HEATER

Abstract

 The present invention relates to a heater (1) for an aerosol generating device (100). The heater includes a capillary sheet (10) comprising a sheet of heat conductive fibre mesh configured to provide capillary action in use and a heating element (20) in contact with the sheet of conductive fibre mesh and arranged to heat the sheet of conductive fibre mesh. By using a dedicated heating component, in particular a heating element in contact with the mesh in order to transfer heat to the mesh, the mesh heater material and structure can be configured to optimise the wicking properties and the heating element can be optimised to provide the required heating function.

Description

[0001] The present invention relates to a heating element for an aerosol generation device or system, such as an electronic cigarette.

Background

[0002] Known aerosol generation devices such as electronic cigarettes often use a heating component, or heater, to heat an aerosol generating liquid in order to generate an aerosol, or vapour, for inhalation by a user. The heating component is typically made of a conductive material which allows an electric current to flow through it when electrical energy is applied across the heating component. The electrical resistance of the conductive material causes heat to be generated as the electric current passes through the material, a process commonly known as resistive heating.

[0003] Heating components in the art include a metal wire or a fibre mesh array formed into different shapes, for example a coil wire. In use the heater is typically in contact or in close proximity to a wicking element that draws aerosol generating liquid from a reservoir or supply in the device to be vapourised. The wicking element commonly has a fibrous or porous structure which causes liquid to be drawn from the liquid supply by capillary action.

[0004] Some heating elements, in particular fibre mesh array heaters, combine the heating and wicking functions, where for example a sheet of electrically conductive porous material uses capillary action to draw the aerosol generating liquid from the reservoir into the heating component, which also provides heat when electrical energy is passed through it. The sheet of electrically conductive porous material can be shaped to optimise the synergy between heating and wicking functions.

[0005] There are several known problems with this kind of known device. In particular, capillary heaters do not always effectively transport the liquid from the liquid store for heating and the liquid may be vaporised outside of the intended area of the heating arrangement. Furthermore, such mesh heaters may place restrictions on the heating parameters achievable due to restrictions in the structure of the heating element necessary to provide the required liquid transport function.

[0006] An object of the invention is to provide a more reliable and effective heating element for an aerosol generation device.

Summary of invention

[0007] According the present invention there is provided heater for an aerosol generating device comprising: a capillary sheet comprising a sheet of heat conductive fibre mesh configured to provide capillary action in use; a heating element in contact with the sheet of conductive fibre mesh and arranged to heat the sheet of conductive fibre mesh.

[0008] By using a dedicated heating component, in particular a heating element in contact with the mesh in order to transfer heat to the mesh, the mesh heater material and structure can be configured to optimise the wicking properties and the heating element can be optimised to provide the required heating function. For example the porosity and/or density of the mesh can be selected to provide improved wicking rather than heating. In this way, an improved performance can be achieved relative to devices which use mesh heaters to provide both the heating and capillary transport functions. Furthermore, a chosen region of the mesh sheet can be contacted with the heating element in order to preferentially heat the chosen region. This can provide temperature gradients across the heater components which can be used to further improve the liquid transport across the capillary sheet.

[0009] Preferably the heating element is a resistive heating element comprising two contact points to which a power source may be connected to provide a current through the heating element to heat the heating element. For example the heating element may comprise a heating rod, a heating wire or coil. This provides an effective way to heat the heating element and accordingly the capillary sheet. Furthermore, the current may also pass into the capillary sheet to provide further resistive heating within the capillary sheet. In particular the fibres of capillary sheet may comprise an electrically conductive material for example the capillary sheet may comprise a sheet of metal fibre mesh. In this way, the current from the resistive heating element may pass into the capillary sheet and cause further resistive heating in the region surrounding the heating element. This provides improved heating performance and associated vapour generation.

[0010] The capillary sheet is preferably configured to transport liquid by capillary action in use. The density of the mesh may be from about 10^-6 to 10^-2 g/mm³, preferably in a range between 5x10^-4 to 5x10^-3 g/mm³, and more preferably approximately 8.5x10^-4 g/mm³.

[0011] The contact points may be positioned at opposite sides of the heating element such that the preferential path runs across the heating element from one side to another. Alternatively the contact points may be provided in the same side such that the preferential path travels out from one side across the heating element and turns to return to the same side.

[0012] The capillary sheet may comprise electrically conductive fibres which are arranged as a woven fabric, such as a mesh, a non-woven fabric, or a bundle of electrically conductive fibres. Preferably the capillary sheet comprises a mesh of electrically conductive fibres configured to transport liquid through the heating element by capillary action in use. In this way the mesh provides a wicking function to the heating element such that an aerosol generating liquid can be effectively drawn onto the heating element for vapourisation.

