EP4704621A1 - Heater assembly comprising a polymer composite material for use in an aerosol-generating system - Google Patents

Abstract

There is provided a heater assembly (212) for an aerosol-generating device, the heater assembly (212) comprising a heating body configured for resistive heating, the heating body comprising a polymer composite comprising a polymeric matrix and at least one of graphite, a graphite-derived material, and hexagonal boron nitride dispersed within the polymeric matrix.

Description

HEATER ASSEMBLY COMPRISING A POLYMER COMPOSITE MATERIAL FOR USE IN AN AEROSOL-GENERATING SYSTEM

The present disclosure relates to a heater assembly for an aerosol-generating device. The disclosure also relates to an aerosol-generating device comprising the heater assembly, as well as to an aerosol-generating system comprising the aerosol-generating device and an aerosol-generating article for use with the aerosol-generating device.

In particular, the present disclosure relates to a heater assembly comprising an electrically resistive body configured to heat an aerosol-generating substrate of an aerosolgenerating article.

Aerosol generating articles in which an aerosol-forming substrate, such as a tobacco containing substrate, is heated rather than combusted are known in the art. Typically, in such aerosol generating articles an aerosol is generated by the transfer of heat from a heat source to an aerosol-forming substrate.

Electrically operated aerosol-generating devices, for example handheld aerosolgenerating devices, may be used with such aerosol generating articles. Such electrically operated aerosol-generating devices may comprise a heating element configured to heat an aerosol-forming substrate to temperatures of several hundred degrees centigrade. This releases volatile compounds from the aerosol-forming substrate which are entrained in air drawn through the aerosol generating article. As the released compounds cool, they condense or nucleate to form an aerosol.

Several examples of aerosol-generating devices for consuming aerosol-generating articles have been disclosed in the art. Such devices include, for example, electrically heated aerosol-generating devices in which an aerosol is generated by the transfer of heat from one or more electrical heater elements of the aerosol-generating device to the aerosol-generating element of an aerosol-generating article. To this purpose, the aerosol-generating article may be partially received within a heating cavity of the aerosol-generating device, such that an upstream end of the aerosol-generating article is inserted into the cavity whereas a downstream end of the aerosol-generating article projects out of the cavity.

For example, electrically heated aerosol-generating devices have been proposed that comprise an internal heater blade which is adapted to be inserted into the aerosol-generating substrate when the aerosol-generating article is received within the heating cavity. As an alternative, heating of the aerosol-generating substrate has been accomplished using external heating, such as by way of a tubular heater element that at least partially defines the heating cavity into which the aerosol-generating article is inserted or that it otherwise coupled with a tubular element defining the heating cavity. Inductively heatable aerosol-generating articles have also been proposed, such as for example in WO 2015/176898. These aerosol-generating articles comprise an aerosolgenerating element comprising an aerosol-generating substrate, such as a tobacco-containing substrate, and a susceptor arranged within the aerosol-generating substrate. Functional coupling between the susceptor and an inductive heater element of the aerosol-generating device is achieved when the aerosol-generating article is partially received within the heating cavity of the aerosol-generating device.

Constructing heater elements for externally heating an aerosol-generating substrate tends to be a rather complex process, as it typically involves imparting a curved or tubular shape to an originally flat heating film. For example, an originally flat heating film may need to be wrapped about a mandrel or a tube with a relatively small curvature radius. This operation may be especially complicated as the heating film may be formed of a plurality of layers of material having different pliability. The manufacturing process may be further complicated by a need to incorporate multiple, distinct heating units within a single aerosolgenerating device with a view to providing different modes of heating the aerosol-generating substrate.

Solid aerosol-generating substrates need to be heated up to temperatures sufficient to promote extraction of aerosol species (for example, nicotine and glycerine). Existing heaters are typically configured to supply heat so that the solid aerosol-generating substrate is exposed to temperatures within such ranges throughout. However, this heating set-up may have the drawback that battery efficiency of use is less than optimal. Further, this heating setup may limit use of a solid aerosol-generating substrate to a predetermined and finite number of puffs or to a predetermined number of minutes. Additionally, maintaining a solid aerosolgenerating substrate at temperatures sufficient to promote extraction of aerosol species in between puffs may also undesirably increase a risk of generating harmful and potentially harmful constituents (HPHCs).

It would be desirable to provide a heater assembly for an aerosol-generating device adapted to at least partially address at least one of the drawbacks discussed above. For example, it would be desirable to provide a novel and improved heater assembly for an aerosol-generating device that is easier to manufacture. Equally, it would be desirable to provide a novel and improved aerosol-generating device comprising a heater assembly that can be configured to provide a more efficient external heating of a solid aerosol-generating substrate.

The present disclosure relates to a heater assembly for an aerosol-generating device.

The heater assembly may comprise a heating body configured for resistive heating.

The heating body may comprise a polymer composite. The polymer composite may comprise a polymeric matrix and at least one of graphite, a graphite-derived material, and hexagonal boron nitride dispersed within the polymeric matrix.

According to a first aspect of the present invention, there is provided a heater assembly for an aerosol-generating device, the heater assembly comprising a heating body configured for resistive heating, the heating body comprising a polymer composite comprising a polymeric matrix and at least one of graphite, a graphite-derived material, and hexagonal boron nitride dispersed within the polymeric matrix.

According to a second aspect of the present invention, there is provided an aerosolgenerating device comprising a heater assembly according to the first aspect of the invention.

According to a third aspect of the present invention, there is provided an aerosolgenerating system comprising an aerosol-generating device according to the second aspect of the invention and an aerosol-generating article for use with the aerosol-generating device.

In contrast to existing heater assemblies for aerosol-generating devices, a heater assembly in accordance with the present invention comprises a heating body configured for resistive heating, wherein the heating body comprises a polymeric matrix and at least one of graphite, a graphite-derived material, and hexagonal boron nitride dispersed within the polymeric matrix.

The inventors have found that a heating body comprising a polymeric matrix and filler particles of at least one of graphite, a graphite-derived material, and hexagonal boron nitride dispersed within the polymeric matrix is generally easier to manufacture compared to similar heating bodies configured for resistive heating made of other conductive materials that are typically used in existing heater assemblies for aerosol-generating devices.

In more detail, the inventors have observed that the thermoplastic properties of the polymeric matrix make it possible for the polymer composite to be tailored to be conveniently malleable, such that it lends itself to precise and controlled shaping. In particular, this makes the polymer composite described briefly above easier to form into elongate, hollow shapes compared with conductive materials typically used in the heater assemblies of existing aerosol-generating devices.

At the same time, by controlling and adjusting the concentration and distribution of the conductive filler particles dispersed within the polymeric matrix, it is advantageously possible to provide a heating body capable of generating enough heat by Joule effect so as to efficiently heat a solid aerosol-generating substrate of an aerosol-generating article thermally coupled with the heating body.

Without wishing to be bound by theory, the inventors have found that by adjusting the formulation of the polymeric matrix and the degree of dispersion of the conductive filler particles within the polymeric matrix it is possible to control the conductivity and, as a consequence, the amount of heat generated resistively by the heater assembly when a voltage is applied to the heating body. In particular, as will be discussed in more detail below, by adjusting the relative proportion of conductive filler to polymer within the polymer composite it may be advantageously possible to ensure that a heating body made of the polymer composite exhibit highly desirable levels of resistivity. Other parameters, such as the length and cross- sectional surface area of the heating body may also be varied to fine-tune the resistive behaviour of the heating body as a whole. In general, this provides for an enhanced capability of controlling and improving the efficiency of heat transfer from the heater assembly to an aerosol-generating substrate, which may also beneficially favour a more effective extraction of aerosol species from the substrate itself.

Thus, a heater assembly having the features described briefly above advantageously finds use in an aerosol-generating device that, in turn, forms part of an aerosol-generating system wherein an elongate aerosol-generating article is at least partially received within a heating chamber of the heating body. This ensures that the aerosol-generating substrate of the aerosol-generating article is thermally coupled with the heating body, and heat can be transferred efficiently from the heater assembly to the aerosol-generating substrate.

Further, the inventors have identified advantageous processing conditions under which a porous heating body comprising the polymer composite may be formed with desirable values of porosity, average pore size specific surface area. Such a porous heating body can advantageously find use in a heater assembly of an aerosol-generating device configured to convectively supply heat to air drawn into the aerosol-generating device and flowing through the porous body heating prior to reaching an aerosol-generating substrate during use.

In practice, such a porous heating body may be configured to convectively transfer heat to the flow of air drawn into an aerosol-generating device, such that the flow of air reaches the aerosol-generating substrate in a pre-heated condition. This may be beneficial in that aerosol-forming species that are present in the aerosol-generating substrate may be more efficiently released upon heating.

Further, it may generally be possible to supply and exchange heat more efficiently during use of the aerosol-generating device, because supply of heat to the incoming flow of air may be combined with supply of heat to the aerosol-generating substrate from a further, independently controlled heat source distinct the porous heating body. By independently activating and controlling the supply of heat from the porous heating body and the further heat source it may advantageously possible to manage the overall supply of heat to an aerosolgenerating article during use more efficiently, such as for example reducing the consumption of heat between consecutive puffs.

Without wishing to be bound by theory, it is understood that the air’s residence time - the average time spent by a fluid parcel in a control volume - in the porous body will generally be a function of the porosity and tortuosity of the porous body, as well as of its geometry. Porosity, average pore size and pore size distribution, specific surface area of the porous body will also have an impact on the amount of heat exchanged convectively. At the same time, porosity and tortuosity of the porous body will have an impact on a resistance to draw (RTD) of the porous body and of the heating body as a whole. By adjusting porosity, length, diameter of the porous body, a satisfactory balance can be struck between the ability to efficiently preheat air flowing through the porous body and an RTD of the porous body.

Thus, for example, the porous body of a heater assembly in accordance with the present invention may be configured to be able to pre-heat to a predetermined temperature a volume of air substantially corresponding to an average volume inhaled by a consumer with each puff. By ensuring that the incoming flow of air reaches the aerosol-generating substrate in such a pre-heated condition, the amount of heat to be supplied to the aerosol-generating substrate via the further heat source can be advantageously reduced.

As a result, it may be possible to configure the further heat source to reach, on the average, comparatively lower temperatures during use. As such, an overall energy consumption is reduced. At the same time, by maintaining the aerosol-generating substrate at comparatively lower temperatures between puffs, it may be possible to make a more efficient use of the aerosol-generating substrate such as to optimise the delivery of aerosol species to the consumer for a longer period of time.

For example, the further heat source may be configured to heat the aerosol-generating substrate of an aerosol-generating article to a stand-by temperature or maintenance temperature during the usage session. An aerosol-generating device comprising the heater assembly described above may further be configured such that the temperature of the aerosolgenerating substrate increases from the stand-by temperature when a user takes a puff, for example to an operational temperature.

For example, the aerosol-generating device may be configured to supply a thermal boost to the aerosol-generating substrate during a user puff taken during the usage session. To this purpose, the aerosol-generating device may rely on a heater assembly in accordance with the present invention, the heater assembly comprising a porous heating body of the type briefly described above.

