AEROSAL GENERATING SYSTEMS AND CARTRIDGES FOR USE IN AEROSOL GENERATING SYSTEMS

Abstract

 A cartridge 14 for an aerosol generating system comprises a reservoir 30 having a reservoir chamber 32 for containing a liquid aerosol generating substrate, a vaporisation region 36, and a fluid transfer medium 34, 34a, 34b, 34c operable to absorb liquid from the reservoir chamber 32 and transfer the absorbed liquid to the vaporisation region 36. The fluid transfer medium 34, 34a, 34b, 34c comprises a porous ceramic, and the porous ceramic comprises a pressure release channel 38, 38a, 38b, 38c formed in an exterior surface 40 of the fluid transfer medium. An aerosol generating system including the cartridge 14 is also described.

Description

Technical Field

[0001] The present invention relates generally to aerosol generating systems. The invention relates particularly, but not exclusively, to cartridges for aerosol generating systems that comprise a base part and a separable cartridge.

Technical Background

[0002] Aerosol generating systems, also commonly termed electronic cigarettes, are an alternative to conventional cigarettes. Instead of generating a combustion smoke, they vaporise a liquid aerosol generating substrate which can be inhaled by a user. The liquid typically comprises an aerosol-forming substance, such as glycerine or propylene glycol, that creates the vapour when heated. Other common substances in the liquid are nicotine and various flavourings.

[0003] An aerosol generating system is a hand-held inhaler system, typically comprising a mouthpiece section, a reservoir configured to hold liquid aerosol generating substrate in a reservoir chamber, and a power supply unit. Vaporisation is achieved in a vaporisation region, such as a vaporisation chamber, by a vaporiser or heater unit which typically comprises a heating element in the form of a heating coil and a fluid transfer medium such as a wick. Vaporisation occurs when the heater heats the liquid in the wick until the liquid is transformed into vapour.

[0004] In general terms, a vapour is 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.

[0005] Conventional cigarette smoke comprises nicotine as well as a multitude of other chemical compounds generated as the products of partial combustion and/or pyrolysis of the plant material. Electronic cigarettes on the other hand deliver primarily an aerosolised version of an initial starting e-liquid composition comprising nicotine and various food safe substances such as propylene glycol and glycerine, etc., but are also efficient in delivering a desired nicotine dose to the user. Electronic cigarettes need to deliver a satisfying amount of vapour for an optimum user experience whilst at the same time maximising energy efficiency.

[0006] WO 2017/179043 discloses an aerosol generating system comprising a disposable cartridge and a reusable base part. The cartridge has a simplified structure which is achieved by keeping the main heating element in the re-usable base part, while the cartridge is provided with a heat transfer unit. The heat transfer unit is configured to transfer heat from the heating element to the proximity of liquid in the cartridge to produce a vapour for inhalation by a user.

[0007] During use of an aerosol generating system, as liquid in the fluid transfer medium is vaporised, the pressure in the reservoir drops. This is because liquid is pulled into the fluid transfer medium by capillary forces in order to re-saturate the fluid transfer medium as liquid already held in the fluid transfer medium is heated and vaporised. The pressure difference between the reservoir chamber and the ambient atmosphere outside the reservoir can become very large unless air is permitted to propagate to the reservoir chamber in order to equalise the pressure. Failure to permit air ingress to the reservoir chamber can prevent the fluid transfer medium from re-saturating correctly. For this reason, aerosol generation systems sometimes include a pressure balance system that is operable to provide a pressure equalisation air path between the reservoir chamber and air at ambient pressure. Such a pressure balance system allows for gas (and in particular, air) transfer into the reservoir as liquid is consumed in the vaporisation process.

[0008] However, since such pressure balance systems permit air ingress to the reservoir chamber, they can also permit fluid to escape from the reservoir chamber. This can undesirably result in leakage from the reservoir chamber, resulting in the need to provide additional structure in the system to combat or contain the leakage.

[0009] It is desirable to provide a cartridge including an alternative pressure balance system that is less prone to leakage.

