GB2496404A - Liquid heating appliances having a steam guiding member - Google Patents

Abstract

A liquid heating appliance 2 comprises a liquid heating vessel 4 and an electric heater 12 arranged under and in thermal contact with a heating base 10 of the vessel 4. A fluid guiding member 32 is provided in the vessel 4 and over the heating base 10 to capture fluid rising from the heating base 10 and to guide the rising fluid on a path that substantially changes direction before fluid is vented out of the vessel 4. The fluid guiding member 32 may comprise an inner ring 34 arranged to partially contain a volume of liquid over the area of the heating base 10 above the electric heater 12. As fluid (steam) is forced to change direction it flows back towards cooler water and thus convective mixing is encouraged such that the liquid is heated more evenly.

Description

Liquid Heatinq ADDlianCes The present invention relates to electric appliances for heating liquids, especially water, and in particular, but not exclusively, to domestic appliances such as kettles and beverage makers.

Current worldwide sales of electric kettles represent about 75 million units a year and it is a growing business, for example in markets like the USA and China. As in all industries, kettle manufacturers find themselves under increasing pressure to reduce the amount of materials used in their products, to reduce the amount of packaging required, and to reduce the volume and weight of products for transportation. Increasingly, consumers are questioning the carbon footprint associated with the products that they buy and seeking those that minimise their negative impact on the environment. It can also be desirable to reduce the size and/or weight of domestic appliances in order to improve ease of use e.g by the elderly or physically impaired.

A typical domestic kettle is designed to hold around.1.5 litres of water (corresponding to six to eight cups. of beverage) and its capacity is indicated by a maximum fill level indicator. However the volume of the water heating chamber itself is usually at least 20% greater than the volume of water that it is intended to hold. The unfilled headspace in the top of the vessel is required for safety reasons; it prevents boiling water from spitting out of the spout. The presence of this headspace limits the capability of manufacturers to make kettles more compact while retaining their water capacity.

It has previously been proposed to use a perforated baffle to help prevent water from spitting out of the spout of a kettle, for example as is disclosed by EP- 1062897-Al. In this document a double-walled baffle at the spout is said break up the turbulent water created at boiling and only allow steam to pass out through the spout. Although such a proposal may allow the headspace in the kettle to be reduced to a degree, the perforated baffles do not affect the way in which steam is generated in the vessel or change the way in which turbulence is created in the water being heated. Thus a headspace is still required to allow steam bubbles to break at the water's surface and to allow the surface level to fluctuate at boiling.

It is an aim of the present invention to provide an improved water heating vessel.

When viewed from a first aspect the invention provides a liquid heating appliance comprising a liquid heating vessel and an electric heater arranged under and in good thermal contact with a heating base of the vessel, wherein a fluid guiding member is provided in the vessel and over the heating base to capture fluid rising from the heating base and to guide the rising fluid on a path that substantially changes direction before fluid is vented out of the vessel.

According to the invention there is provided a fluid guiding member in the vessel that influences the way in which water is heated and steam is vented. It will be understood that the fluid in contact with the heating base may comprise both the liquid being heated and also bubbles of steam that are created in the liquid. The film of liquid at the surface of the heating base may reach its boiling point and create steam, released in the form of rising steam bubbles. The heated liquid closest to the heating base will also rise to be replaced by cooler liquid. The fluid guiding member can have an influence both on the steam bubbles and the convective flow of liquid in the vessel.

In a conventional liquid heating vessel with an underfloor heater, steam bubbles are free to. rise from the surface of the heating base. Some bubbles may collapse as they rise to meet cooler liquid, while others may coalesce to form bubbles large enough to reach the surface. There is also a free convective flow of liquid in the vessel, with heated liquid rising to be replaced by cooler liquid that is further away from the heating base. As the temperature rises towards boiling, the mixing of water in the vessel becomes more turbulent. When the bulk of the liquid volume in the vessel reaches its boiling point then steam is rapidly evolved from the liquid's surface and the breaking steam bubbles across the surface can cause waves.

Droplets of water can spit out of the vessel with the steam bubbles. The surface disturbance and spitting is accommodated by the headspace in a conventional vessel.

