阅读说明：本技术 气溶胶生成系统和用于在气溶胶生成系统中使用的筒 (Aerosol-generating system and cartridge for use in an aerosol-generating system ) 是由 K·D·费尔南多 于 2015-12-07 设计创作，主要内容包括：一种气溶胶生成系统和用于气溶胶生成系统的筒,所述系统包含：空气入口和空气出口；保持液体气溶胶形成基质的液体储存部分,所述液体储存部分具有液体出口；从所述空气入口经过所述液体出口向所述空气出口的气流通道,其中所述气流通道成形为使得当空气从所述空气入口经过所述气流通道流向所述空气出口时,所述液体出口处的所述气流通道内存在压降,所述气流通道在所述液体出口处具有相对于所述空气入口受限的截面；和流动路径内的加热元件,所述加热元件位于所述液体出口与所述空气出口之间。(An aerosol-generating system and cartridge for an aerosol-generating system, the system comprising: an air inlet and an air outlet; a liquid storage portion holding a liquid aerosol-forming substrate, the liquid storage portion having a liquid outlet; an air flow passage from the air inlet to the air outlet through the liquid outlet, wherein the air flow passage is shaped such that there is a pressure drop within the air flow passage at the liquid outlet as air flows from the air inlet to the air outlet through the air flow passage, the air flow passage having a restricted cross-section at the liquid outlet relative to the air inlet; and a heating element within the flow path, the heating element being located between the liquid outlet and the air outlet.)

1. An aerosol-generating system comprising:

an air inlet and an air outlet;

a liquid storage portion holding a liquid aerosol-forming substrate, the liquid storage portion having a liquid outlet;

an air flow passage from the air inlet through the liquid outlet to the air outlet, wherein the air flow passage is shaped such that there is a pressure drop within the air flow passage at the liquid outlet as air flows from the air inlet through the air flow passage to the air outlet, the air flow passage having a restricted cross-section at the liquid outlet relative to the air inlet; and

a heating element within the flow path, the heating element being located between the liquid outlet and the air outlet.

2. An aerosol-generating system according to claim 1, wherein the heating element is positioned downstream of the liquid outlet.

3. An aerosol-generating system according to claim 1 or 2, wherein the liquid storage portion provides a sealed housing for the liquid aerosol-forming substrate such that fluid cannot enter or exit the sealed housing other than through the liquid outlet.

4. An aerosol-generating system according to any preceding claim, wherein the liquid storage portion comprises an air inlet valve which allows air to enter the liquid storage portion when in an open position, but does not allow air to enter the liquid storage portion when in a closed position.

5. An aerosol-generating system according to claim 4, wherein the aerosol-generating system is configured such that the air inlet valve is controlled to be in a closed position when a predetermined flow rate of air is flowing through the airflow passage.

6. An aerosol-generating system according to any preceding claim, wherein the liquid storage portion comprises an annular housing, and wherein the airflow passage extends through the annular housing.

7. An aerosol-generating system according to any preceding claim, wherein the liquid outlet is annular.

8. An aerosol-generating system according to any preceding claim, wherein the heating element spans the airflow passage and is fluid permeable.

9. An aerosol-generating system according to claim 8, wherein an airflow must pass through the heating element to reach the air outlet.

10. An aerosol-generating system according to claim 8 or 9, wherein the heating element comprises a grid, array or fabric of heater filaments.

11. An aerosol-generating system according to any preceding claim comprising a power supply connected to the heating element, wherein in operation the heating element is resistively heated.

12. An aerosol-generating system according to any preceding claim comprising a disposable cartridge and device, wherein the cartridge comprises the liquid storage portion.

13. An aerosol-generating system according to claim 12, wherein the cartridge comprises the heating element.

14. A cartridge for use in an aerosol-generating system, the cartridge comprising:

an air inlet and an air outlet;

a liquid storage portion holding a liquid aerosol-forming substrate, the liquid storage portion having a liquid outlet; and

an air flow passage from the air inlet through the liquid outlet to the air outlet, wherein the air flow passage is shaped such that there is a pressure drop within the air flow passage at the liquid outlet when air flows from the air inlet through the air flow passage to the air outlet, the air flow passage having a restricted cross-section at the liquid outlet relative to the air inlet.