Summary

[0010] According to a first aspect of the present invention, we provide a cartridge for an aerosol generating system, the cartridge comprising:

a reservoir having a reservoir chamber for containing a liquid aerosol generating substrate;

a vaporisation region; and

a fluid transfer medium operable to absorb liquid from the reservoir chamber and transfer the absorbed liquid to the vaporisation region;

wherein the fluid transfer medium comprises a porous ceramic, and the porous ceramic comprises a pressure release channel formed in an exterior surface of the fluid transfer medium.

[0011] Conventional pressure balance systems are typically provided in a wall of the reservoir, or as an additional component in fluid communication with the reservoir, such as a mounting fixture for the fluid transfer medium. This adds complexity to the construction of a cartridge, and so adds to the expense of production. Furthermore, leakage from the reservoir can occur via the pressure balance system, as it provides a fluid path between the reservoir chamber and the exterior of the reservoir. Again, this can result in the need for additional complexity in the form of leakage prevent systems, such as ribs external to the reservoir for collecting the leaked liquid.

[0012] By providing a pressure release channel in an exterior surface of a porous ceramic fluid transfer medium, air can be provided with a pressure equalisation path for ingress to the reservoir chamber. However, any fluid that escapes from the reservoir chamber via the pressure release channel may be absorbed into the porous ceramic of the fluid transfer medium directly from the pressure release channel. This may reduce the risk of leakage from the reservoir via the pressure release channel. Furthermore, providing a pressure release channel in an exterior surface of a ceramic fluid transfer medium allows for a simplified construction as compared to other pressure balance systems, as such a channel can be conveniently machined or cast into the fluid transfer medium during manufacture.

[0013] The pressure release channel is preferably operable to permit air ingress to the reservoir chamber from a location external to the reservoir. The fluid transfer medium may comprise a reservoir end and a vaporisation end, and the pressure release channel may extend across the exterior surface of the fluid transfer medium from the reservoir end towards the vaporisation end. In one example, the cartridge further comprises a vapour transfer channel operable to fluidly connect an inlet with an outlet, with the vaporisation region being in communication with, and preferably located in, the vapour transfer channel between the inlet and the outlet. The pressure release channel may extend between the reservoir chamber and the vapour transfer channel, preferably terminating adjacent the vaporisation region. Thus, in the unlikely event that any fluid which does happen to escape from the reservoir is not absorbed by the porous ceramic, such escaped fluid may be deposited into the vaporisation region, from which it may be vaporised together with fluid that has been wicked through the fluid transfer medium in a more conventional manner.

[0014] The pressure release channel may comprise a gas outlet opening in an interior surface of the fluid transfer medium, said gas outlet being in fluid communication with the reservoir chamber. Pressure within the reservoir may therefore be equalised by means of air ingress to the reservoir chamber via the gas outlet.

[0015] The pressure release channel may alternatively terminate short of an interior surface of the fluid transfer medium at a blind end. In this alternative, no open gas outlet is provided in direct fluid communication with the reservoir chamber, and instead a separating portion of porous ceramic is located between the blind end of the pressure release channel and the interior surface of the fluid transfer medium. Nevertheless, air may enter the reservoir from the pressure release channel if the pressure in the reservoir lowers sufficiently such that a differential pressure between the reservoir chamber and the exterior causes air to be drawn through or around the separating portion of the fluid transfer medium. The separating portion may have a largest dimension that is less than 2mm, or less than 1mm, or less than 0.5mm. At the location of the blind end of the pressure release channel the fluid transfer medium may comprise a wall thickness, and the separating portion may have a largest dimension in the range 20-80% of the wall thickness. By omitting an open gas outlet in the interior surface of the reservoir a direct fluid connection between the reservoir chamber and the exterior is also omitted, further reducing the likelihood of leakage.

[0016] The pressure release channel may have a hydraulic diameter of 2mm or less, or 1mm or less, where the hydraulic diameter is defined as D_h = 4A/P, where A is the cross sectional area of the channel and P is the wetted perimeter of the channel. The pressure release channel may have a hydraulic diameter in the range 1mm-0.1mm, or 1mm-0.2mm, or 1mm-0.5mm. Providing hydraulic diameter in this range may assist in confining fluid leaked from the reservoir chamber within the pressure release channel by means of surface tension.

