Heating chamber for an aerosol generating device

Abstract

A method (400) of manufacturing a heating chamber (200, 300, 350) for an aerosol generating device is disclosed. The method comprises: providing a tube comprising a wall (202, 302, 352) defining a cavity for receiving an aerosol generating substrate through an opening of the tube, wherein the wall comprises an inner surface facing the cavity and an outer surface facing away from the cavity; treating a first surface (201, 203, 301, 303, 351, 353) of the wall, wherein the first surface of the wall is the inner surface, wherein treating the first surface comprises applying a first coating (208, 212, 308, 312, 362) comprising a dielectric material to the first surface, and wherein the treated first surface defines a first heat transfer area of the tube having a first predetermined length along a longitudinal axis of the tube; and attaching a heating element (214, 314, 363) to the tube to correspond with the first heat transfer area such that the attached heating element comprises a second predetermined length along the longitudinal axis of the tube that substantially matches the first predetermined length.

Description

[0001] HEATING CHAMBER FOR AN AEROSOL GENERATING DEVICE

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to an aerosol generating device, and a method of manufacturing a heating chamber for the aerosol generating device. The disclosure is particularly applicable to a portable aerosol generation device, which may be self-contained and low temperature. Such devices may heat, rather than bum, tobacco or other suitable aerosol substrate materials by conduction, convection, and / or radiation, to generate an aerosol for inhalation.

[0004] BACKGROUND

[0005] The popularity and use of reduced-risk or modified-risk devices (also known as vaporisers) has grown rapidly in the past few years as an aid to assist habitual smokers wishing to quit using traditional tobacco products such as cigarettes, cigars, cigarillos, and rolling tobacco. Various devices and systems are available that heat or warm aerosolisable substances as opposed to burning tobacco in conventional tobacco products.

[0006] A commonly available reduced-risk or modified-risk device is the heated substrate aerosol generation device or heat-not-burn (HNB) device. Devices of this type generate an aerosol or vapour by heating an aerosol substrate (i.e. consumable) that typically comprises moist leaf tobacco or other suitable aerosolisable material to a temperature typically in the range 150°C to 300°C. Heating an aerosol substrate, but not combusting or burning it, releases an aerosol that comprises the components sought by the user but not the undesirable by-products of combustion. In addition, the aerosol produced by heating the tobacco or other aerosolisable material does not typically comprise the burnt or bitter taste that may result from combustion that can be unpleasant for the user.

[0007] The aerosol substrate is generally inserted into a cup. The cup is arranged so that its interior can be accessed from the outside. The cup has on its periphery a means of heating the substrate. Using those means, the cup is capable transferring heat from the means of heating it to the material housed inside it. Accordingly, the material housed in the cup, that is, the consumable, is heated and thus vaporised. A user then inhales the vapour that is generated by the heating of the consumable.

[0008] In the prior art, a stainless-steel material is typically used to make such cups. These cups have a thin film heater wrapped around the outside of the cup to heat up the stainless steel. The heat is then conducted to the consumable.

[0009] Such a way of attaching and heating up the cup is rather effective for heat conduction. However, it is less effective for heat radiation, which is another significant method of heat transfer in particular to the aerosol generating substance. Thermal radiation can be expressed through the Stefan-Boltzmann law which contains a value £ for emissivity, that is j*=eoT4

[0010] Here, j* refers to the total energy emitted per unit surface area of a black body across all wavelengths per unit time, o is the Stefan-Boltzmann constant, and T is the temperature of the black body. The emissivity £ is a number between 0 and 1 where 1 would be a perfect black body radiator of heat and 0 would be the opposite.

[0011] In order to have as efficient a heat transfer by thermal radiation as possible, the surface of the cup should have a value close to 1 . However, known heater cups having a wall thickness of around 0.08 mm are made of stainless steel of grade 316L, which has a value of £ of 0.26 which is unsatisfactory.

[0012] An object of the present invention is therefore to optimise the thermal efficiency of heating chambers in heat-not-burn devices whilst also ensuring a reliable operation of the device.

[0013] SUMMARY OF INVENTION

[0014] According to an aspect of the invention, there is provided a method of manufacturing a heating chamber for an aerosol generating device, the method comprising: providing a tube comprising a wall defining a cavity for receiving an aerosol generating substrate through an opening of the tube, wherein the wall comprises an inner surface facing the cavity and an outer surface facing away from the cavity; treating a first surface of the wall, wherein the first surface of the wall is the inner surface, wherein treating the first surface comprises applying a first coating comprising a dielectric material to the first surface, and wherein the treated first surface defines a first heat transfer area of the tube having a first predetermined length along a longitudinal axis of the tube; and attaching a heating element to the tube to correspond with the first heat transfer area such that the attached heating element comprises a second predetermined length along the longitudinal axis of the tube that substantially matches the first predetermined length.

