Aerosol-generating system using venturi effect to deliver substrate to heating element

Abstract

To provide an aerosol-generating system in which aerosol is generated by vaporizing a liquid substrate using a heater.SOLUTION: An aerosol-generating system comprising: an air inlet; an air outlet 24; a liquid storage portion that holds a liquid aerosol-forming substrate and has a liquid outlet; an air flow passage 22 from the air inlet to the air outlet past the liquid outlet, the air flow passage being shaped so that there is a pressure drop within the air flow passage at the liquid outlet when air flows from the air inlet to the air outlet through the air flow passage; and a heating element 26 within the air flow passage, positioned between the liquid outlet and the air outlet. The system is advantageously configured so that when air flows from the air inlet to the air outlet through the air flow passage, pressure at the liquid outlet is lower than pressure within the liquid storage portion. Thereby, liquid is drawn out of the liquid storage portion into an airflow and is delivered to the heating element for vaporization.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an aerosol generating system that generates an aerosol by vaporizing a liquid substrate using a heater. [Background technology]

[0002] One type of aerosol generating system is the electronic cigarette. Electronic cigarettes generally operate by heating a liquid aerosol-forming substrate to generate vapor. The vapor is then cooled to form an aerosol. Many electronic cigarette systems use some form of liquid-retaining material, such as a sponge or wicking material, to hold the liquid aerosol-forming substrate and deliver it to the heater. In such systems, there are several problems associated with the liquid-retaining material. As the liquid-retaining material dries, less liquid is delivered to the heater, resulting in less aerosol being delivered. Also, as the liquid-retaining material dries, it becomes more susceptible to charring or burning. This can result in undesirable compounds in the generated aerosol. Additionally, the liquid-retaining material adds cost and complexity to the manufacturing process.

[0003] One proposed solution for delivering liquid to a heater without the need for a liquid retainer is to use a piezoelectric valve to deliver droplets of liquid to form an aerosol directly or to deliver the liquid to a heater. However, piezoelectric valves have major drawbacks. Compared to liquid retainers, piezoelectric valves increase the cost and system complexity, and require additional control electronics to be added to the system. Valves consume additional power, which is a significant issue for battery-operated systems. Valves are prone to breakage and clogging. And, perhaps most importantly for e-cigarette systems, the valves result in a regulated system in which the amount of liquid delivered to generate aerosol is predetermined, leading to user frustration. Users who inhale more deeply may desire a larger amount of aerosol. Ideally, the amount of aerosol delivered should be determined by the user's inhalation or smoking style, as in traditional cigarettes.

[0004] 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 have the above-mentioned problems associated with piezoelectric valves. Summary of the Invention

[0005] In a first aspect, there is provided an aerosol generation system comprising: an air inlet and an air outlet; a liquid reservoir for holding a liquid aerosol-forming substrate, the liquid reservoir having a liquid outlet; an airflow passage from the air inlet to the air outlet through the liquid outlet, the airflow passage shaped such that as air flows through the airflow passage from the air inlet to the air outlet, there is a pressure drop within the airflow passage at the liquid outlet; a heater element within the flow passageway disposed between the liquid outlet and the air outlet.

[0006] The system is advantageously configured such that when air flows through the air flow passage from the air inlet to the air outlet, the pressure at the liquid outlet is lower than the pressure in the liquid storage portion. The pressure in the liquid storage portion may be equal to atmospheric pressure. The system may be configured to provide a pressure at the liquid outlet that is lower than atmospheric pressure when air flows through the air flow passage from the air inlet to the air outlet. To provide a pressure drop at the liquid outlet, the air flow passage may have a reduced cross section at the liquid outlet compared to the air inlet. Restricting the air flow passage increases the air velocity and reduces the air pressure. This is called the Venturi effect. The reduced pressure creates a suction force at the liquid outlet, drawing the liquid from the liquid outlet into the air flow. The liquid drawn into the air flow is then carried by the air flow to the heater element where it is vaporized. Also, the cross section of the air flow passage at the liquid outlet may be reduced compared to the air outlet. This arrangement increases the pressure of the air at the air outlet compared to the liquid outlet.

