Patent Publication Number: US-2022211111-A1

Title: Electronic aerosol provision system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Phase entry of PCT Application No. PCT/GB2020/051072, filed May 1, 2020, which claims priority to GB 1906279.3, the entire disclosures of which are incorporated herein by reference 
    
    
     FIELD 
     The present disclosure relates to electronic aerosol provision systems such as electronic cigarettes and the like. 
     BACKGROUND 
     Electronic aerosol provision systems such as electronic cigarettes (e-cigarettes) generally contain a reservoir of a source liquid containing a formulation, typically including nicotine, from which a vapor is generated, e.g. through heat vaporisation. A vapor source for an aerosol provision system may thus comprise a heater having a wicking element arranged to receive source liquid from the reservoir, for example through wicking/capillary action. 
     While a user inhales on the system, electrical power is supplied to the heating element to vaporise source liquid in the vicinity of the heating element to generate a vapor for inhalation by the user. Such systems are usually provided with one or more air inlet holes located away from a mouthpiece end of the system. When a user sucks on a mouthpiece connected to the mouthpiece end of the system, air is drawn in through the air inlet holes and past the vapor source. There is a flow path connecting between the vapor source and an opening in the mouthpiece so that air drawn past the vapor source continues along the flow path to the mouthpiece opening, carrying some of the vapor from the vapor source with it in the form of an aerosol. The aerosol exits the aerosol provision system through the mouthpiece opening for inhalation by the user. 
     In such systems, the vapor source and heating element may be provided in a disposable “cartomizer”, which is a component that includes both a reservoir for receiving the source liquid and a heating element. The cartomizer is coupled in use to a reusable part (sometimes referred to as “device” part) that includes various electronic components that can be used to operate the aerosol provision system, such as control circuitry and a battery. The heating element is provided with electrical power from the battery via an electrical connection between the cartomizer and reusable device part. Once the source liquid in the cartomizer is used up (e.g., substantially all the source liquid is vaporised and inhaled), the user replaces the cartomizer and installs a new cartomizer to continue generating and inhaling vaporised liquid. 
     In the electronic aerosol provision systems described above, the source liquid is generally contained in the reservoir, but in some instances can exit the reservoir via the wicking element (which is usually a fibrous material in fluid communication with the reservoir). The wicking element uses the capillary effect to transport liquid from the reservoir. The source liquid may be retained in the wicking element to some extent via the capillary forces or surface tension of the liquid, but leakage of the source liquid still occurs in some instances. This can cause multiple issues for the user of the aerosol provision systems including leakage of the source liquid out of the system (and onto the user&#39;s appendages or clothing) and liquid collection (e.g. pooling) in the system, which can impact the overall aerosol formed leading to less consistent or less pleasant experiences. In addition, leakage of the source liquid may also occur when changing the cartomizer component (which may inherently impart mechanical forces to the liquid held in the wicking element by the user moving the cartomizer). 
     Various approaches are described which seek to help address some of these issues. 
     SUMMARY 
     According to a first aspect of certain embodiments there is provided an aerosol provision system comprising: a reservoir for containing an aerosol precursor material; an inlet port and an outlet port both fluidly connected to the reservoir; and a control unit configured to supply a pressurized fluid to the reservoir via the inlet port to increase the pressure within the reservoir relative to the pressure external to the reservoir to force the aerosol precursor material to exit the reservoir via the outlet port. 
     According to a second aspect of certain embodiments there is provided an aerosol provision device comprising a control unit configured to allow a pressurized fluid to enter a reservoir for containing an aerosol precursor material via an inlet port fluidly connected to the reservoir to increase the pressure within the reservoir relative to the pressure external to the reservoir to force the aerosol precursor material to exit the reservoir via an outlet port fluidly connected to the reservoir. 
     According to a third aspect of certain embodiments there is provided a cartridge including a reservoir for containing an aerosol precursor material, and an inlet port for receiving a pressurized fluid and an outlet port both fluidly connected to the reservoir, wherein the cartridge is configured to permit the release of aerosol precursor material from the outlet port when the pressure in the reservoir exceeds a threshold value. 
     According to a fourth aspect of certain embodiments there is provided a method of dispensing aerosol precursor material from a reservoir, the reservoir comprising an inlet port and an outlet port fluidly coupled to the reservoir, the method comprising permitting a pressurized fluid to enter the reservoir via the inlet port to increase the pressure within the reservoir relative to the pressure external to the reservoir, and 
     dispensing aerosol precursor material from the reservoir in response to the increased pressure forcing the aerosol precursor material to exit the reservoir via the outlet port. 
     According to a fifth aspect of certain embodiments there is provided a method of dispensing aerosol precursor material from a reservoir, the method comprising increasing the pressure within the reservoir to a value greater than or equal to a threshold value, above which aerosol precursor material is permitted to exit the reservoir and below which aerosol precursor material is not permitted to exit the reservoir. 
     It will be appreciated that features and aspects of the disclosure described above in relation to the first and other aspects of the disclosure are equally applicable to, and may be combined with, embodiments of the disclosure according to other aspects of the disclosure as appropriate, and not just in the specific combinations described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  schematically represents an aerosol provision system in accordance with the principles of this disclosure which includes a device part having a pressurized fluid generator for controlling the flow of a liquid or other suitable aerosol precursor material from a reservoir of a cartridge part using the generated pressurized fluid; 
         FIG. 2  schematically represents the cartridge part of the aerosol provision system of  FIG. 1  in more detail, and specifically in cross-section; 
         FIG. 3  schematically represents the reusable device part of the aerosol provision system of  FIG. 1  in more detail, and specifically without the cartridge part present; 
         FIG. 4  shows a flow diagram of an example method of operation of the aerosol provision system of  FIG. 1 ; 
         FIGS. 5 a  to 5 d    schematically show the cartridge part of the aerosol provision system of  FIG. 1  at various times during the operation of the aerosol provision system; 
         FIG. 6  shows a graph representative of the value of pressure within the reservoir of the cartridge part of the aerosol provision system of  FIG. 1  (y-axis) with respect to time (x-axis) during operation of the aerosol provision system; and 
         FIG. 7  schematically represents an alternative implementation of an aerosol provision system in accordance with the principles of this disclosure which includes a device part having a pressurized fluid source for controlling the flow of a liquid or other suitable aerosol precursor material from a reservoir of a cartridge part using pressurized fluid source. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects and features of certain examples and embodiments are discussed/described herein. Some aspects and features of certain examples and embodiments may be implemented conventionally and these are not discussed/described in detail in the interests of brevity. It will thus be appreciated that aspects and features of apparatus and methods discussed herein which are not described in detail may be implemented in accordance with any conventional techniques for implementing such aspects and features. 