[0015] In this way, the first heat transfer area provides a specifically prescribed area on the first surface of the wall for heat to be effectively transferred from the heating element into the wall from the wall to an aerosol generating substrate received in the tube (where the treated first surface is the inner surface of the tube). The specifically prescribed area ensures that heat can be optimally delivered into the wall from the heating element and further into a cavity formed by the wall (in which an aerosol generating substrate may be received). Preferably, the wall is thermally conductive. Preferably, the wall is electrically conductive. As will be appreciated, the wall may comprise a metallic material such as stainless steel.

[0016] In known heating chambers, heat may be less efficiently transferred from the heating element to an aerosol generating substrate if a coating is applied over a wider area across the tube. As such, in known heating chambers, heat may be undesirably retained in the tube and / or transferred toward an undesirable section of an aerosol generating substrate received in the heating chamber.

[0017] The dielectric coating that is applied to the wall is applied specifically to form the heat transfer area (having a predetermined length) to as to increase the thermal emissivity of the surface of the wall, where the coating helps the wall to absorb heat from the heat source (i.e. the heating element) as well as radiate the absorbed heat out. The dielectric coating may be a ceramic and / or glass-like coating. The wall may comprise a metallic material, such as stainless steel SS316L. The heating chamber may further comprise a base wall arranged at an end of the tube distal to the opening so as to form a heater cup.

[0018] Heat transfer from the heating element to the wall mainly takes place by conduction. Therefore, a dielectric coating on the outer surface of the wall may further act as an electrically insulating layer between the heating element and the wall. Heat in the wall is transferred to a received aerosol generating substrate by conduction and radiation.

[0019] By substantially matching the length of the heating element with the length of the first transfer area, the heat transfer I heat exchange efficiency is maximised such that heat generated from the heating element is optimally transferred from the wall into the first coating and optimally radiated toward a received aerosol generating substrate.

[0020] The first and second predetermined lengths may be 14 mm. The predetermined lengths may be longer or shorter according to design requirements. The aerosol generating substrate may comprise a tobacco portion and a paper tube, and the transfer area(s) may be configured to overlap an interface between the top of the tobacco portion and the bottom of a paper tube of an aerosol generating substrate received in the tube. Accordingly, the heat transfer area and first coating should be arranged on the wall so as to provide a heat exchange zone that effectively corresponds with the tobacco portion of the received aerosol generating substrate. Preferably, the other regions of the wall are not coated or surface-treated such that the heat transfer area is better focussed at the heat transfer area(s). To prevent surface-treatment or coating on the areas outside of the heat transfer area(s), a mask may be applied or the tube may be held in a clamp during the surface-treatment process.

[0021] The wall comprises an inner surface facing the cavity and an outer surface facing away from the cavity, and the first surface of the wall is the inner surface. A dielectric coating is applied to the inner and may be applied to the outer surface. A dielectric coating on the outer surface improves thermal emissivity of the wall as well as provides an electrically insulating layer between the heating element and the tube. A dielectric coating of the inner surface improves thermally emissivity of the tube such that heat is effectively transferred to the aerosol generating substrate.

[0022] Preferably, treating the first surface further comprises increasing an average surface roughness of the first surface. In this way, the surface area of the first area is increased so as to improve the effectiveness and efficiency of the surface treatment and heat exchange capability. Exemplary techniques to increase the surface roughness include: sandblasting or other abrasion or polishing techniques (i.e. mechanical processes), and / or pickling or etching techniques (i.e. chemical processes) to cause the first surface to become rougher and duller and improve thermal radiation absorbance.

[0023] Preferably, the method further comprises treating a second surface of the wall to define a second heat transfer area, wherein the treated second surface comprises the outer surface and is opposite to the first surface across the wall. In this way, both the outer surface and the inner surface of the wall is treated to optimise the heat transfer from the heating element to the wall and from the wall to the aerosol generating substrate respectively.