[0007] The system may include an aerosol-forming chamber in the airflow passage between the heater element and the air outlet, the aerosol-forming chamber being a space that allows the vaporized aerosol-forming substrate to cool and condense to form an aerosol that then exits the system via the air outlet.

[0008] The liquid reservoir provides a closed container for the aerosol-forming substrate, such that fluid cannot flow into or out of the container except through the liquid outlet. The closed container ensures that as air flows through the air flow passage, the liquid aerosol-forming substrate will not leak out of the liquid reservoir unless it is drawn out by a pressure drop at the liquid outlet. As liquid is drawn out of the liquid outlet, a pressure drop is created within the liquid reservoir. The higher air pressure outside the liquid reservoir causes the remaining liquid to remain in the liquid reservoir.

[0009] The magnitude of the pressure drop in the airflow passage depends not only on the geometry of the airflow passage, but also on the speed of the airflow through the airflow passage. Faster airflow results in a larger pressure drop. A larger pressure drop results in a larger amount of liquid aerosol-forming substrate being drawn into the airflow. Thus, the faster the airflow velocity through the system, the higher the total particle mass (TPM) of the aerosol generated. In a puff-actuated system, this means that a user who takes a deeper puff will get a larger amount of aerosol than a user who takes a shallower puff.

[0010] Advantageously, the liquid storage portion contains an air pocket at a pressure lower than atmospheric pressure. Liquid will only be drawn into the airflow passage if the pressure at the liquid outlet is lower than the pressure of the air in the liquid storage portion. The liquid storage portion may be configured such that air can flow into the liquid storage portion through the liquid outlet when air is not flowing from the air inlet to the air outlet through the airflow passage to equalize the air pressure inside the liquid storage portion with the air pressure outside the liquid storage portion. This ensures that if there is a break in the cycle of airflow, for example between user inhalations, it does not become increasingly difficult to draw liquid into the airflow as the amount of liquid aerosol-forming substrate in the liquid storage portion decreases.

[0011] Alternatively or additionally, the liquid storage portion may include a low pressure release valve that allows air to flow into the liquid storage portion when in an open position and prevents air from flowing into the liquid storage portion when in a closed position. The valve may be configured to move to the 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 the closed position when a predetermined flow rate of air flows through the air flow passage, such as when a user is taking a puff from the air outlet. The system may be configured such that the valve is in the open position to equalize air pressure inside the liquid storage portion and air pressure outside the liquid storage portion between the user's puffs.

[0012] The liquid reservoir may include an annular housing and the air flow passage may extend through the annular housing, thereby providing a symmetrical and compact system.

[0013] The cross-sectional area of ​​the air flow passage and the amount by which it is reduced at the liquid outlet may be selected to suit the particular requirements of the system. In a preferred embodiment, the cross-sectional area of ​​the air inlet is less than 1 mm 2 ~3.5 mm 2 and the cross-sectional area of ​​the air flow passage at the liquid outlet is 0.1 mm 2 ~0.9 mm 2 The airflow passages may have any desired cross-sectional shape, such as circular or elliptical. The airflow passages may be shaped to promote laminar airflow. Alternatively, or in addition, the airflow passages may include an impingement surface to promote dispersion of the liquid or aerosol. The airflow passages may be configured to provide a pressure drop of at least 250 Pa for a typical user puff.

[0014] The liquid outlet may be annular and surround the airflow passage, or the airflow passage may be annular and surround the liquid outlet. The size of the liquid outlet has a direct effect on the amount of liquid delivered into the airflow passage.

[0015] A heater element is disposed within the airflow passage. The heater element spans the airflow passage and may be fluid permeable such that airflow must pass through the heater element to the air outlet. The heater element may include a mesh, array, or fiber of heater filaments.

[0016] Alternatively, the heater element or elements may surround or extend partially across the airflow passage.