According to the present invention a fluid guiding member is arranged to capture fluid (liquid and/or steam) as it rises from the heating base and to guide the rising fluid on a path that substantially changes direction before steam can be vented out of the vessel. The effect is two-fold. Firstly, because the rising liquid that has been heated is forced to change direction it must flow back towards the cooler water in the bottom of the vessel. Convective mixing is therefore encouraged and the liquid in the vessel is heated more evenly. This reduces the turbulence that would usually occur as the liquid is being heated towards boiling point. Secondly, because there is no direct path for steam bubbles and steam to be vented out of the vessel, any liquid droplets carried along with the steam will impinge on the guiding member and condense back into the bulk, while only the vapour can change direction to escape.

Thus spilling is prevented. The combined result is that the volume of the headspace required at the top of the vessel above the maximum liquid level can be significantly reduced, for example from 20-30% of the vessel's liquid capacity to only 5-10% or less. The appliance may therefore be made more compact than a conventional one designed for the same volume of liquid. Furthermore there is no need for a complex baffle arrangement in the spout that could interfere with pouring and that may require additional cleaning, although preferably a simple baffle or filter is still provided for steam management and possibly to trap scale particles.

The fluid guiding member may be arranged such that it is wholly immersed in the liquid in the vessel during use, however it is preferred that that is only partially immersed with the maximum liquid level below the highest part of the member. The Applicant has recognised that in order to gain most benefit from the member its position relative to the underfloor electric heater can be important. This is because direct heating and steam bubble generation will preferentially take place at the surface of the heating base that is directly above or in contact with the electric heater. If the heater is annular, for example, then a ring of steam bubbles may be generated. It is therefore preferred that the fluid guiding member is positioned over the electric heater, so as to capture the most directly heated liquid and any steam bubbles. Furthermore the footprint of the fluid guiding member preferably matches the shape of the electric heater. In one set of embodiments the heater comprises an annular segment and the fluid guiding member has a footprint in the form of a corresponding annular segment.

The electric heater may comprise a sheathed heating element or a thick film printed element. In one set of embodiments a sheathed heating element is preferred as it may be accommodated in a step or ridge in the base of the vessel. It has been found that forming a step or ridge in the heated base, rather than having a planar base, can be advantageous as it provides one or more edges to encourage and control the release of steam bubbles. The fluid guiding member may then be positioned over the step or ridge to capture steam bubbles as they are formed.

In one set of embodiments the heating base is preferably not planar. As described above, by forming a step or edge in the base the release position of steam bubbles from the base can be controlled. The Applicant has realised that a potential further benefit to a non-planar base is that the base can be shaped so as to accommodate at least part of a thermally sensitive control provided below the base. Thus in a preferred set of embodiments the appliance comprises a thermally sensitive control means under the base and the base comprises a convex portion to accommodate at least part of the control means. Thus the space required in the appliance beneath the heating vessel, or at least below its outer walls, may be reduced. This can contribute towards making the appliance more compact and reducing its carbon footprint.

The Applicant has appreciated that there is a further benefit to providing the vessel with a non-planar heating base. The heating base can be used to define one or more pockets of water that can be used to control the heating profile and/or final temperature of liquid in the vessel. This may be particularly advantageous where it is desired to heat liquid in the vessel to a certain temperature below the boiling point, for example a temperature in the range of 70-95 °C that may be more suited to making beverages such as green tea, herbal infusions or coffee. Furthermore it can be desirable from an ecological standpoint to avoid heating liquid unnecessarily to boiling when a lower temperature would in fact be preferred for use. However it can be difficult to control the electric heater so that liquid in the vessel reaches a desired temperature below boiling point without overshoot. The electric heater is preferably controlled by a thermal sensing means on the dryside of the appliance, mounted underneath the base of the vessel and in contact with the heating base and/or heating element. The temperature of the heating base and the electric heater runs ahead of the actual temperature of the liquid in the vessel. When the electric heater is switched off the thermal energy stored in the heating base will *continue to be transferred into the liquid in the vessel until an equilibrium is reached and thus the liquid temperature will often overshoot its desired temperature. This problem can be particularly acute when a relatively small volume of liquid is being heated in a vessel of larger capacity, for example 1-2 cups of liquid in a vessel having a maximum capacity of 6-8 cups. The smaller the volume of the liquid, the larger the effect of the thermal inequilibrium and the greater the temperature overshoot. It is desirable to be able to heat only the volume of liquid that is required, and only with enough energy to reach the desired temperature, for the appliance to be efficient.