[0024] Preferably, the second heat transfer area comprises a third predetermined length along the longitudinal axis of the tube, wherein the third predetermined length substantially matches the first predetermined length. In this way, the second heat transfer area is configured so as to optimise the heat exchange to / from the wall. By substantially matching the length of the heating element with the length of the second transfer area, the heat transfer I heat exchange efficiency is maximised such that heat generated from the heating element is optimally transferred I absorbed into the wall (through the first coating) and further optimally transferred I radiated toward a received aerosol generating substrate.

[0025] Preferably, the second heat transfer area is substantially in line with the first heat transfer area along a transverse axis across the wall. In this way, the transfer of heat from the outer surface of the wall to the inner surface of the wall is optimised as the distance for heat conduction is minimised.

[0026] Preferably, the respective predetermined lengths are substantially matched to provide a difference of less than 2 mm in length between the respective predetermined lengths, preferably wherein the difference is less than 1 mm. In this way, a minimal overlap is provided to ensure that the portion, e.g. the tobacco or aerosol generating material portion, in the aerosol generating substrate is effectively heated whilst minimising any excess overlap. In some examples, the predetermined length of the respective transfer area(s) to be slightly longer (less than 2 mm or 1 mm) than the predetermined length of the heating element. In this way, the predetermined length of the heating element is within the predetermined length of the transfer area(s).

[0027] Preferably, treating the second surface further comprises increasing an average surface roughness of the second surface. In this way, the surface area of the second heat transfer area may be increased so as to improve the effectiveness and efficiency of the surface treatment and heat exchange capability of the second heat transfer area.

[0028] Preferably, treating the second surface comprises applying a second coating to the second surface. In this way, the thermal emissivity of the second surface is increased.

[0029] Preferably, the first coating is different to the second coating. The coating of the inner surface and the coating of the outer surface are not required to comprise the same coating material. Different coating materials may exhibit different heat absorption or heat irradiation properties and the first and second coatings may be selected to optimise the particular heat transfer function required. For instance, the outer surface coating may be required to be electrically insulating (from the heating element) and exhibit improved heat absorption properties, whilst the inner surface coating may not be required to be electrically insulating, but may exhibit improved heat radiation properties. In another example, the thickness of the first coating may be different to the thickness of the second coating. Alternatively, the first coating is the same as the second coating. Preferably, the first coating and / or the second coating comprises at least one of: hydrogenated amorphous silicon (a-Si:H); a carbon-based coating; a ceramic material; silicon carbide; aluminium- titania; aluminium chromium nitride (e.g. AICrN-based coatings); or aluminium nitride.

[0030] Examples of carbon-based coatings may include a mixture of carbon and metal (such as tungsten carbide I carbon (WC / C)), the carbon may be diamond-like carbon. Carbon-based coatings are biocompatible and suitable for aerosol generating applications. Carbon-based coatings typically also have low friction coefficients which advantageously allow aerosol generating substrates I consumables to be readily received into the heating chamber.

[0031] Preferably, the method further comprises applying a mask to the first surface and / or the second surface before treating the respective surface. In this way, the first and / or second heat transfer zones may be effectively surface-treatment and any misalignment or coating in undesirable areas may be effectively prevented. The coating(s) may be applied by a deposition process, such as chemical vapour deposition (CVD) or physical vapour deposition (PVD). A CVD technique can apply the coating in a micrometre scale such as Silcolloy, developed by SilcoTek. CVD may also be used to apply silicon carbide or aluminium nitride layers. The PVD technique uses a sputter coating, which like CVD typically takes place under a vacuum, and typically does not require high treatment temperatures. The outer surface coating could be also applied by thermal spray, achieved via hard anodisation or Plasma Electrolytic Oxidation. The coating(s) may be applied by a thermal spray technique such as plasma arc coating, plasma spray coating, or sputtering. Such techniques can effectively deposit ceramic coatings which may have higher melting temperatures. Further suitable surface treatment techniques will be apparent to the skilled person.

[0032] Preferably, the treated first surface and / or the treated second surface comprises a layer of electrically insulating material having a thickness between 0.3 pm and 10 pm. In this way, the heat-up times of the tube and overall energy efficiency of the heating chamber is optimised. The coating should be thin so as to reduce the time for coating application and also reduce the thickness of the material through which heat is to be transported, thereby improving the heat transfer efficiency.