[0017] The heater element may operate by resistive heating, where an electrical current is passed through the heater element to generate heat. Alternatively, the heater element may be inductively heated. Alternatively, the heater element may be heated by thermal conduction from another heat source, such as a chemical heat source. The heater element may be part of a heater assembly that includes, for example, electrical contact pads and an electrically insulated substrate.

[0018] The material(s) selected for the heater element may depend on its mode of operation. In a preferred embodiment, the heater element is configured to be resistively heated and includes a mesh, array, or fiber of conductive filaments. The conductive filaments may define gaps between the filaments, and the gaps may be between 10 μm and 100 μm wide.

[0019] The conductive filaments may form a mesh with a size of 160-600 mesh US (±10%) (i.e. 160-600 filaments per inch (±10%)). The gap width is preferably 25 μm-75 μm. The open area fraction of the mesh, which is the ratio of the gap area to the total area of ​​the mesh, is preferably 25-56%. The mesh may be formed using different types of weaves or lattice structures. Alternatively, the conductive filaments consist of an array of filaments aligned parallel to one another.

[0020] The diameter of the conductive filaments may be between 10 μm and 100 μm, preferably between 8 μm and 50 μm, more preferably between 8 μm and 39 μm. The filaments may have a round or flat cross section.

[0021] The area of ​​the mesh, array or fibre of conductive filaments can be small, up to 25 mm 2Preferably, the conductive filament mesh, array or fiber has a thickness of less than 10 mm to allow for incorporation into a handheld system. The conductive filament mesh, array or fiber may be rectangular, for example, with dimensions of 5 mm by 2 mm. Preferably, the conductive filament mesh or array covers an area of ​​10% to 50% of the area of ​​the heater assembly. More preferably, the conductive filament mesh or array covers an area of ​​15% to 25% of the area of ​​the heater assembly.

[0022] The filaments may be formed by etching a sheet material (such as a foil). This may be particularly advantageous when the heater assembly comprises an array of parallel filaments. Where the heater element comprises a mesh or fiber of filaments, the filaments may be formed individually and woven together.

[0023] The heater element filaments may be formed from any material having suitable electrical properties. Suitable materials include, but are not limited to, semiconductors such as doped ceramics, "conductive" ceramics (e.g., molybdenum disilicide, etc.), carbon, graphite, metals, alloys, and composites made of ceramic and metallic materials. Such composites may include doped or undoped ceramics. Examples of suitable doped ceramics include doped silicon carbide. Examples of suitable metals include titanium, zirconium, tantalum, and platinum group metals. Examples of suitable alloys include stainless steel, constantan, nickel-, cobalt-, chromium-, aluminum-titanium-zirconium-, hafnium-, niobium-, molybdenum-, tantalum-, tungsten-, tin-, gallium-, manganese-, and iron-containing alloys, and nickel, iron, cobalt, stainless steel-based superalloys, Timetal®, iron-aluminum-based alloys, and iron-manganese-aluminum-based alloys. Timetal® 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.

[0024] The heater assembly may include an electrically insulating substrate on which the filaments are supported. The electrically insulating substrate may include any suitable material, but is preferably a material that can withstand high temperatures (greater than 300° C.) and rapid temperature changes. One example of a suitable material is a polyimide film, such as Kapton®. The electrically insulating substrate may have an opening formed therein, with the conductive filaments extending across the opening. The heater assembly may include electrical contacts connected to the conductive filaments.

[0025] The electrical resistance of the mesh, array or fiber of conductive filaments of the heater element is preferably 0.3-4 ohms. More preferably, the electrical resistance of the mesh, array or fiber of conductive filaments is 0.5-3 ohms, and more preferably about 1 ohm. The electrical resistance of the mesh, array or fiber of conductive filaments is preferably at least one order of magnitude greater than the electrical resistance of the contacts, and more preferably at least two orders of magnitude greater. This ensures that the heat generated by passing a current through the heater element is localized in the mesh or array of conductive filaments. When the system is powered by a battery, it is advantageous for the heater element to have a low overall resistance. A low resistance, high current system allows high power to be delivered to the heater element. This allows the heater element to heat the conductive filaments quickly to the desired temperature.