in one preferred set of embodiments the heating base comprises a channel extending around at least a part of its outer periphery. Preferably the channel extends around the outside of the electric heater. Accordingly a volume of cold liquid can be trapped in the outer channel that is not readily heated. Further preferably the fluid guiding member is provided inside the peripheral channel. The fluid guiding member may be positioned over the electric heater and inside the peripheral channel such that it sets up a convective flow in a volume of liquid that substantially does not include the liquid in the channel. An advantage of providing such a peripheral sump of cold liquid is that it may only be mixed into the bulk of the liquid in the vessel once the bulk has reached boiling point, or if the liquid is heated to a temperature below the boiling point then it may only be mixed into the bulk once liquid is poured out of the vessel. Depending on the volume of the sump or channel, this may cool down the liquid and lower the overall temperature.

The Applicant has previously proposed, for example in EP-A-1 462039, that a thermally sensitive actuator may be mounted in thermal contact with a waIl of a peripheral channel or sump to be operable in the event of liquid in the vessel boiling. Such an arrangement, sometimes referred to as "sump control", relies on the rapid temperature increase of liquid in the sump to detect when turbulence and boiling occurs. However the Applicant has recognised that a thermally sensitive control may be used with a heating base comprising a sump in a different way in order to achieve a different effect. Instead of using the sump to detect boiling, preferably a dedicated boiling sensitive actuator such as a steam sensor is provided. The Applicant has realised that it is possible to use the liquid in the peripheral sump to help control the final temperature of liquid in the vessel.

In a preferred set of embodiments the appliance comprises a variable temperature thermally sensitive control preferably comprising a bimetallic actuator having a variable operating temperature arranged so as in use to make good thermal contact with the heating base of the vessel, for example a bimetallic actuator wherein a biasing means is arranged to exert a variable force on the actuator so as to vary its operating temperature in use. Such a variable temperature control is described in detail in EP-A-1565037 and is available commercially from Strix Limited in the U19 series. The operating temperature of the actuator may be varied so as to set a desired liquid temperature below boiling. However, as the actuator is mounted in thermal contact with the heating base rather than in direct contact with the liquid, its temperature runs ahead of the actual liquid temperature. In practice, after the actuator senses the desired liquid temperature from the temperature of the heating base and switches off the electric heater, the actual liquid temperature will increase further due to transfer of thermal energy from the heating base. This effect is more pronounced for smaller volumes of liquid.

In order to help counteract this temperature overshoot, a sump in the heating base can be designed to trap a volume of cooler liquid that will bring the liquid temperature back down to the desired temperature when it is mixed in with the bulk.

Although a discrete sump, such as a recess in the base, may be used, preferably the sump is in the form of a channel in the base so as to trap a sufficient volume of liquid. Preferably the channel is at the outer periphery of the heating base so that liquid therein may more easily be isolated from the bulk of the liquid being heated in the vessel. Thus in one set of embodiments it is preferable to combine a variable temperature thermally sensitive control with a heating base that comprises a peripheral sump.

This feature may be considered novel and inventive in its own right, and thus when viewed from a second aspect the invention provides a liquid heating appliance comprising a liquid heating vessel, an electric heater arranged under and in good thermal contact with a heating base of the vessel, and a variable temperature thermally sensitive control comprising a bimetallic actuator having a variable operating temperature arranged so as in use to make good thermal contact with the heating base at or inwardly of the heater, wherein the heating base comprises a liquid channel extending around at least a part of its outer periphery.

As is described above, the channel is preferably arranged radially outside the electric heater. The channel may extend around all or part of the periphery of the vessel. The channel may be formed by a step or ridge in the heating base that accommodates an electric heating element. By providing such a peripheral liquid channel the overshoot effect in the liquid temperature profile can be smoothed out and a desired final liquid temperature that is below boiling may be more accurately achieved using an actuator in thermal contact with the heating base of the vessel.

Furthermore, because the liquid trapped in the peripheral sump has substantially not been heated, less energy will have been used to heat the overall volume of liquid in the vessel to a desired temperature. Avoiding temperature overshoot helps to ensure that energy is not wasted.