15. The cartridge of claim 14, further comprising a heating element located in the airflow channel between the liquid outlet and the air outlet.

Technical Field

The present invention relates to aerosol-generating systems in which an aerosol is produced by vaporising a liquid substrate using a heater.

Background

One type of aerosol-generating system is an electronic cigarette. Electronic cigarettes typically operate by heating a liquid aerosol-forming substrate to produce a vapour. The vapor is then cooled to form an aerosol. Most electronic cigarette systems use some form of liquid retaining material, such as a sponge or an impregnating material, to hold the liquid aerosol-forming substrate and deliver it to the heater. In such systems, there are several problems associated with liquid retaining materials. As the liquid retaining material dries, less liquid is transferred to the heater, resulting in a smaller amount of aerosol being transferred. Additionally, as the liquid retaining material dries, it is more susceptible to charring or burning. This can lead to undesirable compounds in the generated aerosol. The liquid retaining material also increases the cost and complexity of the manufacturing process.

One solution for delivering liquid to the heater that has been proposed and does not require a liquid retaining material would be to deliver droplets of liquid using a piezoelectric valve to form an aerosol directly or to deliver liquid to the heater. However, piezoelectric valves have significant disadvantages. Piezoelectric valves add even more cost and complexity to the system than liquid retaining materials, and require additional control electronics to be added to the system. The valve consumes additional power, which is an important consideration for battery operated systems. The valve is prone to breakage and clogging. And perhaps most important for electronic cigarette systems, the valve results in a regulated system in which the amount of liquid delivered to produce the aerosol is predetermined, resulting in user frustration. A user who inhales deeper may require a larger amount of aerosol. Ideally, the inhalation or puff range of the user should determine the amount of aerosol delivered, as in a conventional cigarette.

It would be desirable to provide an aerosol-generating system that delivers liquid to a heater without the use of a liquid retaining material, but that does not suffer from the described problems associated with piezoelectric valves.

Disclosure of Invention

In a first aspect, there is provided an aerosol-generating system comprising:

an air inlet and an air outlet;

a liquid storage portion holding a liquid aerosol-forming substrate, the liquid storage portion having a liquid outlet;

an air flow passage from the air inlet through the liquid outlet to the air outlet, wherein the air flow passage is shaped such that there is a pressure drop within the air flow passage at the liquid outlet as air flows from the air inlet through the air flow passage to the air outlet; and

a heating element within the flow path between the liquid outlet and the air outlet.

The system is advantageously configured such that when air flows from the air inlet to the air outlet through the air flow passage, the pressure at the liquid outlet is lower than the pressure within the liquid storage portion. The pressure within the liquid storage portion may be allowed to equalize with atmospheric pressure. The system may be configured to provide a sub-atmospheric pressure at the liquid outlet when air flows from the air inlet to the air outlet through the airflow channel. To provide a pressure drop at the liquid outlet, the airflow channel may have a restricted cross-section at the liquid outlet relative to the air inlet. The restriction of the air flow path causes an increase in air velocity and a decrease in air pressure. This is called the Venturi effect. The reduction in pressure creates a suction at the liquid outlet that draws the liquid out of the liquid outlet into the air stream. The liquid drawn into the gas stream is then carried in the gas stream to the heating element where it is vaporized. The cross-section of the air flow channel at the liquid outlet may also be restricted compared to the air outlet. This arrangement raises the air pressure at the outlet compared to the liquid outlet.

The system may include an aerosol-forming chamber in the airflow passage between the heating element and the air outlet. The aerosol-forming chamber is a space that allows the vaporized aerosol-forming substrate to cool and condense to form an aerosol before exiting the system through the air outlet.

The liquid storage portion provides a sealed housing for the aerosol-forming substrate such that fluid cannot enter or exit the housing other than through the liquid outlet. The sealed housing ensures that the liquid aerosol-forming substrate does not leak out of the liquid storage portion unless it is drawn through the reduced pressure at the liquid outlet as the air flows through the airflow channel. As the liquid is drawn out of the liquid, it creates a low pressure inside the liquid storage portion. The higher pressure of the air outside the liquid storage portion holds the rest of the liquid in the liquid storage portion.

