Aerosol-generating system with restricted portion

Abstract

An aerosol-generating system (100) comprising a cartridge (10) comprising a housing (36), a liquid reservoir (44) within the housing (36), and a heater assembly (12) comprising a heating element (16). The heater assembly (12) is configured to convey a liquid from the liquid reservoir (44) across the heating element (16). The aerosol-generating system (100) comprises a device (60) comprising a power supply (72) configured to provide power to the heating element (16), and a cavity (66) configured to receive at least a portion of the cartridge (10). The aerosol-generating system (100) further comprises an airflow path defined between at least one air inlet and an air outlet wherein at least a portion of the heating element (16) is positioned in the airflow path. The airflow path comprises a restricted portion (50) between the housing (36) and the cavity (66), the restricted portion (50) comprises a minimum cross-sectional area of the airflow path.

Description

[0001] AEROSOL-GENERATING SYSTEM WITH RESTRICTED PORTION

[0002] The present disclosure relates to an aerosol-generating system comprising a cartridge and a device.

[0003] Aerosol-generating systems that heat a liquid aerosol-forming substrate in order to generate an aerosol for user inhalation are known in the art. The aerosol-generating systems may comprise a cartridge containing a liquid aerosol-forming substrate and a heating element. Liquid aerosol-forming substrate may be comprised in a liquid storage portion and may be delivered to the heating element via a wicking component. The cartridge may be removably connectable to a device that contains a power supply for supplying power to the heating element.

[0004] In use, the liquid aerosol-forming substrate is heated by the heating element and vaporised to form a vapour. The vapour cools and condenses to form an aerosol, and this aerosol is then inhaled by a user. Such aerosol-generating systems are typically handheld and portable.

[0005] When a user inhales on an aerosol-generating system they experience a draw resistance. This resistance can be quantified as a measure of the pressure drop through the aerosolgenerating system for a given volumetric flow rate through the system, known as the resistance to draw (RTD). An acceptable RTD for consumer comfort is typically in the range of 50 to 100 millimetres of water gauge (mmWg).

[0006] It would be desirable to provide an aerosol-generating system with a precise and predictable RTD.

[0007] According to a first aspect of the present invention, there is provided an aerosol-generating system comprising a cartridge and a device. The cartridge may comprise a housing, a liquid reservoir within the housing, and a heater assembly that may comprise a heating element, wherein the heater assembly may be configured to convey a liquid from the liquid reservoir across the heating element. The device may comprise a power supply that may be configured to provide power to the heating element, and a cavity that may be configured to receive at least a portion of the cartridge. The aerosol-generating system may comprise an airflow path defined between at least one air inlet and an air outlet wherein at least a portion of the heating element may be positioned in the airflow path. The airflow path may comprise a restricted portion between the housing and the cavity. The restricted portion may comprise a minimum cross-sectional area of the air flow path.

[0008] Advantageously, a significant amount of the RTD of the aerosol-generating system is generated by the restricted portion. Therefore, the RTD for the system can be determined and controlled by the design of the restricted portion. The restricted portion being positioned between the housing and the cavity may advantageously prevent the restricted portion from restricting or inhibiting aerosol generation or supply. For example, a restricted portion positioned within the cartridge, could negatively affect the supply of aerosol to a user. In particular, if the restricted portion were downstream of the heating element, and not between the housing and the cavity, the restricted portion could affect flow of aerosol and therefore could cause droplets to condense and cause undesirable large droplets to be delivered to a user.

[0009] The restricted portion may be configured to provide a resistance to draw (RTD). The RTD of the restricted portion may be measured from an upstream end of the restricted portion to a downstream end of the restricted portion. The airflow path may be configured to provide a resistance to draw (the total RTD). The total RTD of the airflow path may be measured from an upstream end of the airflow path to a downstream end of the airflow path. The total RTD of the airflow path may be measured from the at least one air inlet to the air outlet. For example, the total RTD of the airflow path may be the total RTD measured for the full length of the airflow path when the cartridge is received by the device. The ratio of the RTD of the restricted portion to the total RTD of the airflow path is such that a significant portion of the RTD is determined by the restricted portion. A ratio of the RTD of the restricted portion to the total RTD of the airflow path may be at least 0.6. The ratio of the RTD of the restricted portion to the total RTD of the airflow path may be at least 0.65, at least 0.7, at least 0.75, at least 0.8, at least 0.85, or at least 0.9.

[0010] The restricted portion may be formed by a space between the cartridge and the device. The space may be formed between a surface of the cavity of the device and an opposing surface of the housing of the cartridge.

[0011] The at least one air inlet may be defined between the cartridge and the device. An inlet section of the airflow path may extend from the air inlet to the restricted portion. The inlet section may be defined between the cartridge and the device. A cartridge section of the airflow path may extend between a cartridge air inlet and the aerosol-generating system air outlet. The cartridge section of the airflow path may be configured to provide a resistance to draw (a cartridge section RTD). A ratio of the cartridge section RTD to the total RTD of the airflow path may be less than 0.4, preferably less than 0.3.

[0012] The air outlet may be at a mouth end of the cartridge. The mouth end of the cartridge may comprise a mouthpiece. The aerosol-generating system may be configured to allow a user to puff on the mouthpiece to draw an aerosol through the air outlet. The mouthpiece may be formed integrally with the housing. A connection end of the cartridge may be opposite the mouth end of the cartridge. The connection end of the cartridge may be receivable by the cavity of the device. The cavity of the device may be configured to receive the connection end of the cartridge. The cavity may be configured to receive at least a portion of the cartridge in a cavity longitudinal direction. When the cartridge is received by the device the mouth end of the cartridge may be configured to allow a user to access the mouth end.

[0013] The restricted portion may be defined between the connection end of the cartridge and the cavity of the device. The cartridge may comprise a longitudinal axis extending between the mouth end and the connection end of the cartridge. The restricted portion may extend parallel to the longitudinal axis of the cartridge. Alternatively, or in addition, the restricted portion may extend perpendicular to the longitudinal axis of the cartridge.

[0014] The restricted portion may be situated downstream of the air inlet. The restricted portion may be situated upstream of the heating element. Preferably, the restricted portion is situated upstream of the heater assembly.

[0015] The cavity may comprise a base and a surrounding sidewall for receiving the connection end of the cartridge. The restricted portion may be defined between the connection end of the cartridge and the base of the cavity. The restricted portion may therefore be distanced from the at least one air inlet. Advantageously, this may reduce the risk of contaminants, for example dust and dirt, from blocking the restricted portion.

[0016] The airflow path may comprise at least one channel. The at least one channel may be recessed in a surface of the housing of the cartridge, a surface of the cavity of the device, or in both a surface of the housing of the cartridge and a surface of the cavity of the device. The at least one channel may comprise an upstream end of the channel and a downstream end of the channel, wherein the upstream end of the channel is the end further upstream in the airflow path than the downstream end of the channel.