[0017] The pressure release channel may have a substantially U shaped cross-section. Such a cross-section is simple to machine or cast, improving ease of manufacture.

[0018] The pressure release channel may be substantially straight. Alternatively, the pressure release channel comprises at least one bend. The fluid transfer medium may comprise a generally rectangular cross-section defining four exterior faces, and the pressure release channel may extend across one of the exterior faces (if straight) or may extend across at least two of the exterior faces. Providing at least one bend in the pressure release channel may inhibit the flow of leaked fluid through the channel, so promoting absorption into the porous ceramic.

[0019] The fluid transfer medium may comprise a plurality of pressure release channels.

[0020] The fluid transfer medium may be operable to close an opening in the reservoir such that at least a portion of an interior surface of the fluid transfer medium is in direct contact with a liquid held within the reservoir chamber.

[0021] The cartridge may further comprise a seal surrounding at least a portion of the exterior surface of the fluid transfer medium and covering the at least one pressure release channel. The seal may further assist in confining leaked fluid within the pressure release channel, so promoting absorption into the porous ceramic.

[0022] According to a second aspect of the invention, we provide an aerosol generating system comprising:
a cartridge for an aerosol generating system, the cartridge comprising:

a reservoir having a reservoir chamber for containing a liquid aerosol generating substrate;

a vaporisation region; and

a fluid transfer medium operable to absorb liquid from the reservoir chamber and transfer the absorbed liquid to the vaporisation region;

wherein the fluid transfer medium comprises a porous ceramic, and the porous ceramic comprises a pressure release channel formed in an exterior surface of the fluid transfer medium;

the aerosol generating system further comprising a base part configured to removably connect to the cartridge.

[0023] The cartridge may comprise any of the features set out above in relation to the first aspect of the invention, in any combination.

[0024] The base part may comprise a heater operable to supply heat to the vaporisation region when the cartridge is thermically connected to the cartridge. Such an arrangement simplifies the structure of the cartridge and allows reuse of the heater with multiple cartridges.

[0025] The cartridge may further comprise a thermal interface membrane operable to transfer heat from the heater in the base part to the vaporisation region when the cartridge is thermically connected to the base part. Such a thermal interface membrane provides a cartridge having a sealed construction which reduces the risk of leakage.

[0026] It is to be appreciated that the cartridge and the base part may further include any one or more components conventionally included in an aerosol generating system, such as the system described below in connection with Figure 1.

[0027] For example, the cartridge may further comprise a cartridge housing having a proximal end configured as a mouthpiece end, which is in fluid communication with the vaporisation region via the or a vapour transfer channel, and a distal end operable to removably connect with the base part. The mouthpiece end may be configured for providing the vaporised liquid to the user.

[0028] The reservoir may be provided in the cartridge housing with the vapour transfer channel extending from an inlet at the base and one side of the cartridge, along the distal end of the cartridge to the vaporisation region and up one side of the cartridge to an outlet located centrally at the mouthpiece end. Alternatively, the reservoir may be disposed around the vapour transfer channel.

[0029] The cartridge housing may be made of one or more of the following materials: aluminium, polyether ether ketone (PEEK), polyimides, such as Kapton^®, polyethylene terephthalate (PET), polyethylene (PE), high-density polyethylene (HOPE), polypropylene (PP), polystyrene (PS), fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE), polyoxymethylene (POM), polybutylene terephthalate (PBT), Acrylonitrile butadiene styrene (ABS), Polycarbonates (PC), epoxy resins, polyurethane resins and vinyl resins.

[0030] As noted above, the fluid transfer medium comprises a porous ceramic fluid transfer medium, which may be positioned adjacent to an opening of the reservoir chamber and arranged to hold and transfer aerosol generating liquid from the reservoir chamber to the vaporisation region by capillary action. The porous ceramic fluid transfer medium may be substantially rigid and inflexible. The pore size of the porous ceramic may be in the range 10-80 µm, for example 20-60 µm.

