosol-generating device. The connection end may be arranged at a distal end of the cartridge.

The cartridge may comprise a mouthpiece arranged at a mouth end of the cartridge. The mouthpiece may comprise an aerosol outlet through which generated aerosol may be drawn by a user.

The mouth end of the cartridge is opposed to the distal end of the cartridge.

The cartridge may comprise an air inlet. The cartridge may comprise an enclosed airflow passage from the air inlet to the aerosol outlet. The enclosed airflow passage may extend from the air inlet, past the heater assembly, to the aerosol outlet. The enclosed airflow passage may pass around an external surface of the liquid storage portion. Alternatively, the enclosed airflow passage may pass through the liquid storage portion. For example, the liquid storage portion may have an annular cross-section defining an internal passage, and the airflow passage may extend through the internal passage of the liquid storage portion.

The cartridge may comprise a first airflow pathway that extends from the air inlet towards the heater assembly in a first direction. The cartridge may comprise a second airflow pathway that extends past the heating element and is configured to entrain the aerosol. The cartridge may comprise a third airflow pathway that extends from the heater assembly to an aerosol outlet in a second direction. The second direction may be opposite to the first direction. The second airflow pathway may provide a fluid connection between the first airflow pathway and the third airflow pathway.

The cartridge may comprise a cartridge housing. The cartridge may be formed from a durable material. The cartridge housing may be formed from a liquid impermeable material. The cartridge housing may be formed form a mouldable plastics material, such as polypropylene (PP) or polyethylene terephthalate (PET) or a copolymer made from three monomers: dimethyl terephthalate (DMT), cyclohexanedimethanol (CH DM), and 2, 2,4,4- tetramethyl-1 ,3-cyclobutanediol (CBDO), such as Tritan™. The cartridge housing of the cartridge may define a portion of the liquid storage portion or reservoir. The cartridge housing may define the liquid storage portion. The cartridge housing and the liquid storage portion may be integrally formed. Alternatively, the liquid storage portion may be formed separately from the cartridge housing and arranged in the cartridge housing.

The liquid storage portion of the cartridge may comprise a liquid aerosol-forming substrate. In other words, the cartridge may comprise a liquid aerosol-forming substrate that is stored in the liquid storage portion of the cartridge.

The liquid aerosol-forming substrate may be liquid at room temperature. The liquid aerosol-forming substrate may comprise both liquid and solid components.

The liquid aerosol-forming substrate may comprise nicotine. The liquid aerosolforming substrate may have a nicotine concentration of between about 0.5% and about 10%, for example about 2%.

The nicotine containing liquid aerosol-forming substrate may be a nicotine salt matrix.

The liquid aerosol-forming substrate may comprise plant-based material. The liquid aerosol-forming substrate may comprise tobacco. The liquid aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the aerosol-forming substrate upon heating. The liquid aerosol-forming substrate may comprise homogenised tobacco material. The liquid aerosol-forming substrate may comprise a non-tobacco-containing material. The liquid aerosol-forming substrate may comprise homogenised plant-based material.

The liquid aerosol-forming substrate may comprise one or more aerosol-formers. An aerosol-former is any suitable known compound or mixture of compounds that, in use, facilitates formation of a dense and stable aerosol and that is substantially resistant to thermal degradation at the temperature of operation of the system. Examples of suitable aerosolformers include glycerine and propylene glycol. Suitable aerosol-formers are well known in the art and include, but are not limited to: polyhydric alcohols, such as triethylene glycol, 1 ,3- butanediol and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate.

The liquid aerosol-forming substrate may comprise water, solvents, ethanol, plant extracts and natural or artificial flavours.

The liquid aerosol-forming substrate may comprise nicotine and at least one aerosolformer. The aerosol-former may be glycerine or propylene glycol. The aerosol former may comprise both glycerine and propylene glycol.

The liquid storage portion may be disposed at a first side of the heater assembly. An airflow channel may be disposed at an opposite side of the heater assembly to the first side. The airflow channel may be adjacent to the electrical heating element. An airflow path may extend past the electrical heating element. The airflow path may be configured to convey the aerosol. The cartridge body may be configured such that air flow past the heater assembly entrains vapourised aerosol-forming substrate.

The porous outer surface may comprise a first porous outer surface or aerosolization surface of the porous body. The porous body may comprise a second porous outer surface or a liquid absorption surface. The second porous outer surface or liquid absorption surface may be opposite the first porous outer surface. The liquid storage portion may be arranged on the same side of the heater assembly as the second porous outer surface or liquid absorption surface.

An aerosolization cavity may be arranged on the same side of the heater assembly as the first porous outer surface or aerosolization surface. The aerosolization cavity may be in fluid communication with the first porous outer surface or aerosolization surface to receive aerosol from the heater assembly. The aerosolization cavity may be in fluid communication with an airflow pathway to entrain aerosol in the airflow.

The aerosol-generating device may comprise a housing. The housing may be elongate. The housing may comprise any suitable material or combination of materials. Examples of suitable materials include metals, alloys, plastics or composite materials containing one or more of those materials, or thermoplastics that are suitable for food or pharmaceutical applications, for example polypropylene, polyetheretherketone (PEEK) and polyethylene. The material is preferably light and non-brittle.

The aerosol-generating device housing may define a cavity or recess for receiving a portion of a cartridge. The aerosol-generating device may have a connection end configured to connect the aerosol-generating device to a cartridge. The connection end of the aerosolgenerating device may be configured to removably connect the aerosol-generating device to the cartridge. The connection end may comprise the cavity or recess for receiving the cartridge. The connection end of the aerosol-generating device may be at the proximal end of the aerosol-generating device.

The aerosol-generating device has a distal end opposite to the proximal end. The connection end of the aerosol-generating device may be at the proximal end of the device. In other words, the aerosol-generating device may comprise a connection end opposite to the distal end.

The distal end may comprise an electrical connector configured to connect the aerosolgenerating device to an electrical connector of an external power supply, for charging the power supply of the aerosol-generating device.

The aerosol-generating system may comprise an air inlet. The air inlet may be arranged at an interface between the cartridge and the aerosol-generating device. The aerosol-generating system may comprise an enclosed airflow passage from the air inlet to an aerosol outlet in a mouthpiece. The enclosed airflow passage may extend from the air inlet, past the heater assembly, to the aerosol outlet.

The aerosol-generating system may comprise a first airflow pathway that extends from the air inlet towards the heater assembly in a first direction. The aerosol-generating system may comprise a second airflow pathway that extends past the electrical heating element and is configured to entrain the aerosol. The aerosol-generating system may comprise a third airflow pathway that extends from the heater assembly to an aerosol outlet in a second direction. The second direction may be opposite to the first direction. The second airflow pathway may provide a fluid connection between the first airflow pathway and the third airflow pathway.

The heating element may be fluid permeable such that, in use, vapour is emitted from the heater assembly in an average vapour emission direction. The aerosol-generating system may comprise an air inlet and an aerosol outlet. The air inlet may be in fluid communication with the aerosol outlet to define an airflow pathway through the aerosol-generating system. The heater assembly may be arranged in fluid communication with the airflow pathway such that air flows past the heater assembly in an average airflow direction. The heater assembly and airflow pathway may be arranged such that an angle between the average vapour emission direction and the average airflow direction is less than 135 degrees. As used herein, the term “an angle between the average vapour emission direction and the average airflow direction” refers to an angle between the directions of travel of the vapour being emitted from the heater assembly and the airflow within the airflow pathway. For example, an angle of zero degrees would mean that the airflow and vapour emissions are travelling in the same direction, whereas an angle of 180 degrees would mean that the directions of travel of the airflow and vapour emission directly oppose one another.