[0013] Preferably the capillary sheet is shaped so as to following a serpentine path, i.e. the sheet has a serpentine shape, in other words a meandering, zig-zag, periodic or square-wave shape. In this way the temperature distribution across the capillary sheet can be controlled by varying the structure or shape of the capillary such that the current and/or heat flows along a meandering or square-wave pattern. As an electrical current travels along the sheet, different concentrations of current would be provided. In use, areas of relatively high current density will become hotter than areas of relatively low current density, thus establishing a temperature gradient across the sheet. The temperature distribution of the sheet can therefore be controlled by varying the structure of the heating element such that the current flows along a meandering or square-wave pattern.

[0014] Preferably the heating element provides structural support to the capillary sheet. In particular the heating element may provide supporting contact to the capillary sheet, for example the capillary sheet may be one or more of: attached to the heating element, supported on the heating element, wrapped around the heating element and/or enclosed between parts of the heating element. Since the mesh sheet may be a delicate component which may be damaged, by configuring the heating element so as to support the capillary sheet, the capillary sheet is more structurally stable and the lifetime of the heater may be extended.

[0015] In some example the heating element is a heating element is a heating rod. The heating rod may extend adjacent to the heating sheet for example the heating rod may extend along the length or width of the capillary sheet. A heating rod is easy to manufacture and is appropriately shaped to provide preferential heating to a linear region across the capillary sheet which can be advantageous in providing temperature gradients across the capillary sheet.

[0016] Preferably the capillary sheet is folded around the heating rod such that the heating rod provides structural support to the capillary sheet. This provides a compact means in which the heating element may both heat and provide structural support to the capillary sheet.

[0017] Preferably the heating element is welded to the capillary sheet at one or more contact points. This provides a robust means of attaching the capillary sheet to the heating element which can provide both a thermal and mechanical connection between the heating element and capillary sheet. Welding can also provide an electrically conductive connection for a current to pass between the heating element and capillary sheet.

[0018] Preferably the heater comprises a plurality of heating elements each in contact with a different position on one or more capillary sheets. In this way, the temperature gradients across the capillary sheets may be configured by selecting specific contact regions to preferentially heat such that liquid transport and vaporisation across the one or more capillary sheet may be tuned to improve performance.

[0019] In a further aspect of the invention there is provided an aerosol generating device comprising: the heater of any preceding claim; and a liquid store; wherein one or more peripheral edges of the capillary sheet are in contact with the liquid store such that liquid is drawn from the liquid store through the capillary sheet during use. By separating the heating and capillary functions into dedicated components, i.e. the heating element and capillary sheet respectively, these functions may be optimised to provide improved liquid transport and vaporisation. In particular, a capillary sheet can be optimised to provide improved wicking from its peripheral edges to a region which is heated be the heating element. A capillary sheet is particularly beneficial as it allows a greater volume of liquid to be transported from the liquid store compared to conventional wicking components to allow an increased efficiency and volume of vaporisation.

[0020] The term aerosol generating device covers a vaporiser, such as a vaporiser for an electronic cigarette. Therefore the term covers both an electronic cigarette containing a vaporiser and a replaceable cartridge containing a vaporiser (known as a "cartomiser").

[0021] Preferably the heating element is contact with a central region of the capillary sheet such that liquid is drawn from the peripheral edges to the central region for vaporisation.

[0022] Preferably the heating element comprises a U-shaped heating rod and the capillary sheet is folded over a central portion of the heating rod, with opposite edges of the capillary sheet extending into the liquid store. This provides a more compact arrangement of the aerosol generating device. Furthermore temperature gradients can be provided across the capillary sheet from a portion supported on the U-shaped heating rod to the peripheral edges within the liquid store to provide improved wicking.

[0023] Preferably the heating element comprises a heating rod and one or more capillary sheets are welded along the length of the heating rod. This provides a secure means of attaching a capillary sheet to a heating rod which can provide a mechanical, thermal and/or electrical connection.

[0024] Preferably the heating rod has a periodically changing diameter along its length with a plurality of wider diameter portions separated by narrower diameter portions and one or more capillary sheets are welded to the wider diameter portions. In this way periodic temperature gradients can be applied across the capillary sheet to optimise the heat distribution across the capillary sheet to improve performance.

[0025] Preferably the heating rod has a cross-sectional shape comprising a regular polygon defined by three or more flat surfaces wherein one or more capillary sheets are welded to the flat surfaces of the heating rod along its length. This allows for multiple capillary sheets to be attached to a single heating rod to increase the amount of liquid can be vaporised in an efficient manner, only requiring a single heating component to be heated.