[0033] According to another aspect of the invention, there is provided a heating chamber for an aerosol generating device manufactured according to the first aspect, wherein the heating chamber comprises a tube having a wall defining a cavity for receiving an aerosol generating substrate through an opening of the tube, wherein the wall comprises a treated inner surface facing the cavity and an outer surface facing away from the cavity, wherein the treated inner surface defines a first heat transfer area of the tube having a first predetermined length along a longitudinal axis of the tube, and wherein a heating element is attached to the tube to correspond with the first heat transfer area such that the attached heating element comprises a second predetermined length along the longitudinal axis of the tube that substantially matches the first predetermined length.

[0034] According to yet another aspect of the invention, there is provided an aerosol generating device comprising the heating chamber according to the second aspect, wherein the heating chamber comprises a tube having a wall defining a cavity for receiving an aerosol generating substrate through an opening of the tube, wherein the wall comprises a treated inner surface facing the cavity and an outer surface facing away from the cavity, wherein the treated inner surface defines a first heat transfer area of the tube having a first predetermined length along a longitudinal axis of the tube, and wherein a heating element is attached to the tube to correspond with the first heat transfer area such that the attached heating element comprises a second predetermined length along the longitudinal axis of the tube that substantially matches the first predetermined length.

[0035] BRIEF DESCRIPTION OF DRAWINGS

[0036] Embodiments of the invention are now described, by way of example, with reference to the drawings, in which:

[0037] Figure 1 is an exemplary aerosol generating device according the invention; Figure 2 is a schematic cross-sectional view of a heating chamber according the invention;

[0038] Figures 3a and 3b are schematic cross-sectional views of further heating chambers according to the invention; and

[0039] Figure 4 is a flow diagram showing method steps for manufacturing the heating chamber according to an embodiment of the invention.

[0040] DETAILED DESCRIPTION

[0041] As described herein, a vapour is generally understood to refer to a substance in the gas phase at a temperature lower than its critical temperature, which means that the vapour can be condensed to a liquid by increasing its pressure without reducing the temperature, whereas an aerosol is a suspension of fine solid particles or liquid droplets, in air or another gas. It should, however, be noted that the terms ‘aerosol’ and ‘vapour’ may be used interchangeably in this specification, particularly with regard to the form of the inhalable medium that is generated for inhalation by a user.

[0042] Figure 1 illustrates an aerosol generating device 100 according to an embodiment of the invention. The aerosol generating device 100 is illustrated in an assembled configuration with the internal components visible. The aerosol generating device 100 is a heat-not-burn device, which may also be referred to as a tobacco-vapour device, and comprises a heating chamber 150 configured to receive an aerosol generating substrate such as a tobacco rod. The heating chamber 150 is operable to heat, but not bum, a rod of aerosol generating material to produce a vapour or aerosol for inhalation by a user. As will be appreciated, the aerosol generating device 100 depicted in Figure 1 is simply an exemplary aerosol generating device according to the invention. Other types and configurations of tobacco-vapour products, vaporisers, or electronic cigarettes may also be used as the aerosol generating device according to the invention.

[0043] Figure 2 shows a heating chamber 200 according to the present invention. The heating chamber 200 comprises a wall 202 is shaped to form a cavity 204 which is configured to receive the aerosol generating substrate through an opening 206 at a top end of the heating chamber 200.

[0044] The wall 202 is in a tubular, e.g. cylindrical, form, but as will be appreciated may comprise other shapes, such as cuboidal. In use, an aerosol generating substrate is received within the cavity 204 of the heating chamber 200 and interfaces with an inner surface 201 of the wall 202. The length of the wall 202 may be configured such that a mouthpiece portion of the aerosol generating substrate extends out of the cavity 204 from the opening 206 to be received in the mouth of a user for inhalation. The wall 202 is made of a thermally conductive material, such as steel or stainless steel, that allows for heat transfer to an aerosol generating substrate received in the cavity 204 while maintaining sufficient structural stability under temperature stress. As will be appreciated by the skilled person, a metallic material, or steel or stainless steel is electrically conductive.

[0045] A portion of the inner surface 201 of the wall 202 is coated with a ceramic and / or glass-like coating 208, wherein the coating 208 has a high thermal emissivity so as to, in use, enhance heat transfer from the wall 202 to the aerosol generating substrate received in the cavity 204. For example, the coating 208 may comprise silicon carbide or aluminium nitride.

[0046] The inner surface coating 208 covers the inner surface 201 of the wall 202 around the inner circumference of the wall 202 and along a predetermined length along the wall 202 between the opening 206 of the chamber 200 and a closed end 210 of the chamber 200. To put it in another way, the inner surface coating 208 is cylindrically-shaped, where the outer surface of the coating 308 is adjacent to (i.e. adhered to) the inner surface 301 of the wall 202 along the predetermined length of surface treatment of the inner surface 201. In this way, the inner surface coating 208 acts as an inner surface heat transfer zone for heat from the wall 202 to be preferentially transferred to a received consumable.