     The present disclosure relates to aerosol provision systems, which may also be referred to as vapor provision systems, such as e-cigarettes. Throughout the following description the term “e-cigarette” or “electronic cigarette” may sometimes be used; however, it will be appreciated this term may be used interchangeably with aerosol provision system and electronic aerosol provision system. The disclosure is applicable to systems configured to aerosolise, e.g., via heating, a source liquid, which may or may not contain nicotine, to generate an aerosol. However, the disclosure is also applicable to systems configured to release compounds by heating, but not burning, a solid/or amorphous solid substrate material. The substrate material may be for example tobacco or other non-tobacco products, which may or may not contain nicotine. In some systems, the solid/amorphous solid materials are provided in addition to a liquid substrate material so that the present disclosure is also applicable to hybrid systems configured to generate aerosol from a combination of substrate materials. More generally, the substrate materials may comprise for example solid, liquid or amorphous solid, all which may or may not contain nicotine. A hybrid system may comprise any combination of liquid, amorphous solid, and a solid substrate materials. The term “aerosolizable substrate material” or “aerosol precursor material” as used herein is intended to refer to substrate materials which can form an aerosol, either through the application of heat or by some other means. Furthermore, and as is common in the technical field, the terms “vapor” and “aerosol”, and related terms such as “vaporise”, “volatilise” and “aerosolise”, may also be used interchangeably. 
     Aerosol provision systems (e-cigarettes) often, though not always, comprise a modular assembly including both a reusable part (control unit part) and a replaceable (disposable) cartridge part. Often the replaceable cartridge part will comprise the aerosol precursor material and the atomizer assembly, and the control unit part will comprise the power supply (e.g. rechargeable battery) and control circuitry. It will be appreciated these different parts may comprise further elements depending on functionality. For example, the control unit part may comprise a user interface for receiving user input and displaying operating status characteristics. Cartridge parts are mechanically coupled to a control unit part for use, for example using a screw thread, latching or bayonet fixing. When the aerosol precursor material in a cartridge part is exhausted, or the user wishes to switch to a different cartridge part having a different aerosol precursor material, a cartridge part may be removed from the control unit and a replacement cartridge part attached in its place. Devices conforming to this type of two-part modular configuration may generally be referred to as two-part devices. It is also common for electronic cigarettes to have a generally elongate shape. For the sake of providing a concrete example, certain embodiments of the disclosure described herein will be taken to comprise this kind of generally elongate two-part device employing disposable cartridges parts. However, it will be appreciated the underlying principles described herein may equally be adopted for different electronic cigarette configurations, for example single-part devices or modular devices comprising more than two parts, refillable devices and single-use disposable devices, as well as devices conforming to other overall shapes, for example based on so-called box-mod high performance devices that typically have a more box-like shape. 
     The present disclosure relates to an aerosol provision system and device in which a reservoir containing an aerosol precursor material is selectively pressurized via application of a fluid to force at least a portion of the aerosol precursor material from the reservoir, e.g., through an outlet port coupled to the reservoir. The aerosol precursor material is stored within the reservoir in a manner which prevents or substantially reduces the chance of aerosol precursor material leaving the reservoir of its own accord, or in other words, the reservoir is configured to increase the aerosol precursor material retention within the reservoir. For example, the reservoir may include an outlet valve which is actuated to an open position under application of a sufficient force or pressure. In one implementation, the reservoir is provided with an inlet and an outlet valve which act to close off the internal volume of the reservoir when no fluid is applied to the reservoir, thus retaining the liquid within the reservoir to a greater degree. The present disclosure presents implementations in which an aerosol precursor material is sufficiently prevented from exiting the reservoir, thus offering the potential benefits of improved hygiene for both the user handling the device and microbial growth, as well as a reduction in the presence of off-tastes or the like from aerosol precursor material that is not aerosolised or not aerosolised fully and influences the generated aerosol. 
       FIGS. 1 to 3  are schematic diagrams illustrating aspects of an aerosol provision system  10  in accordance with aspects of the present disclosure. The aerosol provision system  10  comprises an aerosol provision device part  20  (herein device part  20  for brevity) and a cartridge part  30  (seen more clearly in  FIG. 2 ). The device part  20  may also be referred to herein as a “control unit” or a “reusable part”, and these terms are to be considered interchangeable with “device part” herein. The cartridge part  30  is arranged to removably couple to the device part  20 , as described in more detail below. 
       FIG. 1  shows a schematic cross-sectional view of the cartridge part  30  coupled to the device part  20 , which is a configuration in which a user would typically use the aerosol provision system  10  to generate aerosol.  FIG. 2  schematically shows a cross-sectional view of the cartridge part  30  in isolation of the device part  20 .  FIG. 3  shows a perspective view of a section of the device part  20  with the cartridge part  30  decoupled from the device part  20 . Note that various components and details, e.g. such as wiring and more complex shaping, have been omitted from  FIGS. 1 to 3  for reasons of clarity. 
     The cartridge part  30  includes a reservoir  32  containing an aerosol precursor material. In this specific implementation, the aerosol precursor material is a liquid aerosol precursor material (sometimes referred to as a source liquid). The source liquid may contain nicotine or other active ingredients, or a one or more flavors. As used herein, the terms “flavor” and “flavorant” refer to materials which, where local regulations permit, may be used to create a desired taste or aroma in a product for adult consumers. The source liquid may also comprise other components, such as propylene glycol or glycerol. As should be appreciated, the cartridge part  30  contains the source liquid which is to be aerosolised for user inhalation. 
     The device part  20  includes an outer housing  21 , a mouthpiece  22  through which generated aerosol can exit the device part  20 , a receptacle  23  for receiving the cartridge part  30 , a power source  24 , control circuity  25 , a pressurized fluid generator  26 , and an atomizer  27 . 