[0026] Preferably the aerosol generating device comprises a tubular heater housing wherein the liquid store surrounds the tubular heater housing; wherein the capillary sheet runs along the length of the tubular heater housing with one or more peripheral edges of the capillary sheet extending radially through a longitudinal gap in the tubular heater housing to interface with the liquid store; and the heating element is a rod which runs axially through the tubular heater housing along a surface of the capillary sheet. This provides a compact arrangement in which the volume of the liquid store can be increased by providing it surrounding the heater housing. Preferably the heater housing comprises a plurality of parts arranged to connect together to form multiple longitudinal gaps at the interface wherein the one or more capillary sheets are held in the longitudinal gaps. In this way the heating element can preferentially heat a central region of the capillary sheets to drive the liquid transport from the peripheral edges held in the gaps.

[0027] Preferably the aerosol generating device comprises two heating rods positioned either side of the capillary sheet to heat opposing sides of the capillary sheet. In this way the capillary sheet may be positioned between two heating rods such that the heating rods provide structural support. The capillary sheet is also more effectively heated to improve vaporisation and liquid transport.

[0028] In a further aspect of the invention there is provided an electronic cigarette comprising the aerosol generating device defined in the claims.

[0029] In a further aspect of the invention there is provided a removable cartridge for electronic cigarette, the cartridge comprising the aerosol generating defined in the claims.

Brief Description of the Drawings

[0030] Embodiments of the invention are now described, by way of example, with reference to the drawings, in which:

Figure 1 is a schematic view of a heater according to the present invention;

Figure 2A to 2C are schematic views of an aerosol generating device incorporating the heater according to the present invention;

Figure 3 is a cross-sectional view of an aerosol generating device according to the present invention;

Figure 4A and 4B are schematic views of heaters according to the present invention;

Figure 5A and 5B are schematic views of heaters according to the present invention supported in a tubular heater housing;

Figure 6A and 6B are schematic views of heaters according to the present invention;

Figure 7A is a schematic view of a heater according to the present invention supported in a tubular heater housing;

Figure 7B and 7C schematically illustrates a capillary sheet with a series of contact points with a heating element according to the present invention;

Figure 8A and 8B schematically illustrates an aerosol generating device according to the present invention;

Figure 9A and 9B schematically illustrates an aerosol generating device according to the present invention.

Detailed description

[0031] Figure 1A schematically illustrates a heater 1 for an aerosol generating device 100 according to the present invention. The heater 1 includes a capillary sheet 10 comprising a sheet of heat conductive fibre mesh configured to provide capillary action in use and a heating element 20 in contact with the sheet of conductive fibre mesh 10 and arranged to heat the sheet of conductive fibre mesh 10. By providing a liquid store in communication with the capillary sheet 10 and by passing a current through the heating element 20, the heating element heats the capillary sheet 20 as liquid is drawn by the capillary sheet 20 from the liquid store in order to vaporise the liquid to produce an inhalable vapour.

[0032] The heating element 20 preferentially heats the capillary sheet 10 in the regions in which the heating element 20 is in contact with the capillary sheet 10, thereby producing temperature gradients across the capillary sheet 10 which enhances the capillary action in drawing liquid from a liquid store through the capillary sheet for vapourisation. Therefore, in comparison to prior art devices which employ capillary heating sheets as a heating element, the present invention provides advantages in that the capillary sheet 10 may be optimised for its wicking function and the heating function can be provided substantially by the heating element 20. In this way an aerosol generating device incorporating the heater 1 can be optimised given the heating and wicking functions are separate and provided by separate components within the heater 1.

[0033] The capillary sheet 10 is preferably a sheet of metal fibre mesh such as a mesh of sintered steel fibres. Sheets of fibre mesh can be configured both to provide capillary action of a vapourisable liquid through the capillary sheet 10 and also may be heated to elevate a temperature in order to vapourise the liquid. The heating element 20, in the example of Figure 1A, is provided by a metal heating rod 20, such as nichrome, configured to provide resistive heating when a current is passed through between the contacts 21. In the example of Figure 1A, a single heating rod 20 is provided along the length of the capillary sheet 10 along a central portion so as to preferentially heat a central longitudinal strip of the capillary sheet 10. In this way, the centre portion of the capillary sheet 10 is at an elevated temperature compared to the peripheral regions such that liquid is preferentially vapourised in the central portion which acts to draw liquid through the capillary sheet 10 from the peripheral regions.