[0017] The connection end of the cartridge may comprise a connection end face perpendicular to the longitudinal axis of the cartridge. The connection end face may face the base of the cavity when the cartridge is received by the device for example when the housing the cartridge is received within the cavity. The connection end face of the cartridge may be an end face of the housing of the cartridge.

[0018] The aerosol-generating system may comprise the at least one channel between the connection end face of the cartridge and the base of the cavity.

[0019] The restricted portion may comprise the at least one channel. Preferably, the at least one channel is recessed in a surface of the cavity of the device. Preferably, the at least one channel is recessed in the base of the cavity. The restricted portion may consist of each of the at least one channels recessed in the base of the cavity. Advantageously, when the restricted portion is predominantly reliant on the dimensions of the at least one channel in the base of the cavity the manufacturing tolerances that may influence the size of the restricted portion are predominantly those associated with the manufacture of the base of the cavity. Therefore, the RTD of the restricted portion and thus the aerosol-generating system may be accurately predicted.

[0020] The at least one channel may comprise one, two, three or four channels. Preferably, the at least one channel consists of two channels.

[0021] Preferably, the at least one channel comprises two channels. The two channels of the at least one channel may be referred to as a first channel and a second channel. Both of the first channel and the second channel may be recessed in the base of the cavity. The restricted portion may comprise the first channel and the second channel. The restricted portion may consist of the first channel and the second channel.

[0022] The at least one air inlet may comprise a single air inlet. The at least one air inlet may comprise a plurality of air inlets. The at least one air inlet may comprise any suitable number of air inlets. For example, the air inlet may comprise one, two, three, four, five or six air inlets.

[0023] Preferably, the at least one air inlet of the aerosol-generating system comprises two air inlets. Two air inlets of the at least one air inlet of the aerosol-generating system may be referred to as a first air inlet and a second air inlet. The first air inlet may be situated upstream of the first channel. The second air inlet may be situated upstream of the second channel. When a user puffs on the aerosol-generating system air may be drawn into the system through the first and second air inlets. The air flow path may comprise a first air stream, a second air stream and a total air stream. The first air stream may extend between the first air inlet and the downstream end of the first channel. The second air stream may extend between the second air inlet and the downstream end of the second channel. When air is drawn into the first and second air inlets, the air may pass through the first air stream and the second air stream simultaneously. The first air stream and the second air stream may combine to form a total air stream of the airflow path. The total air stream may be situated downstream of the first channel and second channel.

[0024] The device may comprise at least one elastomeric component configured to provide at least a partial seal between the cartridge and the device. The elastomeric component may be provided in the base of the cavity. Advantageously, the at least one elastomeric component may improve the engagement between the cartridge and the device. The at least one elastomeric component may provide a closer fit between the cartridge and the device. The device may comprise a first elastomeric component and a second elastomeric component. The at least one channel may be situated between the first and second elastomeric components. Advantageously, the first and second elastomeric component may prevent, or reduce an amount of, air from leaking out of the at least one channel.

[0025] Each channel of the at least one channel may have a quadrangular cross-section, preferably a rectangular cross-section, a circular cross-section, or a semi-circular cross-section. Advantageously, at least one channel having one of these cross-sections may be simple to manufacture.

[0026] Each channel of the at least one channel may have a width of between 0.15 and 0.8 millimetres. Each channel of the at least one channel may have a depth of between 0.3 and 1 .2 millimetres. Each channel of the at least one channel may have a length of between 1 and 5 millimetres of between 1 and 4 millimetres, or of between 1 and 2 millimetres. Each channel of the at least one channel may have a cross-sectional area of between 0.035 and 3 millimetres squared. Advantageously, these dimensions may provide a channel that provides a desired total RTD for the airflow path while achieving the desired pressure drop across the channel. The base of the device may comprise a protrusion and the connection end of the cartridge may comprise a recess into which the protrusion of the base is received. The recess may be situated between the end face of the cartridge and the cartridge air inlet. When the cartridge is coupled to the device, the protrusion may be received by the recess and extend into the cartridge air inlet.

[0027] The protrusion may have a stadium cross-section. The protrusion may have a circular, semi-circular, or quadrangular cross-section.

[0028] The airflow path may comprise a portion defined between the protrusion of the base of the cavity and the recess of the cartridge, herein referred to as a gap. The gap may be situated immediately upstream of the cartridge air inlet. The gap may be situated immediately downstream of the at least one channel. The gap may be configured to allow air to flow into the cartridge air inlet. The gap may be defined between the at least one channel and cartridge air inlet.

[0029] The gap may have an annular cross-section. The gap may have a cross-sectional area of between 4 and 20 millimetres squared. The gap may have a hydraulic diameter of between 0.15 and 0.45 millimetres, preferably 0.3 millimetres. The gap may have a length of between 0.5 millimetres and 1.5 millimetres. Advantageously, these dimensions may provide a gap that provides a desired total RTD for the airflow path while achieving the desired pressure drop across the gap.

[0030] The restricted portion of the airflow path may comprise the gap. The restricted portion of the airflow path may consist of the gap.

[0031] In some examples of the present disclosure, the restricted portion may comprise both the at least one channel and the gap. The restricted portion may be a combination of the channel and the gap.

[0032] The airflow path may comprise a cross-sectional shape that is tubular, annular. The airflow path may comprise two or more tubular, annular, or tubular and annular portions in parallel. The cross-sectional shape of the airflow path may vary along the airflow path.

[0033] The total RTD of the airflow path may be between 50 and 70 millimetres of water gauge. Advantageously, this resistance to draw is selected for user comfort. The resistance to draw of the cartridge may be at least 10 millimetres of water gauge. Preferably, the resistance to draw of the cartridge may be between 10 and 20 millimetres of water gauge.

[0034] Immediately downstream of the restricted portion, the airflow path may comprise an unrestricted portion. The cross-sectional area of the unrestricted portion may be greater than the cross-sectional area of the restricted portion. For example, the cross-sectional area of the unrestricted portion may be at least 1 .5 times, 2 times or at least 2.5 times greater than the cross- sectional area of the restricted portion. During use of the aerosol-generating system, for example when a user is puffing on the system, the minimum pressure in the airflow path may be at the unrestricted portion due to the change in cross-sectional area. In other words, the region of minimum pressure through the airflow path when air is drawn through the airflow path is at the unrestricted portion.

[0035] The unrestricted portion may comprise an airflow chamber. The airflow chamber may be defined between the cartridge housing and a portion of the device.

[0036] The aerosol-generating device may comprise a puff sensor. The puff sensor may be situated downstream of the restricted portion. The puff sensor may be situated immediately after the restricted portion. The puff sensor may be situated at the unrestricted portion of the air flow path. The puff sensor may be pressure sensor. The pressure sensor may comprise any suitable type of pressure sensor. The pressure sensor may be configured to detect that a negative pressure is applied to the air outlet, for example when a user takes a puff. Preferably, the pressure sensor may be arranged to detect the pressure in the airflow chamber. Providing an aerosolgenerating system with a pressure sensor configured to detect the pressure in an airflow path through the aerosol-generating system may enable the aerosol-generating system to detect when a user is taking a puff on the aerosol-generating system.