     The device part  20  includes an outer housing  21  which may be formed from a plastics or metal material, for example. The outer housing  21  has a generally cylindrical shape, extending along a longitudinal axis indicated by dashed line LA, and correspondingly has a generally circular cross-sectional shape when viewed along the longitudinal axis LA. The cartridge part  30  also has a generally cylindrical shape which extends along a central axis of the cartridge part (not shown). It should be appreciated, however, that in other implementations the shape and/or cross sectional shape of the device part  20  and/or cartridge part  30  may be different, having shapes such as elliptical, square, rectangular, hexagonal, or some other regular or irregular shape as desired. 
     The outer housing  21  includes a mouthpiece  22  at one end of the device part  20  which further includes an opening  22   a  through which generated aerosol can be inhaled by the user. The mouthpiece  22  is integrally formed with the housing  21  of the device part  20 , although in other implementations the mouthpiece  22  may be removably coupled to the housing  21  via a suitable mechanism, e.g., a screw thread or push fit, to allow changing of the mouthpiece for hygiene reasons. The mouthpiece  22  defines an end of the device part  20  which is inserted into, or otherwise brought into close proximity with, the user&#39;s mouth during normal usage of the system  10 . The mouthpiece end of the device part  20  may also be referred to as a proximal end. Correspondingly, the end opposite the proximal end may be referred to as the distal end of the device part  20 . The outer housing  21  also includes a side surface between the proximal and distal ends of the device part  20  which, in normal use, is the surface that the user holds with their hand, for example. 
     The device part  20  generally includes components with operating lifetimes longer than the expected lifetime of the replaceable cartridge part  30 , which may be defined by the amount of source liquid present in the reservoir  32 . The device part  20  is intended to be used with multiple cartridge parts  30 , and hence the device part  20  is said to be reusable. With reference to  FIGS. 1 and 3 , the housing  21  includes a receptacle  23  which is sized to receive the cartridge part  30 . The receptacle defines a location at which the cartridge part  30  is coupled to the device part  20 . The receptacle  23  is positioned between the distal and proximal ends of the device part  20 . In  FIG. 1 , the gap between the cartridge part  30  and the inner wall of the receptacle  23  is emphasised for the purposes of clarity, however in practical implementations the receptacle  23 /cartridge part  30  are sized such that cartridge part  30  fits snuggly into the receptacle  23 . The reusable device part  20  and cartridge part  30  are separable/detachable from one another by pulling the cartridge part  30  out of the device part  20  in a direction broadly perpendicular to the longitudinal axis LA. When the cartridge part  30  is coupled to the device part  20 , as broadly indicated by  FIG. 1 , the central axis of the cartridge part  30  aligns with the longitudinal axis LA of the device part  20 , although in other implementations the axes may be offset from one another. 
     As seen in  FIG. 3 , the receptacle  23  of the present implementation can be broadly thought of as a hemi-cylindrical cut-away (e.g., a hemi-cylindrical section void of any part of the outer housing) below which is positioned a hemi-cylindrical recess extending into the device part  20 . The two hemi-cylindrical sections provide a cradle configuration and define a substantially cylindrical volume into which the cylindrical cartridge part  30  can be placed. In this implementation, half of the cylindrical cartridge part  30  fits into the hemi-cylindrical recess and is covered by the outer housing  21 , while the other half of the cartridge part  30  is exposed. The receptacle  23  and/or cartridge part  30  may be shaped such that the outer surface of the cartridge part  30  and broadly aligns with the outer surface of the housing  21 . 
     The cartridge part  30  is inserted into the receptacle  23  by pushing the cartridge part  30  in a direction towards the longitudinal axis LA, and is removed from the receptacle  23  by pulling the cartridge part  30  in a direction away from the longitudinal axis LA. To facilitate removal of the cartridge part  30 , the cartridge part  30  and/or outer housing  21  may have features that enable a user to grip the cartridge part  30 . For example, a protrusion or recess may be placed on the outer surface of the cartridge part  30 . The housing  21  or cartridge part  30  may also be provided with a locking mechanism (not shown) which can be used to retain, or help retain, the cartridge part  30  in the receptacle  23 . Alternatively or additionally, a lid hinged on the device part  20  may be provided to cover the exposed part of the cartridge part  30  to retain, or help retain, the cartridge part  30  within the receptacle  23 . 
     The cartridge part  30  is detached from the reusable device part  20  for replacement of the cartridge part  30  when the supply of source liquid is exhausted or if the user wishes to change the flavor/type of source liquid, and is replaced with another cartridge part  30 , if so desired. The reusable device part  20  further includes a power source  24 , such as a battery or cell (e.g., a lithium ion battery) to provide power to the aerosol provision system  10 . The battery may be rechargeable and/or replaceable. It should be appreciated that any suitable battery may be installed within the reusable device part  20 . 
     The control circuitry  25  includes a circuit board to provide control functionality for the aerosol provision device, e.g. by provision of a (micro) controller, processor, ASIC or similar form of control chip. The control circuitry  25  may be arranged to control any functionality associated with the system  10 , including operation of the atomizer  27  and of the pressurized fluid generator  26  which are explained in more detail below. However, the control circuitry  25  may also control charging or re-charging of the battery  24 , visual indicators (e.g., LEDs)/displays associated with operational states/status of the device part  20 , or communication functionality for communicating with external devices, etc. The control circuity  25  may be comprised of a printed circuit board (PCB). Note also that the functionality provided by the control circuitry  25  may be split across multiple circuit boards and/or across components which are not mounted to a PCB, and these additional components and/or PCBs can be located as appropriate within the aerosol provision device. 
     For example, functionality of the control circuitry  25  for controlling the (re)charging of the battery  24  may be provided separately (e.g. on a different PCB) from the functionality for controlling the discharge. 
     The pressurized fluid generator  26  is a component capable of generating a pressurized fluid from an initial fluid. In other words, the pressurized fluid generator  26  is able to increase the pressure of a fluid at a first pressure up to a second pressure. In the implementation described, the pressurized fluid generator  26  is an air compressor  26  and is thus capable of generating pressurized air. The air compressor  26  is in fluid communication with the environment external to the device part  20  via one or more air compressor inlets  26   b , which may be an aperture located on the outer housing  21  and fluidly coupled to an inlet of the air compressor  26 . In operation, the air compressor  26  is able to draw in air from outside the device part  20  via inlet  26   b  and generate a pressurized fluid (more specifically pressurized air) having a greater pressure than the environmental air. Although the pressurized fluid generator  26  is shown at a specific location in  FIG. 1 , it should be understood the generator  26  could be located at any suitable location within the device part  20  and piping or the like can be used to suitably connect the generator to the cartridge part  30  (described in more detail below). 