[0034] The advantages and features of the heater 1 shown in Figure 1A can be demonstrated by showing how such a heater can be incorporated in an aerosol generating device. Figures 2A to 2C illustrate how the heater 1 may be incorporated in an aerosol generating device, in particular a vapouriser for provision as an integral component of an aerosol generating device or as a removable cartridge to be received in the cartridge seating of an aerosol generating device. Figure 2A shows how the heating element 20 and capillary sheet 10 may be supported within a heater housing 30. In particular the capillary sheet 10 may be held within a housing 30 such that a peripheral edge 11 of the capillary sheet 10 is in communication with an adjacent liquid supply in a liquid store 40. In this example, the capillary sheet 10 is held within a tubular heater housing 30 comprising two parts 31, 32 which are brought together at a longitudinal interface which forms a gap 33, shown in Figure 2B.

[0035] The capillary sheet 10 is held such that it extends along the length of the tubular heater housing 30 and is held within the gap 33 formed at the longitudinal interface 33 between the first and second housing parts 31, 32. As shown in Figure 2B the housing parts 31 and 32 close around the capillary sheet 10 and heating element 20 leaving a gap 33 in which the peripheral edges 11 of the capillary sheet 10 are held. The heater housing 30 and the enclosed capillary sheet 10 and heating element 20 are positioned within a surrounding liquid store 40, as shown in Figure 2C. The liquid store 40 defines the internal storage volume 41 which contains a vapourisable liquid L, to be vapourised by the heater 1. The liquid L can therefore pass through the gap 33 in the heater housing 30 and be transported across the capillary sheet 10 to be vapourised. Returning to Figure 2A, the heating element 21 in this example extends along the length of the capillary sheet 10 and takes the form of a heating rod which is connected at contacts 21 at the opposing ends to which an electrical current can be applied.

[0036] In use an electrical current is applied to the heating element 20 through the contacts 21 which causes resistive heating of the heating element 20. The generated heat is conducted to the heat conductive fibre mesh of the capillary sheet 10 and liquid L is drawn through the gap 33 and along the capillary sheet 10 and is vapourised by the heat generated by the heating rod 20. As can be seen in Figure 2C, the liquid store 40 comprises a longitudinal central vapour flow passage 42 which also extends through the longitudinal axis of the heater housing 30. When liquid is drawn through the capillary sheet and vapourised within the heater housing 30, the generated vapour is drawn through the vapour flow passage 42 and carried to a mouthpiece of the aerosol generating device for inhalation by a user. By providing a heating element 20 configured to heat the sheet of conductive fibre mesh 10, the capillary sheet 10 can be optimised to provide enhanced wicking to effectively transport liquid from the surrounding liquid store 40 through the capillary sheet 10 for vapourisation.

[0037] Figure 3 shows the aerosol generating device 100 of Figure 2C in cross section. In particular, it can be seen how the capillary sheet 10 is held between the first 31 and second 32 heater housing parts and how the housing parts 31, 32 are shaped to provide an internal vapourisation chamber 34 which runs along the length of the heater housing 30 to form part of the vapour flow passage shown in Figure 2C. The surrounding liquid store 40 comprises an internal volume 41 holding a liquid L to be vapourised. The two housing parts 31, 32 are joined at a longitudinal interface arranged such that there is a gap 33 running down each longitudinal side along the length of the heater housing 30 to allow liquid L from the surrounding liquid store 40 to pass through the gap 33 and along the capillary sheet 10 for vapourisation within the vapourisation chamber 34. The heating element 20 is shown in cross section. This example differs from that shown in Figure 1 and Figure 2 in that two heating rods 20 are provided which run along the length of the capillary heating sheet 10 along the longitudinal axis of the heater housing 30 on two opposing sides of the capillary sheet 10.

[0038] As described above, a current is passed through the heating rods 20 from contacts positioned at the ends of the heater housing 30. This causes resistive heating within the heating rods and the heat is transferred to the capillary sheet 10 which increases in temperature and vapourises the liquid held within the interstices between the conductive fibres. Using two heating rods 20 arranged to heat both sides of the capillary sheet 10 provides more efficient heating of the capillary sheet and a greater volume of vapourised liquid is produced. Again, since the heating rods 20 can be optimised to provide the most efficient heating, the properties of the capillary sheet 10 can be optimised for transporting the liquid L by capillary action.