[0037] Advantageously, providing an airflow chamber in the airflow path of the aerosol-generating system, wherein the airflow chamber is defined between a portion of the cartridge housing and a portion of the device, may enable one or both of the cartridge and the device to be made smaller or more compact compared to a system in which the airflow chamber is formed entirely by the cartridge housing or entirely by a housing of the device.

[0038] The restricted portion may be configured to cause a pressure drop in the airflow chamber when air is drawn through the airflow path. The pressure drop at the airflow chamber may result in the pressure in the airflow path being at a minimum in the airflow chamber.

[0039] Advantageously, detecting the pressure after the restricted portion of the air flow path, and particularly at the point of minimum pressure along the airflow path, may provide more accurate puff detection by the aerosol-generating system. Advantageously, detecting the pressure in the airflow chamber after the restricted portion in the airflow path, and particularly at the point of minimum pressure along the airflow path, may provide more prompt puff detection by the aerosolgenerating system. Detecting the pressure after the restricted portion, and particularly at the point of minimum pressure along the airflow path, may enable detection of the pressure drop caused by the restricted portion, which may be used to detect when a user is taking a puff on the aerosolgenerating system.

[0040] Advantageously, detecting pressure after the restricted portion may provide more accurate information on the puff of a user on the aerosol-generating system compared to detecting a puff elsewhere in the system. Detecting the pressure after the restricted portion may enable detection of the pressure drop caused by the restricted portion, which may be used to determine puff characteristics, such as the volume of air drawn through restricted portion. Advantageously, because the restricted portion is situated between the cartridge housing and the device cavity, the puff sensor may be located in the device. As such any electronics associated with the puff sensor may be contained within the device, whilst being separated from the airflow path.

[0041] The aerosol-generating system may comprise a controller. Preferably, the aerosolgenerating device may comprise the controller. The controller may be configured to control the power supplied to the heating element.

[0042] Preferably, the controller may be configured to control the power supplied to the heating element in response to information from the pressure sensor. The controller may be configured to determine when a user is taking a puff on the aerosol-generating device based on pressure measurement information received from the pressure sensor. The controller may be configured to supply power to the heating element in response the detection of a puff by the pressure sensor.

[0043] The at least one heating element may be a mesh heating element configured to wick liquid aerosol-forming substrate. A mesh may relinquish the need for a separate wicking element. Advantageously, this may reduce manufacturing complexity and cost.

[0044] Alternatively, the heater assembly may comprise a heating element and a wicking element configured to wick liquid to the heating element.

[0045] The at least one heating element may be a resistive heating element.

[0046] The at least one heating element may be susceptor element configured to be inductively heated. Advantageously, inductive heating allows for a wireless coupling between the susceptor element arranged within the cartridge and the aerosol-generating device configured to receive the cartridge. In this way, the liquid aerosol-forming substrate contained in the reservoir of the cartridge can be kept sealed from any electrical connections during the shelf life and also in operation when coupled to the device.

[0047] As used herein, “susceptor element” means an element that is heatable by penetration with a varying magnetic field. A susceptor element is typically heatable by at least one of Joule heating through induction of eddy currents in the susceptor element, and hysteresis losses.

[0048] The susceptor element may comprise a magnetic material heatable by penetration with an alternating magnetic field. The term “magnetic material” is used herein to describe a material which is able to interact with a magnetic field, including both paramagnetic and ferromagnetic materials. The first material may be any suitable magnetic material that is heatable by penetration with an alternating magnetic field. In some preferred embodiments, the first material comprises a ferritic stainless steel. Suitable ferritic stainless steels include AISI 400 series stainless steels, such as AISI type 409, 410, 420 and 430 stainless steels.

[0049] The susceptor element may be substantially flat. Substantially flat may be defined as the susceptor element comprising both a width and a height much greater than a depth. The device may comprise one or more inductor element. The inductor element may generate a varying magnetic field when a varying current is supplied to the inductor element. The one or more inductor element may be configured to generate a variable magnetic flux through the susceptor element. The one or more inductor element may be configured to generate a varying magnetic field in the device cavity. The one or more inductor element may be arranged outside of the device cavity. The one or more inductor element may be arranged to at least partially surround the cavity. When the cartridge is coupled to the aerosol-generating device, the one or more inductor element may at least partially surround the susceptor element. The one or more inductor element may be an inductor coil. The inductor coil may be a helical coil.

[0050] As used herein, “varying current” refers to a current that varies with time. An inductor element may generate a varying magnetic field when a varying electric current is supplied to the inductor element. The term “varying current” is intended to include alternating currents. Where the varying current is an alternating current, the alternating current generates an alternating magnetic field. The varying current may be an alternating current.

[0051] As used herein, “alternating current” refers to a current that periodically reverses direction. The alternating current may have any suitable frequency. Suitable frequencies for the alternating current may be between 100 kilohertz (kHz) and 30 megahertz (MHz)

[0052] The inductor element may be formed from any suitable material. The inductor element may be formed from at least one of: silver, gold, aluminium, brass, zinc, iron, nickel, and alloys of thereof, and electrically conductive ceramics, such as yttrium-doped zirconia, indium tin oxide, and yttrium doped titanate.

[0053] The aerosol-generating system may comprise a mechanical engagement mechanism between the cartridge and the device such as a snap fit mechanism, a screw fit mechanism or a push fit mechanism. An engagement mechanism is advantageous, so the cartridge and device stay in contact with one another when the aerosol generating system is in use. Advantageously, the mechanical engagement mechanism may ensure the cartridge and device are correctly aligned so that the cross-sectional area of the restricted portion and therefore the RTD of the restricted portion may be consistently achieved.

[0054] According to a second aspect of the disclosure, there may be provided an aerosolgenerating system. The aerosol-generating system may comprise a cartridge comprising a housing, a liquid reservoir within the housing, and a heater assembly comprising a heating element. The heater assembly may be configured to convey a liquid from the liquid reservoir across the heating element. The aerosol-generating system may comprise a device. The device may comprise a power supply configured to provide power to the heating element. The device may comprise a cavity configured to receive at least a portion of the cartridge. The aerosol generating system may comprise an airflow path defined between at least one air inlet and an air outlet wherein at least a portion of the heating element may be positioned in the airflow path. The airflow path may comprise a first section defined between the cartridge and the device, wherein the ratio of resistance to draw of the first section of the airflow path to the total resistance to draw of the airflow path is at least 0.6.

[0055] The first section may be formed by a space between the cartridge and the device. The first section may comprise a restricted portion configured to restrict the cross-sectional area of the airflow path.