Following the above discussion of using a sump or channel to trap a volume of relatively unheated liquid that can be mixed with heated liquid to achieve a desired temperature, it will be appreciated that the volumes of relatively heated and unheated liquid in the vessel can be an important factor. The cooling effect of the relatively unheated liquid from the sump should be maximised in order to avoid using energy unnecessarily to heat liquid when its temperature will overshoot the desired temperature. The Applicant has realised that a more efficient heating regime may be achieved by controlling the volume of liquid in the vessel that is in direct contact with the heating base, in particular the volume of liquid in the vessel that is in direct contact with the area of the heating base in direct thermal contact with the electric heater. Preferably a separator is arranged in the vessel to partially contain a volume of liquid over the area of the heating base above the electric heater. The separator can ensure that a relatively small volume of liquid is held in close contact with the directly heated part of the base. The separator may interfere with some of the convective flow in the bulk liquid and result in preferential heating of the smaller volume that is partially contained. This smaller volume may then be heated to boiling point more rapidly and using less energy, at which point convective mixing will bring in cooler liquid from the volume outside the separator and overall a desired temperature below boiling may be achieved while minimising the heating energy used. It will be understood that this may be particularly beneficial where the appliance comprises a thermally sensitive control, preferably a variable temperature control, with an actuator arranged in good thermal contact with the heating base that may suffer from overshoot problems, as is described above.

The main purpose of the separator is to partially confine a volume of liquid in contact with the area of the heating base that is directly heated by the electric heater. The separator is a preferred feature of both of the first and second aspects of the invention outlined above. Irrespective of whether or not a fluid guiding member is present, such an arrangement can be used to control mixing between a relatively more heated volume of liquid (provided by the separator) and the relatively less heated liquid bulk. This can result in a more even heating with less turbulence in the liquid before it reaches boiling point.

Advantageously the separator may also be arranged to isolate this volume of liquid from the volume of liquid contained in a sump such as a peripheral channel, where one is provided. In one set of embodiments it is preferred that the heating base comprises a channel extending at least partly around its outside periphery, preferably outboard of the electric heater, and a separator is also positioned radially inwardly of the channel so as to partially confine a volume of liquid over the electric heater.

This may be considered novel and inventive in its own right, and thus when viewed from a further aspect the invention provides a liquid heating appliance comprising a liquid heating vessel, an electric heater arranged under and in good thermal contact with a heating base of the vessel, wherein the heating base comprises a liquid channel extending around at least a part of its outer periphery, and a separator member arranged in the vessel inwardly of the channel to at least partially confine a volume of liquid over an area of the heating base above the electric heater.

Thus it will be understood that there are two volumes of liquid in the vessel that is at least partially contained so that one volume is heated rapidly towards boiling point while the other volume remains relatively unheated until it is mixed in with the heated liquid, either by convection in the vessel (e.g. upon boiling) or by pouring the liquid out of the vessel. This can help to achieve a final liquid temperature below boiling point that compensates for the temperature overshoot often experienced when an underiloor thermally sensitive control is used, especially a variable temperature control, as is described above.

Some preferred features will now be described that may be applied to any of the aspects of the invention described so far.

The separator may be arranged to partially contain a volume of liquid that is preferably less than 1/3, 1/4, 1/5, or 1/6 of the volume of the liquid heating vessel.

The separator may be arranged anywhere in the vessel that allows it to partially confine a volume of liquid over the area of the heating base above the electric heater. The separator may have a surface disposed above and extending over at least pad of the upper surface of the heating base opposite where the heating element is provided, so as in use to partially contain a layer of liquid directly above the heating element. However such a surface may interfere with the intended effect of the fluid guiding member, where provided. In at least one set of embodiments it is preferred that the separator comprises one or more wall(s) extending generally vertically above the upper surface of the heating base to at least partly surround the area where the heating element is provided, so as in use to partially contain a layer of liquid directly above the heating element. Such wall(s) may not interfere with the upward flow of heated liquid and/or steam bubbles from the heated base and preferably the wall(s) are even arranged to assist the fluid guiding member (where provided) in its function. The vertical extent of the wall(s) may be selected to determine the volume of liquid that will be contained in close contact with the directly heated part of the base.