The magnitude of the pressure drop in the airflow passage depends not only on the geometry of the airflow passage, but also on the velocity of the airflow through the airflow passage. Faster gas flow results in a larger pressure drop. A larger pressure drop results in a larger volume of liquid aerosol-forming substrate being drawn into the airflow. Thus, the faster the air flow velocity through the system, the greater the Total Particle Mass (TPM) of the aerosol produced. In a puff actuated system, this means that a user who puffs deeper will receive a greater amount of aerosol than a user who puffs less.

Advantageously, the liquid storage portion contains an air pocket at a pressure lower than atmospheric pressure. Only when the pressure at the liquid outlet is lower than the pressure of the air in the liquid storage portion will liquid be drawn into the air flow channel. The liquid storage portion may be configured such that when air does not flow through the air flow channel from the air inlet to the air outlet, air may enter the liquid storage portion through the liquid outlet to equalize air pressures inside and outside the liquid storage portion. This ensures that as the amount of liquid aerosol-forming substrate in the liquid storage portion decreases, it does not become progressively stiffer to draw liquid into the airflow in the presence of an interruption between periods of airflow, for example between user inhalations.

Alternatively or additionally, the liquid storage portion may include a low pressure release valve that allows air to enter the liquid storage portion when in an open position, but does not allow air when in a closed position. The valve may be configured to move to an open position when a pressure differential across the valve exceeds a pressure threshold. The system may be configured such that the valve is controlled to be in a closed position when a predetermined flow rate of air flows through the airflow channel, such as when a user draws in at the air outlet. The system can be configured such that the valve is in an open position between user puffs to equalize air pressure inside and outside the liquid storage portion.

The liquid storage portion may comprise an annular housing and the gas flow passage may extend through the annular housing. This allows to provide a symmetrical and compact system.

The cross-sectional area of the gas flow channel and the amount by which it is reduced at the liquid outlet can be selected to meet the particular requirements of the system. In a preferred embodiment, the cross-sectional area of the air inlet is 1mm²And 3.5mm²The cross-sectional area of the gas flow passage between the liquid outlet and the liquid outlet is 0.1mm²And 0.9mm²In the meantime. The gas flow passages may have any desired cross-sectional shape, such as circular or oval. The airflow channels may be shaped to promote laminar airflow. Alternatively or additionally, the airflow passage may include an impingement surface to aid in the dispersion of the liquid or aerosol. The airflow passage may be configured to provide a pressure drop of at least 250Pa for typical user suction.

The liquid outlet may be annular and may surround the gas flow channel. Alternatively, the gas flow channel may be annular and may surround the liquid outlet. The size of the liquid outlet has a direct effect on the amount of liquid delivered into the gas flow channel.

The heating element is disposed in the airflow passage. The heating element may span the airflow channel and be fluid permeable such that the airflow must pass through the heating element to reach the air outlet. The heating element may comprise a grid, array or fabric of heater filaments.

Alternatively, the heating element or heaters may surround the gas flow passage or extend partially across the gas flow passage.

The heating element may be operated by resistive heating, wherein an electric current is passed through the heating element to generate heat. Alternatively, the heating element may be inductively heated. Alternatively, the heating element may be heated by heat conduction from another heat source, such as a chemical heat source. The heating element may be part of a heater assembly that includes, for example, electrical contact pads and an electrically insulating substrate.

The material or materials selected for the heating element may depend on its mode of operation. In a preferred embodiment, the heating element is configured to be resistively heated and comprises a mesh, array or fabric of conductive filaments. The conductive filaments may define gaps between the filaments and the width of the gaps may be between 10 μm and 100 μm.