Advantageously, by arranging the heater assembly and airflow pathway such that the angle between the average vapour emission direction and the average airflow direction is less than 135 degrees, the average airflow direction does not directly oppose the average vapour emission direction. Therefore, the momentum of the vapour and the airflow is not reduced to the same extent as when the average airflow direction does directly oppose the average vapour emission direction. This reduces the tendency for recirculation and turbulence to occur in the airflow path and the vapour is less likely to impinge on the internal surfaces of the aerosol-generating system. Accordingly, condensation of aerosol within the aerosolgenerating system is less likely to occur.

The average vapour emission direction may be substantially perpendicular to the heating surface. As used herein, the term “substantially perpendicular” means 90 degrees plus or minus 10 degrees, preferably plus or minus 5 degrees.

An advantage of the average vapour emission direction being substantially perpendicular to the heating surface is that it makes orientating the average vapour emission direction relative to the average airflow direction straightforward because the vapour will be emitted substantially perpendicular to the heating surface of the porous body. Therefore, by angling the heater assembly appropriately relative to the airflow in the airflow pathway or vice versa, a desired angle between the average vapour emission direction and average airflow direction can be achieved.

The heater assembly and airflow pathway may be arranged such that an angle between the average vapour emission direction and the average airflow direction is less than 110 degrees, preferably less than 100 degrees.

The heater assembly and airflow pathway may be arranged such that an angle between the average vapour emission direction and the average airflow direction is approximately 90 degrees. This arrangement results in the vapour being emitted at an angle substantially perpendicular to the average airflow direction. The average vapour emission direction has no speed or direction component that opposes the airflow direction and therefore any loss of momentum of the airflow is reduced. This reduces the tendency for recirculation and turbulence to occur in the airflow path and the vapour is less likely to impinge on the internal surfaces of the aerosol-generating system. Furthermore, entrainment of the vapour in the airflow is improved. Accordingly, condensation of aerosol within the aerosol-generating system is less likely to occur.

The heater assembly and airflow pathway may be arranged such that an angle between the average vapour emission direction and the average airflow direction is less than 90 degrees. In this arrangement, the average vapour emission direction has no speed or direction component that opposes the airflow direction and actually has a speed and direction component in the same direction as the average airflow direction. Therefore, any loss of momentum of the airflow is further reduced. This reduces the tendency for recirculation and turbulence to occur in the airflow path and the vapour is less likely to impinge on the internal surfaces of the aerosol-generating system. Furthermore, entrainment of the vapour in the airflow is improved. Accordingly, condensation of aerosol within the aerosol-generating system is less likely to occur.

The heater assembly and airflow pathway may be arranged such that an angle between the average vapour emission direction and the average airflow direction is approximately 45 degrees. The heater assembly and airflow pathway may be arranged such that an angle between the average vapour emission direction and the average airflow direction is less than 45 degrees.

The heater assembly and airflow pathway may be arranged such that the average vapour emission direction and the average airflow direction are substantially the same. In this arrangement, there is virtually no loss of momentum of the airflow as the average vapour emission direction and average airflow direction are the same. This reduces the tendency for recirculation and turbulence to occur in the airflow path and the vapour is less likely to impinge on the internal surfaces of the aerosol-generating system. Furthermore, entrainment of the vapour in the airflow is improved. Accordingly, condensation of aerosol within the aerosolgenerating system is less likely to occur.

A cross-sectional area of the airflow pathway in the region of the heater assembly may be configured such that, in use, the airflow speed is between 0.1 and 2 metres per second, preferably between 0.5 and 1.5 metres per second and more preferably approximately 1 metre per second. This range of airflow speeds has been found to effectively entrain the vapour emitted from different designs of heating element without excessively cooling the heating element.

The heating element may comprise a porous layer of electrically conductive material. Advantageously, a heating element comprising a porous layer of electrically conductive material allows an electrical current to flow through the heating element such that the heating element can be resistively heated and also allows vapours to travel through the heating element via the pores in its porous structure. Thus vapour emission occurs through the porous heating element. This avoids the build-up of vapour pressure underneath the heating element and high speed vapour emission at the sides of the heating element. The inventors have found that this arrangement produces a consistent vapour across the heating element and a lower vapour emission speed of approximately 0.1 metres per second. Such a low vapour emission speed means that the vapour is easily carried away by the airflow reducing the impingement of vapour on the internal walls of the aerosol-generating system.

The power supply may be any suitable power supply. Preferably, the power supply is a DC power supply. The power supply may be a battery. The battery may be a Lithium based battery, for example a Lithium-Cobalt, a Lithium-lron-Phosphate, a Lithium Titanate or a Lithium-Polymer battery. The battery may be a Nickel-metal hydride battery or a Nickel cadmium battery. The power supply may be another form of charge storage device such as a capacitor. The power supply may be rechargeable and be configured for many cycles of charge and discharge. The power supply may have a capacity that allows for the storage of enough energy for one or more user experiences of the aerosol-generating system; for example, the power supply may have sufficient capacity to allow for the continuous generation of aerosol for a period of around six minutes, corresponding to the typical time taken to smoke a conventional cigarette, or for a period that is a multiple of six minutes. In another example, the power supply may have sufficient capacity to allow for a predetermined number of puffs or discrete activations of the aerosol-generating system.

The control circuitry may comprise any suitable controller or electrical components. The controller may comprise a memory. Information for performing the above-described method may be stored in the memory. The control circuitry may comprise a microprocessor. The microprocessor may be a programmable microprocessor, a microcontroller, or an application specific integrated chip (ASIC) or other electronic circuitry capable of providing control. The control circuitry may be configured to supply power to the heating element continuously following activation of the device, or may be configured to supply power intermittently, such as on a puff-by-puff basis. The power may be supplied to the heating element in the form of pulses of electrical current, for example, by means of pulse width modulation (PWM).

The control circuitry may comprise further electronic components. For example, in some embodiments, the control circuitry may comprise any of: sensors, switches, display elements.

The aerosol-generating system may comprise a puff detector. The puff detector may be configured to detect when a user draws on the aerosol-generating system. The puff detector may be any suitable sensor that is capable of detecting when a user draws on the aerosol-generating device. For example, the puff detector may be an airflow sensor. The control circuitry may be configured to supply power to the heating element when the puff detector detects a user drawing on the aerosol-generating system. Below, there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, or embodiment, or aspect described herein.

EX1 : A heater assembly for an aerosol-generating system, the heater assembly comprising: a heating element for vaporising a liquid aerosol-forming substrate, and a porous body for conveying the liquid aerosol-forming substrate to the heating element, the porous body having a liquid absorption surface and a heating surface, wherein the heating element is located on the heating surface of the porous body.

EX2: A heater assembly according to EX1 , wherein the porous body comprises a porous ceramic body or a porous glass body.

EX3: A heater assembly according to EX1 or EX2, wherein the heating surface of the porous body is convex in one or both of a first transverse direction and a second transverse direction, the first transverse direction being orthogonal to the second transverse direction.

EX4: A heater assembly according to any one of EX1 to EX3, wherein the porous body comprises one or more longitudinal planes of symmetry.

EX5: A heater assembly according to any one of EX1 to EX4, wherein the heating surface of the porous body has a radius of curvature of at least about 1.5 millimetres in one or both of the first transverse direction and the second transverse direction.