[0026] The first and second conductive contact portions may be secured directly to the conductive filament. The contact portions may be disposed between the conductive filament and an electrically insulating substrate. For example, the contact portions may be formed from copper foil plated onto an insulating substrate. The contact portions may also be more easily bonded to the filament than to the insulating substrate.

[0027] 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 the two contact portions.

[0028] The system may include a filter pad, such as a Cambridge filter pad, downstream of the heater element, which may be in contact with the heater element to help prevent liquid from leaking through the air outlet and to help remove any undesirable particulate matter from the aerosol.

[0029] The heater element may comprise at least one filament made from a first material and at least one filament made from 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, such as an iron-aluminium alloy. This allows a measurement of the resistance of the filament to be used to determine temperature or temperature changes. This may be used within a puff detection system and for temperature control of the heater element to keep it within a desired temperature range. Sudden changes in temperature may also be used as a means of detecting changes in airflow through the heater element due to a puff by a user of the system.

[0030] The system may include a disposable cartridge portion and a device portion, the cartridge including a liquid reservoir portion, when the liquid aerosol-forming substrate in the liquid reservoir portion is depleted, the cartridge is discarded and replaced with a new cartridge.

[0031] The cartridge may include a heater element, or the heater element may be provided as part of the device.

[0032] The system may include a mouthpiece portion configured to be received in a user's mouth. The air outlet may be in the mouthpiece portion. The mouthpiece portion may be part of the cartridge portion or part of the device portion, or may comprise a separate portion. A disposable mouthpiece may be provided as part of the mouthpiece portion. The disposable mouthpiece may be flexible and may mimic the feel of a conventional cigarette filter.

[0033] The system may further include an electrical circuit connected to the heater element assembly and to the power source, the electrical circuit configured to monitor an electrical resistance of the heater element or of one or more filaments of the heater element and control the supply of power to the heater element depending on the electrical resistance of the heater element or the electrical resistance of the one or more filaments.

[0034] The electrical circuitry may comprise a microprocessor, which may be a programmable microprocessor. The electrical circuitry may comprise further electronic components. The electrical circuitry may be configured to regulate the supply of power to the heater element. Power may be supplied to the heater element continuously after activation of the system, or intermittently, such as with each puff. Power may be supplied to the heater element in the form of current pulses.

[0035] The system advantageously includes a power source, typically a battery, within the body of the housing. Alternatively, the power source may be another form of charge storage device, such as a capacitor. The power source may require recharging and may have a capacity that allows for storage of sufficient energy for one or more smoking experiences. For example, the power source may have a capacity sufficient to allow for continuous generation of aerosol for approximately six minutes, or a multiple of six minutes, corresponding to the typical time it takes to smoke one conventional cigarette. In another example, the power source may have a capacity sufficient to allow for a predetermined number of puffs, or discontinuous activation of the heater element.

[0036] The aerosol generating system preferably includes a housing. The housing is preferably elongated. The housing may include any suitable material or combination of materials. Examples of suitable materials include metals, alloys, plastics or composites containing one or more of these materials, or thermoplastics suitable for food or pharmaceutical applications, such as, for example, polypropylene, polyetheretherketone (PEEK) and polyethylene. The material is preferably lightweight and not brittle.

[0037] The aerosol generating system is preferably portable. The aerosol generating system may have a size comparable to a conventional cigar or cigarette. The overall length of the smoking system may be from about 30 mm to about 150 mm. The outer diameter of the smoking system may be from about 5 mm to about 30 mm.