[0056] Unless otherwise specified, the resistance to draw (RTD) of the aerosol-generating system or the airflow path, or the cartridge, or any other component of the aerosol-generating system is measured in accordance with ISO 6565-2015. The RTD refers to the pressure required to force air through the full length of a component. The terms “pressure drop” or “draw resistance” of a component may also refer to the “resistance to draw”. Such terms generally refer to the measurements in accordance with ISO 6565-2015 are normally carried out at under test at a volumetric flow rate of about 17.5 millilitres per second at the output or downstream end of the measured component at a temperature of about 22 degrees Celsius, a pressure of about 101 kPa (about 760 Torr) and a relative humidity of about 60%.

[0057] As used herein, the terms “upstream” and “downstream” may be used to describe the relative positions of components, or portions of components, of an aerosol-generating system. The terms upstream and downstream are relative to the direction of aerosol or air flow movement through the aerosol generating system when a consumer draws on the air outlet end of the aerosol-generating system. The air outlet of the aerosol-generating system is downstream of the air inlet of the aerosol-generating system. The air inlet of the aerosol-generating system is upstream of the aerosol-generating system.

[0058] As used herein, an “aerosol-generating system” means a system that generates an aerosol from one or more aerosol-forming substrates.

[0059] As used herein, the term “puff” is used to describe the action of a user of the aerosolgenerating system drawing on the air outlet of the airflow path to receive and inhale aerosol generated by the aerosol-generating system.

[0060] As used herein, the terms “air inlet’ and ‘air outlet” are used to describe one or more apertures through which air may be drawn into, and out of, respectively, of a component or portion of a component of the cartridge, aerosol-generating system or aerosol-generating device.

[0061] As used herein, the term “cartridge” also refers to an article comprising an aerosol-forming substrate that is capable of releasing volatile compounds that can form an aerosol. A cartridge may be disposable.

[0062] As used herein, the term “aerosol-forming substrate” means a substrate capable of releasing volatile compounds that may form an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. The liquid aerosol-forming substrate may comprise nicotine. The nicotine containing liquid aerosol-forming substrate may be a nicotine salt matrix. The liquid aerosol-forming substrate may comprise plant-based material. The liquid aerosol-forming substrate may comprise tobacco. The liquid aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the aerosol-forming substrate upon heating. The liquid aerosol-forming substrate may comprise homogenised tobacco material. The liquid aerosol-forming substrate may comprise a non-tobacco-containing material. The liquid aerosolforming substrate may comprise homogenised plant-based material.

[0063] The liquid aerosol-forming substrate may comprise one or more aerosol-formers. An aerosol-former is any suitable known compound or mixture of compounds that, in use, facilitates formation of a dense and stable aerosol and that is substantially resistant to thermal degradation at the temperature of operation of the system. Examples of suitable aerosol formers include glycerine and propylene glycol. 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 glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. The liquid aerosol-forming substrate may comprise water, solvents, ethanol, plant extracts and natural or artificial flavours. The liquid aerosol-forming substrate may comprise nicotine and at least one aerosol former. The aerosol former may be glycerine or propylene glycol. The aerosol former may comprise both glycerine and propylene glycol. The liquid aerosol-forming substrate may have a nicotine concentration of between about 0.5% and about 10%, for example about 2%.

[0064] The aerosol-generating system may be a handheld aerosol-generating system. The aerosol-generating system may be a handheld aerosol-generating system configured to allow a user to suck on a mouthpiece to draw an aerosol through a first air outlet. The aerosol-generating system may have a size comparable to a conventional cigar or cigarette. The aerosol-generating system may have a total length between about 25 mm and about 150 mm. The aerosol-generating system may have an external diameter between about 5 mm and about 30mm.

[0065] The power supply may be a DC power supply. The power supply may be a battery. The battery may be a Lithium based battery, for example a Lithium-Cobalt, a Lithium-lron-Phosphate, a Lithium Titanate or a Lithium-Polymer battery. The battery may be a Nickel metal hydride battery or a Nickel cadmium battery. The power supply may be another form of charge storage device such as a capacitor.

[0066] Any one or more features of any of the aspects and embodiments described above may be combined with any one or more features of another aspect or embodiment. The invention is defined in the claims. However, below there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

[0067] Ex1 . An aerosol-generating system, comprising: a cartridge comprising a housing, a liquid reservoir within the housing, and a heater assembly comprising a heating element, wherein the heater assembly is configured to convey a liquid from the liquid reservoir across the heating element; a device comprising a power supply configured to provide power to the heating element, and a cavity configured to receive at least a portion of the cartridge; and an airflow path defined between at least one air inlet and an air outlet wherein at least a portion of the heating element is positioned in the airflow path, the airflow path comprising a restricted portion between the housing and the cavity, the restricted portion comprising a minimum cross-sectional area of the air flow path.

[0068] Ex2. The aerosol-generating system according to example EX1 , wherein a ratio of resistance to draw of the restricted portion to the total resistance to draw of the airflow path is at least 0.6.

[0069] Ex3. The aerosol-generating system according to example Ex1 or Ex2, wherein the restricted portion is formed by a space between the cartridge and the device.

[0070] Ex4. The aerosol-generating system according to any one of examples Ex1 to Ex3, wherein the at least one air inlet is defined between the cartridge and the device.

[0071] Ex5. The aerosol-generating system according to any one of examples Ex1 to Ex4, wherein the air outlet is at a mouth end of the cartridge, and a connection end of the cartridge is opposite the mouth end, wherein the connection end is received by the cavity of the device.

[0072] Ex6. The aerosol-generating system according to any one of examples Ex1 to Ex5, wherein the restricted portion is defined between the connection end of the cartridge and the cavity of the device.

[0073] Ex7. The aerosol-generating system according to example Ex6, wherein the cartridge comprises a longitudinal axis extending between the mouth end and the connection end of the cartridge, and the restricted portion extends parallel to, perpendicular to, or parallel and perpendicular to the longitudinal axis of the cartridge.

[0074] Ex8. The aerosol-generating system according to example Ex6 or Ex7, wherein the cavity comprises a base and a surrounding sidewall for receiving the connection end of the cartridge, wherein the restricted portion is defined between the connection end of the cartridge and the base of the cavity.

[0075] Ex9. The aerosol-generating system according to example Ex8, wherein the connection end of the cartridge comprises an end face perpendicular to the longitudinal axis of the cartridge, wherein the restricted portion is defined by at least one channel recessed in at least one of the end face of the cartridge and the base of the cavity. Ex10. The aerosol-generating system according to example Ex9, wherein the at least one channel is defined in the base of the cavity.

[0076] Ex11 . The aerosol-generating system according to any one of examples Ex9 or Ex10, wherein the device comprises at least one elastomeric component configured to provide at least a partial seal between the cartridge and the device.

[0077] Ex12. The aerosol-generating system according to example Ex11 , wherein the device comprises a first elastomeric component and a second elastomeric component and the at least one channel is situated between the first and second elastomeric components.