EX6: A heater assembly according to any one of EX1 to EX5, wherein the heating surface of the porous body has a radius of curvature of less than or equal to about 10 millimetres in one or both of the first transverse direction and the second transverse direction.

EX7: A heater assembly according to any one of EX1 to EX6, wherein a ratio of the radius of curvature of the heating surface to the width of the heating surface in a same transverse direction is at least about 0.5.

EX8: A heater assembly according to any one of EX1 to EX7, wherein a ratio of the radius of curvature of the heating surface to the width of the heating surface in a same transverse direction is less than or equal to about 5

EX9: A heater assembly according to any one of EX1 to EX8, wherein a width of the heating surface is less than or substantially equal to a width of the porous body in a same transverse direction.

EX10: A heater assembly according to any one of EX1 to EX9, wherein a width of the heating surface is greater than a width of the porous body in a same transverse direction.

EX11 : A heater assembly according to any one of EX1 to EX10, wherein a width of the heating surface in one or both of the first transverse direction and the second transverse direction is at least about 0.5 millimetres. EX12: A heater assembly according to any one of EX1 to EX11 , wherein a width of the heating surface in one or both of the first transverse direction and the second transverse direction is less than or equal to about 12 millimetres.

EX13: A heater assembly according to any one of EX1 to EX12, wherein the heating surface of the porous body has a length of at least about 0.5 millimetres.

EX14: A heater assembly according to any one of EX1 to EX13, wherein the heating surface of the porous body has a length of less than about 6 millimetres.

EX15: A heater assembly according to any one of EX1 to EX14, wherein a width of the heating surface in one or both of the first transverse direction and the second transverse direction is greater than the length of the heating surface.

EX16: A heater assembly according to any one of EX1 to EX15, wherein a ratio of the length of the heating surface to the width of the heating surface in one or both of the first transverse direction and the second transverse direction is at least about 0.02.

EX17: A heater assembly according to any one of EX1 to EX16, wherein a ratio of the length of the heating surface to the width of the heating surface in one or both of the first transverse direction and the second transverse direction is less than or equal to about 0.5.

EX18: A heater assembly according to any one of EX1 to EX17, wherein a ratio of the length of the heating surface to the length of the porous body is at least about 0.05.

EX19: A heater assembly according to any one of EX1 to EX18, wherein a ratio of the length of the heating surface to the length of the porous body is less than or equal to about 0.45.

EX20: A heater assembly according to any one of EX1 to EX19, wherein the liquid absorption surface of the porous body has an area that is different to an area of the heating surface of the porous body.

EX21 : A heater assembly according to any one of EX1 to EX20, wherein the width of the heating surface of the porous body is less than the width of the liquid absorption surface of the porous body in a same transverse direction.

EX22: A heater assembly according to any one of EX1 to EX21 , wherein the porous body comprises a shape that tapers from the liquid absorption surface of the porous body towards the heating surface of the porous body.

EX23: A heater assembly according to any one of EX1 to EX22, wherein the porous body comprises a shape that tapers from the heating surface of the porous body towards the liquid absorption surface of the porous body.

EX24: A heater assembly according to any one of EX1 to EX23, wherein the average pore size of the porous body varies between the liquid absorption surface and the heating surface. EX25: A heater assembly according to any one of EX1 to EX24, wherein the heating element comprises a plurality of tracks or track portions arranged electrically in parallel.

EX26: A heater assembly according to any one of EX1 to EX25, wherein the heating element comprises a plurality of tracks or tracks portions defining a path having at least one bend, the inner edge of the bend being curved.

EX27: A heater assembly according to any one of EX1 to EX26, wherein the heating element is convex in one or both of the first transverse direction and the second transverse direction.

EX28: A heater assembly according to any one of EX1 to EX27, wherein the porous body and the heating element are formed as two separate parts assembled together.

EX29: A heater assembly according to any one of EX1 to EX28, wherein the porous body and the heating element are integrally formed.

EX30: A heater assembly according to any one of EX1 to EX29, wherein the heating element is a doped portion of the porous body.

EX31 : A heater assembly according to any one of EX1 to EX30, wherein the heater assembly comprises a thermally insulating layer having a lower thermal conductivity than the porous body, the thermally insulating layer being disposed between the porous body and the heating element, the thermally insulating layer being configured to reduce heat transfer from the heating element to the porous body.

EX32: A heater assembly according to any one of EX1 to EX31 , wherein the heating element is fluid permeable.

EX32: An aerosol-generating system comprising: a heater assembly according to any one of EX1 to EX31 ; a cartridge comprising a liquid storage portion for storing a liquid aerosolforming substrate; and an aerosol-generating device comprising a power supply for supplying power to the heater assembly and control circuitry for controlling the supply of power from the power supply to the heater assembly, wherein the heater assembly is a component of either the cartridge or the aerosol-generating device.

EX33: An aerosol-generating system according to EX32, wherein the heating element is fluid permeable such that, in use vapour is emitted from the heater assembly in an average vapour emission direction, wherein the aerosol-generating system further comprises an air inlet and an aerosol outlet to define an airflow pathway through the aerosol-generating system, wherein the heater assembly is arranged in fluid communication with the airflow pathway such that air flows past the heater assembly in an average airflow direction, and wherein the heater assembly and airflow pathway are arranged such that an angle between the average vapour emission direction and the average airflow direction is less than 135 degrees.

The present invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic perspective view of a heater assembly in accordance with the first aspect of the invention;

Figure 2A shows a schematic side view of another heater assembly in accordance with a the first aspect of the invention;

Figure 2B shows a schematic side view of the porous body of the heater assembly shown in Figure 2A;

Figure 3 shows a schematic perspective view of another heater assembly in accordance with the first aspect of the invention;

Figure 4 shows a schematic perspective view of another heater assembly in accordance with the first aspect of the invention;

Figure 5 shows a schematic perspective view of another heater assembly in accordance with the first aspect of the invention;

Figures 6A, 6B and 6C show schematically examples of heating element tracks of a heating element of a heater assembly in accordance with the first aspect of the invention,

Figures 7A and 7B show schematically examples of current flow around a corner of a heating element track of a heating element of a heater assembly in accordance with the first aspect of the invention;

Figure 8A shows a schematic plan view of a heater assembly in accordance with the first aspect of the invention;

Figure 8B shows a schematic cross-sectional view of the heater assembly of Figure 8;

Figure 9 shows a schematic view of an aerosol-generating system in accordance with the second aspect of the invention;

Figure 10 shows a schematic cross-sectional view of part of an aerosol-generating system in accordance with the second aspect of the invention showing an arrangement of a heater assembly relative to an airflow pathway within the aerosol-generating system; and

Figure 11 shows a schematic cross-sectional view of part of another aerosolgenerating system in accordance with the second aspect of the invention showing an arrangement of a heater assembly relative to an airflow pathway within the aerosol-generating system.

Figure 1 shows a heater assembly 100 for use in an aerosol-generating system. The heater assembly 100 comprises a heating element 110 for vaporising a liquid aerosol-forming substrate. The heater assembly 100 also comprises a porous body 120 for conveying the liquid aerosol-forming substrate to the heating element 110. The porous body 120 has a liquid absorption surface 121 and an opposed heating surface 122. The heating element 110 is located on the heating surface 122 of the porous body 120. The heating surface 122 of the porous body 120 is curved. In particular, the heating surface 122 of the porous body 120 is convexly curved in a single transverse direction (the first transverse direction).