The conductive filaments may form a grid of between 160 and 600Mesh US (+/-10%), i.e. between 160 and 600 filaments per inch (+/-10%). The width of the spaces is preferably between 75 μm and 25 μm. The percentage of the open area of the mesh as the ratio of the area of the gap to the total area of the mesh is preferably between 25% and 56%. The mesh may be formed using different types of weaves or lattice structures. Alternatively, the conductive filaments consist of an array of filaments arranged parallel to each other.

The conductive filaments may have a diameter between 10 μm and 100 μm, preferably between 8 μm and 50 μm and more preferably between 8 μm and 39 μm. The filaments may have a circular cross-section or may have a flat cross-section.

The area of the grid, array or weave of conductive filaments may be small, preferably less than or equal to 25mm²Allowing it to be incorporated into handheld systems. The grid, array or weave of conductive filaments may for example be rectangular and have dimensions of 5mm by 2 mm. Preferably, the grid or array of conductive filaments covers an area between 10% and 50% of the area of the heater assembly. More preferably, the grid or array of conductive filaments covers between 15% and 25% of the area of the heater assembly.

The filaments may be formed by etching a sheet of material, such as foil. This may be particularly advantageous when the heater assembly comprises an array of parallel filaments. If the heating element comprises a mesh or fabric of filaments, the filaments may be formed separately and knitted together.

The filaments of the heating element may be formed of any material having suitable electrical properties. Suitable materials include, but are not limited to: such as ceramic-doped semiconductors, "conductive" ceramics (e.g., molybdenum disilicide), carbon, graphite, metals, metal alloys, and composites made from ceramic and metallic materials. Such composites may include doped or undoped materialsA miscellaneous ceramic. Examples of suitable doped ceramics include doped silicon carbide. Examples of suitable metals include titanium, zirconium, tantalum and platinum group metals. Examples of suitable metal alloys include stainless steel; constantan; nickel-containing alloys, cobalt-containing alloys, chromium-containing alloys, aluminum-containing alloys, titanium-containing alloys, zirconium-containing alloys, hafnium-containing alloys, niobium-containing alloys, molybdenum-containing alloys, tantalum-containing alloys, tungsten-containing alloys, tin-containing alloys, gallium-containing alloys, manganese-containing alloys, and iron-containing alloys; as well as superalloys based on nickel, iron, cobalt, stainless steel,

alloys based on ferro-aluminium and alloys based on ferro-manganese-aluminium.Is a registered trademark of Titanium Metals Corporation. The filaments may be coated with one or more insulators. Preferred materials for the conductive filaments are 304, 316, 304L, 316L stainless steel, and graphite.

The heating assembly may include an electrically insulating matrix on which the wires are supported. The electrically insulating matrix may comprise any suitable material and is preferably a material capable of withstanding high temperatures (in excess of 300 ℃) and rapid changes in temperature. Examples of suitable materials are polyimide films, for exampleThe electrically insulating matrix may have an aperture formed therein, with the conductive filaments extending across the aperture. The heater assembly may include electrical contacts connected to the conductive filaments.

The resistance of the grid, array or weave of conductive filaments of the heater element is preferably between 0.3 ohms and 4 ohms. More preferably, the resistance of the grid, array or weave of conductive filaments is between 0.5 ohms and 3 ohms, and more preferably about 1 ohm. The electrical resistance of the grid, array or weave of conductive filaments is preferably at least one order of magnitude greater than the electrical resistance of the contact portions, and more preferably at least two orders of magnitude greater. This ensures that the heat generated by passing an electric current through the heating element is concentrated to the grid or array of conductive filaments. It is advantageous to have a lower total resistance for the heater element if the system is powered by a battery. The low resistance, high current system allows high power to be delivered to the heater element. This allows the heating element to rapidly heat the conductive filaments to a desired temperature.

The first and second conductive contact portions may be directly fixed to the conductive filaments. The contact portion may be positioned between the conductive filament and the electrically insulating matrix. For example, the contact portion may be formed of a copper foil plated onto an insulating substrate. The contact portion may also bond to the filament more easily than the insulating matrix.

Alternatively, the first and second conductive contact portions may be integral with the conductive filament. For example, the heater element may be formed by etching a conductive sheet to provide a plurality of filaments between two contact portions.