[0031] The base part of the system may include a power supply unit, e.g. a battery, which may be connected to the heater. In operation, upon activating the aerosol generating system, the power supply unit electrically heats the heater of the base part, which then provides its heat by conduction to the fluid transfer medium in the cartridge (optionally via a thermal interface membrane) resulting in vaporisation of the liquid absorbed therein. As this process is continuous, liquid from the reservoir chamber is continuously absorbed by the fluid transfer medium. Vapour created during the above process is transferred from the vaporisation region via the vapour transfer channel so that it can be inhaled via the outlet by a user. Once the liquid in the reservoir chamber is used up, the cartridge may be disconnected from the base part and a new cartridge fitted, enabling the reuse of the base part.

[0032] The heater of the base part may comprise a protruding heater extending from the base part so that, in use, the heater extends into a recess of the cartridge.

[0033] The power supply unit, e.g. battery, may be a DC voltage source. For example, the power supply unit may be a Nickel-metal hydride battery, a Nickel cadmium battery, or a Lithium based battery, for example a Lithium-Cobalt, a Lithium-Iron-Phosphate, a Lithium-Ion or a Lithium-Polymer battery.

[0034] The base part may further comprise a controller associated with electrical components of the aerosol generating system, including the battery and heater.

[0035] The aerosol generating system may comprise an electronic cigarette. As used herein, the term "electronic cigarette" may include an electronic cigarette configured to deliver an aerosol to a user, including an aerosol for inhalation/vaping. An aerosol for inhalation/vaping may refer to an aerosol with particle sizes of 0.01 to 20 µm. The particle size may be between approximately 0.015 µm and 20 µm. The electronic cigarette may be portable.

Brief Description of the Drawings

[0036] The invention will now be described, by way of example only, with reference to the accompanying drawings, in which like features are denoted with the same reference numerals.

Figure 1 is a partial cross-sectional view of an aerosol generating system comprising a base part (only partly visible) and a cartridge;

Figure 2 shows a perspective view of a porous ceramic fluid transfer medium suitable for use in the aerosol generating system of Figure 1, together with a seal (shown in phantom);

Figure 3 shows an alternative perspective view of the porous ceramic fluid transfer medium and seal of Figure 2;

Figure 4 illustrates the functioning of a pressure release channel of a porous ceramic fluid transfer medium;

Figure 5 shows a perspective view of an alternative porous ceramic fluid transfer medium;

Figure 6 shows a perspective view of another alternative porous ceramic fluid transfer medium; and

Figure 7 shows a perspective view of a further alternative porous ceramic fluid transfer medium.

Detailed Description

[0037] Figure 1 shows one example of an aerosol generating system 10, which can be used as a substitute for a conventional cigarette. The aerosol generating system 10 comprises a base part 12 and a cartridge 14 (also referred to in the art as a "capsule" or "pod") thermically connectable to the base part 12. The base part 12 is thus the main body part of the aerosol generating system and is preferably re-usable.

[0038] The base part 12 comprises a housing 16 accommodating therein a power supply unit (not shown) in the form of a battery connected to a heating element located at a first end of the housing 16. The heating element is in the form of a rigid protruding heater 20 that protrudes out of the base part for partial receipt within the cartridge 14. The first end of the housing 16 has an interface configured for matching a corresponding interface of the cartridge 14 and comprises a connector for mechanically coupling the cartridge 14 to the base part. The battery is configured for providing the heater 20 with the necessary power for its operation, via suitable electrical contacts, allowing it to become heated to a required temperature. The heater 20, in the example shown, comprises a ceramic heater. However, it will be appreciated that any suitable type of heater may be selected as required by the implementation.

[0039] The heater and battery are also connected to a controller (not shown), that is operable to control the operations of the aerosol generation system using power supplied by the battery.

[0040] Referring still to Figure 1, the cartridge 14 comprises a cartridge housing 22 having a proximal end 24 and a distal end 26. The proximal end 24 may constitute a mouthpiece end configured for being introduced directly into a user's mouth. In some examples, a mouthpiece may be fitted to the proximal end 24. The distal end 26 of the housing 22 comprises a base 28 into which the heater 20 protrudes when the cartridge 14 is connected to the base unit 12. In particular, an aperture 29 in the base 28 defines a recess into which at least a portion of the heater 20 protrudes when connected.