[0078] Ex13. The aerosol-generating system according to any one of examples Ex9 to Ex12, wherein the at least one channel has a width of between 0.15 and 0.8 millimetres.

[0079] Ex14. The aerosol-generating system according to any one of examples Ex9 to Ex13, wherein the at least one channel has a depth of between 0.3 and 1 .2 millimetres.

[0080] Ex15. The aerosol-generating system according to any one of examples Ex9 to Ex14, wherein the at least one channel has a length of between 1 and 2 millimetres.

[0081] Ex16. The aerosol-generating system according to any one of examples Ex9 to Ex15, wherein the at least one channel has a cross-sectional area of between 0.035 and 3 millimetres squared. Ex17. The aerosol-generating system according to any one of examples Ex8 to Ex16, wherein the base of the device comprises a protrusion and the connection end of the cartridge comprises a recess configured to receive at least a portion of the protrusion of the base, wherein the restricted portion of the airflow path is defined by a gap between the protrusion and the recess.

[0082] Ex18. The aerosol-generating system according to example Ex17, wherein the gap has an annular cross-section.

[0083] Ex19. The aerosol-generating system according to example Ex17 or Ex18, wherein the gap has a cross-sectional area of between 4 and 20 millimetres squared.

[0084] Ex20. The aerosol-generating system according to any one of examples Ex17 to Ex19, wherein the gap has a hydraulic diameter of between 0.15 and 0.45 millimetres, preferably 0.3 millimetres. Ex21 . The aerosol-generating system according to any one of examples Ex17 to Ex20, wherein the gap has a length of between 0.5 millimetres and 1 .5 millimetres.

[0085] Ex22. The aerosol-generating system according to example Ex21 , wherein a ratio of cross sectional area to length of the restricted portion is configured to provide the resistance to draw of the restricted portion.

[0086] Ex23. The aerosol-generating system according to any of example Ex5 to EX22, wherein the airflow path comprises a cartridge section, wherein the cartridge section extends between the cartridge air inlet at the connection end and the air outlet.

[0087] Ex24. The aerosol-generating system according to example Ex23, wherein the ratio of resistance to draw of the cartridge section of the airflow path to the total resistance to draw of the airflow path is less than 0.4, preferably less than 0.3. Ex25. The aerosol-generating system according to any one of examples Ex1 to Ex24, wherein the airflow path comprises a cross-sectional shape that is tubular, annular or comprises two or more tubular and / or annular portions in parallel.

[0088] Ex26. The aerosol-generating system according to example Ex25, wherein the cross-sectional shape of the airflow path varies along the airflow path.

[0089] Ex27. The aerosol-generating system according to any one of examples Ex1 to Ex26, wherein the aerosol-generating device comprises a puff sensor.

[0090] Ex28. The aerosol-generating system according to example Ex27, wherein the puff sensor is situated downstream of the restricted portion.

[0091] Ex29. The aerosol-generating system according to any preceding example, wherein the heating element is a susceptor element and the device comprises one or more inductor coils configured to generate a variable magnetic flux through the susceptor element.

[0092] Ex30. The aerosol-generating system according to any preceding example, wherein the total resistance to draw of the airflow path is between 50 and 70 millimetres of water gauge.

[0093] Ex31. The aerosol-generating system according to any preceding example, wherein the resistance to draw of the cartridge is at least 10 millimetres of water gauge.

[0094] Ex32. The aerosol-generating system according to example Ex31 , wherein the resistance to draw of the cartridge is between 10 and 20 millimetres of water gauge.

[0095] Ex33. The aerosol-generating system according to any preceding example, wherein the ratio of resistance to draw of the restricted portion of the airflow path to the total resistance to draw of the airflow path is at least 0.7, at least 0.8, or at least 0.9.

[0096] Ex34. An aerosol-generating system, comprising: a cartridge comprising a housing, a liquid reservoir within the housing, and a heater assembly comprising a heating element, wherein the heater assembly is configured to convey a liquid from the liquid reservoir across the heating element; a device comprising a power supply configured to provide power to the heating element, and a cavity configured to receive at least a portion of the cartridge; and an airflow path defined between at least one air inlet and an air outlet wherein at least a portion of the heating element is positioned in the airflow path, the airflow path comprising a first section defined between the cartridge and the device, wherein the ratio of resistance to draw of the first section of the airflow path to the total resistance to draw of the airflow path is at least 0.6. Ex35. The aerosol-generating system according to example Ex34, wherein the first section is formed by a gap between the cartridge and the device.

[0097] Ex36. The aerosol-generating system according to example Ex34 or Ex35, wherein the first section comprises a restricted portion configured to restrict the cross-sectional area of the airflow path.

[0098] Examples will now be further described with reference to the figures in which: Figure 1 shows schematic illustration of a cross-section of an aerosol-generating system in accordance with a first embodiment of the present disclosure;

[0099] Figure 2 shows a schematic illustration of the aerosol-generating system of Figure 1 partially disassembled;

[0100] Figure 3 shows a schematic illustration of the airflow in the system of cartridge of Figures 1 and 2;

[0101] Figure 4 shows a schematic illustration of plan view a cavity according of the device in accordance with the first embodiment of the present disclosure;

[0102] Figure 5 shows a schematic illustration of a cross-section of an interface between the cartridge and the device according to the first embodiment of the present disclosure;

[0103] Figure 6 shows a schematic illustration of a cross-section of an interface between a cartridge and a device according to a second embodiment of the present disclosure;

[0104] Figure 7 shows a schematic illustration of a cross-section of an interface between a cartridge and a device according to a third embodiment of the present disclosure; and

[0105] Figure 8 shows a schematic illustration of a cross-section of an interface between a cartridge and a device according to a fourth embodiment of the present disclosure.

[0106] Figures 1 and 2 show schematic illustrations of a cross-section of an aerosol-generating system in accordance with a first embodiment of the present disclosure. The system 100 comprises a cartridge 10 and a device 60. Figure 1 shows the system wherein the cartridge 10 is coupled to the device 60. The aerosol-generating system is portable and has a size comparable to a conventional cigar or cigarette

[0107] The cartridge 10 comprises a heater assembly 12 mounted in a heater holder, wherein the heater holder is configured to support the heater assembly 12. The cartridge comprises an inner housing 14. The inner housing 14 comprises heater holder. The heater assembly is planar, and thin, having a thickness dimension that is substantially smaller than a length dimension and a width dimension. The heater assembly 12 comprises a heating element 16 and a wicking element 18. In this example, the heating element 16 is a susceptor element. The width of the heating element 16 is smaller than the width of the wicking element 18. The heating element 16 covers at least a central portion of a surface of the wicking element 18.

[0108] The cartridge 10 has a mouth end, and a connection end, opposite the mouth end. An outer housing 36 of the cartridge defines a mouth end opening 38, which is the aerosol-generating system air outlet, at the mouth end of the cartridge 10. The connection end is configured for connection of the cartridge 10 to the aerosol-generating device 60, as described in detail below. The heater assembly 12 and the heater holder are located towards the connection end of the cartridge 10.