Although the separator may be independent of the fluid guiding member, it has been found that the separator may conveniently be combined with the fluid guiding member so that together they act to both partially combine a volume of fluid in contact with the heating base and also to direct the convective flow of fluid out of that volume. In a preferred embodiment the separator may be formed at least in part by the fluid guiding member. The separator may comprise a member that is attached to or integral with a wall of the fluid guiding member. This is extremely convenient in that it does not require any special features to be formed on the heating base to position the separator. For example, the fluid guiding member may provide one wall of the separator. In one set of embodiments the separator comprises a pair of circumferential walls arranged either side of an annular area of the heating base that is in contact with the electric heater (preferably a sheathed heating element substantially in a ring or horse-shoe shape). Preferable the fluid guiding member provides the radially outer wall of the separator while the separator comprises a radially inner wall. The curvature and position of the walls may substantially correspond to the shape of the electric element underneath the heating base.

It will be understood that a synergistic effect may be achieved whereby a volume of liquid in close contact with the directly heated part of the base is heated and partially contained by the separator so that it can reach boiling more quickly, while the fluid guiding member controls the movement of steam bubbles out of the contained volume and also the convective mixing that takes place as the liquid boils. There may therefore be provided a smoother heating profile, with the liquid in the vessel being heated more evenly than in conventional appliances so that turbulence is reduced. Accordingly the size of the headspace in the vessel can be reduced. In at least some embodiments the separator may be seen as a sub-component of the fluid guiding member.

Furthermore, because the fluid guiding member/separator creates a partially confined volume of liquid immediately above the heating element, where bubbles tend to form, the temperature of this volume may increase rapidly during heating from ambient to the nucleate boiling phase, thus reducing the time that the liquid is in the temperature range 60 to 80 °C where steam bubbles cause the most noise.

The loud whistling noise associated with liquid in a conventional appliance being heated to boiling may therefore be reduced or even removed.

It will be understood that the invention is mainly directed to domestic liquid heating appliances that are used to heat liquid for making beverages and other uses around the home. The liquid heating vessel in such appliances usually has a volume of 1-2 litres and is provided with an electric heater having a power of 2-3 kW in Europe (or 1.2-1.5 kW in Japan and the US). Such appliances are intended to heat liquid to a temperature and then to turn off the electric heater or to maintain a lower power heating (e.g. 50 to 200 W) to keep liquid in the vessel warm. Some appliances may cycle the heater on and off to keep the liquid simmering, but generally it is not intended for water in the vessel to be continuously boiled to produce steam.

However, the various beneficial effects of the invention as described above may find use in liquid heating appliances other than those used to heat liquid mainly for making beverages. The invention may find use in many appliances that heat liquid to boiling in order to generate steam, for example facial saunas, vaporisers, steam cookers, steam cleaners, wallpaper strippers and other hand-held steam generating appliances. In these appliances it may be desirable to avoid water droplets from spilling out with the steam, to reduce the size of the water boiling chamber, and/or to reduce the weight of the appliance.

Thus from a further broad aspect the invention provides a steam generating appliance comprising a water boiling chamber, an electric heater arranged to heat water in the boiling chamber, a steam vent for the chamber, and a fluid guiding means arranged in the boiling chamber to guide water and steam on a path that substantially changes direction before reaching the vent.

Certain preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure us a perspective view of a liquid heating appliance according to a first embodiment of the invention; Figure 2 is a side sectional view of the appliance of Figure 1; Figure 3 is a plan view of the underside of the appliance with its base cover removed; Figure 4 is a partial perspective view of the heating base and components inside the liquid heating vessel of the appliance of Figures 1 to 3; Figure 5 is a side sectional view of a liquid heating appliance according to a second embodiment of the invention; and Figure 6 is a partial perspective view of the heating base and component inside the liquid heating vessel of the appliance of Figure 5.

There will now be described with respect to Figures 1-4 a first embodiment of a liquid heating appliance 2 in the form of a kettle. The appliance 2 comprises a liquid heating vessel 4 of the cordless type that can be seated on a corded power base (not shown) in use to receive power from the mains supply. The vessel 4 is shown as having the general form of a jug, with a handle 6 and a spout 8. A baffle or filter (not shown) may be positioned in the spout 8. It will be understood that the shape and dimensions of the vessel 4 may be adjusted to make the appliance more compact for a given volume and/or to improve its packaging and transportation. For example, rather than a generally cylindrical vessel there may be provided a vessel that is generally square in cross-section so that appliances can be packed more densely side by side in transit.