[0047] In a similar way, a portion of the outer surface 203 of the wall 202 is coated with a ceramic or glass-like coating 212 to enhance heat transfer from a heating element 214 of the chamber 300 into the wall 202 in use. The heating element 214 is a resistive heater and the outer surface coating 212 is electrically insulating, i.e. a dielectric coating 212, to separate the heating element 214 from the wall 202. In this specific example in Figure 2, the outer surface coating 212 is the same ceramic or glass-like material as the inner surface coating 208, which may comprise silicon carbide or aluminium nitride for example. However, as will be explained by way of further examples below, the surface treatment of the inner surface portion and the outer surface portion may be different.

[0048] The outer surface coating 212 covers the outer surface 203 of the wall 202 around the outer circumference of the wall 202 and along a predetermined length along the wall 202 between the opening 206 of the chamber 200 and the closed end 210 of the chamber 200. The predetermined length of wall for the outer surface coating 212 is substantially the same as (i.e. matches) the predetermined length of wall for the inner surface coating 208 such that the outer surface coating 212 corresponds with the inner surface coating 208 when moving from the outer surface 203 of the wall 202 to the inner surface 201 . To put it in another way, the top end of the outer surface coating 212 is at the same length away from the opening 204 of the chamber 200 as the top end of the inner surface coating 208, and the bottom end of the outer surface coating 212 is at the same length away from the closed end 210 of the chamber 200 as the bottom end of the inner surface coating 208. The outer surface coating 212 is cylindrically-shaped, where the inner surface of the coating 212 is adjacent to (i.e. adhered to) the outer surface 203 of the wall 202 along the predetermined length of surface treatment of the outer surface 203. In this way, the outer surface coating 212 acts as an outer surface heat transfer zone for heat from the heating element 214 to be preferentially transferred to the wall 202.

[0049] In this specific example, the predetermined length of the wall 202 which is coated with the inner and outer surface coatings is 14 mm, but as will be appreciated, may be longer or shorter according to design requirements. The coated sections of the wall 202 may have a length of 14 mm to overlap an interface between the top of a tobacco portion in a consumable received in the cavity 204 and the bottom of a paper tube of the received consumable. As will be appreciated, the coated sections of the wall 202 may have a different length in order to overlap an interface between the tobacco portion in a consumable and the bottom of a paper tube of the consumable. In other words, the length of the coated sections may be shorter or longer than 14 mm and is dependent of the size and length of the tobacco portion in an aerosol forming consumable received in the chamber 200.

[0050] The inner and outer surface coatings each have a thickness between 0.3 pm and 10 pm and may be deposited using vacuum deposition, such as chemical vapour deposition or physical vapour deposition. Vacuum deposition is carried out significantly below atmospheric pressure, i.e. vacuum. As will be understood, importantly, the thickness of the outer surface coating 212 allows the coating to act as an electrically insulating layer between the heating element 214 and the wall 202. A further consideration of the coating thickness(es) is to improve the overall energy efficiency of the heating chamber 200.

[0051] The heating element 214 may comprise one or more heater tracks that are directly printed onto the outer surface coating 212 around the outer circumference of the outer surface coating 212. The heating element 214 comprises a heating material suitable for converting electrical energy into heat (such as stainless steel, titanium, nickel, nichrome, nickel-based alloys, silver, ...). In use, power may be supplied to the heating element 214 from a power source such as a battery (not shown) such that the temperature of the heating element 214 increases and heat energy is transferred across the outer surface coating 212 to the wall 202.

[0052] Alternatively (not shown), the heating element 214 may be part of a thin film heater, where the thin film heater further comprises a flexible backing film on which the heating element 214 is mounted before the thin film heater is applied onto the outer surface coating 212. The flexible backing film may comprise a flexible material preferably having a high dielectric capability and low thermal mass, such as polyamide or polyetheretherketon (PEEK). The thin film heater may be wrapped around the wall 202 in a circumferential direction such that the heating element 214 lies adjacent to (i.e., abuts, contacts) the outer surface coating 212. As explained above, the outer surface coating 212 acts as a separation between the heating element 214 and the wall 202 such that a contact between the heating element 214 and the wall 202 is prevented.