As will be discussed in more detail below, the porous heating body may define an airflow path upstream of a cavity into which the aerosol-generating article is at least partly received. When using the device, a user draws air into the aerosol-generating device through the airflow path, which may connect the cavity with the external environment. Air flowing along the airflow path through the porous heating body is thus heated prior to reaching the cavity, where it supplies a thermal boost to the aerosol-generating substrate of the aerosol-generating article. Such a configuration may allow the aerosol-generating substrate to be maintained at a first temperature, for example the stand-by temperature (that is, a temperature that is at or slightly below a temperature required to form an aerosol) and then be heated to an increased temperature, for example the operational temperature (that is, a temperature above the temperature required to form an aerosol during the user puff).

The stand-by target temperature is preferably a temperature that is greater than room temperature and the operational target temperature is higher than the stand-by target temperature. By selecting an appropriate stand-by temperature, the aerosol-forming substrate can be boosted in temperature almost instantaneously to the operational temperature on application of further thermal energy to the substrate. The temperature can be allowed to drop to the stand-by temperature after a user puff.

The combination of heating to a stand-by temperature and a rapid temperature rise to an operational temperature on puffing, allows efficient harvesting of desirable components of the aerosol-generating substrate, such as nicotine, flavour components, and aerosol-formers such as glycerine, without extensively overheating the aerosol-generating substrate. Formation of undesirable aerosol-constituents may be reduced and an optimal harvest of the desirable components may be obtained.

To implement such a configuration, the aerosol-generating device is preferably equipped with at least a flow detector, for example in the form of a pressure sensor.

The flow detector can be used to control supply of electric power to the heating body. For example, the flow detector can be used to selectively power the air-permeable body portion of the heating body so that only during a puff the air-permeable body portion generates and transfer enough heat to the incoming flow of air to boost the temperature of the aerosolgenerating substrate further downstream.

However, the heater assembly may also be configured to constantly power the air- permeably body portion during a usage session, so that the incoming flow of air associated with a puff will be instantaneously heated, with no puff detection needed. The heater assembly may also be configured to power the air-permeable body portion to be consistently heated to a stand-by temperature and then boosted to a higher temperature upon detection of a puff, which may help counter the fact that the incoming flow of air will typically cool down the air- permeably body portion when flowing through it.

Thus, an aerosol-generating device comprising a heater assembly in accordance with the present invention, the heater assembly comprising a porous heating body of the type briefly described above, may be configured to control the temperature of the aerosolgenerating substrate with reference to the stand-by target temperature during non-puff periods and with respect to the operational target temperature during puff periods. The result is that during non-puff periods the temperature of the substrate is maintained consistently at the stand-by target temperature. Once the start of a user puff is detected, the temperature rises to the operational target temperature, and after the user puff has ended the temperature is allowed to drop to the stand-by target temperature once more.

As used herein with reference to the invention, the term “aerosol-generating article” is used to describe an article comprising an aerosol-generating substrate that is heated to generate an inhalable aerosol for delivery to a user.

As used herein with reference to the invention, the term “aerosol-generating substrate” is used to describe a substrate comprising aerosol-generating material that is capable of releasing upon heating volatile compounds that can generate an aerosol.

As used herein with reference to the invention, the term “aerosol” is used to describe a dispersion of solid particles, or liquid droplets, or a combination of solid particles and liquid droplets, in a gas. 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, or liquid droplets, or a combination of solid particles and liquid droplets.

As used herein with reference to the invention, the term “aerosol-generating device” is used to describe a device that interacts with the aerosol-generating substrate of the aerosolgenerating article to generate an aerosol.

As used herein, the terms ‘“distal”, “upstream” “proximal” and “downstream” describe the relative positions of components, or portions of components, of an aerosol-generating device and aerosol generating article. Aerosol generating articles and devices according to the present disclosure have a proximal end through which, in use, an aerosol exits the article or device for delivery to a user, and have an opposing distal end. The proximal end of the aerosol generating article and device may also be referred to as the mouth end. In use, a user draws on the proximal end of the aerosol generating article in order to inhale an aerosol generated by the aerosol generating article or device. The terms upstream and downstream are relative to the direction of aerosol movement through the aerosol generating article or aerosol-generating device when a user draws on the proximal end of the aerosol-generating article. The proximal end of the aerosol-generating article is downstream of the distal end of the aerosol-generating article. The proximal end of the aerosol-generating article may also be referred to as the downstream end of the aerosol-generating article and the distal end of the aerosol-generating article may also be referred to as the upstream end of the aerosolgenerating article.

As used herein with reference to the invention, the term “longitudinal” is used to describe the direction between the upstream end and the downstream end of the aerosolgenerating article or between the upstream end and the downstream end of the aerosolgenerating device. During use, air is drawn through the aerosol-generating article in the longitudinal direction. As used herein with reference to the invention, the term “length” is used to describe the maximum dimension of the aerosol-generating article or the aerosol-generating device or a component of the aerosol-generating article or the aerosol-generating device in the longitudinal direction.

As used herein with reference to the invention, the term “transverse” is used to describe the direction perpendicular to the longitudinal direction. Unless otherwise stated, references to the “cross-section” of the aerosol-generating article or aerosol-generating device or a component of the aerosol-generating article or aerosol-generating device refer to the transverse cross-section.

As used herein with reference to the invention, the term “width” denotes the maximum dimension of the aerosol-generating article or device or of a component of the aerosolgenerating article or device in a transverse direction. For example, where the aerosolgenerating article has a substantially circular cross-section, the width of the aerosolgenerating article corresponds to the diameter of the aerosol-generating article. Where a component of the aerosol-generating article has a substantially circular cross-section, the width of the component of the aerosol-generating article substantially corresponds to the diameter of the component of the aerosol-generating article.

As used herein with reference to the invention, the term “hollow tubular element” is used to denote a generally cylindrical element having a lumen along a longitudinal axis thereof. The tubular portion may have a substantially circular, oval or elliptical cross-section. The lumen may have a substantially circular, oval or elliptical cross-section. In particular, the term “hollow tubular element” is used to denote an element defining at least one airflow conduit establishing an uninterrupted fluid communication between an upstream end of the hollow tubular element and a downstream end of the tubular element.

As used herein, the term “heating body” denotes a component which is configured to transfer heat energy to the aerosol-generating substrate.

As used herein, the term “air-permeable” is used to describe an entity which allows air to pass through it. The term “air-permeable” also encompasses a volume characteristic of a suitable material, either in relation to all or part of its volume; for example, a material having a porosity in all or part of the volume of the material.

Thus, the term “air-permeable body portion”, as used herein with reference to the present invention, denotes a segment of material that is not blocked, plugged or sealed in a way to completely block air from passing through the air- permeable body.

An air-permeable body portion may be configured so as to enable flow along a desired airflow direction. For example, an air-permeable body portion may be configured so as to enable flow from a first end of the air-permeable body portion to a second end of the air- permeable body portion longitudinally opposite the first end of the air-permeable body portion. To enable flow along a desired airflow direction, the air-permeable body portion may comprise one or more airflow channels extending through the air-permeable body portion. For example, the air-permeable body portion may comprise one or more airflow channels extending from a first end of the air-permeable body portion to a second end of the air- permeable body portion opposite the first end of the air-permeable body portion.

The one or more airflow channels of the air-permeable body portion may be arranged within the air-permeable body portion in regular and orderly fashion. For example, the air- permeable body portion may define a plurality of substantially longitudinal airflow channels extending parallel to each other. In particular, the air-permeable body portion may have a honeycomb structure. The void fraction and cross-sectional porosity of such an air-permeable body portion are easy to define and control by adjusting the number and size of airflow channels in the honeycomb structure.

The air-permeable body portion may otherwise define the one or more airflow channels in a non-regular and generally non-orderly fashion. For example, the air-permeable body portion may be a porous body portion. As used herein, the term “porous body portion” denotes a portion of a body which has a plurality of pores, at least some of which are interconnected. Thus, a porous portion of a body may generally define an airflow path through the porous portion, such that a fluid may be able to flow from one end surface of the porous portion to an second end surface of the porous portion opposite the first end surface. In general, a pressure drop across the porous portion will be greater than a pressure drop across a hollow tubular element having the same length of the porous portion and a free cross-sectional area equal to an overall cross-sectional area of the porous portion. Thus, flow across the porous portion will generally be partially restricted compared to flow through a hollow tubular element of comparable dimensions.

The term “porosity” of a body generally denotes the ratio of the volume of the accessible pores and voids to the bulk volume occupied by the body. The term “cross- sectional porosity” refers to the fraction of void space in a cross-sectional area of an air- permeable body, and particularly in a cross-sectional of a porous body, such as for example a cross-section of an air-permeable body portion of a heating body of a heater assembly in accordance with the present invention.

The cross-sectional porosity is the area fraction of void space of the transverse cross- sectional area of the air-permeable body portion. The transverse cross-sectional area of the air-permeable body portion is the area of the air-permeable body portion in the plane that is perpendicular to a desired airflow direction. In particular, with reference to an air-permeable body portion extending along a longitudinal axis, the transverse cross-sectional area of the air-permeable body portion may be the area of the air-permeable body portion in the plane that is perpendicular to the longitudinal axis of the air-permeable body portion, which is generally also a longitudinal axis of the heater assembly and a longitudinal axis of an aerosolgenerating device comprising the heater assembly.

The porous body will typically be substantially cylindrical, and so a transverse cross- sectional of the porous body will be substantially circular. However, more generally it will be possible to identify a longitudinal axis of the porous body and a transverse cross-section of the porous body will be in a plane substantially perpendicular to said longitudinal axis.

For example, the transverse cross-sectional porosity value may be determined using a digital imaging process. A digital image of a transverse cross-section of the porous body may be obtained, and a threshold may be applied to differentiate pixels that represent solid material from pixels that represent void. A void fraction of the entire cross-section may then be easily obtained. For example, with reference to a porous portion of a heating body of a heater assembly in accordance with the present invention, the characteristics of which will be described in more detail below, a suitable image of a transverse cross-section of the porous portion can be obtained by X-ray microtomography.

As used herein with reference to the invention, the term "specific surface area" is used to denote the total surface area of a solid material per unit of mass. Specific surface area is generally dependent on the size of the particles forming a solid material, as well as on the structure and porosity, pore size distribution, of the solid material.

Unless otherwise specified, the resistance to draw (RTD) of a component or an aerosol-generating article is measured in accordance with ISO 6565:2002. The RTD refers the pressure required to force air through the full length of a component. The terms “pressure drop” or “draw resistance” of a component or article may also refer to the “resistance to draw”. Such terms generally refer to the measurements in accordance with ISO 6565:2002 and are normally carried out at a volumetric flow rate of about 17.5 millilitres per second at the output or downstream end of the measured component, at a temperature of about 22 degrees Celsius, a pressure of about 101 kPa (about 760 Torr) and a relative humidity of about 60%. Any ventilation openings present in the component or aerosol-generating article are blocked when the measurement is carried out. In the operative state for aerosol consumption or inhalation by a user, a static pressure difference between the two ends of the aerosolgenerating article received in a receiving cavity of an aerosol-generating device may be in a range from 10 to 150 mm H2O, more preferably from 20 to 140 mm H2O, even more preferably from 30 to 120 mm H2O.