[0039] As described above, the capillary sheet 10 may be provided by a mesh of metal fibres, for example a sintered mesh of steel fibres which are configured to provide capillary action through the interstices provided between the fibres. Since metal fibres may be used, a current passed through the heating element 20 may also pass into the contacted fibres of the conductive fibre mesh. In other words, the heat conductive fibre mesh may also be electrically conductive in order to transport a current provided to the heating element 20 into the fibre mesh to cause additional resistive heating within the capillary sheet to provide enhanced vapourisation of the liquid L. In this way, although the heating element 20 provides the predominant heat source by resistive heating, further resistive heating may be provided within the capillary sheet 10 to enhance vapour generation.

[0040] Because the current density is increased in the region of the capillary sheet 10 surrounding the heating element 20, in particular the region which is in contact with the capillary sheet 10, increased heating is provided in this area in the vicinity of the heating element 20. This produces temperature gradients across the capillary sheet in particular from the lower temperature region at the peripheral edges to a higher temperature region in the centre of the capillary sheet 10 near the heating element 20. These temperature gradients help to promote capillary action through the capillary sheet 10 and provide efficient vapourisation within the vapourisation chamber 34.

[0041] Figures 4A and 4B show further examples of a heater 1 for an aerosol generating device according to the present invention. In the example of Figure 4A two heating elements 20 are provided. In this example both heating elements 20 are a heating rod or heating wire, each comprising a longitudinal heating portion with contacts 21 positioned at each end for connection to a power source in order to provide a current through the heating element 20. By providing multiple heating elements, the temperature gradients across the capillary sheet 10 can be tuned by applying heating to different regions of the heating element. In the example of Figure 4A, two longitudinal portions of the capillary sheet 10 are preferentially heated to provide an increased volume of vapour generated when employed in aerosol generating device. Multiple heating elements 20 may also be used to provide further structural stability to the capillary sheet 10 to prevent breakage and prolong the lifetime of the heater 1 when applied in a device.

[0042] In the example of Figure 4B, the heater 1 is similar to that described with respect to Figure 1 apart from the capillary sheet 10 does not have a uniform rectangular shape but a square wave periodic shape provided between the first 12 and second 13 ends of the capillary sheet 10. A non-uniform shape can have advantages in that it facilitates the further generation of temperature gradients across the capillary sheet 10 which can aid with enhancing the capillary action across and through the capillary sheet 10. For example, when a current is applied to the heating element 20 in the example of Figure 4B and the current travels through the capillary sheet 10, the inner corners (provided by the slots 19 extending in from the side peripheral edges 11 of the capillary sheet) have a higher current density than the peripheral edge regions 11. This results in increased heating in the areas of high current density which can further enhance temperature gradients and promote capillary action of the liquid through the capillary sheet 10.

[0043] Figures 5A and 5B illustrate alternative examples of a heater 1 according to the present invention shown in cross section. In Figure 5A the heating element 20 is split longitudinally into two halves 20A and 20B, these portions 20A, 20B of the heating element 20 (which may be considered as two individual heating rods on opposing sides of the capillary sheet 10) run longitudinally through the heater housing 30 on either side of the capillary sheet 10. The heating element portions 20A, 20B may be welded to the surface of the capillary sheet 10 to provide an improved connection. By providing two portions 20A, 20B of a heating rod 20 which is attached to the capillary sheet 10, further structural stability may be provided to the delicate capillary sheet 10 to support it within the device. Again, a current is applied to both portions 20A, 20B of the heating element 20 at the longitudinal end of the heating element 20 in order to provide resistive heating of the heating element which preferentially heats a central portion of the capillary sheet 10 to provide improved capillary action of the liquid through the capillary sheet 10 for vapourisation within the vapourisation chamber 34.

[0044] Figure 5B illustrates an alternative example of a heater 1 which uses two capillary sheets 10. In this example, the heating element 20 comprises four portions 20A, 20B, 20C, 20D which extend longitudinally along the length of the heater housing 30 (and again may be provided by four individual heating rods 20). The heating element portions 20A, 20B, 20C, 20D act to both support the capillary sheet 10 and provide resistive heating to preferentially heat central portions of both capillary sheets 10. In particular, each capillary sheet 10 is folded around a portion of the heating element 20A, 20B, 20C, 20D which run longitudinally along the length of the housing 30 against the capillary sheet 10.

[0045] Each capillary sheet 10 is folded approximately perpendicularly such that peripheral edges 11 extend out through gaps 33 in the housing 30 to interface with the surrounding liquid store 40. In this example, the heater housing 30 is divided into four longitudinal parts 31A, 31B, 32A, 32B. These parts each provide a circumferential quarter of the tubular heater housing. As can be seen in Figure 5B the cross section of the heater housing 30 is divided into quarters with each part interfacing at longitudinal gaps 30 which run along the length of the housing and hold the peripheral edges 31 of the capillary sheet 10. The two capillary sheets 10 are both folded perpendicularly to interface with the gaps 33 provided between the four portions of the heater housing 30 and are supported along the central axis of the housing 30 by the heater rods 20. As before, the heater element portions (or heater rods) 20A, 20B, 20C, 20D may be welded to the capillary sheet 10 to provide further structural support and an improved electrical and mechanical contact between the heater portions and the capillary sheet 10.