[0109] The cartridge 10 further comprises a liquid reservoir 44. The liquid reservoir 44 holds a liquid aerosol-forming substrate 42. The liquid reservoir 44 extends from the mouth end of the outer housing 36 to the connection end of the cartridge 10, and comprises an annular space defined between the outer housing 36 and the inner housing 14. An internal passage 48 extends through the reservoir between the mouth end opening 38 and an open end of an internal passage 26 of the inner housing 14.

[0110] Outer, exposed portions of the wicking element 18 which are not covered by the heating element 16 protrude through a pair of openings arranged on opposed sides of an internal side wall 27 of the inner housing 14, into the liquid reservoir 44. The internal side wall 27 defines the internal passage 26 of the heater holder 14. The heating element 16 comprises a sintered mesh formed from ferritic stainless steel filaments and austenitic stainless steel filaments. The wicking element 18 comprises a porous body of rayon filaments. The wicking element 18 is configured to draw liquid, via the outer, exposed portions of the wicking element 18, to the heating element 16. The outer, exposed portions of the wicking element 18 extend through the openings in the internal side wall 27 of the inner housing 14 into the liquid reservoir 44.

[0111] The inner housing 14 is movable relative to the outer housing 36 between a storage position, as shown in Figure 2, and a use position, as shown in Figure 1 . In this embodiment, the inner housing 14 is slidable relative to the outer housing 36 along a longitudinal axis of the inner housing 14 and the outer housing 36. An inner tube 37 extends from the air outlet 38 of the outer housing 36 along the longitudinal axis of the outer housing 36. An O-ring 24 is provided between the inner tube 37 of the outer housing 36 and inner housing 14.

[0112] When the cartridge is moved to the use position, as shown in Figure 1 , the inner housing 14 is slid along the aligned longitudinal axes towards the mouth end of the outer housing 36, until a first stop 28 reaches a wider region of the liquid reservoir 44. When the first stop 28 reaches the wider region of the liquid reservoir 44, the first stop 28 no longer contacts an inner surface of the outer housing 36, and a space is provided between the outer housing 36 and the inner housing 14, such that liquid aerosol-forming substrate 42 in the liquid reservoir 44 is able to flow to the heater assembly 12.

[0113] A second stop 30 is provided at the connection end of the inner housing 14. The second stop 30 is substantially similar to the first stop 28, and contacts the inner surface of outer housing 36, below the wider region at the mouth end, when the system is in the use position. An additional O-ring seal 29 is also provided at the second stop 30 to improve the seal between the second stop 30 and the inner surface of the outer housing 36.

[0114] The connection end of the cartridge 10 comprises an end face perpendicular to a longitudinal axis of the cartridge. The end face is a face of an outer surface of the outer housing 36. The end face comprises an opening that is the cartridge air inlet 32. The cartridge air inlet enables air to be drawn into the internal passage 26.

[0115] A cartridge section of an airflow path of the aerosol-generating system is formed through the cartridge 10 by the internal passage 26 of the inner housing 14, and the internal passage 48 of the liquid reservoir 44. The air passage extends from the cartridge air inlet 32 at the connection end of the cartridge 10, through the internal passage 26 of the inner housing 14, and through the internal passage 48 of the liquid reservoir 44 to the mouth end opening, air outlet 38. The airflow passage enables air to be drawn through the cartridge 10 from the connection end to the mouth end.

[0116] The aerosol-generating device 60 comprises a generally cylindrical device outer housing 62 having a connection end and a distal end opposite the connection end. A cavity 66 (shown in Figure 2) for receiving a connection end of the cartridge is located at the connection end of the device 60.

[0117] In this example, two air inlets 65 are provided between the device outer housing 62 and the cartridge outer housing 36 to enable ambient air to be drawn into the cavity 66. It should be understood that any number of air inlets may be suitable. The airflow path of the aerosolgenerating system is defined between the air inlets 65 and the air outlet 38 at a mouth end of the cartridge. At least a portion of the heating element 16 is positioned in the airflow path. The airflow path comprises a restricted portion between the outer housing 36 and the cavity of the device 60, the restricted portion is formed by a space between the cartridge 10 and the device 60. The restricted portion comprises a minimum cross-sectional area of the airflow path and a ratio of resistance to draw of the restricted portion to a total resistance to draw of the airflow path is at least 0.6. The total resistance to draw of the airflow path of the aerosol-generating system 100 is between 50 and 70 millimetres of water gauge. The airflow path of the aerosol-generating system 100 therefore generates a RTD which is similar to that of a conventional cigarette.

[0118] Two channels are defined in the base of the cavity 66. A first channel is positioned downstream of the first air inlet 65 and a second channel is positioned downstream of the second air inlet 65.

[0119] The cavity 66 of the device 60 comprises a base and a surrounding sidewall for receiving the connection end of the cartridge 10. The restricted portion is defined between the connection end of the cartridge 10 and the base of the cavity 66. The base of the cavity 66 of the device 60 comprises a protrusion 68, and the connection end of the cartridge 10 comprises a recess 46 into which at least a portion of the protrusion 68 of the base of the cavity 66 is received.

[0120] The restricted portion is defined between the connection end of the cartridge 10 and the cavity 66 of the device 60 The cartridge 10 comprises a longitudinal axis extending between the mouth end and the connection end. In this example, the restricted portion extends parallel to the longitudinal axis of the cartridge, with the restricted portion comprising a gap described in further detail in relation to Figure 3, below.

[0121] As shown in Figure 1 , when the connection end of the cartridge 10 is received in the device cavity 66, the protrusion 68 pushes a portion of the inner housing 14 relative to the outer housing 36, from the storage position to the use position, towards the mouth end of the cartridge 10.The device 60 further comprises an inductive heating arrangement arranged within the device outer housing 62. The inductive heating arrangement includes an inductor coil 90, control circuitry 70 and a power supply 72. The power supply 72 comprises a rechargeable lithium ion battery, which is rechargeable via an electrical connector (not shown) at the distal end of the device. The control circuitry 70 is connected to the power supply 72, and to the inductor coil 90, such that the control circuitry 70 controls the supply of power to the inductor coil 90. The control circuitry 70 is configured to supply an alternating current to the inductor coil 90.

[0122] The inductor coil 90 is positioned around the heater assembly 12 when the cartridge 10 is received in the cavity 66. The inductor coil 90 has a size and a shape matching the size and shape of a heating region of the heater assembly. The inductor coil 90 is made with a copper wire having a round circular section, and is arranged on a coil former element (not shown). The inductor coil 90 is a helical coil, and has a circular cross-section when viewed parallel to the longitudinal axis of the aerosol-generating device.

[0123] The inductor coil 90 is configured such that when the alternating current is supplied to the inductor coil, the inductor coil generates an alternating magnetic field in the region of the susceptor assembly 12 when the cartridge 10 is received in the cavity 66.