     Any suitable air compressor  26  can be used in accordance with principles of the present disclosure. For example, in one embodiment, the air compressor  26  is a piezo-electric pump. The pressure to which the air compressor  26  raises the air to may vary from implementation to implementation depending on the properties of the cartridge part  30  (discussed in more detail below). In the implementation described the pressure of the pressurized air output from the air compressor is between 100 to 600 mBar, although this value may depend on the operating frequency of the piezo-electric pump and the desired output flow-rate. The atomizer  27  is any component which is capable of generating an aerosol from an aerosol precursor material. The atomizer  27  may include a resistively heated element, an inductively heated element, a vibrating mesh, an irradiative heat source, a chemical substance, etc. The choice and suitability of the atomizer  27  may depend upon the aerosol precursor material that is to be aerosolised. By way of a concrete example, in the implementation described, the atomizer is a heating element  27  that comprises a non-electrically conductive substrate (such as a ceramic) and an electrically conductive material (such as NiChrome) that is heated when an electric current is passed through the material. The heating element  27  takes the form of a (rectangular) planar plate. The electrically conductive material is resistively heated (e.g., via application of electrical power from the battery  24 ). The heating element  27  is suitable for reaching temperatures capable of vaporising the source liquid to generate an aerosol, e.g. in the range of 150 to 350° C. The temperature of the heating element  27  may also be controlled to achieve and/or maintain a certain temperature, in certain implementations. Although not shown in  FIG. 1 , the device part  30  may optionally include a heating element temperature sensor, such as a resistance temperature detector (RTD), configured to sense a temperature of the heating element  27 . In these implementations, the control circuitry  25  is able to control the power supplied to the heating element  27  to achieve or maintain a certain temperature, based on the sensed temperature of the heating element  27 . In other implementations, however, the temperature of the heating element  27  may be obtained without using a separate temperature sensor, e.g., via the control circuitry  25  being configured to determine the electrical resistance of the heating element  27 . With reference to  FIGS. 1 and 2 , the cartridge part  30  includes an outer housing  31 , a reservoir  32  defined by the inner surfaces of the outer housing  31 , source liquid  33  within the reservoir  32 , an inlet port  34  and an outlet port  35 . 
     The outer housing  31  of the cartridge part  30  is arranged such that a hollow region within the outer housing  31  is present. The hollow region defines the reservoir  32  of the cartridge and provides a volume configured to store a quantity of source liquid  33 , e.g., up to  2  ml of source liquid. The source liquid  33  is provided free in the implementation described, meaning that the source liquid  33  is held predominantly only by the inner surfaces of the outer housing  31  and is otherwise free to move within the reservoir  32 . However, in other implementations, the reservoir  32  may include, for example, a cotton or foam soaked in the source liquid  33 . 
     The inlet port  34  and outlet port  35  define an inlet and outlet to the cartridge part  30 . The inlet and outlet ports  34 ,  35  are fluidly coupled to the reservoir  32 , and thus provide an inlet and an outlet of the reservoir  32 , respectively. The inlet port  34  is arranged such that when cartridge part  30  coupled to the device part  20 , e.g., when placed in the receptacle  23 , the inlet port  34  is additionally brought into fluid communication with the air compressor  26  via a pressurized fluid passage  26   a.  The pressurized fluid passage  26   a  is a channel fluidly coupling an outlet of the air compressor  26  with the receptacle  23  (and inlet port  34  when the cartridge part  30  is installed in the receptacle  23 ). Thus, pressurized air generated by the air compressor  26  is able to pass to the inlet port  34  of the cartridge part  30  via the pressurized fluid passage  26   a.    
     When the pressurized fluid passage  26   a  and cartridge part  30  are coupled together (e.g., when the cartridge part  30  is inserted in the receptacle  32 ), pressurized air is directed along the fluid passage  26   a  to the inlet port  34 . In this regard, the pressurized fluid passage  26   a  and cartridge part  30  (or rather the mating between pressurized fluid passage  26   a  and cartridge part  30 ) are configured to prevent or reduce leakage of pressurized air from the pressurized fluid passage  26   a.  In other words, the pressurized fluid passage  26   a  is engaged with the cartridge part  30  and/or the inlet port  34  to form an air-tight (or substantially air-tight) seal. In the implementation shown in  FIG. 1  and more prominently in  FIGS. 2 and 3 , the pressurized fluid passage  26   a  extends slightly into the receptacle  23 . The extended part of the pressurized fluid passage  26   a  is arranged to fit within a recessed section  34   a  of the cartridge part  30 , thereby forming a seal. The recessed section  34   a  and/or the exposed part of the pressurized fluid passage  26   a  may optionally comprise a sealing element, such as an O-ring or the like to aid in creating the air-tight seal. To facilitate inserting the exposed part of the pressurized fluid passage  26   a  into the recessed section  34   a,  one or both of the pressurized fluid passage  26   a  and the recessed section  34   a  are formed of flexible material (such as an elastomer) and/or the receptacle  23  is sized slightly longer than the length of cartridge part  30  to enable the user to insert the cartridge part  30  into the receptacle  23  and then push (in a direction along the longitudinal axis LA) the recessed section  34   a  of the cartridge part  30  onto the exposed part of the pressurized fluid passage  26   a.  It should be appreciated that this is one example of how an air tight, or substantially air tight, mating between the cartridge part  30  and pressurized fluid passage  26   a  can be achieved. In other implementations, a recess may be formed in the receptacle  23  and the input port  34  may be arranged to extend into the recess of the receptacle  23 . Alternatively, the cartridge part  30  may be provided with another coupling mechanism, such as a screw thread or the like for coupling to a corresponding thread in the device part  20 . 