[0053] The heating element 214, whether directly printed onto the outer surface coating 212 or applied as a thin film heater, is arranged to correspond with the outer surface coating 212. In other words, the length of the heating element along the longitudinal axis of the wall 202 substantially matches length of the outer surface coating 212 along the longitudinal axis of the wall 202. In this way, the heating element 214 is arranged on the outer surface coating 212 such that heat generated by the heating element 214 is preferentially transferred into the wall 202 via the outer surface coating 212 (i.e. the outer surface heat transfer zone).

[0054] The outer surface coating 212 may be slightly longer than the length of the heating element 214 (along the longitudinal axis of the wall) such that the heating element 214 is positioned just within the limits of the outer surface coating 212. For example, the upper and lower limits of the heating element 214 may each no more than 1 mm away from the top and bottom ends of the outer surface coating 212 respectively. In this way, it can be better ensured that the heating element 214 is attached on the outer surface coating 212 (and not in direct contact with the wall 202). A further example of the gap between the upper I lower limits of the heating element 214 and the top and bottom ends of the outer surface coating 212 may be no more than 0.5 mm respectively.

[0055] In this example, the length of the inner surface coating 208 along the longitudinal axis of the chamber 200 is the same as the length of the outer surface coating 212 along the longitudinal axis of the chamber 200 to match the respective inner and outer surface heat transfer zones.

[0056] In another example, the length of the inner surface coating 208 may be slightly shorter than the outer surface coating 212, where the inner surface coating matches a corresponding tobacco I aerosol generating material portion of a received aerosol generating substrate. In this way, a slightly longer outer surface coating 212 (respective to the inner surface coating) may absorb more heat from a heating element 214 into the wall 202 and the slightly shorter inner surface coating 208 can effectively focus the absorbed heat in the wall 202 and emit the heat out toward a received aerosol generating substrate. As will be appreciated, if the lengths of the inner and outer surface coatings are too different, heat may be undesirably lost out from the uncoated surface of the wall 202.

[0057] Figure 3a shows a further heating chamber 300 according to the present invention. Similar to the heating chamber 200 of Figure 2, the heating chamber 300 of Figure 3a comprises a tubular wall 302 shaped to form a cavity 304 which is configured to receive the aerosol generating substrate through an opening 306 at a top end of the heating chamber 300.

[0058] In this specific example, a portion of the inner surface 301 of the wall 302 is surface-treated with a coating 308 that is selected for having a high thermal emissivity to enhance heat transfer from the wall 302 to the aerosol generating substrate received in the cavity 304. The coating 308 may comprise silicon carbide or aluminium nitride.

[0059] The inner surface coating 308 covers the inner surface 301 of the wall 302 around the inner circumference of the wall 302 and along a predetermined length along the longitudinal axis of the wall 202 between the opening 306 a closed end 310 of the chamber 300. In this way, the inner surface coating 308 defines an inner surface heat transfer zone for heat from the wall 302 to be optimally transferred to a received consumable.

[0060] In this example, a portion of the outer surface 303 of the wall 302 is coated with a dielectric coating 312 that is different to the inner surface coating. The outer surface coating 312 is selected to optimally enhance heat absorption from a heating element 314 of the chamber 300 into the wall 302 in use. The inner surface coating 308 comprises a different material to the outer surface coating 312. As will be appreciated, there may be other differences between the inner surface coating 308 and the outer surface coating 312, such as thickness or density for example. The outer surface coating 312 covers the outer surface 303 of the wall 302 around the outer circumference of the wall 302 and along a predetermined length along the longitudinal axis of the wall 302 between the opening 306 and the closed end 310 of the chamber 300.

[0061] The heating chamber 300 further comprises a heating element 314 that may comprise one or more heater tracks that are directly printed onto the outer surface coating 312 around the outer circumference of the outer surface coating 312, in a similar way as that described in the heating chamber 200 of Figure 2. Alternatively (not shown), the heating element 314 may be part of a thin film heater, where the thin film heater further comprises a flexible backing film on which the heating element 314 is mounted before the thin film heater is applied onto the outer surface coating 312.

[0062] As will be understood by the skilled person, the lengths of the heating element 314 and the inner and outer surface coatings may be selected in accordance with the present invention in the same way as described above in reference to Figure 2.

[0063] Figure 3b shows a further heating chamber 350 according to the present invention. Similar to the heating chamber 200 of Figure 2 and heating chamber 300 of Figure 3a, the heating chamber 350 of Figure 3b comprises a tubular wall 352 shaped to form a cavity 354 which is configured to receive the aerosol generating substrate through an opening 356 at a top end of the heating chamber 350.