The liquid heating vessel 4 in this embodiment comprises glass side walls connected to a stainless steel base 10. As can be seen from Figures 2-4, the base is not planar but comprises a raised step inboard of its periphery. A sheathed electric heating element 12 is accommodated in the step of the heating base 10 and extends in the shape of a horse shoe. Radially outward of the heating element 12 the base 10 provides a peripheral channel 14 between the step and the walls of the vessel 4. A certain volume of liquid is trapped in the peripheral channel 14 in use, as will be described in more detail below.

Underneath the heating base 10 there is provided an integrated connector and thermally sensitive control 16 such as one of the U19 series of controls available from Strix Limited. The control 16 is partly accommodated in the step in the base 10. A base cover 17 is fitted underneath the vessel 4 to house the heater 10, 12 and the control 16. It can be seen from Figure 3 that the control 16 includes a male connector part 19 of the type that permits the appliance to be placed on a power base at substantially any angular orientation (a so-called 360° cordless connector), for example a P72 cordless system available from Strix Limited. The male connector part 19 passes through an aperture in the base cover 17.

The control 16 transfers power from the cordless connector to the electric heating element 12. The control 16 includes two snap-action bimetallic actuators 18, 20 that are mounted against the underside of the base 10, close to the element 12.

One bimetallic actuator iBis acted upon by a torsion spring 22 that is connected to a rotatable knob 24. By turning the knob 24, a user is able to change the force applied by the spring 22 against the blade of the bimetallic actuator 18 and thus its operating temperature. A user can therefore adjust the temperature at which the control 16 will act to disconnect power from the heating element 12. The other bimetallic actuator 20 provides a safety back-up. It has an operating temperature set above 100 °C and therefore acts to detect when the base 10 is overheating as a result of being operated without water present or due to boiling dry.

The control ISis provided with a lever 26 that a user can depress to switch on the appliance by connecting power to the heating element 12. The lever 26 is spring-mounted to automatically return when the appliance 2 is lifted from its power base, so that the heater is switched off even when the appliance 2 is placed back on the power base. The lever 26 also is operated by an integrated steam switch 28. It can be seen from Figures 1 and 2 that steam is ducted down from the top part of the vessel 4 by pipes 30 that pass through the heating base 10 to exhaust steam onto the switch 28. The control 16 will operate to disconnect power to the heating element 12 when the steam switch 28 detects that water in the vessel 4 is boiling.

Although in this embodiment the steam pipes 30 are shown as passing inside the glass walls of the vessel 4, ri other embodiments one or more steam pipe(s) may be hidden inside the body mouldings of a plastic handle or vessel walls.

Looking inside the vessel 4, it can be seen from Figures 1 and 2 that there is provided a baffle arrangement 32 above the heating base 10 and inwardly of the peripheral channel 14. In this embodiment the baffle arrangement 32 comprises an inner ring 34 and an outer hood 36. The baffle arrangement 32 is seen in more detail in Figure 4. The inner ring 34 is arranged over the heating base lOso as to coincide with the inner periphery of the heating element 12, substantially in the shape of a horseshoe. The lower wall of the hood 36 is arranged over the heating base 10 so as to coincide with the outer periphery of the heating element 12.

Together, the inner ring 34 and the lower wall of the hood 36 provide a separator that acts to partially confine an annular volume of liquid above the heating element 12.

The inner ring 34 and the hood 36 may be integrally provided, for example as a single moulding, but in this embodiment the ring 34 is a separate piece that is provided with three circumferentially spaced connecting clips 38 that pass over the base 10 above the heating element 12 and clip onto the lower wall of the hood 36.

The moulded hood 36 is itself located in position in the vessel 4 by four apertures through which the steam pipes 30 pass. The lower wall of the hood 36 also rests on an annular support 42 that is arranged in the peripheral channel 14 and circumscribes the step that accommodates the heating element 12.

The hood 36 of the baffle arrangement 32 comprises a wall that is annular at its base, corresponding to the horse-shoe shape of the heating element 12, and that extends upwardly in a generally conical shape so as to concentrate the flow of fluid.