[0046] This arrangement has advantages in that it provides an improved heated surface area of the capillary sheets 10 by folding the capillary sheets 10 around the heating elements 20A, 20B, 20C, 20D to provide an increased surface area of capillary sheet 10 within the heater housing 30 to generate an increased volume of vapour. As described above, the heating element 20 preferentially heats the central portions of the two capillary sheets 10 and the current may pass into the conductive fibres of the sheets in order to generate further resistive heating within the capillary sheets 10 with greater resistive heating provided at the central portions with a decreasing effect towards the peripheral edges 11 which interface with the surrounding liquid store 40. In this way, significant temperature gradients are provided along the capillary sheet which helps in drawing the surrounding liquid through the capillary sheet for vapourisation.

[0047] Figures 6A and 6B show alternative ways of connecting two folded capillary sheets 10 with a central longitudinal heating rod 20. As shown in Figure 6A the capillary sheet 10 may each be welded to the heating rod 20 at welding points 22 running along the length of the heating rod 20. As described above, this provides structural support to the capillary sheet 10 and provides an improved mechanical and electrical connection for supporting the heating rod 20 and capillary sheets 10 and providing a flow of current between the heating rod 20 and the capillary sheet 20 to provide resistive heating in both the heating rod 20 and the capillary sheets 10.

[0048] As shown in Figure 6B, the welded connection points 22 may be strengthened by providing a heating rod with a cross sectional shape comprising a regular polygon defined by three or more flat surfaces. The example of Figure 6B the heating rod 20 has a square shaped cross section with four flat surfaces. In this way, the capillary sheets 10 can be welded across the flat surfaces at weld points 22 shown in Figure 6B. The greater surface area of the weld points 22 provides an improved mechanical connection as well as increased heat and current transfer between the heating rod 20 and the capillary sheets 10. This provides improved heating and vapour generation when the heater 1 is employed in an aerosol generating device.

[0049] Figure 7 shows an alternative example of a heater 1 according to the present invention. In this example, the heating rod 20 has a periodically changing diameter along its length with a periodic array of wider portions 23 and narrower portions 24. Although in this example the heating rod 20 comprises a periodic alternating diameter it may in other examples have a non-regular shape with wider portions 23 and narrower portions 24. In the example of Figure 7, the capillary sheets 10 are welded to opposing surfaces on the wider diameter portions 23 of the heating rod 20. In particular, each sheet is welded to the heating rod 20 at a number of weld points along the length of the heating rod at positions corresponding to the wider diameter portions. In this way, unlike the previous examples in which the heating rod has been connected in a uniform manner to the heating sheet along the length of the heating rod, in the example of Figure 7 the heating rod 20 is connected at periodic points along the length of the heating rod 20.

[0050] These multiple contact points generate temperature gradients within the capillary sheet 10to provide improved capillary action and vapourisation performance of the heater 1 when employed in the aerosol generating device. In particular, as shown in the side view of the capillary sheet 10 shown in Figure 7B, the arrangement of Figure 7A provides a periodic series of contact points 22 along the length of the capillary sheet. Heat is therefore transferred to the capillary sheet 20 from the heating element 20 at each of these points. This creates hot points on the capillary sheet 10 at points 22 with heat dissipation with increasing distance from these points. The resulting temperature gradients within the thermal sheet act to promote capillary action as vaporisation is rapid at the hot spots 22 and is reduced with increasing distance from the hotspots 22. This drives liquid transport from the edges 11 in contact with the liquid store to the central hot spots 22.

[0051] Although in Figure 7A a uniform rectangular capillary sheet 10 is used, a square wave or periodic shaped capillary sheet 10 may equally be incorporated. This type of capillary sheet can be welded to the heating rod 20 shown in Figure 7 in exactly the same way at periodic points along the length of the heating rod 20, Figure 7C illustrates a side profile of square wave shaped capillary sheet 10 showing the contact points 22 along the length of a square-wave shaped capillary sheet 10. Again the preferential heating at the contact points 22 (weld points) provides temperature gradients across the surface of the capillary sheet 10. These are further influenced by the shape of the capillary sheet 10 as heat is prevented from spreading uniformly by the slots 19 which extend inwardly from the edges 11 of the capillary sheet 10 and therefore the temperature gradients can be further tailored using the combination of the position of the contact points 22 and the shape of the capillary sheet 10.