As described briefly above, a heater assembly for an aerosol-generating device in accordance with the present invention comprises a heating body configured for resistive heating. Resistive heating, also known as Joule heating, is the process by which the passage of an electric current through a conductive body generates heat. In general, the heat evolved per second (that is, the thermal power generated) equals the current squared times the resistance of the conductive body.

In more detail, in heater assemblies according to a first aspect of the present invention, the heating body comprises a polymer composite comprising a polymeric matrix and at least one of graphite, a graphite-derived material, and hexagonal boron nitride dispersed within the polymeric matrix.

The heating body may comprise an air-permeable body portion defining an airflow path through the air-permeable body portion.

The air-permeable body portion may be a porous body portion.

The heating body may comprise a hollow tubular body portion defining a chamber having an open end for receiving at least a portion of an aerosol-generating article.

In some embodiments, the heating body comprises both an air-permeable body portion defining an airflow path through the air-permeable body portion and a hollow tubular body portion defining a chamber having an open end for receiving at least a portion of an aerosolgenerating article, the airflow path being upstream of, and in fluid communication with, the chamber. In these embodiments, an equivalent free cross-sectional area of the airflow path is preferably smaller than a free cross-sectional area of the chamber.

The provision of an air-permeable body portion defining an airflow path upstream of and in fluid communication with a tubular chamber has the benefit that the air-permeable body portion can be used to supply heat convectively to an incoming flow of air, prior to the flow of air reaching the aerosol-generating substrate of an aerosol-generating article that has been at least partially received within the tubular chamber. Thus, the flow of air reaches the aerosolgenerating substrate in a pre-heated condition.

In some preferred embodiments, the heater assembly comprises a coating on an exposed surface of the airflow path defined by the air-permeable body portion. The coating may be a protective coating. The coating may be a thermally conductive coating. The coating may be arranged on an exposed surface of the air-permeable body portion such that the potential release of material from the air-permeable body portion into the airflow path is advantageously prevented. During use, the protective layer advantageously provides a separation between the material forming the air-permeable body portion and the air flowing through the air-permeable body portion and then into the aerosol-generating substrate received within the tubular chamber further downstream. In particular, the protective layer forms a “skin” capable of preventing accidental release of any conductive material (graphite, etc.) from the polymer composite into the airflow path. Additionally, the coating may improve heat transfer from the heater assembly to the aerosol-generating article.

For example, the heater assembly comprising the air-permeable body portion may be dipped into a bath containing the protective coating formulation or protective coating precursors. Thus, all the internal cavities, ducts and channels defining the airflow path may conveniently be reached and their surface may be covered with the protective coating.

In preferred embodiments, in an aerosol-generating device comprising a heater assembly comprising an air-permeable body portion as described above, the aerosolgenerating device is configured to heat the aerosol-generating substrate of an aerosolgenerating article during a usage session with reference to two different target temperatures, a stand-by or maintenance target temperature and an operational target temperature.

More preferably, the aerosol-generating device is configured to supply a thermal boost to the aerosol-generating substrate during a user puff taken during the usage session. In particular, the heater assembly is preferably configured so that when, during a usage session, a user draws air into the aerosol-generating device through the airflow path, air flowing along the airflow path through the air-permeable body portion is heated prior to reaching the chamber of the hollow tubular body portion, wherein the aerosol-generating article is at least partly received. This is so the air that has been heated by the porous heating body can convectively supply a thermal boost to the aerosol-generating substrate of the aerosolgenerating article once it reaches the chamber of the hollow tubular body portion.

Advantageously, this enables configuring the aerosol-generating device so that the aerosol-generating substrate is maintained at a first temperature, for example the stand-by temperature (that is, a temperature that is at or slightly below a temperature required to form an aerosol) and then heated to an increased temperature, for example the operational temperature (that is, a temperature above the temperature required to form an aerosol during the user puff). The stand-by target temperature is preferably a temperature that is greater than room temperature and the operational target temperature is higher than the stand-by target temperature.

A stand-by target temperature is preferably a temperature that is too low to evolve a substantial aerosol from the aerosol-forming substrate. In other words, the stand-by temperature may be below an effective aerosolization temperature for the substrate. For example, the stand-by target temperature may be lower than a vaporisation temperature or effective boiling point of the aerosol-former or aerosol-former mixture of the aerosol-forming substrate. For example, the stand-by target temperature may be set to be lower than the boiling point of propylene glycol, or lower than the boiling point of glycerol, or lower than the boiling point of the specific mixture of propylene glycol and glycerol used as an aerosol-former in the aerosol-forming substrate. The stand-by temperature may be alternatively termed a maintenance temperature.

The stand-by target temperature may be lower than 250 degrees Celsius, for example lower than 230 degrees Celsius, for example lower than 210 degrees Celsius, preferably lower than 200 degrees Celsius, for example lower than 180 degrees Celsius, or lower than 160 degrees Celsius. The stand-by target temperature may be a temperature of between 50 degrees Celsius and 250 degrees Celsius, for example between 80 degrees Celsius and 200 degrees Celsius, for example between 100 degrees Celsius and 180 degrees Celsius.

An operational target temperature is preferably a temperature that is high enough to evolve an aerosol from the aerosol-forming substrate. In other words, the operational temperature may be above an effective aerosolization temperature for the substrate. For example, the operational target temperature may be higher than an effective boiling point of the aerosol-former or aerosol-former mixture of the aerosol-forming substrate, for example higher than the boiling point of propylene glycol, or higher than the boiling point of glycerol, or higher than the boiling point of the specific mixture of propylene glycol and glycerol used as an aerosol-former in the aerosol-forming substrate.

The operational target temperature may be greater than 160 degrees Celsius, for example greater than 180 degrees Celsius, or greater than 200 degrees Celsius, or greater than 250 degrees Celsius, for example greater than 280 degrees Celsius, or greater than 300 degrees Celsius, or greater than 320 degrees Celsius, or greater than 340 degrees Celsius. The operational target temperature may be a temperature of between 160 degrees Celsius and 400 degrees Celsius, for example between 180 degrees Celsius and 340 degrees Celsius, for example between 220 degrees Celsius and 300 degrees Celsius.

Because the temperature of the aerosol-generating substrate is substantially maintained at a stand-by temperature in between puffs, and increased rapidly to an operational temperature on puffing, desirable components of the aerosol-generating substrate, such as nicotine, flavour components, and aerosol-formers such as glycerine, can be efficiently harvested without extensively overheating the substrate. This has the benefit that formation of undesirable aerosol-constituents may be curtailed or prevented, whilst at the same time an optimal harvest of the desirable components may be obtained.

The stand-by target temperature may be constant throughout the duration of the usage session. Alternatively, the stand-by target temperature may vary over the duration of the usage session. That is, the stand-by target temperature may evolve over the course of a usage session to account for depletion of aerosol-forming components as the user puffs during the usage session.

The operational target temperature may be constant throughout the duration of the usage session. Alternatively, the operational target temperature may vary over the duration of the usage session. The operational target temperature may vary from puff to puff. A variation in operational target temperature, for example an increase in operational target temperature, may help optimise aerosol delivery from an aerosol forming substrate that becomes depleted in aerosol-forming components over the course of a usage session. In an aerosol-generating device comprising a heater assembly comprising an air-permeable body portion configured as described above, at least a flow detector, for example in the form of a pressure sensor, is provided to control the temperature to either the stand-by target temperature or the operational target temperature. The flow detector may be located in fluid communication with the airflow path through the air-permeable body portion. Signals from the flow detector may be used to detect one or more user puffs taken during the usage session.

For example, the device may be configured to detect one or more user puffs taken during the usage session. Preferably, the device is configured to detect the start of a user puff taken during the usage session, for example each user puff taken during the usage session. The device is preferably configured to detect the end of a user puff taken during the usage session, for example each user puff taken during the usage session. Thus, the device may be configured to determine the duration of a user puff taken during the usage session, for example each user puff taken during the usage session. In some preferred embodiments, the air-permeable body portion is at least partly arranged within the hollow tubular body portion of the heating body. Preferably, the air-permeable body portion is substantially integral with the hollow tubular body portion of the heating body.

This configuration presents a number of advantages from a manufacturing viewpoint, as it may be convenient to form the air-permeable body portion as a porous body portion, for example by sintering a predetermined amount of particles of the polymer composite that have been arranged to form a plug at one end of the hollow tubular body portion. By controlling the particle size and selecting suitable sintering temperature and duration, it may advantageously possible to form the porous body portion integral to the hollow tubular body portion, whilst at the same time ensuring that the porous body portion has desirable values of total pore volume, average pore size, specific surface area, etc.

Additionally, providing the air-permeable body portion at least partly within the hollow tubular body portion of the heating body allows for a compact configuration, wherein different functionalities can be combined into a relatively small volume.

A length of the air-permeable body portion may be at least 1 millimetre. Preferably, a length of the air-permeable body portion is at least 1.5 millimetres. More preferably, a length of the air-permeable body portion is at least 2 millimetres. Even more preferably, a length of the air-permeable body portion is at least 2.5 millimetres.

In some embodiments, a length of the air-permeable body portion may be up to 10 millimetres. Preferably, a length of the air-permeable body portion is less than or equal to 8 millimetres. More preferably, a length of the air-permeable body portion is less than or equal to 6 millimetres. Even more preferably, a length of the air-permeable body portion is less than or equal to 5 millimetres. For example, a length of the air-permeable body portion is from 1 millimetre to 10 millimetres, preferably from 1.5 millimetres to 10 millimetres, more preferably from 2 millimetres to 10 millimetres, even more preferably from 2.5 millimetres to 10 millimetres.

For example, a length of the air-permeable body portion is from 1 millimetre to 8 millimetres, preferably from 1.5 millimetres to 8 millimetres, more preferably from 2 millimetres to 8 millimetres, even more preferably from 2.5 millimetres to 8 millimetres.

For example, a length of the air-permeable body portion is from 1 millimetre to 6 millimetres, preferably from 1.5 millimetres to 6 millimetres, more preferably from 2 millimetres to 6 millimetres, even more preferably from 2.5 millimetres to 6 millimetres.

For example, a length of the air-permeable body portion is from 1 millimetre to 5 millimetres, preferably from 1.5 millimetres to 5 millimetres, more preferably from 2 millimetres to 5 millimetres, even more preferably from 2.5 millimetres to 5 millimetres.

An outer diameter of the air-permeable body portion may be at least 4 millimetres. Preferably, an outer diameter of the air-permeable body portion is at least 5 millimetres. More preferably, an outer diameter of the air-permeable body portion is at least 6 millimetres.

In some embodiments, an outer diameter of the air-permeable body portion may be up to 12 millimetres. Preferably, an outer diameter of the air-permeable body portion is less than or equal to 10 millimetres. More preferably, an outer diameter of the air-permeable body portion is less than or equal to 8 millimetres.

