Aerosol-generating device with improved aerosol discharge

Abstract

An aerosol-generating system (400) comprising: a heater assembly (100) comprising: a heating element (104) and a porous body (102) having a liquid absorbing surface (102b) and a heating surface (102a), the heating element being located on the heating surface of the porous body; wherein the heating element is fluid permeable such that, in use, vapor is discharged from the heater assembly in an average vapor discharge direction; wherein the aerosol-generating system further comprises an air inlet and an aerosol outlet to define an airflow path through the aerosol-generating system; wherein the heater assembly is arranged in fluid communication with the airflow path such that air flows through the heater assembly in an average airflow direction, and wherein the heater assembly and the airflow path are arranged such that an angle between an average vapor discharge direction and the average airflow direction is less than 90 degrees.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an aerosol-generating system. In particular, but not exclusively, the present disclosure relates to a hand-held electrically operated aerosol-generating system for heating an aerosol-forming substrate to generate an aerosol and for delivering the aerosol into a user’s mouth. BACKGROUND

[0002] Aerosol-generating systems that heat a liquid aerosol-forming substrate in order to generate an aerosol for delivery to a user are generally known in the art. These aerosol-generating systems typically comprise a portion for holding a liquid aerosol-forming substrate and a heater assembly for heating the liquid aerosol-forming substrate. In one known type of aerosol-generating system, the heater assembly comprises an electrically resistive heating element that is wrapped around a wick that supplies the liquid aerosol-forming substrate to the heating element. In another known type of aerosol-generating system, the heater assembly comprises a solid porous body having a heating element arranged on one of its surfaces. The porous body delivers the liquid aerosol-forming substrate to the heating element. When a user takes a puff on the aerosol-generating system, air is drawn through the aerosol-generating system and an electric current is passed through the heating element, which is thereby heated by resistive or Joule heating. The heating element heats the liquid aerosol-forming substrate supplied by the wick or porous body, thereby releasing volatile compounds from the liquid aerosol-forming substrate, which cool to form an aerosol. The aerosol is then drawn through a mouthpiece of the aerosol-generating system and into the user’s mouth.

[0003] A problem that is known to be encountered with aerosol-generating systems is that the aerosol generated by the heater is not properly entrained in the airflow through the aerosol-generating system. As a result, the aerosol can condense on the inner surfaces of the aerosol-generating system. If enough aerosol condenses on the inner surfaces of the aerosol-generating system, large droplets of the liquid aerosol-forming substrate can form and flow into the user’s mouth. This can result in an unpleasant and undesirable user experience. Furthermore, condensation within the aerosol-generating system can damage the aerosol-generating system, for example, by corroding surfaces or damaging circuitry.

[0004] The present inventors have found that condensation can occur within aerosol-generating systems, possibly due to a number of factors. One factor is the arrangement of the heater assembly relative to the airflow path. Figure 1 shows a schematic cross-sectional view of a known type of heater assembly 1 arranged in an airflow path. The heater assembly 1 comprises a solid porous body 2 and a heating element 4. The heating element 4 is formed as a continuous track on the lower surface of the solid porous body 2, and a plurality of track sections 4a of the heating element 4 are visible in the cross-section in Figure 1. The heater assembly 1 is designed to be arranged in an opening at the base of a reservoir or liquid storage portion (not shown) for holding a liquid aerosol-forming substrate. The upper surface of the heater assembly 1 receives the liquid aerosol-forming substrate from the liquid storage portion, and the liquid aerosol-forming substrate is transported through the solid porous body 2 to the heating element 4, as represented by arrow A in Figure 1.

[0005] The liquid aerosol-forming substrate is vaporised by heat from the heating element 4, and as represented by arrow B in Figure 1, vapour is discharged from the lower surface of the solid porous body 2 between the heating element track sections 4a. The heater assembly 1 is arranged so that its lower surface faces the oncoming airflow path, as represented by arrow C in Figure 1. The airflow path C flows from an air inlet (not shown) towards the lower surface of the heater assembly 1, so that the airflow direction is opposite to the vapour discharge direction B from the lower surface of the heater assembly 1. The vapour discharged from the heater assembly is entrained in the airflow path C, and cools to form an aerosol. The air carrying the aerosol then follows the airflow path C around and past the heater assembly 1, and continues to an aerosol outlet (not shown) where the aerosol is delivered into the mouth of a user.

[0006] In order to entrain the vapour in the airflow, the direction of the vapour needs to change from its vapour discharge direction B to the direction of the airflow path C. The change in direction of the vapour is represented by arrow D in Figure 1. As can be seen in Figure 1, the entrainment of the vapour in the airflow path C requires the airflow to almost completely reverse the vapour discharge direction, so that the vapour flows in the opposite direction to the airflow. The opposite directions of the vapour and the airflow result in a significant loss of momentum of the vapour and the airflow, and can result in recirculation or turbulence in the airflow path C, so that the aerosol is not properly entrained in the airflow and is expelled from the device. Furthermore, the loss of momentum and turbulence of the aerosol and the airflow can result in the vapour impinging on the inner surface (not shown) defining the airflow path C to form condensate, which can accumulate to form droplets of liquid aerosol-forming substrate. This problem can be overcome to some extent by increasing the velocity of the airflow. However, the increased airflow velocity can adversely affect the heater assembly by cooling the heating element, so that it takes a longer time to reach the boiling point of the liquid aerosol-forming substrate, and the aerosolisation performance is reduced.