     When the cartridge part  30  is coupled to the device part  20 , the outlet port  35  is arranged in the proximity of the heating element  27 . Source liquid  33  is able to pass from the outlet port  35  (as described in more detail below), and towards the heating element  27 . In this way, the source liquid  33  is able to be heated after exiting the cartridge part  30 , and subsequently form an aerosol with air entering the device at air inlet  28 . Although not shown, a guide element (such as a hollow cylindrical tube) may be provided to help guide the source liquid  33  ejected from the cartridge part  30  towards the heater element  27 . 
     The inlet and outlet ports  34 ,  35  of the implementation described include respective valves, as shown more clearly in  FIG. 3 . The valves are configured to be biased to a closed/sealed (at least liquid tight) configuration, and are therefore arranged to open in response to a certain threshold pressure being applied to the respective valve. Strictly speaking, the threshold pressure at which the valve is arranged to open is in fact a threshold pressure differential relative to the environmental pressure outside of the reservoir  32 . Accordingly, the cartridge part  30  is liquid tight when removed from the device part  20 , thus meaning that the chance for source liquid  33  to leak from the cartridge part  30  is low. 
     It should be appreciated, however, that in other implementations one or more of the inlet and outlet valves are not present, and instead the inlet and outlet ports  34 ,  35  may always be open. In these implementations, the liquid-tight sealing configuration is provided by careful consideration of the aperture size (e.g., diameter) of the inlet or outlet ports relative to the source liquid  33 , whereby the surface tension of the source liquid  33  is used to prevent the source liquid  33  from exiting the cartridge part  30  below a certain threshold pressure. In this case, when the pressure exceeds the point at which the surface tension can no longer hold the liquid, the liquid is ejected from the outlet port  35 . With reference back to  FIG. 1 , the arrangement of the cartridge part  30  and the components of the device part  20  is such that the compressed air generated by the compressor  26  is forced into the side of the reservoir  32  of cartridge part  30  closest to the mouthpiece  22 . That is, the inlet  34  is generally closer to the mouthpiece  22  than the outlet  35 . Generally speaking, during normal use of the aerosol provision system  10 , the user holds the system such that the mouthpiece  22  is located in or in close proximity to the user&#39;s mouth, while the distal end (e.g., the end opposite the mouthpiece  22 ) is held slightly lower down than the mouthpiece end. That is, the device in normal use is held at an incline with the mouthpiece end elevated above the distal end. This means that the liquid in the reservoir  32  tends to be located closer to the outlet  35 . Subsequently, this arrangement helps reduce the chances of air being forced out of outlet  35  as, in normal use, there is a volume of liquid in contact with the outlet  35 . It should be appreciated that the outlet  35  and inlet  34  may be located at various positions within the cartridge part  30  (e.g., offset in the axial direction) to help improve this effect. 
     The operation of such an aerosol provision system  10  is now described with reference to  FIG. 4 . Firstly, if not already done so, the user installs a cartridge part  30  containing source liquid  33  in the receptacle  23  of the device part  20  (step S 1 ). As mentioned, in the described implementation, this involves inserting the cartridge part  30  by pushing the cartridge part  30  towards the axis LA of the device part  20  so that the axis of the cartridge part  30  aligns with the axis LA of the device part  20 . 
     Then, at step S 2 , the user powers on the aerosol provision system  10 . In this regard, the housing  21  includes a button or other actuation mechanism for transitioning the device part  20  from an OFF mode to an ON mode, at which point power from the power source  24  is supplied to the control circuitry  25 . Note that in some implementations a small amount of power may be supplied to the control circuitry  25  even when the device part  20  is switched OFF; however at step S 2  a greater power is supplied enabling more functions of the control circuitry  25  to be provided with power. 
     At step S 3 , the device part  20  monitors for a user action. The user action is one which signifies that the user wants to inhale aerosol. For example, the action might be actuating a button or the like on the surface of the housing  21 . For example, the user may push the button and then bring the mouthpiece  22  to their lips and begin inhaling. Alternatively, the action might be based on the user actually inhaling on the mouthpiece  22 . For example, the device part  20  may include a pressure or airflow sensor (not shown) configured to detect when a user is inhaling on the device part  20 . If any of the above user actions are detected, the method proceeds to step S 4 , otherwise the device part  20  continues to monitor for a user action. 
     Once a user action has been detected at step S 3 , the control circuity  25  then supplies power to the air compressor  26  to begin generating pressurized fluid (air) at step S 4 . In this regard, the control circuitry  25  controls, for example, a motor of the air compressor  26  by supplying a certain power from the battery  24  to generate pressurized air. At step S 5 , the generated air is applied (or supplied) to the inlet port  34  of the cartridge part  30  via the pressurized fluid passage  26   a.  When the pressurized air is applied to the inlet port, and when the pressure is sufficient to overcome the threshold of the valve of the inlet port  34 , the valve of the inlet port  34  is opened (and thus exposes the reservoir  32 ). 
     It should be appreciated that although steps S 4  and S 5  are shown as separate steps, they may in fact be implemented at substantially the same time. An air compressor operates by forcing air into an enclosed volume and gradually building up the pressure of the air within that volume. The enclosed volume may be a separate storage volume (e.g., which is formed as part of the air compressor  26 ) or may the volume formed by the compressed fluid passage  26   a  and the (closed) inlet port  34 . 
     Accordingly, in cases where the compressed air is stored within the compressor  26  or is separate to the passage  26   a,  the release of the compressed air can be controlled (e.g., by the control circuitry  25 ). For example, once the pressure within the storage volume reaches a certain limit, the control circuitry  25  can be configured to release the compressed air (which subsequently travels along the passage  26 ) by opening a valve. Alternatively, the air compressor  26  may continually supply air to the passage  26   a  which gradually increases the pressure within the passage  26   a,  and hence steps S 4  and S 5  occur substantially simultaneously. In this case, the air pressure within passage  26   a  may gradually increase until the time at which the valve of the inlet port  34  opens (and at which time the compressed air can enter the reservoir  32 ). 
     It should be appreciated that the air compressor  26  may have certain operational parameters that can determine how the pressure within the reservoir is changed. For example, an air compressor  26  can be characterised by an output flow rate, e.g., X ml of air per second. Depending on the value of X, the pressure threshold of the valve of the input port  34 , and of the additional “empty” volume defined by the reservoir, the valve of the input port  34  can either effectively remain open or can close (until such a time as the pressure has built up enough to force the valve of the input port  34  open again). For the sake of providing a concrete example, it is assumed in the present implementation that the valve of the input port  34  remains open. 