The porous body may be a porous ceramic body or a porous glass body.

The porous body 120 is prismatic in shape. When viewing a longitudinal cross-section perpendicular to the direction of curvature of the porous body 120, the heating surface 122 of the porous body 120 is shown as arc. The porous body 120 has two longitudinal planes of symmetry.

The heating surface 122 of the porous body 120 has a width 123 in the first transverse direction substantially the same as the width of the porous body 120 in the first transverse direction, and substantially the same as the width of the heater assembly 100 in the first transverse direction. The heating surface 122 of the porous body 120 has a width of about 5 millimetres in the first transverse direction.

The heating surface 122 of the porous body 120 has a length or thickness 124 of about 1 millimetre. The porous body 120 has a length or thickness 125 of about 3 millimetres.

The heating surface 122 of the porous body has a radius of curvature of about 3.6 millimetres. The heating surface 122 of the porous body has a surface area of about 28 square millimetres.

The porous body 120 comprises four longitudinal surfaces or side walls extending from the liquid absorption surface 121 to the heating surface 122. The four side walls are substantially perpendicular to the liquid absorption surface 121 , which is substantially flat. The liquid absorption surface 121 is square in shape.

The heating element 110 is a resistive heating element 110.

The heating element 110 is curved. In particular, the curvature of the heating element is substantially the same as the curvature of the heating surface 122 of the porous body 120. As such, the heating element 110 is also convexly curved in a single transverse direction.

The heating element 110 is located directly on the heating surface 122 of the porous body 120. The heating element 110 extends across a majority of the heating surface 122 of the porous body 120. Substantially the entirety of the heating element 110 is in contact with the heating surface 122 of the porous body 120.

In the example shown in Figure 1 , the pore size of the pores of the porous body 120 is the same between the liquid absorption surface 121 and the heating surface 122.

In another example, the pore size of the pores in the porous body 120 vary between the liquid absorption surface 121 and the heating surface 122.

The porous body 120 may include a heating end and a liquid absorption end, the heating surface 122 being disposed at the heating end, and the liquid absorption surface 121 being disposed at the liquid absorption end. The porous body 120 may include a first average pore size at the liquid absorption end, and a second average pore size at the heating end. The first average pore size is greater than the second average pore size.

In this alternative example, the first average pore size at the liquid absorption end is about 150 micrometres. The second average pore size at the heating end is about 20 micrometres. The pore size varies linearly between the first average pore size and the second average pore size to provide a pore size gradient between the liquid absorption end and the heating end of the porous body 120.

The pore structure and pore size gradient in the porous body 120 is achieved by etching the pores into a portion of the porous body 120.

Figure 2A shows a schematic side view of a heater assembly 200 for use in an aerosolgenerating system, the heater assembly 200 being in accordance with the first aspect of the invention.

Similarly to the heater assembly 100 shown in Figure 1 , the heater assembly 200 shown in Figure 2A comprises a heating element 210 for vaporising a liquid aerosol-forming substrate and a porous body 220 for conveying the liquid aerosol-forming substrate to the heating element 210. The porous body 220 has a liquid absorption surface 221 and an opposed heating surface 222. The heating element 210 is located on the heating surface 222 of the porous body 220.

The heating surface 222 of the porous body 220 is curved. In particular, the heating surface 222 of the porous body 220 is curved in a convex manner in two transverse directions. The heating surface 222 of the porous body 220 is convex in both a first transverse direction and a second transverse direction.

The heating surface 222 of the porous body 220 has substantially the same shape as a surface of a spherical cap or spherical dome. The porous body 220 is substantially radially symmetric.

The porous body 220 comprises a longitudinal surface or side wall extending from the liquid absorption surface 221 to the heating surface 222. The side wall is substantially perpendicular to the liquid absorption surface 221 , which is substantially flat. The liquid absorption surface 221 is substantially circular in shape.

The heating element 210 is a resistive heating element 210.

The heating element 210 is curved. In particular, the curvature of the heating element 210 is substantially the same as the curvature of the heating surface 222 of the porous body 220. As such, the heating element 210 is also convex in both the first transverse direction and the second transverse direction.

The heating element 210 is located directly on the heating surface 222 of the porous body 220. The heating element 210 extends across a majority of the heating surface 222 of the porous body 220. Substantially the entirety of the heating element 210 is in contact with the heating surface 222 of the porous body 220.

The heating element 210 is in the form of a spiral.

Figure 2B shows the porous body 220 of the heater assembly 200. The heating element 210 of the heater assembly 200 is not shown in Figure 2B.

The part of the edge of the heating surface 222 not visible in the schematic side view shown in Figure 2A is illustrated by the dotted line in Figure 2B.

The heating surface 220 of the porous body 220 has a width 223 substantially the same as the width of the porous body 220, and substantially the same as the width of the heater assembly 200. As shown in Figure 2B, the heating surface 200 of the porous body 220 has a width 223 of about 5 millimetres. Accordingly, the diameter of the liquid absorption surface 221 is about 5 millimetres.

The heating surface 220 of the porous body 120 has a length or thickness 124 of about 2 millimetres. The porous body 220 has length or thickness 225 of about 7 millimetres.

The heating surface 220 of the porous body has a radius of curvature in both the first transverse direction and the second transverse direction of about 2.6 millimetres.

Figure 3 shows a heater assembly 300 for use in an aerosol-generating system, the heater assembly 300 being in accordance with the first aspect of the invention. The heater assembly 300 shown in Figure 3 is of substantially similar construction to the heater assembly 100 shown in Figure 1. Like reference numerals are used in Figures 1 and 3 to designate like parts.

The heating surface 122 of the heater assembly 300 shown in Figure 3 is the same as the heating surface 122 of the heater assembly 100 shown in Figure 1.

The heater assembly 300 shown in Figure 3 differs from the heater assembly 100 shown in Figure 1 in that the width 323 of the liquid absorption surface 321 in the first transverse direction is less than the width 123 of the heating surface 122 in the first transverse direction. The width 123 of the heating surface 122 in the first transverse direction corresponds to the width of the porous body 320 of the heater assembly 300 in the first transverse direction.

The width of the liquid absorption surface 321 in a second transverse direction is substantially the same as the width of the heating surface 122 in the second transverse direction, the second transverse direction being orthogonal to the first transverse direction.

The porous body 320 is prismatic in shape.

The liquid absorption surface 321 is substantially flat and rectangular in shape. The liquid absorption surface 321 has an area that is less than the surface area of the heating surface 122. The porous body 320 comprises four side walls extending from the liquid absorption surface 321 to the heating surface 122. Two of the side walls are substantially perpendicular to the liquid absorption surface 321 . The other two of the side walls have a rectangle shape and are angled with respect to the liquid absorption surface 321.

Figure 4 shows a heater assembly 400 for use in an aerosol-generating system, the heater assembly 400 being in accordance with the first aspect of the invention. The heater assembly 400 shown in Figure 4 is of substantially similar construction to the heater assembly 100 shown in Figure 1. Like reference numerals are used in Figures 1 and 4 to designate like parts.

The heating surface 122 of the heater assembly 400 shown in Figure 4 is the same as the heating surface 122 of the heater assembly 100 shown in Figure 1.