[0124] The inductive heating arrangement further includes a flux concentrator element 91. The flux concentrator element 91 has a greater radius than the inductor coil 90, and so partially surrounds the inductor coil 90. The flux concentrator element 91 is configured to attenuate the alternating magnetic field outside of the aerosol-generating system. This may reduce interference between the alternating magnetic field and other nearby electronic devices and reduce the risk of the alternating magnetic field inductively heating nearby objects outside of the aerosol-generating system.

[0125] In use, the cartridge 10 is received within the device 60, as shown in Figure 1. When a user puffs on the air outlet 38 of the cartridge 10, ambient air is drawn into aerosol-generating system 10 through the air inlets 65, into the device cavity 66, through the restricted portion, and into the cartridge 10 through the cartridge air inlet 32. The air flows through the cartridge 10 from the connection end of the cartridge, across the heater assembly 12, through the airflow passage and to the cartridge air outlet 38 in the mouth end opening. The air flow through the system is shown in more detail in Figure 3, and described in relation to Figure 3, below.

[0126] The control circuitry 70 controls the supply of electrical power from the power supply 72 to the inductor coil 90 when the system is activated.

[0127] When the system is activated, an alternating current is established in the inductor coil 90 which generates alternating magnetic fields in the cavity 66 that penetrate the heater assembly, causing the electrically conductive material of the susceptor element to heat. Liquid aerosolforming substrate is drawn into the heater assembly 12 by the wicking material and supplied to the heating element. The liquid aerosol-forming substrate 42 at the heating element is heated, and volatile compounds from the heated aerosol-forming substrate are released into the air passage of the cartridge 10, which cool to form an aerosol. The aerosol is entrained in the air being drawn through the air passage of the cartridge 10, and is drawn out of the cartridge 10 at the air outlet 38 for inhalation by the user.

[0128] Figure 2 shows a schematic illustration of the aerosol-generating system of Figure 1 partially disassembled. In Figure 2, the cartridge 10 is shown uncoupled from the aerosolgenerating device 60, and the cartridge is shown in the storage position.

[0129] Figure 3 shows a schematic illustration of an interface between the cartridge and the device in an aerosol-generating system of according to the first embodiment of the present disclosure. The direction of air flow through the system is schematically illustrated by dashed arrows in Figure 3.

[0130] The system comprises the cartridge 10 and the device 60. A connection end of the cartridge 10 is opposite the mouth end of the cartridge. The connection end of the cartridge is received by the cavity of the device 60. The cartridge 10 comprises the outer housing 36. A portion of the housing 36 is received into the cavity of the device.

[0131] An airflow path is defined between at least one air inlet and an air outlet of the aerosolgenerating system. A portion of the airflow path is defined between the cartridge 10 and the device 60. In particular, a portion of the airflow path is defined between the housing 36 of the cartridge 10 and the cavity of the device 60. The airflow path comprises the restricted portion 50 formed by a space between the housing 36 and the cavity. The restricted portion 50 comprises a minimum cross-sectional area of the air flow path.

[0132] The restricted portion 50 is defined between the connection end of the cartridge 10 and the cavity of the device 60. The cartridge comprises a longitudinal axis extending between the mouth end and the connection end, and the restricted portion 50 extends parallel to the longitudinal axis of the cartridge 10. When the cartridge 10 is coupled to the device 60, as shown in Figure 3, the restricted portion 50 is situated upstream of the heater assembly 12.

[0133] The cavity comprises a base and a surrounding sidewall for receiving the connection end of the cartridge, wherein the restricted portion 50 is defined between the connection end of the cartridge, in particular the cartridge air inlet 32, and the base of the cavity.

[0134] The base of the cavity comprises two channels 64 arranged on opposite sides of a central protrusion 68 in the base of the cavity. The connection end of the cartridge 10 comprises a recess 46 into which at least a portion of the protrusion 68 of the base of the cavity is received. The central protrusion 68 is in contact with the inner housing 14, when the cartridge 10 is received within the device 60.

[0135] The restricted portion 50 of the airflow path is defined by a gap between the protrusion 68 and the recess 46. The gap has an annular cross-section with a hydraulic diameter of between 0.15 and 0.45 millimetres, preferably 0.3 millimetres. The length of the gap is between 0.5 millimetres and 1.5 millimetres.

[0136] The aerosol-generating system comprises an airflow chamber 22 defined within the housing 36 of the cartridge 10. The airflow chamber 22 is situated immediately downstream of the restricted portion 50, and has a cross-sectional area greater than the cross-sectional area of the restricted portion 50. During use of the aerosol-generating system, for example when a user is puffing on the system, the minimum pressure of the airflow path is at the airflow chamber 22 due to the change in cross-sectional area.

[0137] The aerosol-generating device comprises a puff sensor 63, situated within the protrusion 68 of the cavity. The puff sensor 63 is electrically connected to control circuitry of the device 60. The puff sensor 63 is configured to sense when a user has taken a puff. The puff sensor 63 is in fluid communication with air which is drawn through the system by the user. The puff sensor is in fluid communication with the airflow chamber 22. The control circuitry supplies electrical power to the inductor coil 90 when user puffs on the cartridge 10 are detected by the puff sensor 63.

[0138] As shown by the dashed arrows in Figure 3, in use, when a user puffs on the air outlet of the cartridge 10, ambient air is drawn into aerosol-generating system 10 through the air inlets 65, into the device 60 cavity. The air flows through the channels 64 and then through the annular gap between the recess 46 and the protrusion 68, that is the restricted portion 50. The air then flows into the cartridge 10 through the cartridge air inlet 32. The air flows through the cartridge 10 from the connection end of the cartridge, through the airflow chamber 22 and through an opening in the inner housing 14.

[0139] Inside the inner housing, the air flows across the heater assembly 12, in particular across the heating element 16 so that the air flow can entrain aerosol-forming substrate vaporised by the heating element 16. The air flow including aerosol then flows through the airflow passage defined by the inner housing 14 and to the cartridge air outlet.