[0038] The aerosol-forming substrate is a substrate capable of releasing volatile compounds capable of forming an aerosol. The volatile compounds may be released upon heating of the aerosol-forming substrate. The aerosol-forming substrate may comprise a plant-derived material. The aerosol-forming substrate may comprise tobacco. The aerosol-forming substrate may comprise a tobacco-containing material comprising volatile tobacco flavour compounds that are released from the aerosol-forming substrate upon heating. Alternatively, the aerosol-forming substrate may comprise a non-tobacco-containing material. The aerosol-forming substrate may comprise a homogenised plant-derived material. The aerosol-forming substrate may comprise a 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 that, in use, facilitates the formation of a dense and stable aerosol and is substantially resistant to thermal decomposition at the operating temperature of the system. Suitable aerosol formers 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 monoacetate, diacetate, or triacetate), and aliphatic esters of mono-, di-, or polycarboxylic acids (such as dimethyl dodecanedioate and dimethyl tetradecanedioate). Preferred aerosol formers are polyhydric alcohols or mixtures thereof (e.g., triethylene glycol, 1,3-butanediol, and most preferably glycerin or propylene glycol, such as glycerin). The aerosol-forming substrate may include other additives and ingredients, such as flavoring agents. In one example, the aerosol-forming substrate includes a mixture of glycerin, propylene glycol (PG), water, and flavoring agents, and nicotine. In a preferred embodiment, the aerosol-forming substrate includes about 40% PG by volume, about 40% glycerin by volume, about 18% water, and about 2% nicotine by volume. The viscosity of this substrate is 20 Pa·s.

[0039] In a second aspect, there is provided a cartridge for use in an aerosol generation system, the cartridge comprising: an air inlet and an air outlet; a liquid reservoir for holding a liquid aerosol-forming substrate, the liquid reservoir having a liquid outlet; an airflow passage from the air inlet to the air outlet through the liquid outlet, the airflow passage shaped such that there is a pressure drop in the airflow passage at the liquid outlet as air flows through the airflow passage from the air inlet to the air outlet.

[0040] The cartridge may include a heater element in the air flow passage between the liquid outlet and the air outlet. The heater element may be as described with reference to the first aspect of the invention.

[0041] The cartridge may include electrical contacts configured to contact corresponding features on the device that engage to enable electrical current to be supplied to the heater element from a power source on the device.

[0042] In a third aspect of the present invention, there is provided a method of generating an aerosol from a liquid aerosol-forming substrate, the method comprising: providing a liquid storage portion having a liquid outlet; providing an air flow passage through the liquid outlet; drawing a liquid aerosol-forming substrate from the liquid outlet into an airflow in the airflow passage by creating a pressure drop in the airflow at the liquid outlet, and conveying the liquid in the airflow to a heater element in the airflow passage, the heater element vaporizing the liquid to provide a vapor; and cooling the vapor to provide an aerosol.

[0043] Features described in relation to one embodiment may be equally applied to the other embodiments of the invention, in particular the features of the liquid reservoir, air flow passages, heater element and aerosol-forming substrate described in relation to the first embodiment may be equally applied to the second and third embodiments. Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: [Brief description of the drawings]

[0044] [Figure 1] FIG. 1 is a schematic cross-sectional view of a system according to a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the cartridge of FIG. [Diagram 3] FIG. 3 is an exploded view of the cartridge of FIG. [Figure 4] FIG. 4 is a cross-sectional view of the cartridge of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Figure 1 is a schematic cross-sectional view of an aerosol generation system according to one embodiment of the present invention. The system shown in Figure 1 is an electrically operated, hand-held smoking system, often referred to as an e-cigarette. The system includes a device 10 and a cartridge 20, which together with a disposable mouthpiece 50 form a smoking system.

[0046] The device includes a housing 12 with a battery 14, such as a lithium iron phosphate battery, control electronics 16, a cavity 15 that receives a portion of a cartridge 20, and an air inlet 18. The device has a circular cross section and includes a plurality of air inlets 18 arranged around the circumference of the device housing 12. The cavity 15 has threads (not shown) that engage corresponding threads on the cartridge 20. However, it will be apparent that many other styles of connection between the cartridge and the device may be used. The battery 14 and control electronics 16 provide power to the cartridge through electrical connections (not shown), as described below. Also, any style of connection, such as a snap-fit ​​connection, an interference-fit connection, or a bayonet connection, may be used to provide electrical contact between the cartridge and the device.