The heater assembly 400 shown in Figure 4 differs from the heater assembly 100 shown in Figure 1 in that the width 423 of the liquid absorption surface 421 in the first transverse direction is greater than the width 123 of the heating surface 122 in the first transverse direction. The width 423 of the liquid absorption surface 421 in the first transverse direction corresponds to the width of the porous body 420 of the heater assembly 400.

The width of the liquid absorption surface 421 in a second transverse direction is substantially the same as the width of the heating surface 122 in the second transverse direction, the second transverse direction being orthogonal to the first transverse direction.

The porous body 420 is prismatic in shape.

The liquid absorption surface 421 is substantially flat and rectangular in shape. The liquid absorption surface 421 has an area that is greater than the surface area of the heating surface 122.

The porous body 420 comprises four side walls extending from the liquid absorption surface 421 to the heating surface 122. Two of the side walls are substantially perpendicular to the liquid absorption surface 421 . The other two of the side walls have a rectangle shape and are angled with respect to the liquid absorption surface 421.

The porous body 420 tapers from the liquid absorption surface 421 towards the heating surface 122. The cross-sectional area of the porous body 420 gradually becomes smaller from the liquid absorption surface 421 towards the heating surface 122.

Figure 5 shows a heater assembly 500 for use in an aerosol-generating system, the heater assembly 500 being in accordance with the first aspect of the invention. The heater assembly 500 shown in Figure 5 is of substantially similar construction to the heater assembly 100 shown in Figure 1. Like reference numerals are used in Figures 1 and 5 to designate like parts.

The porous body 120 shown in Figure 5 is the same as the porous body 120 shown in Figure 1. The heater assembly 500 shown in Figure 5 differs from the heater assembly 100 shown in Figure 1 in that the heater assembly 500 comprises a thermally insulating layer 530 located between the porous body 120 and the heating element 110. The thermally insulating layer 530 is in direct contact with both the heating surface 122 of the porous body 120 and the heating element 110. The thermally insulating layer 120 substantially covers the entirety of the heating surface 122 of the porous body 120.

The thermally insulating layer 530 is arranged to enhance thermal insulation between the heating element 110 and the porous body 120. The thermally insulating layer 530 is configured to reduce heat dissipation through the porous body 120, so as to enhance energy efficiency of the heater assembly 500 by reducing energy losses.

The thermally insulating layer 530 is curved. In particular, the thermally insulating layer 530 is convexly curved in a single transverse direction (the first transverse direction). The curvature of the thermally insulating layer 530 corresponds to the curvature of the heating surface 122 of the porous body 120.

In particular, the thermally insulating layer 520 has a first end face and an opposing second end face. The first end face is a liquid absorption surface 531 and the second end face is a heating surface 532. Both the liquid absorption surface 531 of the thermally insulating layer 530 and the heating surface 532 of the thermally insulating layer are convexly curved in the first transverse direction with the curvature thereof corresponding to the curvature of the heating surface 122 of the porous body 120.

The liquid absorption surface 531 of the thermally insulating layer is in direct contact with the heating surface 122 of the porous body.

The thermally insulating layer 530 has a thickness defined between its liquid absorption surface 531 and its heating surface 532. The thickness of the thermally insulating layer 530 is less than the thickness of the porous body 120. The thermally insulating layer may have a thickness between about 0.1 millimetres and about 2 millimetres, preferably between about 0.5 millimetres and about 1.5 millimetres.

The thermally insulating layer 530 comprises a material having a low thermal conductivity. The thermally insulating layer 530 comprises or consists of a material with a lower thermal conductivity than the porous body 120. The thermally insulating layer 530 may have a higher porosity than the porous body 120. The thermally insulating layer 530 may comprise a material such as one or more of: alumina, zirconia, zirconia with magnesium oxide, glass ceramic, quartz, a porous polymer. It will be appreciated that the thermally insulating layer 530 may have a different shape or comprise a different material.

Referring to Figures 6A to 6C, there are shown schematic illustrations of examples of different heating elements 610 for an aerosol-generating system. Each heating element 610 comprises a plurality of tracks or track portions 617 arranged electrically in parallel. By being arranged electrically in parallel, current flow is split into separate parallel flow paths. The flow paths are subsequently re-combined.

In the heating elements 610 of Figures 6A to 6C, each heating element 610 comprises a first connecting pad 613 and a second connecting pad 614. The first and second connecting pads 613, 614 are configured to allow connection to an external circuit. An aperture or plurality of apertures 615 in the heating element 610 separate each track 617. Each heating element 160 comprises a diverging portion, in which current is split from the first connecting pad 613 into tracks 617 which define electrically parallel paths. Each heating element 610 comprises a converging portion, in which current is combined from tracks 617 which define electrically parallel paths, into the second connecting pad 614.

Various different arrangements are possible of tracks or track portions arranged electrically in parallel. In Figure 6A, four tracks 617 are separated by three apertures 615 to define four electrically parallel paths. In Figure 6B, six track portions 617 are separated by one aperture 615 to define two electrically parallel paths. In Figure 6B, each electrically parallel path defines a serpentine path between the first connecting pad 613 and the second connecting pad 614. In Figure 6C, eight track portions 617 are separated by four apertures 615 to define four pairs of electrically parallel paths. Each pair of electrically parallel path in Figure 6C is separated by an intermediate connection 616, of which three are shown in Figure 6C.

By having tracks or track portions arranged electrically in parallel, if one track portion is defective, current can be redistributed and can still flow through the heating element 610, i.e. the electrical connection between the first connecting pad 613 and the second connecting pad 614 is not broken. This has the advantage of increasing the number of puffs before full failure of the heater, and potentially increasing the heater lifetime up to the lifetime of the device. In contrast, in a simple serpentine heater defining a single electrical path between a first connecting pad 613 and a second connecting pad 614, if a part of the serpentine heating element is broken, then the heating element will stop working due to an increase in local resistance at the breakage or defect point. A defect in a simple serpentine heater causes an increase in local resistance. An increase in local resistance causes increased power dissipation. Increased power dissipation in turn increases the resistance until breakage.

The inventors have also identified that the parallel tracks or track portions arranged electrically in parallel, explained with reference to Figures 6A to 6C, has a surprising additional advantage. In such an arrangement, in case of breakage of one track portion, the heating element 610 will still operate and can, for an initial transitory period, operate in an advantageous way, because the breakage of one track or track portion would result in a higher energy density on the remaining tracks or track portions. In such a case, the same power would still be provided but on a smaller area, so the throughput would be increased. While such a breakage causing an increase in current on unbroken tracks or track portions can eventually degrade the user experience, the device or cartridge can include a mechanism to alert the user about possible future below optimal performance of the heater assembly.

Such a mechanism relies on the following principles. The total electrical resistance of the heating element depends on the following factors:

1) the number of heating tracks in parallel (more parallel tracks decrease the total resistance);

2) the cross-sectional area (width or thickness (or width and thickness)) of the parallel heating tracks (a higher cross-sectional area leads to a lower resistance);

3) the length of the parallel heating tracks (longer tracks have a higher resistance);

4) if the heating element is porous, tuning the porosity of heating element (higher porosity increases resistance);

5) particular chemical or material composition (e.g. alloys by doping).

The overall total heating element resistance R_tot of an arrangement of a number of heating tracks or track portions (i) arranged in parallel such that electric current in at least two neighbouring tracks or track portions flows in the same direction, Rj is set out in equation 1 : (-1) where n is the total number of heating tracks arranged electrically in parallel.