The system can include a filter pad, such as a Cambridge filter pad, downstream of the heating element. The filter mat may be in contact with the heater element. This may help prevent leakage of liquid through the air outlet and may remove any unwanted particulate matter from the aerosol.

The heating element may comprise at least one filament made of a first material and at least one filament made of a second material different from the first material. This may be beneficial for electrical or mechanical reasons. For example, one or more of the filaments may be formed from a material having a resistance that varies significantly with temperature (e.g., an iron-aluminum alloy). This allows the measurement of the resistance of the filament to be used to determine the temperature or change in temperature. This can be used in a puff detection system and can be used to control the heating element temperature to keep it within a desired temperature range. Sudden changes in temperature may also be used as a means of detecting changes in airflow past the heating element as a result of a user sucking the system.

The system may comprise a disposable cartridge portion and a device portion, wherein the cartridge comprises a liquid storage portion. Once the liquid aerosol-forming substrate in the liquid storage portion is exhausted, the cartridge is thrown away and replaced with a new cartridge.

The cartridge may contain a heating element. Alternatively, the heating element may be provided as part of the device.

The system may include a mouthpiece portion configured to be received in a mouth of a user. The air outlet may be in the mouthpiece portion. The mouthpiece portion may be part of the cartridge portion or the device portion, or may include a separate portion. The disposable mouthpiece may be provided as part of the mouthpiece portion. The disposable mouthpiece may be flexible and may simulate the feel of a conventional cigarette filter.

The system may further include a circuit connected to the heating element and to the power source, the circuit being configured to monitor the resistance of the heating element or one or more filaments of the heating element, and to control the supply of power to the heating element in dependence on the resistance of the heating element or one or more filaments.

The circuit may include a microprocessor, which may be a programmable microprocessor. The circuit may also include electronic components. The electrical circuit may be configured to regulate the supply of electrical power to the heating element. Power may be supplied to the heating element continuously after activation of the system or may be supplied intermittently, for example on a puff-by-puff basis. The power may be supplied to the heating element in the form of current pulses.

The system advantageously comprises a power source, typically a battery, within the body of the housing. Alternatively, the power supply may be another form of charge storage device, such as a capacitor. The power source may need to be recharged and may have a capacity to allow storage of sufficient energy for one or more smoking sessions; for example, the power source may have sufficient capacity to allow continuous aerosol generation for a period of about six minutes, corresponding to the typical time taken to smoke a conventional cigarette, or for a period of more than six minutes. In another example, the power source may have sufficient capacity to allow a predetermined number of puffs or discrete activations of the heating element.

Preferably, the aerosol-generating system comprises a housing. Preferably, the housing is elongate. The housing may comprise any suitable material or combination of materials. Examples of suitable materials include metals, alloys, plastics or composites containing one or more of those materials, or thermoplastics suitable for food or pharmaceutical applications, such as polypropylene, Polyetheretherketone (PEEK) and polyethylene. Preferably, the material is lightweight and non-breakable.

Preferably, the aerosol-generating system is portable. The aerosol-generating system may have a size comparable to a conventional cigar or cigarette. The smoking system may have a total length of between about 30mm and about 150 mm. The smoking system may have an outer diameter of between about 5mm and about 30 mm.