[0064] A portion of the inner surface 351 of the wall 352 is surface-treated to provide an inner surface heat transfer zone 358 enhance heat transfer from the wall 352 to the aerosol generating substrate received in the cavity 354. The inner surface treatment may comprise coating the inner surface portion or comprise a technique to increase the surface roughness of the inner surface heat transfer zone 358. The inner surface heat transfer zone 358 covers the inner surface 351 of the wall 352 around the inner circumference of the wall 352 and along a predetermined length along the longitudinal axis of the wall 352 between the opening 356 a closed end 360 of the chamber 350. In this example, a portion of the outer surface 353 of the wall 352 is coated with a dielectric coating 362. The outer surface coating material may be a ceramic or glass-like material or alternatively, the coating material may comprise polyamide. The outer surface coating 362 covers the outer surface 353 of the wall 362 around the outer circumference of the wall 352 and along a predetermined length along the longitudinal axis of the wall 352 between the opening 356 and the closed end 360 of the chamber 300.

[0065] The heating chamber 350 further comprises a heating element 364 that may comprise one or more heater tracks that are directly printed onto the outer surface coating 362 around the outer circumference of the outer surface coating 362, in a similar way as that described in the heating chamber 200 of Figure 2 or heating chamber 300 of Figure 3a. Alternatively (not shown), the heating element 364 may be part of a thin film heater, where the thin film heater further comprises a flexible backing film on which the heating element 364 is mounted before the thin film heater is applied onto the outer surface coating 362.

[0066] As will be understood by the skilled person, the lengths of the heating element 364, the inner surface heat transfer zone 358 and outer surface coating 362 may be selected in accordance with the present invention in the same way as heating element 214 and the inner and outer surface coatings respectively described above in reference to Figure 2.

[0067] Figure 4 illustrates a flow chart which is a method 400 of manufacturing a heating chamber according to an embodiment of the invention.

[0068] The method 400 begins at step 402, wherein a heating chamber comprising a wall in the form of a tube and an opening for receiving an aerosol substrate within the heating chamber is provided. At step 404, a first surface of the wall is treated with a dielectric material by applying a coating of dielectric material circumferentially to the first surface and to a predetermined length along a longitudinal axis of the wall, such that the applied coating comprises the predetermined length. The surface- treated I coated area of the wall defines a first heat transfer area of the heating chamber. The coating may be deposited by vacuum deposition below atmospheric pressure, i.e. vacuum. For example, the layer of dielectric material may be deposited using chemical vapour deposition. However, in some examples, the layer of dielectric material may be deposited using physical vapour deposition.

[0069] Chemical vapour deposition is a technique in which a substrate is exposed to one or more volatile precursors in a vacuum (or low-pressure plasma) environment, which react and / or decompose on a surface of the substrate to produce a thin film deposit. In this case, the substrate is the wall and the layer of dielectric material is the thin film deposit.

[0070] In some embodiments, plasma enhanced vapour deposition may be used to form the layer of dielectric material. Plasma enhanced vapour deposition utilizes a plasma to provide some of the energy which is required for the deposition reaction to occur. In particular, deposition is achieved by introducing reactant gases between parallel electrodes, wherein a capacitive coupling between the electrodes excites the reactant gases into a plasma. This induces a chemical reaction and results in the reaction product (i.e. the dielectric material) being deposited on the substrate (i.e. the wall). Advantageously, plasma enhanced vapour deposition takes place at lower temperatures than other chemical vapour deposition techniques.

[0071] In one example, a radio frequency electrical discharge between two electrodes may be used to create a plasma from a carrier gas comprising CH4. The resultant chemical reaction deposits a thin film comprising diamond or diamond-like-carbon (DLC) on the wall. The thin film corresponds to the layer of dielectric material.

[0072] In another example, a microwave frequency electrical discharge between two electrodes may be used to excite oxygen to form a plasma. A mixture of silane (SiH4) diluted in a carrier gas, such as argon, is then introduced in an afterglow of the plasma. For example, a mixture of 5% silane in argon may be introduced. The resultant chemical reaction deposits a thin film comprising silicon oxide (e.g. silicon dioxide) on the wall. The thin film corresponds to the layer of dielectric material. For example, the deposited thin film may comprise a functionalized silica-like coating.