For example, an outer diameter of the air-permeable body portion is from 4 millimetres to 12 millimetres, preferably from 5 millimetres to 12 millimetres, more preferably from 6 millimetres to 12 millimetres.

For example, an outer diameter of the air-permeable body portion is from 4 millimetres to 10 millimetres, preferably from 5 millimetres to 10 millimetres, more preferably from 6 millimetres to 10 millimetres.

For example, an outer diameter of the air-permeable body portion is from 4 millimetres to 8 millimetres, preferably from 5 millimetres to 8 millimetres, more preferably from 6 millimetres to 8 millimetres.

Preferably, the air-permeable body portion comprises at least 50 percent by weight of the polymer composite. More preferably, the air-permeable body portion comprises at least 60 percent by weight of the polymer composite. Even more preferably, the air-permeable body portion comprises at least 75 percent by weight of the polymer composite. In particularly preferred embodiments, the air-permeable body portion comprises at least 90 percent by weight of the polymer composite, preferably at least 95 percent by weight of the polymer composite. In certain embodiments, the air-permeable body portion is made entirely of the polymer composite. Where the air-permeable body portion is made primarily of the polymer composite it is advantageously easier to control characteristics of the air-permeable body portion, such as resistivity, porosity, etc. that will have some impact on heat generation and heat transfer during use. In particular, forming the air-permeable body portion substantially entirely of the polymer composite is advantageous from a manufacturing viewpoint and is beneficial in that it is easier to ensure that properties such as density, porosity, resistivity, etc. are substantially homogenous across the air-permeable body portion.

In certain embodiments, the air-permeable body portion is provided in the form of a porous body portion formed by sintering particles of the polymer composite. Sintering is the process by which a collation of particles of a certain material are heated to a temperature above a calcination temperature of the material and compacted to form a solid body without melting the material to the point of liquefaction. In practice, sintering involves diffusion of atoms across the boundaries between adjacent particles of the material, such that adjacent particles become fused together in one piece.

Temperature and duration of the sintering process may be selected to enhance the strength and integrity to the resulting body, as higher temperatures and longer exposure to heat will generally induce densification of the material. At the same time, temperature and duration of the sintering process may be selected to preserve a desired porosity of the body at the end of the sintering process.

The size of the particles of the polymer composite may also be selected with a view to controlling, to an extent, a fraction of voids in the sintered porous body portion.

In some embodiments, the porous body portion may be sintered from particles of the polymer composite having an average diameter of at least 50 micrometres. Preferably, the porous body portion is sintered from particles of the polymer composite having an average diameter of at least 100 micrometres. More preferably, the porous body portion is sintered from particles of the polymer composite having an average diameter of at least 200 micrometres.

In some embodiments, the porous body portion may be sintered from particles of the polymer composite having an average diameter of up to 1000 micrometres. Preferably, the porous body portion is sintered from particles of the polymer composite having an average diameter of less than or equal to 800 micrometres. More preferably, Preferably, the porous body portion is sintered from particles of the polymer composite having an average diameter of less than or equal to 600 micrometres.

For example, the porous body portion is sintered from particles of the polymer composite having an average diameter from 50 micrometres to 1000 micrometres or an average diameter from 50 micrometres to 800 micrometres or an average diameter from 50 micrometres to 600 micrometres or an average diameter from 100 micrometres to 1000 micrometres or an average diameter from 100 micrometres to 800 micrometres or an average diameter from 100 micrometres to 600 micrometres or an average diameter from 200 micrometres to 1000 micrometres or an average diameter from 200 micrometres to 800 micrometres or an average diameter from 200 micrometres to 600 micrometres.

Technologies other than sintering may be used for forming the porous body portion. For example, a 3D printing process may be used, wherein the porous body portion is formed layer by layer, each layer comprising a plurality of linear elements formed of the polymer composite that intersect each other such as to ultimately form a three-dimensional object with a fraction of voids that may be finely controlled by controlling how the polymer composite is dispensed throughout the 3D printing process. Additionally, or as an alternative, by adjusting the size of the nozzle from which the polymer composite is dispensed it may be possible to exert some control over a cross-sectional porosity and a RTD of the porous body portion.

As another alternative, an air-permeable body portion comprising the polymer composite may be formed by extrusion. For example, the polymer composite may be extruded to form an air-permeable body portion having a honeycomb structure, that is, one defining a plurality of open channels extending substantially parallel to one another from a first end surface of the air-permeable body portion to a second end surface of the air-permeable body portion longitudinally opposite the first end surface. Such a manufacturing process may desirably enable an easier and finer control over parameters of the air-permeable body portion. For example, the number of open channels and the cross-sectional area of each open channel may be selected with a view to controlling a resistance to draw and a transverse cross-sectional porosity of the air-permeable body portion. In addition, or as an alternative, the length of the air-permeable body portion may be selected to control a resistance to draw and a surface area available for heat exchange of the air-permeable body portion.

A transverse cross-sectional porosity of the air-permeable body portion may be at least 15 percent. Preferably, a transverse cross-sectional porosity of the air-permeable body portion is at least 20 percent. More preferably, a transverse cross-sectional porosity of the air-permeable body portion is at least 25 percent.

A transverse cross-sectional porosity of the air-permeable body portion is preferably less than or equal to 45 percent. More preferably, a transverse cross-sectional porosity of the air-permeable body portion is less than or equal to 40 percent. Even more preferably, a transverse cross-sectional porosity of the air-permeable body portion is less than or equal to 35 percent.

For example, a transverse cross-sectional porosity of the air-permeable body portion may be from 15 percent to 45 percent, preferably from 15 percent to 40 percent, more preferably from 15 percent to 35 percent. For example, a transverse cross-sectional porosity of the air-permeable body portion may be from 20 percent to 45 percent, preferably from 20 percent to 40 percent, more preferably from 20 percent to 35 percent.

For example, a transverse cross-sectional porosity of the air-permeable body portion may be from 25 percent to 45 percent, preferably from 25 percent to 40 percent, more preferably from 25 percent to 35 percent.

Air-permeable body portions having a transverse cross-sectional porosity in the ranges described above have been found to be associated with particularly desirable values of RTD. Additionally, values of transverse cross-sectional porosity in the ranges described above have been found to be associated with particularly desirable values of specific surface areas, such that heat can be exchanged between the air-permeable body portion and a flow of air flowing through the air-permeable body portion fairly efficiently.

A total pore volume of the air-permeable body portion may be at least 0.5 cubic centimetres. Preferably, a total pore volume of the air-permeable body portion is at least 1 cubic centimetre. More preferably, a total pore volume of the air-permeable body portion is at least 1.5 cubic centimetres. Even more preferably, a total pore volume of the air-permeable body portion is at least 2 cubic centimetres.

A total pore volume of the air-permeable body portion may be up to 5 cubic centimetres. Preferably, a total pore volume of the air-permeable body portion is less than or equal to 4.5 cubic centimetres. More preferably, a total pore volume of the air-permeable body portion less than or equal to 4 cubic centimetres. Even more preferably, a total pore volume of the air-permeable body portion less than or equal to 3.5 cubic centimetres.

For example, a total pore volume of the air-permeable body portion may be from 0.5 cubic centimetres to 5 cubic centimetres, preferably from 1 cubic centimetre to 5 cubic centimetres, more preferably from 1.5 cubic centimetres to 5 cubic centimetres, even more preferably from 2 cubic centimetres to 5 cubic centimetres.

For example, a total pore volume of the air-permeable body portion may be from 0.5 cubic centimetres to 4.5 cubic centimetres, preferably from 1 cubic centimetre to 4.5 cubic centimetres, more preferably from 1.5 cubic centimetres to 4.5 cubic centimetres, even more preferably from 2 cubic centimetres to 4.5 cubic centimetres.

For example, a total pore volume of the air-permeable body portion may be from 0.5 cubic centimetres to 4 cubic centimetres, preferably from 1 cubic centimetre to 4 cubic centimetres, more preferably from 1.5 cubic centimetres to 4 cubic centimetres, even more preferably from 2 cubic centimetres to 4 cubic centimetres.

For example, a total pore volume of the air-permeable body portion may be from 0.5 cubic centimetres to 3.5 cubic centimetres, preferably from 1 cubic centimetre to 3.5 cubic centimetres, more preferably from 1.5 cubic centimetres to 3.5 cubic centimetres, even more preferably from 2 cubic centimetres to 3.5 cubic centimetres.

The air-permeable body portion may be configured such as to be able to hold a volume of air corresponding to part of a puff or even to an entire puff (up to 75 millilitres or more). This may advantageously enable the pre-heating of a volume of air corresponding to part of a puff or to an entire puff. In order to be able to hold a volume of air corresponding to the volume of a whole puff, the total pore volume of the porous body is considerably higher. In some embodiments, a total pore volume of the air-permeable body portion may be at least 10 cubic centimetres. Preferably, a total pore volume of the air-permeable body portion is at least 20 cubic centimetres. More preferably, a total pore volume of the air-permeable body portion is at least 30 cubic centimetres. Even more preferably, a total pore volume of the air-permeable body portion is at least 40 cubic centimetres.

A total pore volume of the air-permeable body portion may be up to 80 cubic centimetres, preferably less than or equal to 70 cubic centimetres, more preferably less than or equal to 60 cubic centimetres.

In some embodiments, a total pore volume of the air-permeable body portion is from 10 cubic centimetres to 80 cubic centimetres, preferably from 10 cubic centimetres to 70 cubic centimetres, more preferably from 10 cubic centimetres to 60 cubic centimetres.

In other embodiments, a total pore volume of the air-permeable body portion is from 20 cubic centimetres to 80 cubic centimetres, preferably from 20 cubic centimetres to 70 cubic centimetres, more preferably from 20 cubic centimetres to 60 cubic centimetres.

In further embodiments, a total pore volume of the air-permeable body portion is from 30 cubic centimetres to 80 cubic centimetres, preferably from 30 cubic centimetres to 70 cubic centimetres, more preferably from 30 cubic centimetres to 60 cubic centimetres.

In certain embodiments, a total pore volume of the air-permeable body portion is from 40 cubic centimetres to 80 cubic centimetres, preferably from 40 cubic centimetres to 70 cubic centimetres, more preferably from 40 cubic centimetres to 60 cubic centimetres.

A resistance to draw (RTD) of the air-permeable body portion may be at least 10 millimetres H2O. Preferably, an RTD of the air-permeable body portion is at least 20 millimetres H2O. More preferably, an RTD of the air-permeable body portion is at least 30 millimetres H2O. Even more preferably, an RTD of the air-permeable body portion is at least 40 millimetres H2O. In particularly preferred embodiments, an RTD of the air-permeable body portion is at least 50 millimetres H2O.

An RTD of the air-permeable body portion may be up to 150 millimetres H2O. Preferably, an RTD of the air-permeable body portion is less than or equal to 120 millimetres H2O. More preferably, an RTD of the air-permeable body portion is less than or equal to 100 millimetres H2O. Even more preferably, an RTD of the air-permeable body portion is less than or equal to 80 millimetres H2O. In particularly preferred embodiments, an RTD of the air- permeable body portion is less than or equal to 60 millimetres H2O.