An aerosol-forming substrate is a substrate capable of releasing volatile compounds that can form an aerosol. The volatile compounds may be released by heating the aerosol-forming substrate. The aerosol-forming substrate may comprise a plant-based material. The aerosol-forming substrate may comprise tobacco. The aerosol-forming substrate may comprise a tobacco-containing material comprising volatile tobacco flavour compounds which are released from the aerosol-forming substrate when heated. The aerosol-forming substrate may alternatively comprise a tobacco-free material. The aerosol-forming substrate may comprise a homogeneous vegetable material. The aerosol-forming substrate may comprise homogenised tobacco material. The aerosol-forming substrate may comprise at least one aerosol-former. The aerosol former is any suitable known compound or mixture of compounds which, in use, helps to form a dense and stable aerosol and is substantially resistant to thermal degradation at the operating temperature of the system. Suitable aerosol-forming agents are well known in the art and include, but are not limited to: polyhydric alcohols such as triethylene glycol, 1, 3-butanediol and glycerin; esters of polyhydric alcohols, such as glycerol mono-, di-or triacetate; and fatty acid esters of mono-, di-or polycarboxylic acids, such as dimethyldodecanedioate and dimethyltetradecanedioate. Preferred aerosol formers are polyols or mixtures thereof, such as triethylene glycol, 1, 3-butanediol, and most preferably glycerol, such as glycerol or propylene glycol. The aerosol-forming substrate may comprise other additives and ingredients, for example flavourants. In one example, the aerosol-forming substrate comprises a mixture of glycerol, Propylene Glycol (PG), water and flavourings, and nicotine. In a preferred embodiment, the aerosol-forming substrate comprises approximately 40% PG by volume, 40% glycerol by volume, 18% water by volume and 2% nicotine by volume. The matrix has a viscosity of 20 pa.s.

In a second aspect, there is provided a cartridge for an aerosol-generating system, the cartridge comprising:

an air inlet and an air outlet;

a liquid storage portion holding a liquid aerosol-forming substrate, the liquid storage portion having a liquid outlet; and

an air flow passage from the air inlet through the liquid outlet to the air outlet, wherein the air flow passage is shaped such that there is a pressure drop in the air flow passage at the liquid outlet as air flows from the air inlet through the air flow passage to the air outlet.

The cartridge may include a heater element in the airflow path between the liquid outlet and the air outlet. The heater element may be as described with reference to the first aspect of the invention.

The cartridge may include electrical contact portions configured to contact corresponding features on a device with which the cartridge engages to allow electrical current to be supplied to the heating element from a power source in the device.

In a third aspect of the invention there is provided a method of generating an aerosol from a liquid aerosol-forming substrate comprising:

providing a liquid storage portion having a liquid outlet;

providing a gas flow path through the liquid outlet;

drawing the liquid aerosol-forming substrate out of the liquid outlet by creating a pressure drop in the airflow at the liquid outlet, into the airflow in the airflow passage and transporting the liquid in the airflow to a heater element in the airflow passage which vaporises the liquid to give a vapour;

the vapor is cooled to obtain an aerosol.

Features described in relation to one aspect may equally be applied to other aspects of the invention. In particular features of the liquid storage portion, the gas flow channels, heating element and aerosol-forming substrate described in relation to the first aspect may equally be applied to the second and third aspects.

Drawings

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

fig. 1 is a schematic cross-section of a system according to a first embodiment;

FIG. 2 is a cross-section of the cartridge of FIG. 1;

FIG. 3 is an exploded view of the cartridge of FIG. 2; and is

Fig. 4 is a cross-section of the cartridge of fig. 2.

Detailed Description

Figure 1 is a schematic cross-sectional view of an aerosol-generating system according to an embodiment of the invention. The system shown in figure 1 is an electrically operated, hand-held smoking system commonly referred to as an electronic cigarette. The system includes a device 10 and a cartridge 20, which together with a disposable mouthpiece 50 form a smoking system.

The device comprises a housing 12 containing a battery 14 (such as a lithium iron phosphate battery), control electronics 16, a cavity 15 for receiving a portion of a cartridge 20, and an air inlet 18. The device has an annular cross-section and includes a plurality of air inlets 18 disposed around the circumference of the device housing 12. The cavity 15 has threads (not shown) for engaging corresponding threads on the barrel 20. However, it should be clear that many other types of connections between the cartridge and the device may be used. The battery 14 and control electronics 16 provide electrical power to the cartridge via electrical connections (not shown), as will be described. Also, any type of connector may be used for the connector that provides electrical contact between the cartridge and the device, such as a snap-fit, interference fit, or bayonet type connector.

The cartridge 20 is shown engaged with the device 10 of fig. 1, but shown separately and in more detail in fig. 2, 3 and 4.