[0047] Cartridge 20 is shown engaged with device 10 in FIG. 1, but is shown separately and in greater detail in FIGS. 2, 3, and 4.

[0048] The cartridge 20 has an outer cartridge housing 21. A liquid storage portion 30 with a liquid storage housing 34 is provided inside the outer cartridge housing 21. The liquid storage portion housing is annular with an air flow passage 22 formed through its center. The air flow passage has an inlet end with a narrowed portion 40 narrowing the air flow passage within the liquid storage housing for air flow through the inlet end. The orifice in the inlet plate 41 has a radius of 1 mm and the air flow passage within the liquid storage housing has a radius of 0.375 mm.

[0049] A reservoir of liquid aerosol-forming substrate is contained between the inner and outer walls of a liquid storage housing 34. A plug 32 extends into the reservoir to define a constricted liquid flow path 36 for the liquid from the reservoir to a liquid outlet 38 in the air flow passage. The liquid outlet 38 is substantially annular, as shown most clearly in FIG. 4. The inner diameter of the liquid outlet at the base of the liquid storage portion is about 1.5 mm and the outer diameter of the liquid outlet is about 1.75 mm. A small slot or opening (not shown) is provided in the base of the reservoir to properly position the plug and ensure that it is centered relative to the reservoir.

[0050] The air flow passage immediately downstream of the liquid outlet is defined by a plug and widens at a diverging section 42 .

[0051] The heater element 26 is supported on a plug 32 downstream of the liquid outlet. The heater element comprises a mesh formed from 304L stainless steel with a mesh size of about 400 mesh US (about 400 filaments per inch). The filaments of the mesh have a diameter of about 16 μm. The mesh is connected to electrical contacts 46 formed of copper. The electrical contacts 32 are provided on a polyimide substrate 44. The filaments forming the mesh define gaps between the filaments. In this example, the gaps have a width of about 37 μm, but larger or smaller gaps may be used. The ratio of the open area of ​​the mesh, i.e. the area of ​​the gaps to the total area of ​​the mesh, 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, as most of the heat is generated by the mesh. In this example, the mesh has an electrical resistance more than 100 times higher than the electrical contacts 46.

[0052] Provided downstream from the heater is an aerosol formation chamber 28. The aerosol formation chamber 28 is an area where vapor from the heater can be cooled and condensed to form an aerosol that can then flow through the air outlet 24 to the user's mouth.

[0053] As shown most clearly in Figure 3, the outer cartridge housing is formed of two assembleable parts. The lower cartridge housing 21a supports the liquid reservoir, bung and heater assembly. The upper cartridge housing 21b defines the mouthpiece portion of the cartridge and holds the aerosol formation chamber and air outlet 24. A disposable mouthpiece 50 is disposed about the upper cartridge housing as shown in Figure 1. The upper and lower cartridge housings are secured together by a pair of threaded bolts 23 and corresponding nuts (not shown).

[0054] The cartridge housing and device housing may comprise any suitable material or combination of materials, in this example polypropylene, polyetheretherketone (PEEK) is used.

[0055] The removable mouthpiece 50 may mimic the look and feel of a traditional cigarette filter. For example, the removable mouthpiece 50 may be formed from cellulose acetate, rubber, or plastic (such as polyethylene or polypropylene, or a mixture of both) and may be covered with a layer of paper.

[0056] In operation, as a user draws on the mouthpiece portion, air is drawn through the air flow passage from the air inlet 18 to the air outlet 24. The air is drawn via the air flow passage through the liquid outlet, past the heater and to the aerosol-forming chamber. The pressure of the air flow at the liquid outlet is less than atmospheric pressure and, importantly, less than the pressure of the air 35 in the liquid storage portion. The pressure differential causes the liquid aerosol-forming substrate to be drawn from the liquid outlet into the air flow passage.