For example, an RTD of the air-permeable body portion is from 10 to 150 millimetres H2O, preferably from 20 to 150 millimetres H2O, more preferably from 30 to 150 millimetres H2O, even more preferably from 40 to 150 millimetres H2O, particularly preferably from 50 to 150 millimetres H2O.

For example, an RTD of the air-permeable body portion is from 10 to 120 millimetres H2O, preferably from 20 to 120 millimetres H2O, more preferably from 30 to 120 millimetres H2O, even more preferably from 40 to 120 millimetres H2O, particularly preferably from 50 to 120 millimetres H2O.

For example, an RTD of the air-permeable body portion is from 10 to 100 millimetres H2O, preferably from 20 to 100 millimetres H2O, more preferably from 30 to 100 millimetres H2O, even more preferably from 40 to 100 millimetres H2O, particularly preferably from 50 to 100 millimetres H2O.

For example, an RTD of the air-permeable body portion is from 10 to 80 millimetres H2O, preferably from 20 to 80 millimetres H2O, more preferably from 30 to 80 millimetres H2O, even more preferably from 40 to 80 millimetres H2O, particularly preferably from 50 to 80 millimetres H2O.

It will be understood that, in a system comprising an aerosol-generating device comprising a heater assembly with a heating body including an air-permeable body portion as described above, as well as an aerosol-generating article, the overall RTD experienced by a user will generally be the sum of the RTD of the air-permeable body portion and of the RTD of other components of the aerosol-generating device as well as of the RTD of the aerosolgenerating article. For example, other airflow path portions defined by the aerosol-generating device will generally contribute to the overall RTD.

As described briefly above, in some embodiments the heater assembly comprises a hollow tubular body portion defining a chamber having an open end for receiving at least a portion of an aerosol-generating article.

In some preferred embodiments, the heater assembly comprises a coating on an internal surface of the chamber. The coating may be a protective coating. The coating may be a thermally conductive coating. The coating may be arranged on an internal surface of the chamber such that when an aerosol-generating article is received within the chamber the coating contacts the aerosol-generating article and does not contact the hollow tubular body made of the polymer composite. During use, the protective layer advantageously provides a separation between the hollow tubular body portion and an aerosol-generating article received within the chamber. In other words, the protective layer forms a “skin” capable of preventing accidental release of any conductive material (graphite, etc.) from the polymer composite into the chamber or into the aerosol-generating article. Additionally, the coating may improve heat transfer from the heater assembly to the aerosol-generating article.

Preferably, the hollow tubular body portion comprises at least 50 percent by weight of the polymer composite. More preferably, the hollow tubular body portion comprises at least 60 percent by weight of the polymer composite. Even more preferably, the hollow tubular body portion comprises at least 75 percent by weight of the polymer composite.

In preferred embodiments, the hollow tubular body portion comprises at least 80 percent by weight of the polymer composite, preferably at least 90 percent by weight of the polymer composite, more preferably at least 95 percent by weight of the polymer composite.

In some particularly preferred embodiments, the hollow tubular body portion is made substantially entirely of the polymer composite.

Where the hollow tubular body portion is made primarily of the polymer composite it is advantageously easier to impart the body portion the desired shape. In particular, forming the hollow tubular body portion substantially entirely of the polymer composite is advantageous from a manufacturing viewpoint, as it is generally easier to process the body portion as a whole, such as by moulding or extrusion. This has the benefit that properties such as density, resistivity, etc. are substantially homogenous across the hollow tubular body portion, and it is easier to control a wall thickness of hollow tubular element.

In certain embodiments, the hollow tubular body portion is arranged so that, when an aerosol-generating article is inserted into the chamber, the heating body directly contacts the aerosol-generating article. This may favour the transfer of heat by conduction from the heating body to the aerosol-generating substrate when the aerosol-generating article is received within the chamber. At the same time, this may help hold the aerosol-generating article stably within the chamber.

In some embodiments, the hollow tubular body portion comprises a hollow tube element having an internal diameter of at least 4 millimetres. Preferably, the hollow tube element has an internal diameter of at least 5 millimetres. More preferably, the hollow tube element has an internal diameter of at least 6 millimetres.

In some embodiments, the hollow tube element has an internal diameter of less than or equal to 8 millimetres. Preferably, the hollow tube element has an internal diameter of less than or equal to 9 millimetres. More preferably, the hollow tube element has an internal diameter of less than or equal to 10 millimetres.

In some embodiments, the hollow tube element has an internal diameter from 4 millimetres to 10 millimetres, preferably from 5 millimetres to 10 millimetres, more preferably from 6 millimetres to 10 millimetres. In some embodiments, the hollow tube element has an internal diameter from 4 millimetres to 9 millimetres, preferably from 5 millimetres to 9 millimetres, more preferably from 6 millimetres to 9 millimetres.

In some embodiments, the hollow tube element has an internal diameter from 4 millimetres to 8 millimetres, preferably from 5 millimetres to 8 millimetres, more preferably from 6 millimetres to 8 millimetres.

The internal diameter of the hollow tube element may be selected and adjusted to accommodate aerosol-generating articles of a given shape and size.

A thickness of the hollow tube element may be at least 0.5 millimetres. Preferably, a thickness of the hollow tube element is at least 0.6 millimetres. More preferably, a thickness of the hollow tube element is at least 0.8 millimetres. Even more preferably, a thickness of the hollow tube element is at least 1 millimetre.

A thickness of the hollow tube element is preferably less than or equal to 5 millimetres. More preferably, a thickness of the hollow tube element is less than or equal to 4 millimetres. Even more preferably, a thickness of the hollow tube element is less than or equal to 3 millimetres.

In some embodiments, a thickness of the hollow tube element is from 0.5 millimetres to 5 millimetres, preferably from 0.6 millimetres to 5 millimetres, more preferably from 0.8 millimetres to 5 millimetres, even more preferably from 1 millimetre to 5 millimetres.

In some embodiments, a thickness of the hollow tube element is from 0.5 millimetres to 4 millimetres, preferably from 0.6 millimetres to 4 millimetres, more preferably from 0.8 millimetres to 4 millimetres, even more preferably from 1 millimetre to 4 millimetres.

In some embodiments, a thickness of the hollow tube element is from 0.5 millimetres to 3 millimetres, preferably from 0.6 millimetres to 3 millimetres, more preferably from 0.8 millimetres to 3 millimetres, even more preferably from 1 millimetre to 3 millimetres.

Without wishing to be bound by theory, when a potential difference is applied between the ends of the hollow tube element, the electrical resistance of the hollow tube element will be generally inversely proportional to the area of the cross-section of the hollow tube element. Thus, the thickness of the hollow tube element may be selected both to impart sufficient structural strength to the heater assembly and to adjust an overall resistance of the heating body, which in turn has an impact on the overall thermal power generated during use.

In a heater assembly in accordance with an embodiment of the present invention, an overall resistance of the heating body is preferably from 0.75 ohm to 1.25 ohm, more preferably from 0.8 ohm to 1.2 ohm, even more preferably from 0.9 ohm to 1.1 ohm.

Without wishing to be bound by theory, an exemplary heating body having a resistance within the ranges described above can advantageously be paired with a commercially available battery, such as for example a lithium battery, to generate a power in the range from 8 to 10 watts. Such a power is suitable for efficiently and reliably heating the aerosolgenerating substrate of an aerosol-generating article to temperatures in the range from about 200 degrees Celsius to about 250 degrees Celsius.

As described briefly above, the heating body of a heater assembly in accordance with the present invention comprises a polymer composite comprising a polymeric matrix and at least one of graphite, a graphite-derived material, and hexagonal boron nitride dispersed within the polymeric matrix.

Preferably, the polymeric matrix comprises at least one of polyether ether ketone (PEEK) and a liquid crystal polymer (LCP).

The polymeric matrix may account for at least 10 percent by weight of the heating body. Preferably, the polymeric matrix accounts for at least 15 percent by weight of the heating body. More preferably, the polymeric matrix accounts for at least 20 percent by weight of the heating body. Even more preferably, the polymeric matrix accounts for at least 22 percent by weight of the heating body.

The polymeric matrix may account up to 55 percent by weight of the heating body. Preferably, the polymeric matrix accounts for less than or equal to 45 percent by weight of the heating body. More preferably, the polymeric matrix accounts for less than or equal to 35 percent by weight of the heating body. Even more preferably, the polymeric matrix accounts for less than or equal to 33 percent by weight of the heating body.

In some embodiments, the polymeric matrix accounts for from 10 to 55 percent by weight of the heating body, preferably from 15 to 55 percent by weight of the heating body, more preferably from 20 to 55 percent by weight of the heating body, even more preferably from 22 to 55 percent by weight of the heating body.

In other embodiments, the polymeric matrix accounts for from 10 to 45 percent by weight of the heating body, preferably from 15 to 45 percent by weight of the heating body, more preferably from 20 to 45 percent by weight of the heating body, even more preferably from 22 to 45 percent by weight of the heating body.

In further embodiments, the polymeric matrix accounts for from 10 to 35 percent by weight of the heating body, preferably from 15 to 35 percent by weight of the heating body, more preferably from 20 to 35 percent by weight of the heating body, even more preferably from 22 to 35 percent by weight of the heating body.

In yet other embodiments, the polymeric matrix accounts for from 10 to 33 percent by weight of the heating body, preferably from 15 to 33 percent by weight of the heating body, more preferably from 20 to 33 percent by weight of the heating body, even more preferably from 22 to 33 percent by weight of the heating body.

Where the polymeric matrix accounts for a percentage content as described above it is advantageously possible to benefit from satisfactory levels of malleability and overall processability of the polymer composite, which may facilitate the manufacturing process as a whole.

Preferably, the graphite-derived material comprises at least one of expanded graphite and graphite nanoplatelets.

In a heater assembly in accordance with the present invention, the at least one of graphite, a graphite-derived material, and hexagonal boron nitride may account for at least 30 percent by weight of the heating body. Preferably, the at least one of graphite, a graphite- derived material, and hexagonal boron nitride accounts for at least 45 percent by weight of the heating body. More preferably, the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for at least 60 percent by weight of the heating body. Even more preferably, the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for at least 62 percent by weight of the heating body.

The at least one of graphite, a graphite-derived material, and hexagonal boron nitride may account for up to 80 percent by weight of the heating body. Preferably, the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for less than or equal to 75 percent by weight of the heating body. More preferably, the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for less than or equal to 70 percent by weight of the heating body. Even more preferably, the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for less than or equal to 69 percent by weight of the heating body.

In some embodiments, the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for from 30 percent by weight to 80 percent by weight of the heating body, preferably from 45 percent by weight to 80 percent by weight of the heating body, more preferably from 60 percent by weight to 80 percent by weight of the heating body, even more preferably from 62 percent by weight to 80 percent by weight of the heating body.

In some embodiments, the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for from 30 percent by weight to 75 percent by weight of the heating body, preferably from 45 percent by weight to 75 percent by weight of the heating body, more preferably from 60 percent by weight to 75 percent by weight of the heating body, even more preferably from 62 percent by weight to 75 percent by weight of the heating body.