The cartridge 20 has an outer cartridge housing 21. A liquid storage section 30 having a liquid storage case 34 is provided inside the outer cylinder case 21. The liquid storage portion housing is annular and forms an air flow passage 22 through its center. The air flow passage has an inlet end with a narrowed portion 40 to constrict the air flow passage within the liquid storage housing relative to the air flow through the inlet end. The holes in the inlet plate 41 have a radius of 1mm and the air flow passages in the liquid storage housing have a radius of 0.375 mm.

A reservoir of liquid aerosol-forming substrate is held between the interior and the outer wall of the liquid storage housing 34. The plug 32 extends into the reservoir to define a liquid flow path 36 for the liquid that converges from the reservoir to a liquid outlet 38 in the gas flow channel. The liquid outlet 38 is substantially annular, as best seen in fig. 4. The inner diameter of the liquid outlet at the base of the liquid storage portion was about 1.5mm and the outer diameter of the liquid outlet was about 1.75 mm. A small groove or opening (not shown) is provided in the base of the reservoir to properly locate and ensure that the plug is centered with respect to the reservoir.

The gas flow passage immediately downstream of the liquid outlet is defined by a plug and widens in the divergent portion 42.

The heating element 26 is carried on a plug 32 downstream of the liquid outlet. The heating element was a Mesh formed from 304L stainless steel, with the Mesh size being about 400Mesh US (about 400 filaments per inch). The filaments of the mesh have a diameter of about 16 μm. The mesh is connected to an electrical contact portion 46 formed of copper. The electrical contact portions 32 are provided on a polyimide substrate 44. The filaments forming the lattice define interstices between the filaments. The voids in this example have a width of about 37 μm, although larger or smaller voids may be used. The ratio of the open area of the grid, i.e. the area of the voids, to the total area of the grid is advantageously between 25% and 56%. The total resistance of the heater assembly is about 1 ohm. The mesh provides the majority of this resistance so that most of the heat is generated by the mesh. In this example, the mesh has a resistance that is more than 100 times higher than the electrical contact portion 46.

An aerosol-forming chamber 28 is provided downstream of the heater. The aerosol-forming chamber 28 is a region in which vapour from the heater can cool and condense to form an aerosol before exiting the air outlet 24 into the user's mouth.

As can be seen most clearly in fig. 3, the outer cartridge housing is formed in two parts to permit assembly. The lower cartridge housing 21a supports the liquid storage portion, the plug and the heater assembly. The upper cartridge housing 21b defines the mouthpiece portion of the cartridge and holds the aerosol-forming chamber and the air outlet 24. The disposable mouthpiece 50 is placed around the upper cartridge housing as shown in figure 1. The upper and lower cartridge housings are secured to each other by a pair of threaded bolts 23 and corresponding nuts (not shown).

The cartridge housing and the device housing may comprise any suitable material or combination of materials. In this example, polypropylene, Polyetheretherketone (PEEK) is used.

The removable mouthpiece 50 may simulate the filter of a conventional cigarette in appearance and feel. For example, the removable mouthpiece 50 may be formed of cellulose acetate, rubber or plastic (such as polyethylene or polypropylene or a mixture of the two) and may be covered with a paper layer.

In operation, when a user draws on the mouthpiece portion, air is drawn from the air inlet 18 through the airflow channel to the air outlet 24. Air is drawn through the airflow passage, through the liquid outlet, through the heater to the aerosol-forming chamber. The pressure of the air stream at the liquid outlet is lower than atmospheric pressure and critically lower than the pressure of the air 35 within the liquid storage portion. This pressure difference causes the liquid aerosol-forming substrate to be drawn out of the liquid outlet into the airflow channel.

The approximate volume of liquid drawn into the gas stream from the liquid outlet can be calculated using poisson's equation. For the purpose of calculation, a 1 second puff volume of 40ml is considered.