     Turning to  FIGS. 5 and 6 , it is now explained what happens when a compressed fluid (e.g., compressed air) is applied to the reservoir  32  containing source liquid  33 .  FIGS. 5( a ) to 5( d )  show a cross-section of the cartridge part  30  (and specifically the outlet port  35 ) at various stages in the cycle of applying pressure to the reservoir  32 , while  FIG. 6  is a graph showing pressure P in the reservoir  32  on the y-axis and time t on the x-axis. 
       FIG. 5( a )  shows the cartridge part  32  when no pressurized fluid is applied to the reservoir  32 . In this state, the valve of the outlet port  35  is closed. The pressure within the reservoir  32  is at a first pressure P 1 . This state is represented in  FIG. 6  from t=0 to t=t 1 , which shows a constant pressure P 1  within the reservoir  32 . As described above, this is the state prior to which the valve of the inlet port  34  is open, and thus it should be appreciated that the air compressor  26  may be running in the period up to t 1  and compressed fluid may be being applied to the valve of the input port  34  between t 0  and t 1 . 
     At time t 1 , the inlet valve of the inlet port  34  is opened by the compressed fluid (air) from the air compressor  26 . At this point, compressed air can begin entering the reservoir  32 . This is shown by the arrow in  FIG. 5( b ) . At time t 1 , the pressure within the reservoir begins to increase (as indicated by the inclined line in  FIG. 6  after t 1 ). 
     At a certain point in time, t 2 , the pressure within the reservoir  32  is large enough to cause the outlet valve of the outlet port  35  to open. In other words, there exits a differential pressure between the inside of the reservoir and the external environment of the valve of the outlet port  35  to cause the valve of the outlet port  35  to open. In  FIG. 6 , this is represented as pressure P 2 . Hence, when the pressure within the reservoir  32  reaches pressure P 2 , the outlet valve of the outlet port  35  opens and, in doing so, a portion of the contents of the reservoir  32  (e.g., a portion of the source liquid  33 ) is permitted to escape from the reservoir  32 .  FIG. 5( c )  shows such a scenario where a droplet of source liquid  33  escapes from (exits) the reservoir  32 . 
     At this time, the pressure within the reservoir  32  decreases. One can rationalise this using the ideal gas equation PV=nRT, under the assumptions that air acts as an ideal gas, that the temperature of the air does not change during this process, and that the source liquid  33  is incompressible. In the ideal gas equation, P represents pressure, V represents the volume of the container the ideal gas occupies, n represents the number of moles of the ideal gas, R is the gas constant, and T is the temperature of the ideal gas. Under the above assumptions, it should be clear that RT is a constant. Shortly before and shortly after the moment at which the source liquid is ejected from the reservoir  32 , we can assume that the number of moles of air within the reservoir is reasonably constant (in other words, n is constant). This means that PV is equal to a constant value. As mentioned, some of the source liquid  33  is ejected from the reservoir  32 . This ejected source liquid has a certain volume. When the source liquid is ejected, the volume within the reservoir  32  that air can occupy has increased (by an amount proportional to the volume of the ejected source liquid—assuming the source liquid is relatively incompressible, the amount of increase is equal to the volume of the source liquid). This implies that the pressure within the reservoir  32  decreases in order to maintain the constant value nRT. 
     In  FIG. 6 , the pressure decreases from pressure P 2  to P 1  from time t 2  to time t 3 . The period between t 2  and t 3  is shown exaggerated in  FIG. 6  for clarity. In practical applications, t 3  is likely much closer to t 2 . It should also be appreciated that while  FIG. 6  shows the pressure going to P 1  at time t 3 , this may not necessarily be the case as the pressure may be slightly above P 1  depending on the output flow rate of the air compressor  26  (e.g., the rate at which moles of the gas are entering the reservoir). 
     As a result of the pressure within the reservoir  32  decreasing, the outlet valve of the outlet port  35  is biased to the closed position, thus stopping additional source liquid  33  from exiting the reservoir  32 . This is shown in  FIG. 5( d ) . 
     Hence, it can be seen that the pressure within the cartridge part  30  of the present disclosure starts at a first pressure, increases to a second pressure due to the presence of a pressurized fluid in the reservoir  32 , and falls back to a lower pressure once a part of the contents of the reservoir  32  has been ejected from the reservoir  32 . 
     This cycle may be repeated multiple times. Depending upon the amount of source liquid  33  that exits the reservoir  32  in each cycle, each cycle described above may be suitable for one puff/one inhalation on the device part  20 , or it may be that multiple cycles are required for a single puff. The latter case offers finer control on the amount of aerosol that can be generated per puff. In other words, the system  10  can be set to control the amount of aerosol generating material that is ejected per second from the cartridge part  30 . It should also be appreciated that the former or latter case can be realised by changing the parameters of the components of the device part  20  and the cartridge part  30 . The volume of source liquid that exits the cartridge part  30  may be dependent on a variety of parameters, including the geometry of the outlet port, the characteristics of the valve, characteristics of the reservoir, etc. Moreover, the amount of source liquid  33  ejected per second is dependent on the output flow rate of the air compressor, and in some implementations, the control circuitry  25  is configured to control the amount of liquid exiting the cartridge part  30  by adjusting the output flow rate of the air compressor  26  (or more generally the flow rate of pressurized fluid into the reservoir  32 ). The flow rate may be adjusted based on a user input, such as an instruction to provide a certain amount of aerosol generating material or in response to the characteristics of a user&#39;s inhalation. 
     Turning back to  FIG. 4 , after steps S 4  and S 5 , the method proceeds to step S 6  where the control circuitry  25  supplies power to the atomizer  27 . More specifically, the control circuitry  25  supplies power to the resistive element(s) of the heating element  27  causing the resistive element(s) to heat up. The control circuitry  25  is configured to cause the heating element  27  to reach a temperature suitable for vaporising the source liquid  33  that exits the reservoir  32 . As mentioned, this may be in the range of 150° C. to 350° C. depending upon the source liquid  33  to be vaporised. The source liquid  33  that has left the reservoir  32  is subsequently vaporised by the heating element  27 . 