[0052] As before, the heating element 20 and capillary sheets 10 may be housed in a heater housing 30 comprising a number of longitudinal gaps 33 which run along the length of the housing 30, as shown in Figure 7A. The longitudinal edges 11 of the capillary sheets 10 interface with the surrounding liquid store through the longitudinal gaps 33 in the heater housing 30. In this example, the capillary sheet 10 form curved surfaces which curve between two longitudinal gaps 33 between the housing parts in order to engage the peripheral edges 11. In other examples the capillary sheets may be flat or may be bent so that corresponding edges of the capillary sheets are held within a single gap. For example, the two capillary sheets may bend towards each other such that the corresponding peripheral edges 11 meet and are held in two longitudinal gaps 33 running along the length of the housing 30. The example of Figure 7 provides enhanced vapour generation by the inclusion of a greater surface area of capillary sheets 10 and the non-uniform heating along the length of the capillary sheets providing temperature gradients.

[0053] In each of the examples of Figures 1 to 7, a heating rod 20 is used which runs along the length of a heater housing with the heating sheets similarly running longitudinally adjacent to the heating rod 20. However, such an arrangement is not essential and the advantages on the present invention can be achieved with a large number of different variations which each incorporate the essential features of a heating element in contact with a capillary sheet such that the wicking and heating properties may be separated and optimised within the heater 1.

[0054] Figure 8A shows a cross sectional side view through an aerosol generating device which uses a capillary sheet 10 and the heating element 20 in a different arrangement to that of Figures 1 to 7. The aerosol generating device 100 is substantially tubular with a central vapourisation passage 42 running between an air inlet and vapour outlet 44. The internal vapour passage 42 is defined by the heater housing 30 which again houses the heating element 20 and capillary sheet 10. The liquid store 40 is provided as a cylindrical heating store surrounding the internal vapour passage 42. The configuration of the heater 1 is shown in Figure 8B and includes a U-shaped heating rod 20 over which the capillary sheet 10 is folded. Therefore, unlike the previous examples in which the heating rod runs along the length of the heater housing 30, in this example the heating rod is positioned at one end of the housing 30. As can be seen in the cross section of Figure 8A, a central portion of the heating rod 20 supports the capillary sheet 10 which is folded over the central portion of the heating rod 20.

[0055] The peripheral edges 11 of the capillary sheet 10 extend away from the heating element 20 and extend through gaps 33 in the central vapour flow passageway 42 into the surrounding cylindrical liquid store 40, which defines an internal volume 41 holding a liquid L for vapourisation. As with the previous examples a current is applied through the heating element 20 through the contact point 21 shown in Figure 8B. The heating element 20 increases temperature due to resistive heating and accordingly preferentially heats a central portion of the capillary sheet 10 which is in contact with the heating element 20. As with previous examples, electrically conductive fibres may be used for the conductive fibre mesh of the capillary sheet 10 and as such current can also pass into the capillary sheet 10 causing further resistive heating, particularly in the region in the vicinity of the contact points with the heating element 20.

[0056] When a power source is connected to the heating element 20 and a current applied whilst a user inhales at the vapour generating device to produce an air flow shown by arrows A, the heating element 20 heats up due to resistive heating and preferentially heats the capillary sheet 10 which draws liquid from the surrounding liquid store 40 through the capillary sheet 10 to the preferentially heated region where it is vapourised. The vapour is then drawn along the vapour flow route shown by arrows A. As with all other examples of the invention, because the heater 1 incorporates a separate heating element 20 and a capillary sheet 10 comprising a sheet of heat conductive fibre mesh, the wicking function may be optimised within the capillary sheet, for example by choosing an appropriate porosity or density, and the heating function optimised within the heating element 20, whilst still providing improved heating within the capillary sheet given that it comprises heat conductive fibres.

[0057] Figures 9A and 9B illustrate an alternative example of a heater 1 for an aerosol generating device 100 according to the present invention. Figure 9A shows an end on cross-section through the aerosol generating device incorporating a heater 1 including a capillary sheet 10 comprising a sheet of heat conductive fibre mesh and a heating element 20 in the form of a heating rod 20 which the capillary sheet 10 is folded around in a similar way to that illustrated in Figure 8B. This aerosol generating device comprises an asymmetric structure which differs from the previously described examples. In the end on view of Figure 9A it can be seen that the heating rod 20 runs along one side of the cartridge along the length of the device 100. The heating element is housed in a heater housing 300, which incorporates a vapour flow route 42 which runs in parallel with the heating element 20 through the heater housing 300 the aerosol generating device 100 includes a neighbouring liquid store 400 defining an internal volume 401 which holds a liquid L to be vapourised.