[0041] The cartridge 14 further comprises a reservoir 30 defining a reservoir chamber 32 configured for containing therein a liquid to be vaporised. The liquid may comprise an aerosol-forming substance such as propylene glycol and/or glycerol and may contain other substances such as nicotine and acids. The liquid may also comprise flavourings such as e.g. tobacco, menthol or fruit flavour. The reservoir 30 extends between the proximal end 24 towards the distal end 26 and is spaced from the distal end 26. A vapour transfer channel 31 extends from one or more inlets 33 across the distal end 26 of the cartridge and up the side of the cartridge to an outlet 35 located centrally in the proximal end 24 of the cartridge. Many configurations for the vapour transfer channel are possible. In the example shown, the inlet 33 is located in the base part 12, and fluidly connected to the remainder of the vapour transfer channel 31 in the cartridge 14 at a fluidly sealable joint 37. Alternatively, the reservoir may surround, and coextend with, the vapour transfer channel. The inlet(s) may be provided in the cartridge 14 or in the base part 12, as required.

[0042] The cartridge 14 is further provided with a fluid transfer medium in the form of a porous ceramic fluid transfer medium 34, also referred to herein as a porous ceramic wick, in fluid communication with the reservoir chamber 32. The porous ceramic fluid transfer medium 34 is operable to absorb liquid aerosol generating substrate from the reservoir and deliver said liquid aerosol generating substrate to a vaporisation region 36. As used herein, the term "vaporisation region" 36 refers to the region in which liquid is vaporised and may alternatively be termed a vaporisation chamber or area. Typically, the vaporisation region is an area within and/or adjacent to the porous ceramic wick 34 in which liquid is heated to a sufficiently high temperature to achieve vaporisation / aerosolization. Vaporised liquid may then be entrained in air within the vapour transfer channel 31 as said air flows past the wick, for example during a user's inhalation.

[0043] Upon connection of the interfaces between the cartridge 14 and the base part 12 of the device, the heater 20 protrudes into the vapour transfer channel 31 immediately below the porous wick 34, thereby enabling heating of liquid in the wick until the liquid is transformed into vapour when the heater is activated.

[0044] A thermal interface membrane 50 is provided between the heater 20 and the porous wick 34. The membrane 50 is a thin membrane such as a metal foil that is configured to ensure rapid and even heating of the vaporisation region 36 in an accurate and defined geometry, reducing the amount of lateral thermal spreading (i.e. thermal losses). The thermal interface membrane 50 is flexible, and so is able to deform, and so at least partially conform, to the shape of the heater 20 when a connection is made between the cartridge 14 and the base part 12. Heat from the heater 20 in the base part is thus transferred to the fluid transfer medium 34 through the thermal interface membrane 50 by conduction, convection and/or radiation (but primarily via conduction) when the cartridge is thermically connected to the base part 12 in order to effect vaporisation of the aerosol generating liquid held in the fluid transfer medium.

[0045] Referring now to Figures 2 and 3, a porous ceramic fluid transfer medium 34 is shown. The porous ceramic fluid transfer medium 34 is shown separately from a cartridge 14 for clarity, but it will be appreciated that the porous ceramic fluid transfer medium 34 may be used in a cartridge 14, such as the cartridge shown in Figure 1, which comprises a reservoir having a reservoir chamber for containing a liquid aerosol generating substrate, and a vaporisation region. In use, the fluid transfer medium 34 is operable to absorb liquid from the reservoir chamber 32 and transfer the absorbed liquid to the vaporisation region in a conventional manner.

[0046] Unlike a conventional fluid transfer medium, however, the porous ceramic fluid transfer medium comprises a pressure release channel 38 formed in an exterior surface 40 of the fluid transfer medium. The pressure release channel 38 is operable to permit air ingress to the reservoir chamber 32 from a location external to the reservoir. Since the fluid transfer medium 34 is comprised of a porous ceramic material, and preferably is comprised solely of a porous ceramic material, the pressure release channel is located in the porous ceramic material of the fluid transfer medium. The pressure release channel thus comprises porous channel walls. This reduces the risk of leakage as compared with a pressure balance system formed in the reservoir wall or wick fixture, as liquid which escapes from the reservoir chamber 32 into the pressure release channel 38 is not travelling through a channel with smooth surfaces, as is the case in state-of-the-art approaches. Instead, such escaped liquid may be absorbed into the fluid transfer medium through the porous channel walls of the pressure release channel 38.