[0057] The approximate volume of liquid drawn from the liquid outlet into the air stream can be calculated using the Poiseuille equation. For the purposes of the calculation, consider a 40 ml puff per second.

[0058] The velocity of air flowing through the unconstricted and constricted sections of the airflow passage is calculated as follows: speed (2) :(40mm 3 * 10 3 ) / [3.14 * (1 mm) 2 ] = 12.7 * 10 3 mm / s speed (1) :(40mm 3 * 10 3 ) / [3.14 * (0.375 mm) 2 ] = 90 * 10 3 mm / s

[0059] From these velocities the pressure difference can be calculated. P 2 -P 1 = ρ / 2 (ν 2 2 - ν 1 2 ) = 1 / 2 (90 2 - 12.7 2 ) = approx. 4000 kg mm -1 s -2 In this example, the liquid droplet emerges from a circular tube having a width of 0.25 mm, and its "area equivalent" for the cartridge can be estimated by multiplying the circumference of the tube (2*π*r = 2 * π * 1 mm) by the width of 0.25 mm. Approximate area (liquid discharge amount) = 2πr * width = 2 * 3.14 * 1 * 0.25mm = 1.57 mm 2

[0060] Therefore, the approximate "radius equivalent" for estimating the liquid ejection amount is as follows: (1.57 / π) 0.5 = 0.75 mm

[0061] The liquid viscosity of the liquid aerosol-forming substrate can be estimated from the composition of the liquid, in this example: PG (52%), glycerin (20%), water (15%), and nicotine (5%). A rough estimate would be: 0.6 * 52 + 0.2 * 1.4 + 0.15*1.0022 + 0.05 * 1.004 = 32 Pa s

[0062] Finally, the liquid output can be calculated using the pressure difference (ΔP), the equivalent radius (r), the liquid viscosity (μ), and the liquid flow path length (L). Q = (ΔP*πr 4 ) / (8μ L) = [4000* π*(0.75 * 10 -3 ) 4] / (8 * 32 * 14) = 0.8 mm 3 s -1 ~1 mm 3 s -1

[0063] It can be suggested that the main parameters for calculating the volume of droplet ejection are the surface area of ​​the cartridge liquid outlet, 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 total length of the cartridge, but for a handheld system, it would be desirable to have a length of 10 mm to 30 mm. This formula also shows that the viscosity of the liquid aerosol-forming substrate is an important factor, and if the liquid viscosity is increased to obtain the same liquid ejection volume, it will be necessary to change the dimensions of the liquid outlet and / or the dimensions of the liquid flow path.

[0064] The liquid aerosol-forming substrate within the air stream is carried to a mesh heater element which may be activated by a user's puff, causing the liquid aerosol-forming substrate to vaporize as it contacts or passes through the heater element. The vaporized substrate and heated air then pass through an aerosol-forming chamber where it cools to form an aerosol. The aerosol is then drawn through air outlet 24 and into the user's mouth.

[0065] As the user puffs on the system and liquid is drawn from the liquid reservoir, the pressure in the liquid reservoir drops. In order to provide a consistent liquid output per puff, it is advantageous to allow the pressure in the liquid reservoir to return to its initial pressure, typically atmospheric pressure, between puffs. The liquid outlet may be large enough to allow air bubbles to flow through the liquid outlet into the liquid reservoir between puffs. Alternatively, a pressure relief valve 48 may be included in the liquid reservoir, which opens when the pressure difference between the inside of the liquid reservoir and the outside of the liquid reservoir exceeds a threshold pressure difference. The pressure relief valve 48 is illustrated in Figures 2 and 3. The pressure relief valve 48 may be controlled to remain closed between each puff by the user.