     It should be appreciated that while steps S 4 , S 5  and S 6  are described in sequence, the steps may be implemented in any order. In some instances, the heating element  27  may be provided with power before the source liquid  33  is ejected from the reservoir  32 . This may be the case if the heating element  27  requires a certain time to reach an operational temperature (in other words to accommodate for a thermal lag). Equally, step S 5  may be implemented after step S 6 , again if both the air compressor  26  and heating element  27  require a certain time to reach an operational condition. 
     When the user inhales on the mouthpiece  22  of the device part  20 , air is drawn into the device part  20  via air inlet  28  positioned on the device part housing  21 . The air path is arranged to pass via the heating element  27 . The air path is shown in  FIG. 1  via the series of arrows starting at the inlet  28 . Hence, when the source liquid  33  is vaporised by the heating element  27  as described above, air mixes with the generated vapor from the heating element  27  to form an aerosol. The sucking action of the user means that the aerosol is then passed through the device part  20  to the opening  22   a  of the mouthpiece  22  where it is then passed to the mouth/lungs of the user. 
     At step S 7 , the control circuitry  25  continues to monitor for the presence of the user action as detected at step S 3 . If the action is maintained, then the process continues as discussed above (which may include performing another cycle of steps S 4  to S 6  as described above). In the event that the user action is not maintained, the method proceeds to step S 8 , where the power may be stopped to one of the air compressor  26  and/or the heating element  27 . The method then proceeds to step S 3  and the cycle is repeated for a subsequent user action. 
     It should be appreciated that the method shown in  FIG. 4  is exemplary only and the device may operate according to a method modified from that shown in  FIG. 4 , as hinted at above. Hence, according to the application at hand, the components used in the device or the user&#39;s preferences, the device can be configured or set-up accordingly. 
     The pressurized fluid generator  26  as described above may, more generally, be referred to as a source of pressurized fluid. That is, the “source of pressurized fluid” as used herein is considered to include mechanisms not only where pressurized fluid is generated from an initial (non-pressurized or low-pressurized) fluid as described above, but also includes sources of stored pre-pressurized (i.e., already pressurized) fluid, for example in the form of a compressed air canister or the like. 
       FIG. 7  shows a schematic cross-sectional view of an aerosol provision system  110  including a store of pressured fluid. The system  110  of  FIG. 7  includes many components that are similar or identical to those described with respect to  FIG. 1 . These components are indicated with the same reference signs as used in relation to  FIG. 1 , and hence a repeat of the description of these components is not presented herein for brevity. 
     The device part  120  of the aerosol provision system  110  differs from the device part  20  of aerosol provision system  10  of  FIG. 1  in that it includes a store of pressurized fluid  126  and control circuitry  125  suitable for controlling the release of pressurized fluid to the cartridge part  30  (which is largely identical to the cartridge part  30  described in  FIG. 1 ), as opposed to an air compressor  26  and control circuitry  25 . 
     More specifically, the device part  120  comprises a store of pressurized fluid  126 , which in this example includes a compressed air canister. However, it should be understood that any suitable container for housing a pressurized fluid of any description could be used in accordance with the principles of the present disclosure. The store of pressurized fluid is pre-pressurized before being installed in the device part  120 , for instance using known techniques for filling containers for holding pressurized fluid. Hence, the store of pressurized fluid may also herein be referred to as a pre-pressurized store of fluid. The pre-pressurized store of fluid may be separable from the device part  120  in a similar manner as cartridge part  30  is separable from device part  120 . Hence, the pre-pressurized store is able to be removed and replaced with another pre-pressurized store, in the event that the pressurized fluid runs out or the pressure becomes too low to enable actuation of the inlet valve of the inlet port  34 . The control circuitry  125  may be provided with the functionality to identify when the pre-pressurized store is running low, for example by monitoring the pressure of the fluid released from the pre-pressurized store using a suitable sensor (not shown) or by recording the usage of the pre-pressurized store. 
     The device part  120  further comprises a pressurized fluid passage  126   a  which is largely similar to the fluid passage  26   a  described in relation to  FIG. 1 . However, the fluid passage  126   a  in this example further includes a release element  126   c.  The release element  126   c  is an actuatable member that is configured to selectively block the fluid passage  126   a . The release element  126   c  may be biased to the blocked position. The release element  126   c  is controllable by the control circuitry  125 . More specifically, when the user action is detected at step S 3  of  FIG. 4 , the control circuitry  125  is configured to actuate the release element  126   c  causing the passage  126   a  to be open. In the blocked state, the release element  126   c  prevents (or substantially reduces) the flow of pre-pressurized fluid from the store  126  to the inlet port  34 . However in the open state, the pre-pressurized fluid is able to escape from the store  126  and pass along to the inlet port  34 . The release element  126   c  may employ any suitable technology that can be used to selectively allow fluid, such as compressed air, to exit an otherwise sealed container, e.g., such as actuators used on pressurized deodorant or paint cans. It should be appreciated that the release element  126   c  may be located in the device (e.g., as part of the fluid passage  126   a,  as described) or as part of the container forming store  126  (e.g., as part of a nozzle or valve on the container). In the latter case, the store  126  or device part  120  may include an engagement mechanism that enables the release element  126   c  to engage with, and be actuated by, device part  120 . 
     In some implementations, the control circuitry  125  can be configured to control the flow of fluid to the inlet port  34  (and thus to the reservoir  32 ) based on actuating the release element  126   c  to varying degrees. For example, a slower flow rate can be achieved by only partially opening the actuator. In this way, the control circuitry  125  can be configured to provide dosing control of the source liquid  33  to the heating element  27 . 
     It should also be noted that the housing  121  of device part  120  is largely similar to housing  21  described in relation to  FIG. 1 . However, because device part  120  includes a pre-pressurized store of fluid  120 , there is no necessity for an air inlet  26   b  as descried in relation to  FIG. 1  because the pre-pressurized store of fluid does not generate pressurized fluid from outside of the device part  120 . 
     Thus there has been described an aerosol provision system comprising: a reservoir for containing an aerosol precursor material; an inlet port and an outlet port both fluidly connected to the reservoir; and a control unit configured to supply a pressurized fluid to the reservoir via the inlet port to increase the pressure within the reservoir relative to the pressure external to the reservoir to force the aerosol precursor material to exit the reservoir via the outlet port. 