[0047] When installed in a cartridge, such as the cartridge shown in Figure 1, the fluid transfer medium 34 is operable to close an opening 42 in the reservoir, and in particular at a distal end of the reservoir. Thus at least a portion of an interior surface 44 of the fluid transfer medium 34 is in direct contact with a liquid held within the reservoir chamber. Liquid from the reservoir may thus be absorbed into the fluid transfer medium through the inner surface 44, and wicked towards the vaporisation region.

[0048] A first end of the fluid transfer medium 34, which is located closest to the opening 42 in the reservoir, may be thought of as a reservoir end 46. A second end of the fluid transfer medium, which is remote from the reservoir end 46 and adjacent and/or including the vaporisation region 36, may be thought of as a vaporisation end 48. The pressure release channel 38 extends across the exterior surface 40 of the fluid transfer medium 34 between the reservoir end 46 and the vaporisation end 48. This helps to direct escaped liquid held in the pressure release channel 38 towards the vaporisation region 36, from where it may be vaporised in the event that it is not absorbed / fully absorbed by the porous ceramic before it exits the pressure release channel 38.

[0049] In the example shown in Figures 2 and 3, the pressure release channel 38 includes a gas outlet 52 opening in the interior surface 44 of the fluid transfer medium 34. The gas outlet 52 is in fluid communication with the reservoir chamber, and opens directly into the reservoir chamber 32, thus providing an unobstructed air path into the reservoir chamber from a gas inlet 54 at the opposite end of the pressure release channel.

[0050] The pressure release channel 38 has a hydraulic diameter that is selected to assist in confining fluid leaked from the reservoir chamber within the pressure release channel by means of surface tension. As used herein, the hydraulic diameter is defined as D_h = 4A/P, where A is the cross-sectional area of the channel and P is the wetted perimeter of the channel. For example, in the case of a channel having a circular cross-section, the hydraulic diameter may be written as D_h = 4πR²/2πR = 2R. In contrast, for a channel having a rectangular cross-section of width a and depth b, the hydraulic diameter may be written as D_h = 4ab/2(a+b) = 2ab/(a+b). In the example shown in Figures 2 and 3, the pressure release channel is generally U-shaped, and has a broadly rectangular cross section. The U-shaped pressure release channel has a hydraulic diameter of approximately 1mm. It will be appreciated that the design of the channel is dependent on the wick geometry, wick porous properties and e-liquid properties. However, in general the hydraulic diameter may be 2mm or less, for example in the range 1mm-0.1mm, or 1mm-0.2mm.

[0051] The fluid transfer medium 34 illustrated in Figure 2 has a generally rectangular cross-section defining four exterior faces. The pressure release channel 38 does not follow a direct path between the reservoir end and the vaporisation end, and instead follows a convoluted and/or tortuous path that extends across more than one of the exterior faces. In particular, the pressure release channel 38 includes at least one angle or bend 56, and changes direction so as to extend around one or more corners of the fluid transfer medium.

[0052] A seal 60 surrounds at least a portion of the exterior surface 40 of the fluid transfer medium and covers the at least one pressure release channel 38. The seal may additionally extend over the reservoir end of the fluid transfer medium. As shown in Figures 2 and 3, the seal may cover the entire length of the pressure release channel, such that only the gas inlet 52 and gas outlet 54 are exposed. Thus, the seal may further assist in preventing leakage from the reservoir, by ensuring a sealing connection between the fluid transfer medium and the reservoir and/or by confining leaked fluid within the pressure release channel. The seal may be formed from any suitable resilient sealing material, such as silicon.