[0066] The described system has several advantages over conventional systems. It is a mechanically robust system that does not require wrapping a heater around a flexible wicking material. It eliminates the possibility of charring or burning of the capillary material in contact with the heater element. It reduces manufacturing costs and steps by eliminating the need for a liquid retaining material. It also eliminates the problem of aerosol taper found in capillary systems where the amount of liquid delivered to the heater element decreases as the liquid is depleted, similar to the taper of a felt tip pen.

[0067] Compared to piezoelectric delivery systems, the present system is more energy efficient because it uses the pressure release that occurs during a puff to deliver droplets of liquid to the heater, and instead of the amount of liquid delivered being regulated by a piezoelectric valve, the amount of liquid can be controlled by the user's puff action. The above exemplary embodiments are illustrative and not limiting. In light of the exemplary embodiments discussed above, other embodiments consistent with the above exemplary embodiments will now be apparent to those skilled in the art. For example, although the described embodiment is an electrically operated smoking system, the present invention may be applied to any type of aerosol generating system, and different liquid and airflow arrangements may be used.

Claims

1. 1. An aerosol generation system comprising: an air inlet and an air outlet; a liquid reservoir for holding a liquid aerosol-forming substrate, the liquid reservoir having a liquid outlet; an airflow passage from the air inlet to the air outlet through the liquid outlet, the airflow passage shaped such that there is a pressure drop within the airflow passage at the liquid outlet as air flows through the airflow passage from the air inlet to the air outlet; a heater element within the flow passage disposed between the liquid outlet and the air outlet.

2. 2. The aerosol generation system of claim 1, wherein the air flow passage has a reduced cross-section at the liquid outlet compared to the air inlet.

3. 3. The aerosol generating system of claim 1 or claim 2, wherein the liquid storage portion provides a sealed container for the aerosol-forming substrate such that fluid cannot flow into or out of the container except through the liquid outlet.

4. 4. The aerosol generation system of claim 1, wherein the liquid storage portion includes an air inlet valve that allows air to flow into the liquid storage portion when the valve is in an open position and prevents air from flowing into the liquid storage portion when the valve is in a closed position.

5. 5. The aerosol generation system of claim 4, wherein the system is configured such that the valve is controlled to a closed position when a predetermined flow rate of air flows through the air flow passage.

6. 6. The aerosol generation system of claim 1, wherein the liquid storage portion comprises an annular housing and the air flow passage extends through the annular housing.

7. 7. The aerosol generating system of claim 1, wherein the liquid outlet is annular.

8. 8. The aerosol generating system of claim 1, wherein the heater element spans the airflow passage and is fluid permeable.

9. 9. The aerosol generating system of claim 8, wherein the heater element comprises a mesh, array, or fiber of heater filaments.

10. 10. The aerosol generation system of claim 1, further comprising a power source connected to the heater element, the heater element being resistively heated during operation.

11. 11. An aerosol generation system according to any one of claims 1 to 10, comprising a disposable cartridge and a device, the cartridge containing the liquid storage portion.

12. The aerosol generation system of claim 11 , wherein the cartridge contains the heater element.

13. 1. A cartridge for use in an aerosol generation system, comprising: an air inlet and an air outlet; a liquid reservoir for holding a liquid aerosol-forming substrate, the liquid reservoir having a liquid outlet; an airflow passage through the liquid outlet from the air inlet to the air outlet, the airflow passage shaped such that there is a pressure drop in the airflow passage at the liquid outlet as air flows through the airflow passage from the air inlet to the air outlet.

14. 14. The cartridge of claim 13, further comprising a heater element in the air flow passage between the liquid outlet and the air outlet.

15. 1. A method for generating an aerosol from a liquid aerosol-forming substrate, comprising: providing a liquid reservoir having a liquid outlet; providing an air flow passage through said liquid outlet; drawing a liquid aerosol-forming substrate from the liquid outlet into the airflow of the airflow passage by creating a pressure drop in the airflow at the liquid outlet, and conveying liquid in the airflow to a heater element in the airflow passage, the heater element vaporizing the liquid to provide a vapor; and cooling the vapor to provide an aerosol.

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