The velocity of the air passing through the amorphous and constricted sections of the airflow passage is calculated as follows:

speed of rotation₍₂₎：(40mm³*10³)/[3.14*(1mm)²]＝12.7*10³mm/s

Speed of rotation₍₁₎：(40mm³*10³)/[3.14*(0.375mm)²]＝90*10³mm/s

From these velocities, the pressure difference can be calculated:

P₂-P₁＝ρ/2(ν₂ ²-ν₁ ²)＝1/2(90²-12.7²) About 4000kg mm^-1s^-2

In this example, the droplets originate from a circular tube with a width of 0.25mm, and we can estimate their "area equivalent" with respect to the cartridge by multiplying the circumference of the ring (2 × pi r ═ 2 × pi × 1mm) by its width of 0.25 mm:

approximate (liquid-transmissive) area 2 π r width 2 3.14 1 0.25mm 1.57mm²

Thus, the approximate "radial equivalent" for purposes of estimating liquid transfer is:

(1.57/π)^0.5＝0.75mm

the liquid viscosity of the liquid aerosol-forming substrate may be estimated from the composition of the liquid, which in this example is:

PG (52%), glycerol (20%), water (15%) and nicotine (5%)

Approximately: 0.6 × 52+0.2 × 1.4+0.15 × 1.0022+0.05 × 1.004 ═ 32Pa s

Finally, the liquid transfer can be calculated using the differential pressure (Δ Ρ), the radial equivalent weight (r), the liquid viscosity (μ), and the length of the liquid flow path (L):

Q＝(ΔP*πr⁴)/(8μL)＝[4000*π*(0.75*10^-3)⁴](8X 32X 14) ═ 0.8mm³s^-1And 1mm³s^-1In the meantime.

It can be seen that the key parameters for determining the drop transfer volume are the surface area of the liquid outlet in the cartridge, the pressure drop at the liquid outlet and the length of the liquid flow path. The liquid flow path is limited to some extent by the overall length of the cartridge and for a handheld system will desirably be between 10mm and 30 mm. It can also be seen from this equation that the viscosity of the liquid aerosol-forming substrate is also an important factor, so that if the viscosity of the liquid increases, the size of the liquid outlet and/or the liquid path will need to be changed in order to achieve the same liquid transfer.

The liquid aerosol-forming substrate in the airflow is conveyed to the mesh heating element. A mesh heating element which may be activated in response to sensed user puff vaporises the liquid aerosol-forming substrate as it contacts or passes through the heating element. The vaporized substrate and heated air are then passed into an aerosol-forming chamber where they are cooled to form an aerosol. The aerosol is then drawn out of the air outlet 24 and into the user's mouth.

As the user draws on the system and liquid out of the liquid storage portion, the pressure inside the liquid storage portion drops. In order to provide consistent liquid transfer between aspirations, it is advantageous to allow the pressure inside the liquid storage portion to return to its original pressure, typically atmospheric pressure, between aspirations. The liquid outlet may be large enough to allow gas bubbles to pass through the liquid outlet into the liquid storage portion between puffs. Alternatively, a pressure relief valve 48 may be included in the liquid storage portion that opens when the pressure differential between the interior of the liquid storage portion and the exterior of the liquid storage portion exceeds a threshold pressure differential. This is illustrated in fig. 2 and 3. The pressure relief valve 48 may be controlled to remain closed during each user puff.

The system as described has several advantages over previous systems. It is a mechanically robust system that does not require a heater to be wrapped around the flexible infiltration material. Which eliminates the possibility of burning or charring of the capillary material in contact with the heating element. Which eliminates the need for liquid retaining materials and thus reduces manufacturing costs and manufacturing steps. It also eliminates the potential aerosol discoloration problem found with capillary-based systems, while the liquid is depleted and the amount of liquid delivered to the heating element is reduced, similar to the discoloration of a marker pen.

It is energy efficient when compared to piezo-based delivery systems because it uses the reduced pressure that occurs during pumping to deliver the droplets to the heater. It also allows the pumping action of the user to control the amount of liquid delivered, rather than dosing the amount of liquid through a piezoelectric valve.

The exemplary embodiments described above are illustrative and not restrictive. In view of the exemplary embodiments described above, those of ordinary skill in the art will now appreciate other embodiments consistent with the above exemplary embodiments. For example, the embodiments described are electrically operated smoking systems, but the invention may be applied to any type of aerosol-generating system, and different liquid and airflow geometric arrangements may be used.