[0053] Referring now to Figure 4, during use of an aerosol generating system, liquid in the fluid transfer medium 34 is heated 57 by the heater 20. The heated liquid is vaporised in the vaporisation region 36, and the resulting vapour 58 is removed from the vaporisation region by air drawn through the vapor transfer channel by a user of the system. The vaporisation of liquid within the porous ceramic causes pressure in the reservoir chamber 32 to drop. This is because new liquid 62 is pulled into the fluid transfer medium 34 due to capillary forces in order to re-saturate the fluid transfer medium 34 as the liquid already held in the fluid transfer medium is heated and vaporised.

[0054] The pressure difference between the reservoir chamber 32 and the ambient atmosphere outside the reservoir chamber 32 can become very large unless air is permitted to propagate to the reservoir chamber 32 in order to equalise the pressure. Failure to permit air ingress to the reservoir chamber 32 can prevent the fluid transfer medium 34 from re-saturating correctly.

[0055] In aerosol generating systems having flexible fluid transfer media, such as cotton wicks, the wick itself is typically a soft fibrous structure which can deform, and hence can create gaps that enable air to travel to the reservoir and thereby equalise the pressure. This is not possible in aerosol generating systems that utilise ceramic wicks however, since such wicks are hard inflexible structures which do not deform during operation. Depending on the pore size and structure of the porosity inside a ceramic wick, the pressure difference between the reservoir and the outside may need to become very large (e.g. up to 20Pa) before it is strong enough to cause air to propagate to the reservoir through the ceramic (which may typically have a minimum wall thickness in the range 1.5mm-2mm) in order to equalize the pressure and re-saturate the wick. This can lead to dry puffing and inconsistent delivery, which is why most commercial products with a ceramic wick include a pressure balance system in the form of a small channel in the reservoir or wick fixture that acts to permit pressure equalisation. However, such channels also lead to leakage, meaning such cartridges are typically also provided with additional features to address the problem of leakage, such as numerous ribs in a "dead" space outside the reservoir, intended to hold the leaked liquid.

[0056] In contrast, a fluid transfer medium 34 of the type described herein includes a pressure release channel 38 provided in the porous ceramic material of the exterior surface 40 of the fluid transfer medium. Pressure within the reservoir may be equalised by permitting air ingress 64 to the reservoir chamber 32 via the pressure release channel 38.

[0057] Figures 5-7 show three alternative fluid transfer mediums 34a, 34b, 34c. Where appropriate, like reference numerals are used to refer to like features, and so for brevity features common to the fluid transfer medium 34 shown in Figures 2-4 will not be described again in detail. The alternative ceramic fluid transfer mediums shown in Figures 5-7 each include a pressure release channel 38a, 38b, 38c which terminates short of an interior surface of the fluid transfer medium at a blind end 66. In these alternatives, no open gas outlet is provided in direct fluid communication with the reservoir chamber, and instead a separating portion 68 of porous ceramic is located between the blind end 66 of the pressure release channel 38a, 38b, 38c and the interior surface 44 of the fluid transfer medium. Nevertheless, air may enter the reservoir chamber 32 from the pressure release channel 38a, 38b, 38c if the pressure in the reservoir lowers sufficiently such that a differential pressure between the reservoir chamber and the exterior causes air to be drawn through the separating portion 68 of the fluid transfer medium or around the separating portion 68, for example between the porous ceramic and a seal 60 of the type shown in Figures 2-4. This requires a smaller pressure differential than if the air were required to be drawn through the full depth of the ceramic wick. For example, at or adjacent the blind end 66 of the pressure release channel 38, the fluid transfer medium may have a wall thickness in the range 0.5mm-2.5mm. The separating portion 38 may have a largest dimension that is in the range 20-80% of the wall thickness. This may equate to a largest dimension that is in the range 0.1mm-2mm. The separating portion 68 may have a largest dimension that is less than 2mm, for example, or less than 1mm, or less than 0.5mm.

[0058] Like the pressure release channel 38 shown in Figures 2-4, the pressure release channel 38a shown in Figure 5 comprises first and second bends 56 so as to extend across multiple faces of the exterior surface of the fluid transfer medium. In contrast, the pressure release channel 38b shown in Figure 6 is straight and extends longitudinally between the reservoir end and the vaporisation end. Figure 7 shows a fluid transfer medium 38c having a pair of pressure release channels 38c, each of which is straight, similar to the channel 38b of Figure 6. The pair of pressure release channels shown in Figure 7 are on opposing faces of the exterior surface of the fluid transfer medium, and each extends longitudinally between the reservoir end and the vaporisation end.