[0073] The chemical vapour deposition process is continued until a desired thickness of the layer of dielectric material is deposited, e.g. between 0.3 pm and 10 pm. At step 406, a heating element is attached to the heating chamber such that the heating element is positioned to correspond with the first heat transfer area. The attached heating element has a length that is measurable along the longitudinal axis of the wall, and the length of the heating element is predetermined to substantially match (i.e. be the same as) the predetermined length of the first heat transfer area of the wall.

[0074] If the first heat transfer area is on the outer surface of the wall, then the heating element may be attached to the dielectric coating of the coating on the outer surface. If the first heat transfer area is on the inner surface of the wall, the heating element may be attached to the outer surface of the wall by using a thin film heater, where an electrically-insulating layer is provided between the heating element and the thermal conductive wall. Alternatively, the wall may comprise a second electrically insulating I dielectric coating on the outer surface of the wall which defines a second heat transfer area and on which the heating element is attached.

Claims

CLAIMS1 . A method of manufacturing a heating chamber for an aerosol generating device, the method comprising: providing a tube comprising a wall defining a cavity for receiving an aerosol generating substrate through an opening of the tube, wherein the wall comprises an inner surface facing the cavity and an outer surface facing away from the cavity; treating a first surface of the wall, wherein the first surface of the wall is the inner surface, wherein treating the first surface comprises applying a first coating comprising a dielectric material to the first surface, and wherein the treated first surface defines a first heat transfer area of the tube having a first predetermined length along a longitudinal axis of the tube; and attaching a heating element to the tube to correspond with the first heat transfer area such that the attached heating element comprises a second predetermined length along the longitudinal axis of the tube that substantially matches the first predetermined length.

2. The method of claim 1 , wherein treating the first surface further comprises increasing an average surface roughness of the first surface.

3. The method of any preceding claim, further comprising treating a second surface of the wall to define a second heat transfer area, wherein the treated second surface comprises the outer surface and is opposite to the first surface across the wall.

4. The method of claim 3, wherein the second heat transfer area comprises a third predetermined length along the longitudinal axis of the tube, wherein the third predetermined length substantially matches the first predetermined length.

5. The method of claims 3 or 4, wherein the second heat transfer area is substantially in line with the first heat transfer area along a transverse axis across the wall.

6. The method of any preceding claim, wherein the respective predetermined lengths are substantially matched to provide a difference of less than 2 mm in length between the respective predetermined lengths,7. The method of claim 6, wherein the difference is less than 1 mm.

8. The method of any of claims 3 to 7, wherein treating the second surface further comprises increasing an average surface roughness of the second surface.

9. The method of any of claims 3 to 8, wherein treating the second surface comprises applying a second coating to the second surface.

10. The method of claim 9, wherein the first coating is different to the second coating.11 . The method of claims 9 or 10, wherein the first coating and / or the second coating comprises at least one of: hydrogenated amorphous silicon (a-Si:H); a carbon-based coating; a ceramic material; silicon carbide; aluminium-titania; aluminium chromium nitride; or aluminium nitride.

12. The method of any preceding claim, further comprising applying a mask to the first surface and / or the second surface before treating the respective surface.

13. The method of any preceding claim, wherein the treated first surface and / or the treated second surface comprises a layer of electrically insulating material having a thickness between 0.3 pm and 10 pm.

14. A heating chamber for an aerosol generating device manufactured by the method of any preceding claim, wherein the heating chamber comprises a tubehaving a wall defining a cavity for receiving an aerosol generating substrate through an opening of the tube, wherein the wall comprises a treated inner surface facing the cavity and an outer surface facing away from the cavity, wherein the treated inner surface defines a first heat transfer area of the tube having a first predetermined length along a longitudinal axis of the tube, and wherein a heating element is attached to the tube to correspond with the first heat transfer area such that the attached heating element comprises a second predetermined length along the longitudinal axis of the tube that substantially matches the first predetermined length.

15. An aerosol generating device comprising the heating chamber of claim 14, wherein the heating chamber comprises a tube having a wall defining a cavity for receiving an aerosol generating substrate through an opening of the tube, wherein the wall comprises a treated inner surface facing the cavity and an outer surface facing away from the cavity, wherein the treated inner surface defines a first heat transfer area of the tube having a first predetermined length along a longitudinal axis of the tube, and wherein a heating element is attached to the tube to correspond with the first heat transfer area such that the attached heating element comprises a second predetermined length along the longitudinal axis of the tube that substantially matches the first predetermined length.

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