Towards the top of the vessel 4, the hood 36 curves over so that the flow path that it defines changes direction by 90°. In the top of the hood 36 there is provided a steam vent 44 in the form of a slot. The steam slot 44 is positioned underneath a steam inlet 46 that is connected to the steam pipes 30. Steam that does not enter the steam inlet 46 is ducted out of the vessel 4 through the spout 8.

Operation of the appliance 2 will now be described. The vessel 4 can be filled with water either through the spout 8 or by lifting the lid 48. Depending on the amount of water to be heated, the baffle arrangement 32 will be partially immersed and the inner ring 34 may be fully submerged. It is an advantage of the invention that the headspace in the vessel 4 above the hood 36 is smaller than in a conventional kettle. The maximum fill level may be indicated on the vessel 4 and is preferably close to the top of the hood 36 but below the steam vent 44. The reduced headspace is just enough to allow for expansion of the liquid and release of steam bubbles upon boiling.

If a user desires to boil the water in the vessel 4 then the lever 26 can simply be depressed to connect power to the heating element 12. If the user wishes to heat water in the vessel 4 to a temperature below the boiling point, for example 85 °C, then, as well as depressing the lever 26, the knob 24 can be turned to adjust the target temperature. Power will be supplied as long as the appliance 2 is positioned on a base (not shown).

Water in the vessel 4 trapped between the lower wall of the hood 36 and the inner ring 34 is separated laterally from the bulk and confined over the annular area of the base 10 that is directly heated by the element 12. This separated volume of water is preferentially heated and will start to reach its target temperature while water on the inside of the ring 34 will be heated to a lesser degree. Water trapped in the peripheral channel 14 outside the step in the base and the heating element 12 will experience very little heating and remain relatively cold. As the water directly above the element 12 starts to heat up it will rise and be guided by the conical hood 36 to change direction and flow back down into the bulk volume of cooler water inside the ring 34. The hood 34 therefore encourages mixing so that that the water is heated more evenly. In this way turbulence during heating is largely avoided. Colder water that drops down towards the base 10 is constrained to flow between the walls of the ring 34 and the hood 36 and over the area of the heating element 12. In this way heat is transferred more efficiently to water in the vessel 4.

Through the heating process the convective mixing is mainly confined to the volume of water surrounded by the hood 36. If the user has set a target temperature below boiling then the bimetallic actuator 18 will act when the base 10 reaches its adjusted operating temperature, say 85 °C, to disconnect power from the heating element 12. However the thermal energy stored in the element 12 and heating base 10 will continue to be transferred into the liquid in the vessel 4 until a temperature equilibrium is reached. This temperature may be above the user's target temperature. However, when water is poured out of the vessel 4 the water from the peripheral channel 14 that has been relatively unheated will be mixed in with the bulk and lower the temperature towards its target. This compensates for the temperature overshoot to ensure that a desired liquid temperature below boiling point can be achieved.

If the user has not set a target temperature below boiling point then the heating element 12 will continue to heat the water in the vessel 4 until steam passes through the inlet 46 to the steam pipes 30 and passes down to activate the steam iwitch 28. During this time, bubbles of steam that are formed in the liquid are guided by the hood 36 as they rise up. lithe water level is below the steam vent 44 in the hood 36 then the steam bubbles will break the surface below the hood 36.

Any water droplets that are carried with the steam are forced to change direction and impinge on the hood 36 rather than passing through the vent 44 with the steam vapour. The steam vent 44 is also positioned on the side of the vessel 4 away from the spout 8. In this way no water can spit out of the spout 8 with the steam and it is ensured that only steam vapour is vented out of the spout 8. Ills also advantageous that steam is directed into the inlet 46 for the steam pipes 30. The water outside of the hood 36 does not contain any steam bubbles as they are only generated on the surface of the heating base 10 above the element 12. As the water in the vessel 4 boils, convective currents will mix in the water from the peripheral channel 14 so that all of the water is substantially at the same temperature when the steam switch 28 operates.