The behaviour of a parallel track heating element 610 when one heating track fails can be considered with reference to a heating element with 4 parallel heating tracks, for example as shown in Figure 6A. The heating tracks each have a resistance of 3 Ohms. The total resistance of the heating element is 0.75 Ohms, calculated using equation 1.

When one heating track starts to fail, the resistance of the failing heating track increases. The total resistance of the heating element 610 also starts to increase, following a linear relationship with the failing heating track resistance. However, as the heating track resistance continues to increase, the heating element resistance asymptotes to a constant resistance value. At this constant resistance value, the influence of the failing heating track on the heating element resistance is capped. In this example where unbroken heating tracks each have a resistance of 3 Ohms, the total resistance of the heating element that asymptotes to 1 Ohm when the failed track can be considered as an open circuit (i.e. no more current can flow through it). When one track breaks in this example, only three tracks remain for the purpose of calculating the total heating element resistance.

To consider the behaviour of such a heating element 610, a supply voltage of 3.5 Volts and target power of 5.5 Watts are considered. In this example, unbroken parallel heating tracks remain with their initial resistance of 3 Ohms. In the failing track, the total maximum current decreases with increasing resistance. In the failing track, current decreases to zero once broken. The current through the unbroken parallel tracks remains substantially constant as the resistance of the failing track increases (if resistance change due to temperature increase is ignored).

A similar behaviour is observed for the maximum power generation . Less total power is generated once a heating track has failed. However, in this example, the maximum power remains higher than the target of 5.5 Watts despite failure of one of the heating tracks.

In contrast to a porous heater film, the overall heating element resistance increase of the parallel track heating element can be monitored by control electronics. In a heater film, a damaged area may widen with time until failure occurs, because the current density across the heater film (perpendicular to the current flow) increases at the damaged area, generating more power, elevating the local temperature. This locally increases the resistance of the heater film, further increasing the temperature until breakdown (i.e. , positive feedback). In the parallel track heating element 610, in contrast, the overall heating element resistance increase can be monitored by the control electronics. The device or system may be configured such that when a predetermined threshold is reached, the device or system tells the user through a user interface that the heater assembly should be exchanged.

The aerosol-generating device or system may comprise control circuitry. The control circuitry may be configured to, after detecting the failure of a heating track for example by a feedback loop, adjust the power fed to the heater. The control circuitry may be configured to provide a pulse width modulation (“PWM”) signal to control the power fed to the heater. The control circuitry may adjust the power fed to the heater by adjusting the duty cycle of the pulse width modulation signal. In an example, control circuitry may be configured to have a duty cycle at 33.7 percent when the heating tracks are in a normal condition. The duty cycle may increase to 44.9 percent when one of the heating tracks has failed. When one of the heating tracks fails, the power density (heating power generated by surface area) increases, enhancing the thermal efficiency of the heater body. Therefore, the proper operation of the heater is not jeopardized with one failed heating track. A similar result occurs if a second heating track breaks. The control circuitry may be configured such that the duty cycle further increases (to 67.4 percent in the current example). Thus, a heating element with four parallel heating tracks can still operate with the nominal condition of 5.5 Watts even if two of these heating tracks are broken, since the duty cycle remains below 100 percent.

The control circuitry may be configured such that, based on the change of nominal total resistance of the heating element 610 once a parallel heating track has failed, it is possible for the control circuitry to assess the state of the heating element (i.e., number of heating tracks which have failed). The control circuitry may be configured such that, after a predefined number of heating track(s) have failed, the device can tell the user that the heater assembly should be changed.

Referring to Figures 7A and 7B, there are shown schematic illustrations of current flow 709 around a corner of a heating element track.

Figure 7A is a schematic illustration of current flow 709 around a known heating element in which a track portion defines a path having a bend, the inner edge of the bend having a sharp corner. In such a track, current flow depicted by arrows 709, which follows a path of least resistance, is concentrated (i.e., there is an increase in current density). This concentration occurs at an inner edge of the corner. Current concentration can increases the local temperature, and can lead to the presence of hot spot at the corner. A hot spot is disadvantageous, as it can affect the efficiency and reliability of the heating element. A hot spot occurs despite the potential for local resistivity of the heater track material to increase due to a local increase in temperature (which would direct current flow away to a path of lower resistance).

Figure 7B is a schematic illustration of current flow 709 around a heating element in which a track portion 717 defines a path having a bend, the inner edge of the bend being curved. In such a track 717, current flow 709 does not form a local hot spot.

In contrast to the track shape shown in Figure 7A, current flow 709 in the smoother curved track portion 717 as shown in Figure 7B remains more evenly distributed across the heating track 717, as depicted by dashed arrows 709. Current flow 709 is guided to flow more evenly, to avoid a concentration of current at any point. This in turn limits hot spot creation. The heater track 717 may have a gradient of electrical resistivity perpendicular to current flow in a corner or corners, such that the electrical resistivity is higher at an inner part of the corner and lower at an outer part of the corner. Such a gradient is beneficial to counterbalance localized high current density and reduce hot spot creation.

Referring to Figure 8A, there is shown a heater assembly 800 comprising a heating element 804 for vaporising a liquid aerosol-forming substrate and a porous body 802 for supplying the liquid aerosol-forming substrate from a reservoir or liquid storage portion (not shown) to the heating element 808. The porous body 802 has a liquid absorption surface (not shown) and a heating surface 802a. The heating element 804 is arranged on the heating surface 802a of the porous body 802.

The heating element 804 is formed from a layer of electrically conductive material such that an electrical current can pass through the heating element 804 to heat the heating element 804 by resistive or Joule heating. The heating element 804 is also porous such that it is fluid permeable and vapours can pass through it from the heating surface 802a of the porous body 802. Therefore, in the heater assembly 800 of Figure 8A, vapour emission occurs through the heating element 804. The heating element 804 may comprise a thin metallic layer or film having pores that pass through the thickness of the layer or film. Alternatively, the heating element may comprise a metallic foam having interconnected open pores that pass through the thickness of the foam. In this example, the porous body 802 comprises a porous ceramic body formed from a suitable ceramic material such as AI2O3. Furthermore, the heating element 804 has been deposited on the porous ceramic body 802 using a suitable physical or chemical vapour deposition process.

The heater assembly 800 further comprises electrical contacts 806 that are electrically connected to the heating element 804. The electrical contacts 806 are arranged on the heating surface 802a and at or near opposite ends of the heating surface 802a. The heating element 804 extends between the electrical contacts 806. The electrical contacts 806 are arranged to be connected to control circuitry for controlling the supply of electrical power to the heating element. The electrical contacts 806 are formed from a more electrically conductive material than the heating elements such as copper, gold or zinc, although other suitable materials may be used. This avoids excess wasted heat being generated in the electrical contacts.

Figure 8B shows a schematic cross-sectional view of the heater assembly 800 of Figure 8A. For clarity and simplicity, the electrical contacts 806 from Figure 8A have been omitted in Figure 8B and the features are not drawn to scale. The liquid absorption surface 802b is shown as the lower surface of the porous body 802 in Figure 8B and the heating surface 802a is shown as the upper surface of the porous body 802, although it will be appreciated that the orientation of these surfaces may differ in use or once the heater assembly 800 is installed in an aerosol-generating device. Liquid stored within a liquid reservoir or liquid storage portion (not shown) contacts the liquid absorption surface 802b and is conveyed through the porous body 802 to the heating surface 802a, as indicated by arrows E in Figure 8B. The porous heating element 804 is arranged on the heating surface 802a of the porous body 802 and heats the liquid aerosol-forming substrate conveyed to it such that the liquid aerosol-forming substrate boils and generates a vapour. The porous heating element 804 has a plurality of pores 808 which pass through the thickness of the heating element from the heating surface 802a to an exterior of the heater assembly 800.