     Although it has been described above that a device part  20 ,  120  is configured to supply pressurized air to inlet port  34  of a cartridge part  30 , it should be appreciated that other pressurized fluids may be supplied to the cartridge part  30 . For instance, other gases may be pressurized and supplied to the cartridge part  30 . Alternatively, liquids, such as water or oil, may also be supplied to the cartridge part  30 . In implementations where the cartridge part  30  contains a liquid, such as source liquid  33 , the liquid to be supplied is preferably not miscible (or immiscible) with the source liquid  33 . In this way, the immiscible liquid acts to displace the source liquid  33  from the cartridge part  30 . Depending on how the device part  20 ,  120  is orientated during normal usage, the fluid may be lighter or heavier than the source liquid  33  to ensure that the source liquid is ejected from the cartridge part  30 . 
     Although it has been described above that a device part  20  which includes a pressurized fluid generator (such as air compressor  26 ) additionally includes an air inlet  26   b  for drawing in air from outside the device part  20  via the inlet  26   b,  this is not always necessary. In some implementations, the pressurized fluid generator  26  is configured to pressurise a liquid, such as water, or a gas which is not air. In these implementations, the water or gas to be pressurized is provided in a store/container which can be integral with or insertable into device part  20  (in a similar way to store  126 ). However, in these implementations, the pressurized fluid generator  26  is configured to pressurise the fluid stored in the container in response to a user input. This may be advantageous as the container does not need to be pressurized before use (as in the case for device part  120 ), and so in some cases can be easier for a user to refill or replace. 
     It has also been described above that cartridge part  30  includes a liquid reservoir containing a source liquid which acts as a vapor/aerosol precursor. However, in other implementations, the cartridge part  30  may contain other forms of aerosol precursor material, such as tobacco leaves, ground tobacco, reconstituted tobacco, gels, etc. In accordance with the principles of the present disclosure described herein, while the degree to which more solid/gel type aerosol precursor materials may exit the cartridge part  30  when the cartridge part  30  is not in a normal orientations may be relatively less, the disclosure nevertheless applies to any form of aerosol precursor materials. That is, the present disclosure relates to non-combustible aerosol provision systems such as heating products that release compounds from substrate materials without burning the substrate materials, such as electronic cigarettes, tobacco heating products, and hybrid systems to generate aerosol from a combination of substrate materials. The substrate materials, sometimes referred to herein as aerosol precursor materials or aerosolizable materials, may include any of a liquid, a gel or a solid substrate. 
     It should also be understood that cartridge parts  30  may be provided with combinations of aerosol precursor materials. It should be appreciated that any suitable type of vaporisation element/heating element may be selected in accordance with aspects of the present disclosure, e.g., a wick and coil, an oven-type heater, an LED type heater, a vibrator, etc. 
     It has also generally been described above that the cartridge part  30  does not include a heating element  27  (or more generally a vaporisation element). In some implementations, the cartridge part  30  may include a heating element  27  integrated with the cartridge part  30 , with the intention that the heating element  27  is disposed of with the cartridge part  30 . In this case, the cartridge part  30  may include electrical connections for electrically connecting the heating element  27  to the power source  24  of the device part  20 . 
     In other implementations, the cartridge part  30  may be omitted and instead the device part  20  may be provided with an aerosol precursor material reservoir which can receive a quantity of aerosol precursor material directly. For example, the device part may include a reservoir having a removable cap (e.g., a threadingly engaged cap) which enables source liquid to be inserted into the device part  20 . (Or an alternative way to view such implementations is that the cartridge part  30  is integrated with the device part  20 ). The present disclosure also applies to such vapor provision systems  10 . 
     Although it has been described above that the receptacle  23  forms a cradle-like recess, it should be appreciated that other mechanisms for housing the cartridge part  30  may be implemented instead. For example, the housing  21 ,  121  may comprise two detachable parts which are separable from each other along the longitudinal direction LA. When coupled together, the two parts define an enclosed cylindrical receptacle  23 , but when separated the two parts enable access to the cylindrical receptacle  23 . Thus in the separated state a user can insert or remove a cartridge part  30  by pulling or pushing the cartridge along the direction of the longitudinal axis LA. Alternative mechanisms may include a movable cradle which is hinged to the housing  21  and moves in a direction perpendicular to the longitudinal axis LA, for example. The skilled person will be aware of alternative approaches for enabling loading of the cartridge part  30  into device part  20 ,  120 . 
     While the above described embodiments have in some respects focussed on some specific example aerosol provision systems, it will be appreciated the same principles can be applied for aerosol provision systems using other technologies. That is to say, the specific manner in which various aspects of the aerosol provision system function are not directly relevant to the principles underlying the examples described herein. 
     The above disclosure is applicable to systems configured to aerosolise, e.g., via heating, a source liquid, which may or may not contain nicotine, to generate an aerosol. However, it should be appreciated that the disclosure is also applicable to systems configured to release compounds by heating, but not burning, a solid/or amorphous solid substrate material. The substrate material may be for example tobacco or other non-tobacco products, which may or may not contain nicotine. In some systems, the solid/amorphous solid materials are provided in addition to source liquid so that the present disclosure is also applicable to hybrid systems configured to generate aerosol by heating, but not burning, a combination of substrate materials. Other combinations, such as solid and amorphous solid substrate materials also fall within the scope of this disclosure. More generally, the substrate materials may comprise for example solid, liquid or amorphous solid, which may or may not contain nicotine. 
     In order to address various issues and advance the art, this disclosure shows by way of illustration various embodiments in which the disclosure may be practiced. The advantages and features of the disclosure are of a representative sample of embodiments only, and are not exhaustive or exclusive. They are presented only to assist in understanding and to teach the disclosure. It is to be understood that advantages, embodiments, examples, functions, features, structures, or other aspects of the disclosure are not to be considered limitations on the disclosure as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the scope of the claims. Various embodiments may suitably comprise, consist of, or consist essentially of, various combinations of the disclosed elements, components, features, parts, steps, means, etc. other than those specifically described herein, and it will thus be appreciated that features of the dependent claims may be combined with features of the independent claims in combinations other than those explicitly set out in the claims. The disclosure may include other embodiments not presently claimed, but which may be claimed in future.