In Figures 5 and 6 there is seen an alternative embodiment of the invention that is similar to the embodiment described above and thus only the main differences will be described. In this embodiment the appliance 2' has a baffle arrangement 32' that comprises a conical hood 36' without an inner ring member. As the baffle arrangement 32' comprises a single piece, the hood 36' can be integrally moulded with the plastic walls of the vessel 4'. The entire moulding can then be assembled with a heating base 10' to form the vessel 4'. The shape of the hood 36' is similar to that of the first embodiment and acts to guide fluid (liquid and steam bubbles) as it rises from the heated surface of the base 10' on a path that changes direction.

Accordingly heated liquid that rises in the hood 36' is directed back down to encourage circulation in the vessel 4', while steam bubbles and vapour can rise through the steam vent 44' in the top of the hood 36' to escape.

In this embodiment the step in the base 10' has an angled wall rather than a near vertical wall. The shape of the step and the peripheral channel 14' may be a compromise between achieving a desired volume for the peripheral channel 14' and providing enough space inside the step and below the base 10' to accommodate the control 16'. The control 16' may be a variable temperature control, such as a U19 control as described above, or a control that only operates at boiling, such as one of the U17 or U 1830 series available from Strix Limited. Steam pipes (not shown) may be provided to duct steam to a switch in the control 16' under the base 10'.

It will be seen from Figures 5 and 6 that the appliance 2' is shaped less like a traditional jug and has a smaller aspect ratio (height/width). Such appliances may be packed more closely together during transportation.

Although not shown in either of the embodiments described above, the baffle arrangement 32, 32' could comprise a vertical plate arranged next to the steam duct 44, 44'. Thus water droplets carried in the steam as tar as the duct 44, 44' could be guided by the hood 36, 36' to impinge on the plate and then condense to drip back down into the vessel 4, 4'. Of course the baffle arrangement may take any suitable shape and form, and is not limited to the conical hood shown in the Figures. -18-

Claims (1)

1. <claim-text>Claims 1. A liquid heating appliance comprising a liquid heating vessel and an electric heater arranged under and in good thermal contact with a heating base of the vessel, wherein a fluid guiding member is provided in the vessel and over the heating base to capture fluid rising from the heating base and to guide the rising fluid on a path that substantially changes direction before fluid is vented out of the vessel.</claim-text> <claim-text>2. A liquid heating appliance according to claim 1, wherein the fluid guiding member is arranged such that it is partially immersed.</claim-text> <claim-text>3. A liquid heating appliance according to claim 1 or 2, wherein the fluid guiding member is positioned over the electric heater.</claim-text> <claim-text>(\J 15 4. A liquid heating appliance according to claim 3, wherein the fluid guiding 1' member has a footprint that matches the shape of the electric heater.</claim-text> <claim-text>CQ 5. A liquid heating appliance according to any preceding claim, wherein the 0 20 electric heater comprises a sheathed heating element accommodated in a step or ridge in the base of the vessel.</claim-text> <claim-text>6. A liquid heating appliance according to any preceding claim, comprising a thermally sensitive control means under the base and the base comprising a convex portion to accommodate at least pad of the control means.</claim-text> <claim-text>7. A liquid heating appliance according to any preceding claim, wherein the heating base comprises a channel extending around at least a part of its outer periphery.</claim-text> <claim-text>8. A liquid heating appliance according to claim 7, wherein the channel is arranged radially outside the electric heater.</claim-text> <claim-text>9. A liquid heating appliance according to claim 7 or 8, wherein the fluid guiding member is provided inside the channel. -19-</claim-text> <claim-text>10. A liquid heating appliance according to any preceding claim, wherein a separator is arranged in the vessel to partially contain a volume of liquid over the area of the heating base above the electric heater.</claim-text> <claim-text>11. A liquid heating appliance according to claim 10, wherein the separator is positioned radially inwardly of a or the channel extending around the outer periphery of the base.</claim-text> <claim-text>12. A liquid heating appliance according to claim 10 or 11, wherein the separator comprises one or more wall(s) extending generally vertically above the upper surface of the heating base to at least partly surround the area where the heating element is provided, so as in use to partially contain a layer of liquid directly above the heating element.(\J 15 13. A liquid heating appliance according to claim 10, 11 or 12, wherein the 1' separator is formed at least in part by the fluid guiding member.CQ 14. A liquid heating appliance according to claim 13, wherein the fluid guiding 0 20 member provides the radially outer wall of the separator while the separator comprises a radially inner wall.</claim-text>