[0140] Figure 4 shows a schematic illustration of plan view a cavity according to the first embodiment of the present disclosure. The cavity comprises two channels 64, a central protrusion 68, a base 80 and a surrounding sidewall 84. The device comprises a first elastomeric component 82 and a second elastomeric component 83 situated at the base 80 of the cavity. The first and second elastomeric components 82, 83 are configured to provide at least a partial seal between the cartridge and the device. The two channels 64 are situated between the first and second elastomeric components 82, 83. In use, a connection end of a cartridge will be received within the cavity so that the end face of the housing of the cartridge abuts the first 82 and second 83 elastomeric components. Although the cavity shown in Figure 4 is described with reference to the first embodiment of the present disclosure, it should be understood that the cavity is suitable for other embodiments of the disclosure. Figure 5 shows a schematic illustration of a cross-section of the interface between the cartridge and the device according to the first embodiment of the present disclosure. Figure 5 shows the outer housing 36 of the cartridge received into a cavity of the device. An end face of the outer housing 36 of the cartridge is in contact with a base of the cavity. A recess 46 in the outer housing of the cartridge is situated opposite and facing a protrusion 568 of the base of the cavity, with a gap 65 is defined between the protrusion 68 and the recess 46. In this embodiment, the gap defines the restricted portion 50 of the airflow path of the aerosol-generating system. The gap therefore defines a minimum cross-section of the aerosol-generating system. The RTD of the restricted portion 50, that is the gap 65, is at least 0.6 of a total RTD of the aerosol-generating system. The gap 65 has an annular cross-section, with a cross-sectional area of between 4 and 20 millimetres squared. The hydraulic diameter of the gap 65 is between 0.15 and 0.45 millimetres, preferably 0.3 millimetres. The length of the gap 65 is between 0.5 millimetres and 1 .5 millimetres.

[0141] The base of the cavity comprises a channel 64 for air to flow through to reach the restricted portion 50.

[0142] An airflow chamber 22 is situated immediately downstream of the restricted portion 50 and has a much larger cross-sectional area than that of the restricted portion 50. As such, the minimum pressure of the airflow path is found in the airflow chamber 22.

[0143] Except where described below, aerosol-generating systems according to the second, third, and fourth embodiments of the present disclosure may contain the same features as described herein for the first embodiment.

[0144] Figure 6 shows a schematic illustration of a cross-section of an interface between a cartridge and a device according to a second embodiment of the present disclosure. In the embodiment shown in Figure 6, a gap 665 is defined between a recess 646 of a housing of the cartridge, and a protrusion 668 of a base of a cavity of the device. In this embodiment, a channel 664 recessed into the base of the cavity of the device defines a restricted portion 650 of the airflow path of the aerosol-generating system. The restricted portion 650 comprises a minimum cross- sectional area of the air flow path. In this embodiment, the channel 664, that is the restricted portion, has a rectangular cross-section with a cross-sectional area of between 0.035 and 3 millimetres squared.

[0145] Downstream of the restricted portion 650 is the gap 665. The gap 665 has a cross- sectional area that is much larger than that of the restricted portion 650, so that when a user puffs on the aerosol-generating system, the minimum pressure of the airflow path is found downstream of the restricted portion 650.

[0146] Figure 7 shows a schematic illustration of a cross-section of an interface between a cartridge and a device according to a third embodiment of the present disclosure. In the embodiment shown in Figure 7, a restricted portion 750 is defined by a channel 764 in the base of a cavity of the device, in conjunction with a gap 765. The gap 765 is defined between a protrusion 768 of the base of the cavity and a recess 746 in an outer housing 736 of the cartridge. The channel and the gap have approximately same cross-sectional area, which is the minimum cross-sectional area of the air flow path. The minimum pressure of the system is found at the chamber 722, which is immediately downstream of the channel 764 and the gap 765.

[0147] Figure 8 shows a schematic illustration of a cross-section of an interface between a cartridge and a device according to a fourth embodiment of the present disclosure. In this embodiment, the airflow path does not comprise a channel. There is a space 864 between the device and the cartridge that forms part of the airflow path. The restricted portion 850 is defined by gap 865 between a recess 846 of the outer housing 836 of the cartridge and a protrusion 868 in the base of a cavity of the device. It will be appreciated that in other embodiments the space may define the restricted portion, or that the space and the gap together form the restricted portion, for example in a similar manner as the channel and gap shown in Figures 5 to 7. For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number A is understood as A ± {5 %} of A. Within this context, a number A may be considered to include numerical values that are within general standard error for the measurement of the property that the number A modifies. The number A, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which A deviates does not materially affect the basic and novel characteristic(s) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

Claims

Claims1 . An aerosol-generating system, comprising: a cartridge comprising a housing, a liquid reservoir within the housing, and a heater assembly comprising a heating element, wherein the heater assembly is configured to convey a liquid from the liquid reservoir across the heating element; a device comprising a power supply configured to provide power to the heating element, and a cavity configured to receive at least a portion of the cartridge; and an airflow path defined between at least one air inlet and an air outlet wherein at least a portion of the heating element is positioned in the airflow path, the airflow path comprising a restricted portion between the housing and the cavity, the restricted portion comprising a minimum cross-sectional area of the air flow path.

2. The aerosol-generating system according to claim 1 , wherein a ratio of resistance to draw of the restricted portion to a total resistance to draw of the airflow path is at least 0.6.

3. The aerosol-generating system according to claim 1 or 2, wherein the restricted portion is formed by a space between the cartridge and the device.

4. The aerosol-generating system according to any one of claims 1 to 3, wherein the at least one air inlet is defined between the cartridge and the device, the air outlet is at a mouth end of the cartridge, and a connection end of the cartridge is opposite the mouth end, wherein the connection end is received by the cavity of the device.

5. The aerosol-generating system according to claim 4, wherein the restricted portion is defined between the connection end of the cartridge and the cavity of the device, and wherein the cartridge comprises a longitudinal axis extending between the mouth end and the connection end, and the restricted portion extends parallel and / or perpendicular to the longitudinal axis of the cartridge.

6. The aerosol-generating system according to claim 5, wherein the cavity comprises a base and a surrounding sidewall for receiving the connection end of the cartridge, wherein the restricted portion is defined between the connection end of the cartridge and the base of the cavity.

7. The aerosol-generating system according to claim 6, wherein the connection end of the cartridge comprises an end face perpendicular to the longitudinal axis of the cartridge, whereinthe restricted portion of the airflow path is defined by at least one channel between the end face of the cartridge and the base of the cavity.

8. The aerosol-generating system according to claim 7, wherein the at least one channel is defined in the base of the cavity.

9. The aerosol-generating system according to claim 7 or 8, wherein the at least one channel has a width of between 0.15 and 0.8 millimetres.

10. The aerosol-generating system according to any one of claims 7 to 9, wherein the at least one channel has a depth of between 0.3 and 1 .2 millimetres.11 . The aerosol-generating system according to any one of claims 6 to 10, wherein the cavity comprises at least one elastomeric component configured to provide at least a partial seal between the cartridge and the device.

12. The aerosol-generating system according to any one of claims 6 to 1 1 , wherein the base of the device comprises a protrusion and the connection end of the cartridge comprises a recess configured to receive at least a portion of the protrusion of the base, wherein the restricted portion of the airflow path is defined by a gap between the protrusion and the recess.

13. The aerosol-generating system according to claim 12, wherein the gap has an annular cross-section and has a hydraulic diameter of between 0.15 and 0.45 millimetres, preferably 0.3 millimetres.

14. The aerosol-generating system according to claim 12 or 13, wherein the gap has a length of between 0.5 millimetres and 1.5 millimetres.

15. The aerosol-generating system according to any preceding claim, wherein the aerosolgenerating device comprises a puff sensor.

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