In some embodiments, the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for from 30 percent by weight to 70 percent by weight of the heating body, preferably from 45 percent by weight to 70 percent by weight of the heating body, more preferably from 60 percent by weight to 70 percent by weight of the heating body, even more preferably from 62 percent by weight to 70 percent by weight of the heating body.

In some embodiments, the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for from 30 percent by weight to 69 percent by weight of the heating body, preferably from 45 percent by weight to 69 percent by weight of the heating body, more preferably from 60 percent by weight to 69 percent by weight of the heating body, even more preferably from 62 percent by weight to 69 percent by weight of the heating body.

The inventors have observed that conductivity of the polymer composite in the heating body of heater assemblies in accordance with the present invention is generally controlled, to an extent, by the degree of dispersion and agglomeration of the particles of at least one of graphite, a graphite-derived material, and hexagonal boron nitride within the polymeric matrix.

High dispersion of the conductive particles of the at least one of graphite, a graphite- derived material, and hexagonal boron nitride within the polymeric matrix is generally to be avoided, as it is understood to lead to very low - or even no - conductivity of the polymer composite. High agglomeration without dispersion of the conductive particles should also be avoided, as it will typically lead to a severely anisotropic distribution of properties throughout the heating body.

The inventors have observed that, as long as the concentration of the at least one of graphite, a graphite-derived material, and hexagonal boron nitride within the polymeric matrix remains below a certain value, the particles remain substantially isolated, and so the polymer composite as a whole may behave substantially as a dielectric medium. On the other hand, when a certain critical volume (a “percolation threshold”) of conductive particles is combined with the otherwise inherently insulating polymeric matrix, the electrical conductivity of the resulting polymer composite is suddenly elevated by orders of magnitude. Without wishing to be bound by theory, this is understood to occur because, at contents of particles of the at least one of graphite, a graphite-derived material, and hexagonal boron nitride approaching the percolation threshold, the particles tend to form a quasi-continuous network within the polymeric matrix.

Further increasing the concentration of conductive particles will generally induce smaller increases in conductivity of the polymer composite as a whole, which will approach a plateau value.

Inclusion within the polymeric matrix of the at least one of graphite, a graphite-derived material, and hexagonal boron nitride within the polymeric matrix in the ranges described above has been found to generally encompass or approximate the percolation threshold. As a result, inclusion of amounts of the at least one of graphite, a graphite-derived material, and hexagonal boron nitride within the polymeric matrix in the ranges described above has been found to lead to generally satisfactory levels of conductivity of the heating body.

In turn, these have been found to be associated with the ability of the heating body to generate sufficient thermal power to heat an aerosol-generating substrate - directly or indirectly by way of a pre-heated flow of air or both - to temperatures sufficient to release and deliver desirable amounts of aerosol species to the consumer. For example, heater assemblies comprising a heating body having the compositions described above have been used to successfully and consistently heat tobacco-containing aerosol-generating substrates to temperatures in the range of 200 to 250 degrees Celsius.

The heating body may comprise one or more additives. In some embodiments, the heating body comprises at least one additive dispersed within the polymeric matrix.

The at least one additive may comprise carbon black.

The at least one additive may comprise a wax. The term “wax” is used here to refer to an organic compound that is a lipophilic, malleable solid near room temperature. Waxes include higher alkanes and lipids, typically with melting points above about 40 degrees Celsius. Upon melting, waxes give low viscosity liquids. Waxes are insoluble in water but soluble in nonpolar organic solvents such as hexane, benzene and chloroform. Suitable waxes include natural waxes, such as animal waxes and plant waxes, as well as synthetic waxes derived from petroleum.

The at least one additive may comprise a dispersing agent or dispersant. The term “dispersant” or “dispersing agent” is used here to denote a compound or composition that, when added to a suspension of solid or liquid particles in a liquid (such as for example a colloid or an emulsion), is adapted to improve the separation of the particles to prevent them from settling or clumping into agglomerates. Dispersants typically find application in paints, wherein they facilitate dispersion of solid pigments.

In the context of the present invention, the addition of a dispersant may facilitate dispersion of the conductive particles of graphite, graphite-derived material, hexagonal boron nitride within the polymeric matrix. Additionally, the dispersant may advantageously hinder the tendency of the conductive particles to agglomerate, which could be detrimental in terms of electrical conductivity of the heating body as a whole. The at least one additive may account for at least 1 percent by weight of the heating body. Preferably, the at least one additive accounts for at least 2 percent by weight of the heating body. More preferably, the at least one additive accounts for at least 4 percent by weight of the heating body. Even more preferably, the at least one additive accounts for at least 5 percent by weight of the heating body.

The at least one additive may account for up to 15 percent by weight of the heating body. Preferably, the at least one additive accounts for less than or equal to 12 percent by weight of the heating body. More preferably, the at least one additive accounts for less than or equal to 10 percent by weight of the heating body. Even more preferably, the at least one additive accounts for less than or equal to 9 percent by weight of the heating body.

In some embodiments, the at least one additive accounts for from 1 percent by weight to 15 percent by weight of the heating body, preferably from 2 percent by weight to 15 percent by weight of the heating body, more preferably from 4 percent by weight to 15 percent by weight of the heating body, even more preferably from 5 percent by weight to 15 percent by weight of the heating body.

In some embodiments, the at least one additive accounts for from 1 percent by weight to 12 percent by weight of the heating body, preferably from 2 percent by weight to 12 percent by weight of the heating body, more preferably from 4 percent by weight to 12 percent by weight of the heating body, even more preferably from 5 percent by weight to 12 percent by weight of the heating body.

In some embodiments, the at least one additive accounts for from 1 percent by weight to 10 percent by weight of the heating body, preferably from 2 percent by weight to 10 percent by weight of the heating body, more preferably from 4 percent by weight to 10 percent by weight of the heating body, even more preferably from 5 percent by weight to 10 percent by weight of the heating body.

In some embodiments, the at least one additive accounts for from 1 percent by weight to 9 percent by weight of the heating body, preferably from 2 percent by weight to 9 percent by weight of the heating body, more preferably from 4 percent by weight to 9 percent by weight of the heating body, even more preferably from 5 percent by weight to 9 percent by weight of the heating body.

As described briefly above, the heating body is configured for resistive heating. In some embodiments, the heater assembly comprises two or more electrodes in operative connection with the heating body.

The two or more electrodes may be connected with the heating body in a number of ways. For example, the heater assembly may comprise two ring-shaped electrodes attached at opposite ends (that is at an upstream end and at a downstream end, respectively) of the hollow tubular body portion of the heating body. As an alternative, the heater assembly may comprise two elongate electrodes extending along a longitudinal axis of the heating body and attached, preferably at diametrically opposed locations, onto the outer surface of the hollow tubular body portion. Both arrangements are suitable for causing a current to flow through the heating body and therefore for generating heat by Joule effect.

In some embodiments, the two or more electrodes may be partially or fully embedded within the heating body. This may advantageously be achieved by over-moulding the polymer composite forming the heating body over two or more conductive elements - for example, two or more metallic elements - which serve as the electrical connection electrodes. This is beneficial both from a manufacturing viewpoint and because it may ensure a better and more durable electric connection between the electrodes and the polymer composite from which the heating body is formed.

A heater assembly as described above finds use, in particular, in an aerosol-generating device for heating an aerosol-generating substrate of an aerosol-generating article. The aerosol-generating device comprises a heater assembly in line with the foregoing description and a power supply and a controller connected to the heating body and configured to apply a voltage to the heating body such that, in use, passage of an electric current in the heating body generates heat by way of resistive heating.

In some embodiments, the aerosol-generating device comprises an inductor coil extending around at least a portion of the heating body. The power supply and controller are connected to the inductor coil and configured to provide a varying electric current to the inductor coil such that, in use, the inductor coil generates a varying magnetic field.

The inductor coil may be positioned in direct contact with an outer surface of the heating body.

The controller may be configured to supply electric energy from the power supply to the inductor coil as an alternating current such that the inductor coil is operable to generate heat through one or a combination of i) resistive heating of the inductor coil and ii) heating of the heating body through inductive coupling of the inductor coil with the heating body. The controller may be configured to adjust at least one parameter of the alternating current to change the inductive coupling of the inductor coil with the heating body, thereby adjusting the balance of heat generated through inductive coupling of the inductor coil with the heating body relative to heat generated through resistive heating of the inductor coil.

As used herein, the terms “inductively couple” and “inductive coupling” refer to the heating of a susceptor element - such as the heating body of the heater assembly - when penetrated by an alternative magnetic field. The heating may be caused by the generation of eddy currents in the heating body. The heating may be caused by magnetic hysteresis losses.

In preferred embodiments, at least one of the controller and the heating body is configured to prevent inductive coupling between the heating body and the inductor coil during use.

For example, this may be achieved by configuring the controller to adjust a frequency of the alternating current. The inductive coupling between the inductor coil and the heating body varies with changes in the frequency of the alternating current. The frequency may be adjusted to have a value fsusceptor, associated with an alternating current creating an alternating magnetic field that provides optimum coupling with the heating body to allow transfer of almost the totality of the energy from the inductor coil to the heating body, resulting in most of the heat being generated by inductive heating of the heating body. The frequency may also be adjusted to have a value Eductor coii, associated with an alternating current creating an alternating magnetic field that provides little to no coupling with the heating body and allows almost the totality of the energy to remain within the inductor coil, resulting in most of the heat being generated by resistive heating of the inductor coil. The frequency may also be adjusted to have a value f_totai, associated with an alternating current which results in a combination of inductive heating of the heating body and resistive heating of the inductor coil. Each of these frequencies will vary depending on the materials, physical properties and configuration of the inductor coil and the heating body, such as the inductance of the inductor coil and the magnetic permeability of the polymer composite from which the heating body is formed.

Another way of achieving inductive de-coupling of the inductor coil and the heating body may be by configuring the heating body such that the heating body is substantially transparent to the alternating magnetic field generated by the inductor coil when the inductor coil is supplied with an alternating current.

The inventors have found that a heating body comprising at least 50 percent by weight of the polymer composite described herein may inherently be sufficiently transparent to the alternating magnetic field generated by the inductor coil when the inductor coil is supplied with an alternating current. Without wishing to be bound by theory, it is understood that the polymer composite is anisotropic from the viewpoint of resistivity in the polymer composite material. In more detail, the resistivity in the tangential direction has been observed to be more than twice (and even more than 2.5 times) the resistivity in the axial direction. As a result, only a marginal current flow is generated in the hollow tubular body portion of the heating body, which greatly limits power losses.

Additionally, the inventors have found that the hollow tubular heating body may be made fully transparent to the alternating magnetic field generated by the inductor coil when the inductor coil is supplied with an alternating current by providing a plurality of longitudinal slits in the wall of the hollow tube element.

In certain embodiments, wherein the controller is configured to provide the varying electric current in the form of an alternative current having a frequency selected to prevent inductive coupling between the heating body and the inductor coil during use.

Preferably, the aerosol-generating device further comprises a housing, and the inductor coil (where present), the heater assembly, the power supply and the controller are positioned within the 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, polyether-ether- ketone (PEEK) and polyethylene. The material is preferably light and non-brittle.