Since the heating element 804 is porous, vapour generated during heating of the heating element 804 can pass through the heating element 804 via the pores 108 and be emitted from the heating surface 802a, as indicated by arrows F in Figure 8B. The heating element does not have any impermeable sections which prevent vapour release and cause a build up of vapour pressure underneath the heating element. This reduces the speed of vapour emission from the heating element 804 compared to conventional impermeable track heating elements. Simulations have demonstrated that an average vapour emission speed of the vapour from the heating surface 802a is 0.1 metres per second at a power of 6.3 watts . Such a low vapour emission speed means that the vapour can easily be carried away by the airflow in an airflow pathway without impinging on the internal walls of the airflow pathway and causing condensation. The average vapour emission direction is substantially perpendicular to the liquid absorption surface 802b of the porous body 802, the liquid absorption surface 802b being substantially flat.

Figure 9 is a schematic illustration of the interior of an aerosol-generating system 900 according to an example of the second aspect of the invention. The aerosol-generating system comprises two main components, a cartridge 902 and a main body part or aerosol-generating device 904. A connection end 902a of the cartridge 902 is removably connected to a corresponding connection end 904a of the aerosol-generating device 904. The connection end 902a of the cartridge 902 and connection end 904a of the aerosol-generating device 904 each have electrical contacts or connections (not shown) which are arranged to cooperate to provide an electrical connection between the cartridge 902 and the aerosol-generating device 904. The aerosol-generating device 904 comprises a device housing 909 that contains a power source in the form of a battery 906, which in this example is a rechargeable lithium ion battery, and control circuitry 908. The aerosol-generating system 900 is portable and has a size comparable to a conventional cigar or cigarette. A mouthpiece 910 is arranged at a mouth end 902b of the cartridge 902. The mouth end 902b is located opposite the connection end 902a of the cartridge 902.

The cartridge 202 comprises a cartridge housing 912 containing a heater assembly 800 and a liquid reservoir or liquid storage portion 918 for holding a liquid aerosol-forming substrate. The heater assembly 800 in Figure 9 has a similar construction to that of Figures 8A and 8B but is inverted compared to its orientation in Figures 8A and 8B such that the liquid absorption surface 802b faces upwards and is in fluid communication with the liquid storage portion 818 and the heating surface 802a carrying the heating element (not shown) faces downwards. Liquid aerosol-forming substrate is conveyed downwards from the liquid absorption surface 802b through the porous body 802 to the heating element and vaporised aerosol-forming substrate is emitted from the heating surface 802a when electrical power is supplied to the heating element. As indicated by arrows F in Figure 8B, the average vapour emission direction is substantially perpendicular to the liquid absorption surface 802b of the porous body 802.

The cartridge 902 comprises one or more air inlets 922 formed in the cartridge housing 912 at a location along the length of the cartridge 902 corresponding to the location of the heating surface 802a of the heater assembly 800. An aerosol outlet 926 is located in the mouthpiece 910 at the mouth end 902b of the cartridge 902. The one or more air inlets 922 are in fluid communication with the aerosol outlet 926 to define an airflow pathway 920 through the cartridge 902 of the aerosol-generating system 900. The airflow pathway 920 flows from the one or more air inlets 922 to the heater assembly 800 in an airflow channel 923. The heater assembly 900 is arranged in fluid communication with the airflow pathway 920 in the airflow channel 923. Air enters the one or more air inlets 922 and flows through the airflow channel 923 past the heater assembly 800 in an average airflow direction as indicated by arrows I in Figure 9. As can be seen in Figure 9, the heater assembly 800 and airflow pathway 920 in the airflow channel 923 are arranged such that an angle between the average vapour emission direction F and the average airflow direction I is approximately 90 degrees, that is, at an angle substantially perpendicular to the average airflow direction I. The average vapour emission direction F has no speed or direction component that opposes the average airflow direction I and therefore any loss of momentum of the vapour is reduced. This reduces the tendency for recirculation and turbulence of vapour to occur in the airflow path 920 and the vapour is less likely to impinge on the internal surfaces of the airflow channel 923.

In the example of Figure 9, the liquid storage portion 918 is annular in cross-section and is arranged around a central sealed aerosol channel 924. Once the airflow pathway 920 reaches the heater assembly 800, it is diverted upwards around the sides of the heater assembly 800 and flows through the aerosol channel 924 to the aerosol outlet 926. It will be appreciated that other arrangements of liquid storage portion and airflow pathway could be implemented, such as those discussed below in respect of Figures 10 and 11.

The aerosol-generating system 900 is configured so that a user can puff or draw on the mouthpiece 910 of the cartridge 902 to draw aerosol into their mouth through the aerosol outlet 926. In operation, when a user puffs on the mouthpiece 910, air is drawn in through the one or more air inlets 922, along the airflow pathway 920 through the airflow channel 923, past and around the heater assembly 800 and along the airflow pathway 920 through the aerosol channel 924 to the aerosol outlet 926. The control circuitry 908 controls the supply of electrical power from the battery 906 to the cartridge 902 when the system is activated. This in turn controls the amount and properties of the vapour produced by the heater assembly 800. The control circuitry 908 may include an airflow sensor (not shown) and the control circuitry 920 may supply electrical power to the heater assembly 800 when user puffs are detected by the airflow sensor. This type of control arrangement is well established in aerosolgenerating systems such as inhalers and e-cigarettes. When a user puffs on the mouthpiece 910 of the cartridge 902, the heater assembly 800 is activated and generates a vapour that is entrained in the airflow pathway 920. The vapour cools within the airflow pathway 920 to form an aerosol, which is then drawn into the user’s mouth through the aerosol outlet 926.

Figure 10 is a schematic cross-sectional view of part of an aerosol-generating system 1000 according to another example of the second aspect of the invention showing an arrangement of a heater assembly relative 800 to an airflow pathway 1020 within the aerosolgenerating system 1000. For simplicity, other components of the aerosol-generating system have been omitted from Figure 10. The heater assembly 800 of Figure 10 is identical to the heater assemblies 800 of Figures 8A and 8B. The aerosol-generating system 1000 comprises a liquid storage portion 1022 that holds a liquid aerosol-forming substrate in contact with the liquid absorption surface 802b of the porous body 802. Liquid aerosol-forming substrate is conveyed from the liquid storage portion 1022 through the porous body 802 to the heating surface 802a, as indicated by arrows E. Vaporised aerosol-forming substrate is emitted through the porous heating element 804 from the heating surface 802a. As indicated by arrows F, the average vapour emission direction is substantially perpendicular to the liquid absorption surface 802b of the porous body 802.

In the example of Figure 10, the heater assembly 800 is arranged below or to one side of the airflow channel or pathway 1020, which airflow pathway 1020 is defined by airflow channel walls 1024. As viewed in Figure 10, a left-hand end of the visible portion of the airflow pathway 1020 receives airflow from an air inlet (not shown) and the right-hand end of the visible portion of the airflow pathway delivers airflow to an aerosol outlet (not shown). The liquid absorption surface 802b of the porous body 802 is arranged parallel to the airflow pathway 1020. The heating surface 802a of the porous body faces into the airflow pathway 1020. The heater assembly 800 is in fluid communication with the airflow pathway such that the airflow in the airflow pathway flows past the heater assembly 800 in an average airflow direction, as indicated by arrows G. The heater assembly 800 and airflow pathway 1020 are arranged such that an angle 0 between the average vapour emission direction F and the average airflow direction G is approximately 90 degrees, that is, at an angle 0 substantially perpendicular to the average airflow direction G. The average vapour emission direction F has no speed or direction component that opposes the average airflow direction G and therefore any loss of momentum of the airflow is reduced. This reduces the tendency for recirculation and turbulence to occur in the airflow path 1020 and the vapour is less likely to impinge on the internal surfaces of the airflow channel walls 1024.