[0058] As shown in Figure 9B, the heating rod 20 extends along the length of the aerosol generating device 100 with the capillary sheet 10 wrapped around the length and extending from the heater housing 300 through a gap 33 shown in Figure 9A into the internal volume 401 of the liquid store 400. This example can provide efficient use of space of the internal volume of the aerosol generating device 100 to fit a larger liquid store 400 within the device 100. As before, an electric current is applied to contact 21 of the longitudinal ends of the heating rod 20 to heat the heating rod 20 via a resistive heating. The capillary sheet 10 is wrapped around the heating rod such that the central portion of the capillary sheet 10 in contact with the heating rod is heated to provide preferential heating of this region. Since the capillary sheet 10 comprises a capillary structure of conductive fibres, the liquid L from the liquid store 400 is drawn along the capillary sheet through the gap 33 in the heater housing 30 into the heater housing to be vapourised. As shown in Figure 9B, as a user inhales at a device incorporating the aerosol generating device 100 air passes through the vapour flow passage 42 picks up the vapour generated which exits the device as shown by the arrows A.

[0059] As described above, the heater according to the present invention provides a number of advantages over known devices. By using a capillary sheet of heat conductive fibre mesh improved wicking through the capillary sheet can be achieved whilst also configuring the capillary sheet such that it also provides heating in order to assist in generating the inhalable vapour. By separating the heating and capillary functions, the heater can be better optimised to provide improved aerosol generating properties. In particular, temperature gradients can be provided across a capillary sheet to provide both heating and an enhanced liquid transport function from a liquid store into the capillary sheet for vapourisation.

Claims

1. A heater for an aerosol generating device comprising:

a capillary sheet comprising a sheet of heat conductive fibre mesh configured to provide capillary action in use;

a heating element in contact with the sheet of heat conductive fibre mesh and arranged to heat the sheet of conductive fibre mesh.

2. The heater of claim 1 wherein the heating element is a resistive heating element comprising two contact points to which a power source may be connected to provide a current through the heating element to heat the heating element.

3. The heater of any preceding claim wherein the heating element is in contact with a portion of the capillary sheet and arranged to preferentially heat the contacted portion of the capillary sheet.

4. The heater of any preceding claim wherein the heating element provides structural support to the capillary sheet.

5. The heater of any preceding claim wherein the heating element is a heating rod.

6. The heater of claim 5 wherein the capillary sheet is folded around the heating rod such that the heating rod provides structural support to the capillary sheet.

7. The heater of any preceding claim wherein the heating element is welded to the capillary sheet at one or more welding contact points.

8. The heater of any preceding claim comprising a plurality of heating elements each in contact with a different position on one or more capillary sheets.

9. An aerosol generating device comprising:

the heater of any preceding claim; and

a liquid store; wherein

one or more peripheral edges of the capillary sheet are in contact with the liquid store such that liquid is drawn from the liquid store through the capillary sheet during use.

10. The aerosol generating device of claim 9 wherein the heating element comprises a U-shaped heating rod and the capillary sheet is folded over a central portion of the U-shaped heating rod, with opposite edges of the capillary sheet extending into the liquid store.

11. The aerosol generating device of claim 9 or 10 wherein the heating element comprises a heating rod and one or more capillary sheets are welded along the length of the heating rod.

12. The aerosol generating device of claim 11 wherein the heating rod has a periodically changing diameter along its length with a plurality of wider diameter portions separated by narrower diameter portions and one or more capillary sheets are welded to the wider diameter portions.

13. The aerosol generating device of claim 11 or 12 wherein the heating rod has a cross-sectional shape comprising a regular polygon defined by three or more flat surfaces wherein one or more capillary sheets are welded to the flat surfaces of the heating rod along its length.

14. The aerosol generating device of any of claims 9 to 13 comprising a tubular heater housing wherein the liquid store surrounds the tubular heater housing; wherein

the capillary sheet runs along the length of the tubular heater housing with one or more peripheral edges of the capillary sheet extending radially through a longitudinal gap in the tubular heater housing to interface with the liquid store; and

the heating element is a rod which runs axially through the tubular heater housing along a surface of the capillary sheet.

15. The aerosol generating device of claim 14 comprising two heating rods positioned either side of the capillary sheet to heat opposing sides of the capillary sheet.

Drawing