The controller may be configured to enter stand-by mode at the start of the usage sessions, detect the start of a user puff, in response to the detection of the start of the user puff to switch from stand-by mode to operational mode, detect the end of the user puff, and in response to the detection of the end of the user puff to switch from operational mode to standby mode. The power supply may be in the form of a battery. The battery may be rechargeable. 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 aerosolgenerating 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 controller or control circuitry may be, or comprise, 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 controller may be configured to increase the power supplied to the one or more heater during an operational mode relative to a stand-by mode.

In an aerosol-generating device comprising a heater assembly in line with the foregoing description the air-permeable body portion of the heating body may be configured as a first heater.

In some embodiments of an aerosol-generating device comprising a heater assembly in line with the foregoing description the air-permeable body portion of the heating body is configured as a first heater and the hollow tubular body portion of the heating body is configured as a second heater.

In other embodiments of an aerosol-generating device comprising a heater assembly in line with the foregoing description the air-permeable body portion of the heating body is configured as a first heater and a further heat source (for example, an inductor coil) is configured as a second heater. The first heater may be arranged to heat the aerosol-generating substrate during stand-by mode and the second heater may be arranged so that it does not heat the aerosolgenerating substrate during stand-by mode.

Both the first heater and the second heater may be arranged to simultaneously heat the aerosol-forming substrate during operational mode.

The first heater may be arranged to operate throughout the usage session and the second heater may be arranged to be actuated only during user puffs. For example, the second heater may be only switched on during user puffs. Alternatively, the second heater may operate throughout the usage session, but power supplied to the second heater may be increased during user puffs.

An aerosol-generating device as described above may form an aerosol-generating system with an aerosol-generating article for use with the aerosol-generating device, namely one that comprises an aerosol-forming substrate, the aerosol-generating device configured to receive at least a portion of the aerosol-generating article. Preferably, the aerosol-generating article is configured such that at least a portion of the aerosol-forming substrate is thermally coupled with the heating body when the aerosol-generating article is inserted into the aerosolgenerating device.

In some embodiments, the aerosol-generating article further comprises a susceptor element. For example, the susceptor element may be provided within the aerosol-generating substrate, such as embedded within the aerosol-generating substrate.

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.

Example EX 1 : A heater assembly for an aerosol-generating device, the heater assembly comprising a heating body configured for resistive heating, the heating body comprising a polymer composite comprising a polymeric matrix and at least one conductive particulate material dispersed within the polymeric matrix.

Example EX 2: A heater assembly according to Example EX1 , wherein the at least one conductive particulate material is at least one of graphite, a graphite-derived material, and hexagonal boron nitride.

Example EX 3: A heater assembly according to Example EX1 or Example EX2, wherein the heating body comprises an air-permeable body portion defining an airflow path through the air-permeable body portion.

Example EX4: A heater assembly according to Example EX3, wherein the heating body comprises a hollow tubular body portion defining a chamber having an open end for receiving at least a portion of an aerosol-generating article, the airflow path being upstream of, and in fluid communication with, the chamber. Example EX5: A heater assembly according to Example EX4, wherein an equivalent free cross-sectional area of the airflow path is smaller than a free cross-sectional area of the chamber.

Example EX6: A heater assembly according to Example EX4 or Example EX5, wherein the air-permeable body portion is at least partially arranged within the hollow tubular body portion of the heating body.

Example EX7: A heater assembly according to Example EX6, wherein the air- permeable body portion is substantially integral with the hollow tubular body portion of the heating body.

Example EX8: A heater assembly according to any one of Examples EX3 to

EX7, wherein the air-permeable body portion is a porous body portion.

Example EX8: A heater assembly according to any one of Examples EX4 to

EX7, wherein the air-permeable body portion comprises at least 50 percent by weight of the polymer composite or at least 60 percent by weight of the polymer composite or at least 75 percent by weight of the polymer composite or at least 90 percent by weight of the polymer composite or at least 95 percent by weight of the polymer composite or wherein the air- permeable body portion is made entirely of the polymer composite.

Example EX9: A heater assembly according to any one of Examples EX4 to

EX8, wherein the air-permeable body portion is porous body portion formed by sintering particles of the polymer composite.

Example EX10: A heater assembly according to any one Examples EX4 to EX9, wherein a cross-sectional porosity of the air-permeable body portion is at least 15 percent.

Example EX11 : A heater assembly according to any one Examples EX4 to EX9, wherein a cross-sectional porosity of the air-permeable body portion is at least 20 percent.

Example EX12: A heater assembly according to any one Examples EX4 to EX9, wherein a cross-sectional porosity of the air-permeable body portion is at least 25 percent.

Example EX13: A heater assembly according to any one Examples EX4 to

EX12, wherein a cross-sectional porosity of the air-permeable body portion is less than or equal to 45 percent.

Example EX14: A heater assembly according to any one Examples EX4 to

EX12, wherein a cross-sectional porosity of the air-permeable body portion is less than or equal to 40 percent.

Example EX15: A heater assembly according to any one Examples EX4 to

EX12, wherein a cross-sectional porosity of the air-permeable body portion is less than or equal to 35 percent. Example EX16: A heater assembly according to any one Examples EX4 to

EX15, wherein a resistance to draw (RTD) of the air-permeable body portion is at least 10 millimetres H2O.

Example EX17: A heater assembly according to any one Examples EX4 to

EX15, wherein a resistance to draw (RTD) of the air-permeable body portion is at least 20 millimetres H2O.

Example EX18: A heater assembly according to any one Examples EX4 to

EX15, wherein a resistance to draw (RTD) of the air-permeable body portion is at least 30 millimetres H2O.

Example EX19: A heater assembly according to any one Examples EX4 to

EX15, wherein a resistance to draw (RTD) of the air-permeable body portion is at least 40 millimetres H2O.

Example EX20: A heater assembly according to any one Examples EX4 to

EX15, wherein a resistance to draw (RTD) of the air-permeable body portion is at least 50 millimetres H2O.

Example EX21 : A heater assembly according to any one Examples EX4 to

EX20, wherein a resistance to draw (RTD) of the air-permeable body portion is less than or equal to 150 millimetres H2O.

Example EX22: A heater assembly according to any one Examples EX4 to

EX20, wherein a resistance to draw (RTD) of the air-permeable body portion is less than or equal to 120 millimetres H2O.

Example EX23: A heater assembly according to any one Examples EX4 to

EX20, wherein a resistance to draw (RTD) of the air-permeable body portion is less than or equal to 100 millimetres H2O.

Example EX24: A heater assembly according to any one Examples EX4 to

EX20, wherein a resistance to draw (RTD) of the air-permeable body portion is less than or equal to 80 millimetres H2O.

Example EX25: A heater assembly according to any one of Examples EX1 to

EX3, wherein the heating body comprises a hollow tubular body portion defining a chamber having an open end for receiving at least a portion of an aerosol-generating article.

Example EX26: A heater assembly according to any one Examples EX4 to

EX25, wherein the hollow tubular body portion comprises at least 50 percent by weight of the polymer composite or at least 60 percent by weight of the polymer composite or at least 75 percent by weight of the polymer composite or at least 90 percent by weight of the polymer composite or at least 95 percent by weight of the polymer composite or wherein the hollow tubular body portion is made entirely of the polymer composite. Example EX27: A heater assembly according to any one of Examples EX4 to

EX26, wherein the hollow tubular body portion is arranged so that, when an aerosol-generating article is inserted into the chamber, the heating body directly contacts the aerosol-generating article.

Example EX28: A heater assembly according to any one of Examples EX4 to

EX27, wherein the hollow tubular body portion comprises a hollow tube element having an internal diameter of at least 4 millimetres.

Example EX29: A heater assembly according to any one of Examples EX4 to

EX27, wherein the hollow tubular body portion comprises a hollow tube element having an internal diameter of at least 5 millimetres.

Example EX30: A heater assembly according to any one of Examples EX4 to

EX27, wherein the hollow tubular body portion comprises a hollow tube element having an internal diameter of at least 6 millimetres.

Example EX31 : A heater assembly according to any one of Examples EX4 to

EX30, wherein the hollow tubular body portion comprises a hollow tube element having an internal diameter of less than or equal to 10 millimetres.

Example EX32: A heater assembly according to any one of Examples EX 4 to

EX30, wherein the hollow tubular body portion comprises a hollow tube element having an internal diameter of less than or equal to 9 millimetres.

Example EX33: A heater assembly according to any one of Examples EX4 to

EX30, wherein the hollow tubular body portion comprises a hollow tube element having an internal diameter of less than or equal to 8 millimetres.

Example EX34: A heater assembly according to any one of Examples EX4 to

EX33, wherein a thickness of the hollow tube element is at least 0.5 millimetres.

Example EX35: A heater assembly according to any one of Examples EX4 to

EX33, wherein a thickness of the hollow tube element is at least 1 millimetre.

Example EX36: A heater assembly according to any one of Examples EX4 to

EX33, wherein a thickness of the hollow tube element is at least 1.5 millimetres.

Example EX37: A heater assembly according to any one of Examples EX4 to

EX36, wherein a thickness of the hollow tube element is less than or equal to 5 millimetres.

Example EX38: A heater assembly according to any one of Examples EX4 to

EX36, wherein a thickness of the hollow tube element is less than or equal to 3 millimetres.

Example EX39: A heater assembly according to any one of Examples EX1 to

EX38, wherein the polymeric matrix comprises at least one of polyether ether ketone (PEEK) and a liquid crystal polymer (LCP). Example EX40: A heater assembly according to any one of Examples EX1 to

EX39, wherein the polymeric matrix accounts for at least 10 percent by weight of the heating body.

Example EX41 : A heater assembly according to any one of Examples EX1 to

EX39, wherein the polymeric matrix accounts for at least 15 percent by weight of the heating body.

Example EX42: A heater assembly according to any one of Examples EX1 to

EX39, wherein the polymeric matrix accounts for at least 20 percent by weight of the heating body.

Example EX43: A heater assembly according to any one of Examples EX1 to

EX42, wherein the polymeric matrix accounts for less than or equal to 55 percent by weight of the heating body.

Example EX44: A heater assembly according to any one of Examples EX1 to

EX42, wherein the polymeric matrix accounts for less than or equal to 45 percent by weight of the heating body.

Example EX45: A heater assembly according to any one of Examples EX1 to

EX42, wherein the polymeric matrix accounts for less than or equal to 35 percent by weight of the heating body.

Example EX46: A heater assembly according to any one of Examples EX2 to

EX45, wherein the graphite-derived material comprises at least one of expanded graphite and graphite nanoplatelets.

Example EX47: A heater assembly according to any one of Examples EX2 to

EX46, wherein the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for at least 30 percent by weight of the heating body.

Example EX48: A heater assembly according to any one of Examples EX2 to

EX46, wherein the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for at least 45 percent by weight of the heating body.

Example EX49: A heater assembly according to any one of Examples EX2 to

EX46, wherein the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for at least 60 percent by weight of the heating body.

Example EX50: A heater assembly according to any one of Examples EX2 to

EX49, wherein the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for less than or equal to 80 percent by weight of the heating body.