Figure 11 is a schematic cross-sectional view of part of an aerosol-generating system 1100 according to another example of the second aspect of the invention disclosure showing another arrangement of a heater assembly 800 relative to an airflow pathway 1120 within the aerosol-generating system 1100. For simplicity, other components of the aerosol-generating system have been omitted from Figure 11. The heater assembly 800 of Figure 1 is identical to the heater assemblies 800 of Figures 8A and 8B. The aerosol-generating system 1100 comprises a liquid storage portion 1122 that holds a liquid aerosol-forming substrate in contact with the liquid absorption surface 802b of the porous body 802. Liquid aerosol-forming substrate is conveyed from the liquid storage portion 1122 through the porous body 802 to the heating surface 802a, as indicated by arrows E. Vaporised aerosol-forming substrate is emitted through the porous heating element 804 from the heating surface 802a. As indicated by arrows F, the average vapour emission direction is substantially perpendicular to the liquid absorption surface 802b of the porous body 802.

In the example of Figure 11 , the airflow channel or pathway 1120 is split into first and second airflow pathway sections 1120a and 1120b which pass either side of the heater assembly 800. The first and second airflow pathway sections 1120a and 1120b combine downstream of the heater assembly 800 into a third airflow pathway section 1120c. The first and second airflow pathway sections 1120a and 1120b receive airflow from one or more air inlets (not shown) and the third airflow pathway section 1120c delivers airflow to an aerosol outlet (not shown). The airflow pathway 1120 is defined by airflow channel walls 1124. The liquid absorption surface 802b of the porous body 802 is arranged substantially perpendicular to the airflow pathway 1120. The heating surface 802a of the porous body 802 faces in a downstream direction of the airflow pathway 1120. The heater assembly 800 is in fluid communication with the airflow pathway such that the airflow in the airflow pathway flows past the heater assembly 800 in an average airflow direction, as indicated by arrows G.

The heater assembly 800 and airflow pathway 1120 are arranged such that an angle 0 between the average vapour emission direction F and the average airflow direction G is less than 90 degrees. Upstream of the heating surface 802a of the porous body 802, the average airflow direction G past the heater assembly 800 is substantially the same as the average vapour emission direction F. At the point along the airflow pathway 1120 corresponding to the heating surface 802a the airflow pathway 1120 starts to narrow or taper inwards, at which point the average airflow direction G past the heater assembly 800 changes to an angle 0 relative to the average vapour emission direction F of approximately 45 degrees. Downstream of the heating surface 802a of the porous body 802 in the third airflow pathway section 1120c, the average airflow direction G of the combined airflow is again substantially the same as the average vapour emission direction F. It will be appreciated that the narrowing or tapering of the airflow pathway 1120 could be omitted. In which case, the average airflow direction G past the heater assembly 800 would be substantially the same as the vapour emission direction F.

The specific embodiments and examples described above illustrate, but do not limit, the invention. It is to be understood that other embodiments of the invention may be made and the specific embodiments and examples described herein are not exhaustive.

Claims

CLAIMS:

1. A heater assembly for an aerosol-generating system, the heater assembly comprising: a heating element for vaporising a liquid aerosol-forming substrate; and a porous body for conveying the liquid aerosol-forming substrate to the heating element, the porous body having a liquid absorption surface, a heating surface and at least one side surface extending from the liquid absorption surface to the heating surface, wherein the heating element is located on the heating surface of the porous body, wherein the heating surface of the porous body is convex in one or both of a first transverse direction and a second transverse direction, the first transverse direction being orthogonal to the second transverse direction, wherein the heating surface of the porous body has a width that is different to a width of the liquid absorption surface in a same transverse direction, and wherein the porous body comprises a porous ceramic body or a porous glass body.

2. A heater assembly according to claim 1, wherein the heating surface of the porous body has a radius of curvature of at least about 1.5 millimetres in one or both of the first transverse direction and the second transverse direction.

3. A heater assembly according to claim 1 or 2, wherein the heating surface of the porous body has a radius of curvature of less than or equal to about 10 millimetres in one or both of the first transverse direction and the second transverse direction.

4. A heater assembly according to any one of claims 1 to 3, wherein a ratio of the radius of curvature of the heating surface to the width of the heating surface in a same transverse direction is at least about 0.5.

5. A heater assembly according to any one of claims 1 to 4, wherein a ratio of the radius of curvature of the heating surface to the width of the heating surface in a same transverse direction is less than or equal to about 5.

6. A heater assembly according to any one of claims 1 to 5, wherein a ratio of the length of the heating surface to the width of the heating surface in one or both of the first transverse direction is at least about 0.02.

7. A heater assembly according to any one of claims 1 to 6, wherein a ratio of the length of the heating surface to the length of the porous body is at least about 0.05.

8. A heater assembly according to any one of claims 1 to 7, wherein a ratio of the length of the heating surface to the length of the porous body is less than or equal to about 0.45.

9. A heater assembly according to any one of claims 1 to 8, wherein the heating surface of the porous body has a surface area greater than the square of the width of the heating surface in one or both of the first transverse direction and the second transverse direction by at least about 10 percent.

10. A heater assembly according to any one of claims 1 to 9, wherein the heating surface of the porous body has a surface area greater than the square of the width of the heating surface in one or both of the first transverse direction and the second transverse direction by less than or equal to about 55 percent.

11. A heater assembly according to any one of claims 1 to 10, wherein the curvature of the heating element in the first transverse direction is substantially the same as the curvature of the heating surface of the porous body in the first transverse direction, and wherein the curvature of the heating element in the second transverse direction is substantially the same as the curvature of the heating surface of the porous body in the second transverse direction.

12. A heater assembly according to any one of claims 1 to 11 , wherein the porous body has a shape that tapers along the entire length of the porous body.

13. A heater assembly according to any one of claims 1 to 12, wherein the heating surface of the porous body has a width that is greater than a width of the liquid absorption surface in a same transverse direction.

14. An aerosol-generating system comprising: a heater assembly according to any one of claims 1 to 13; a cartridge comprising a liquid storage portion for storing a liquid aerosol-forming substrate; and an aerosol-generating device comprising a power supply for supplying power to the heater assembly and control circuitry for controlling the supply of power from the power supply to the heater assembly, wherein the heater assembly is a component of either the cartridge or the aerosolgenerating device.

15. An aerosol-generating system according to claim 14, wherein the heating element is fluid permeable such that, in use vapour is emitted from the heater assembly in an average vapour emission direction, wherein the aerosol-generating system further comprises an air inlet and an aerosol outlet to define an airflow pathway through the aerosol-generating system, wherein the heater assembly is arranged in fluid communication with the airflow pathway such that air flows past the heater assembly in an average airflow direction, and wherein the heater assembly and airflow pathway are arranged such that an angle between the average vapour emission direction and the average airflow direction is less than 135 degrees.