[0059] Although exemplary embodiments have been described in the preceding paragraphs, it should be understood that various modifications may be made to the examples described herein without departing from the scope of the appended claims. For example, more or fewer pressure release channels could be provided if required, and/or pressure release channels could be provided at different locations to those shown. Similarly, the pressure release channels could have different cross-sectional shapes to those shown. Thus, the breadth and scope of the claims should not be limited to the above-described exemplary embodiments.

[0060] Any combination of the above-described features in all possible variations thereof is encompassed by the present disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

1. A cartridge (14) for an aerosol generating system, the cartridge (14) comprising:

a reservoir (30) having a reservoir chamber (32) for containing a liquid aerosol generating substrate;

a vaporisation region (36); and

a fluid transfer medium (34, 34a, 34b, 34c) operable to absorb liquid from the reservoir chamber (32) and transfer the absorbed liquid to the vaporisation region (36);

wherein the fluid transfer medium (34, 34a, 34b, 34c) comprises a porous ceramic, and the porous ceramic comprises a pressure release channel (38, 38a, 38b, 38c) formed in an exterior surface (40) of the fluid transfer medium.

2. The cartridge of claim 1, wherein the pressure release channel (38, 38a, 38b, 38c) is operable to permit air ingress to the reservoir chamber (32) from a location external to the reservoir.

3. The cartridge of claim 1 or claim 2, wherein the cartridge (14) further comprises a vapour transfer channel (31) operable to fluidly connect an inlet (33) with an outlet (35), the vaporisation region (36) being located in the vapour transfer channel (31) between the inlet (33) and the outlet (35), wherein the pressure release channel (38, 38a, 38b, 38c) extends between the vapour transfer channel (31) and the reservoir chamber (32).

4. The cartridge of any preceding claim, wherein the pressure release channel (38) comprises a gas outlet (52) in an interior surface (44) of the fluid transfer medium, said gas outlet (52) being in fluid communication with the reservoir chamber (32).

5. The cartridge of any one of claims 1-3, wherein the pressure release channel (38a, 38b, 38c) terminates short of an interior surface (44) of the fluid transfer medium at a blind end (66).

6. The cartridge of any preceding claim, wherein the pressure release channel (38, 38a, 38b, 38c) has a hydraulic diameter in the range 0.1mm-1mm.

7. The cartridge of any preceding claim, wherein the pressure release channel (38, 38a, 38b, 38c) has a substantially U-shaped cross-section.

8. The cartridge of any preceding claim, wherein the pressure release channel (38b, 38c) is substantially straight.

9. The cartridge of any one of claims 1-7, wherein the pressure release channel (38, 38a) comprises at least one bend.

10. The cartridge of claim 9, wherein the fluid transfer medium (34, 34a) comprises a generally rectangular cross-section defining four exterior faces, and the pressure release channel (38, 38a) extends across at least two of the exterior faces.

11. The cartridge of any preceding claim, wherein the fluid transfer medium (34c) comprises a plurality of pressure release channels (38c).

12. The cartridge of any preceding claim, wherein the fluid transfer medium (34, 34a, 34b, 34c) is operable to close an opening (42) in the reservoir (30) such that at least a portion of an interior surface (44) of the fluid transfer medium is in direct contact with a liquid held within the reservoir chamber (32).

13. The cartridge of any preceding claim, wherein the fluid transfer medium (34, 34a, 34b, 34c) comprises a reservoir end (46) and a vaporisation end (48), and the pressure release channel (38, 38a, 38b, 38c) extends from the reservoir end (46) towards the vaporisation end (48).

14. The cartridge of any preceding claim, wherein the cartridge (14) further comprises a seal (60) surrounding at least a portion of the exterior surface (40) of the fluid transfer medium and covering the at least one pressure release channel (34, 34a, 34b, 34c).

15. An aerosol generating system comprising the cartridge (14) of any one of claims 1-14 and a base part (12) configured to removably connect to the cartridge (14).

Drawing