Example EX51 : A heater assembly according to any one of Examples EX2 to

EX49, wherein the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for less than or equal to 75 percent by weight of the heating body. Example EX50: A heater assembly according to any one of Examples EX2 to

EX49, wherein the at least one of graphite, a graphite-derived material, and hexagonal boron nitride accounts for less than or equal to 70 percent by weight of the heating body.

Example EX51 : A heater assembly according to any one of the preceding

Examples, wherein the heating body further comprises at least one additive dispersed within the polymeric matrix.

Example EX52: A heater assembly according to Example EX51 , wherein the at least one additive comprises carbon black.

Example EX53: A heater assembly according to Example EX51 or Example

EX52, wherein the at least one additive comprises a dispersant.

Example EX54: A heater assembly according to any one of Examples EX51 to

EX53, wherein the at least one additive accounts for at least 1 percent by weight of the heating body.

Example EX55: A heater assembly according to any one of Examples EX51 to

EX53, wherein the at least one additive accounts for at least 2 percent by weight of the heating body.

Example EX56: A heater assembly according to any one of Examples EX51 to

EX53, wherein the at least one additive accounts for at least 4 percent by weight of the heating body.

Example EX57: A heater assembly according to any one of Examples EX51 to

EX53, wherein the at least one additive accounts for at least 5 percent by weight of the heating body.

Example EX58: A heater assembly according to any one of Examples EX51 to

EX57, wherein the at least one additive accounts for less than or equal to 15 percent by weight of the heating body.

Example EX59: A heater assembly according to any one of Examples EX51 to

EX57, wherein the at least one additive accounts for less than or equal to 12 percent by weight of the heating body.

Example EX60: A heater assembly according to any one of Examples EX51 to

EX57, wherein the at least one additive accounts for less than or equal to 10 percent by weight of the heating body.

Example EX61 : A heater assembly according to any one of the preceding

Examples, further comprising at least two electrodes in operative connection with the heating body.

Example EX62: An aerosol-generating device comprising a heater assembly according to any one of the preceding Examples; and a power supply and a controller connected to the heating body and configured to apply a voltage to the heating body such that, in use, passage of an electric current in the heating body generates heat by way of resistive heating.

Example EX63: An aerosol-generating device according to Example EX62, further comprising an inductor coil extending around at least a portion of the heating body; wherein the power supply and controller are connected to the inductor coil and configured to provide a varying electric current to the inductor coil such that, in use, the inductor coil generates a varying magnetic field.

Example EX64: An aerosol-generating device according to Example EX63, wherein the inductor coil is positioned in direct contact with an outer surface of the heating body.

Example EX65: An aerosol-generating device according to any one of Examples

EX62 to EX64, wherein at least one of the controller and the heating body is configured to prevent inductive coupling between the heating body and the inductor coil during use.

Example EX66: An aerosol-generating device according to Example EX65, wherein the controller is configured to provide the varying electric current in the form of an alternative current having a frequency selected to prevent inductive coupling between the heating body and the inductor coil during use.

Example EX67: An aerosol-generating device according to any one of Examples

EX62 to EX66, further comprising a housing, wherein the inductor coil, the heating body, the power supply and the controller are positioned within the housing.

Example EX68: An aerosol-generating system comprising an aerosolgenerating device according to any one of Examples EX62 to EX67, and an aerosolgenerating article comprising an aerosol-forming substrate, the aerosol-generating device configured to receive at least a portion of the aerosol-generating article.

Example EX69: An aerosol-generating system according to Example EX68, wherein the aerosol-generating article is configured such that at least a portion of the aerosolforming substrate is thermally coupled with the heating body when the aerosol-generating article is inserted into the aerosol-generating device.

Example EX70: An aerosol-generating system according to Example EX68 or

Example EX69, wherein the aerosol-generating article further comprises a susceptor element. The invention is further described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a side cross-sectional view of an aerosol-generating device comprising a heater assembly according to the present invention; and

Figure 2 shows a side cross-sectional view of an aerosol-generating system comprising the aerosol-generating device of Figure 1. Figures 1 and 2 show an aerosol-generating device 210 including a heater assembly 212 in accordance with the present invention.

The heater assembly 212 comprises a heating body including a hollow body portion 214 partially defining a chamber 216 for receiving a portion of an aerosol-generating article. The chamber 216 comprises an open end 218 through which an aerosol-generating article may be inserted into the chamber 216 and a closed end 220 opposite the open end 218. In more detail, the hollow body portion 214 comprises a tubular element 228, which partially defines a cylindrical wall 222 of the chamber 216 that extends between the open end 218 and the closed end 220.

The tubular element 228 is arranged so that an aerosol-generating article is received within the tubular element 228 and in direct contact with the tubular element 228 when the aerosol-generating article is inserted into the chamber 216. Advantageously, direct contact between the tubular element 228 and an aerosol-generating article facilitates the transfer of heat - generated within the tubular element 228 by Joule effect when a voltage is applied to the hollow body portion 214 - to the aerosol-generating article.

The heating body of the heater assembly 212 further comprises an air-permeable body portion in the form of a porous body portion 230 defining an airflow path through the porous body portion 230. The airflow path is upstream of, and in fluid communication with the chamber 216. An equivalent free cross-sectional area of the airflow path is smaller than a free cross-sectional area of the chamber 216. In the embodiment illustrated in Figures 1 and 2, the porous body portion 230 comprises a porous plug 234 provided within the tubular element 228.

The porous body portion has a cross-sectional porosity of 30 percent. A length of the porous body portion as measured along the longitudinal axis of the heater assembly is from 2 millimetres to 5 millimetres. A RTD of the porous body portion is from 50 millimetres H2O to 60 millimetres H2O.

An inductor coil 224 comprising a plurality of windings 226 extends around an outer surface of the tubular element 228. The inductor coil 224 is arranged so that the plurality of windings are in direct contact with the outer surface of the tubular element 228. Advantageously, positioning the inductor coil 224 in direct contact with an outer surface of the tubular element 228 facilitates the transfer of heat generated by resistive heating of the inductor coil 224 to the tubular element 228. The inductor coil 24 and the heat-conducting element 228 are arranged concentrically about a central axis 236 of the aerosol-generating device 210.

The aerosol-generating device 210 also comprises a controller 240 and a power supply

242 connected to the inductor coil 224. The controller 240 is configured to provide an alternating electric current from the power supply 242 to the inductor coil 224 to generate an alternating magnetic field.

Figure 2 shows a cross-sectional view of an aerosol-generating system 300 comprising the aerosol-generating device 210 of Figure 1 and an aerosol-generating article 302.

The aerosol-generating article 302 comprises an aerosol-forming substrate 304 in the form of a tobacco plug, a first hollow acetate tube 306, a second hollow acetate tube 308, a mouthpiece 310, and an outer wrapper 312. The aerosol-generating article 302 also comprises a susceptor element 314 arranged within the aerosol-forming substrate 304.

During use, a portion of the aerosol-generating article 302 is inserted into the chamber 216 so that the aerosol-forming substrate 304 and the susceptor element 314 are positioned inside the heating body of the heater assembly 212 and the inductor coil 224. The controller 240 provides an alternating electric current from the power supply 42 to the inductor coil 224 to generate an alternating magnetic field that inductively heats the susceptor element 314, which heats the aerosol-forming substrate 304 to generate an aerosol. Additionally, heat generated in the inductor coil 224 itself by resistive losses in the inductor coil 224 is conducted from the inductor coil 224 to the aerosol-forming substrate 304 by the heat-conducting element 228.

Airflow through the aerosol-generating system 300 during use is illustrated by the dashed line 316 in Figure 2. When a user draws on the mouthpiece 310 of the aerosolgenerating article 302, a negative pressure is generated in the chamber 216. The negative pressure draws air into the aerosol-generating device 210 and through the porous body portion 230 of the heater assembly 212, where the airflow is pre-heated by heat generated resistively in the porous body portion 230. The airflow then continues on and flows through the aerosolforming substrate 304 received into the chamber 216 of the hollow body portion 214.

As the airflow passes through the aerosol-forming substrate 304, aerosol generated by heating of the aerosol-forming substrate 304 is entrained in the airflow. The aerosol then flows along the length of the aerosol-generating article 302 and through the mouthpiece 310 to the user.

For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number A is understood as A ± 10 percent (10%) of A. Within this context, a number A may be considered to include numerical values that are within general standard error for the measurement of the property that the number A modifies. The number A, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which A deviates does not materially affect the basic and novel characteristic(s) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

Claims

1 . A heater assembly for an aerosol-generating device, the heater assembly comprising a heating body configured for resistive heating, the heating body comprising a polymer composite comprising a polymeric matrix and at least one of graphite, a graphite-derived material, and hexagonal boron nitride dispersed within the polymeric matrix.

2. A heater assembly according to claim 1 , wherein the heating body comprises an air-permeable body portion defining an airflow path through the porous body portion.

3. A heater assembly according to claim 2, wherein the heating body comprises a hollow tubular body portion defining a chamber having an open end for receiving at least a portion of an aerosol-generating article, the airflow path being upstream of, and in fluid communication with, the chamber.

4. A heater assembly according to claim 3, wherein the air-permeable body portion is at least partially arranged within the hollow tubular body portion of the heating body.

5. A heater assembly according to claim 4, wherein the air-permeable body portion is substantially integral with the hollow tubular body portion of the heating body.

6. A heater assembly according to any one of claims 3 to 5, wherein the air- permeable body portion comprises at least 50 percent by weight of the polymer composite.

7. A heater assembly according to any one of claims 3 to 6, wherein the air- permeable body portion is formed by sintering particles of the polymer composite.

8. A heater assembly according to any one of claims 3 to 7, wherein a cross- sectional porosity of the air-permeable body portion is at least 15 percent.

9. A heater assembly according to any one of claims 3 to 8, wherein a resistance to draw (RTD) of the air-permeable body portion is less than or equal to 100 millimetres H2O.

10. A heater assembly according to claim 1 , wherein the heating body comprises a hollow tubular body portion defining a chamber having an open end for receiving at least a portion of an aerosol-generating article.

11. A heater assembly according to any one of the preceding claims, wherein the polymeric matrix comprises at least one of polyether ether ketone (PEEK) and a liquid crystal polymer (LCP).

12. An aerosol-generating device comprising: a heater assembly according to any one of the preceding claims; and a power supply and a controller connected to the heating body and configured to apply a voltage to the heating body such that, in use, passage of an electric current in the heating body generates heat by way of resistive heating.

13. An aerosol-generating system comprising: an aerosol-generating device according to claim 12; and an aerosol-generating article comprising an aerosol-forming substrate, the aerosol-generating device configured to receive at least a portion of the aerosolgenerating article.

14. An aerosol-generating system according to claim 13, wherein the aerosolgenerating article is configured such that at least a portion of the aerosol-forming substrate is thermally coupled with the heating body when the aerosol-generating article is inserted into the aerosol-generating device.

15. An aerosol-generating system according to claim 13 or 14, wherein the aerosolgenerating article further comprises a susceptor element.