[0007] Another factor that causes condensation within an aerosol-generating system is the vapour jet velocity. A vapour jet is produced in the heater assembly 1 of Figure 1 when the liquid aerosol-forming substrate evaporates in the solid porous body 2 as heat energy is provided by the heating element 4. The heat energy or heat increases the temperature of the heating track 4a, the solid porous body 2 and the liquid aerosol-forming substrate contained within the porous body 2. Once the boiling temperature of the liquid aerosol-forming substrate is reached, the liquid evaporates. The heating element track 4a of known heater assemblies is typically formed from an electrically resistive metal element which is not fluid permeable. Therefore, vapour cannot escape from the solid porous body 2 in the areas underneath the heating element track 4a and vapour pressure builds up in these areas of the porous body 2. The vapour cannot pass through the heating track 4a and must go around the heating track. Therefore, as shown in Figure 1 by the arrows B, vapour is ejected on either side of the heating track. The present inventors have found that the vapour jet produced by known heater assemblies can have a relatively high velocity when a standard operating amount of power is supplied to the heater assembly. For example, a vapour discharge velocity of 0.5 metres per second was measured when 6.3 Watts of power was provided to the heater assembly. Such a velocity was found to be sufficient to cause the vapour to impact the inner walls of the airflow path C within the aerosol-generating system and form condensation. SUMMARY

[0008] It is desirable to provide an aerosol-generating system which reduces condensation of aerosol within it. It is also desirable to provide an aerosol-generating system which increases the entrainment of aerosol in the airflow through the system to improve the discharge of aerosol.

[0009] According to an example of the present disclosure, there is provided an aerosol-generating system. The aerosol-generating system can comprise a heater assembly. The heater assembly can comprise a heating element. The heating element can be configured to vaporise a liquid aerosol-forming substrate. The heater assembly can comprise a porous body. The porous body can be configured to deliver the liquid aerosol-forming substrate to the heating element. The porous body can have a liquid- absorbing surface. The porous body can have a heating surface. The heating element can be located on the heating surface of the porous body. The heating element can be fluid permeable. In use, vapour can be discharged from the heater assembly in a mean vapour discharge direction. The aerosol-generating system can comprise an air inlet. The aerosol-generating system can comprise an aerosol outlet. The air inlet can be in fluid communication with the aerosol outlet. An airflow path can be defined through the aerosol-generating system. The heater assembly can be arranged in fluid communication with the airflow path. In use, air can flow past the heater assembly in a mean airflow direction. The heater assembly and the airflow path can be arranged such that the angle between the mean vapour discharge direction and the mean airflow direction is less than 135 degrees.

[0010] According to examples of the present disclosure, there is provided an aerosol-generating system comprising a heater assembly. The heater assembly comprises a heating element for vaporising a liquid aerosol-forming substrate and a porous body for conveying the liquid aerosol-forming substrate to the heating element. The porous body has a liquid- absorbing surface and a heating surface. The heating element is located on the heating surface of the porous body. The heating element is fluid permeable such that, in use, vapour is discharged from the heater assembly in a mean vapour discharge direction. The aerosol-generating system further comprises an air inlet and an aerosol outlet. The air inlet is in fluid communication with the aerosol outlet to define an airflow path through the aerosol-generating system. The heater assembly is arranged in fluid communication with the airflow path such that air flows through the heater assembly in a mean airflow direction. The heater assembly and the airflow path are arranged such that the angle between the mean vapour discharge direction and the mean airflow direction is less than 135 degrees.

[0011] As used herein, the term "located on" encompasses arrangements in which the heating element is positioned in direct contact with the heating surface of the porous body, as well as arrangements in which the heating element is indirectly located on the heating surface of the porous body (i.e. another component or layer can be arranged between the heating element and the heating surface).

[0012] As used herein, the term "angle between the mean vapour discharge direction and the mean airflow direction" refers to the angle between the direction of travel of the vapour discharged from the heater assembly and the airflow within the airflow path. For example, an angle of zero degrees would mean that the airflow and the vapour discharge travel in the same direction, while an angle of 180 degrees would mean that the directions of travel of the airflow and the vapour discharge are directly opposite to each other.

[0013] Advantageously, by arranging the heater assembly and the airflow path such that the angle between the mean vapour discharge direction and the mean airflow direction is less than 135 degrees, the mean airflow direction is not directly opposite to the mean vapour discharge direction. As a result, the momentum of the vapour and the airflow is not reduced to the same extent as when the mean airflow direction is directly opposite to the mean vapour discharge direction. This reduces the tendency for recirculation and turbulence to occur in the airflow path, and the vapour is less likely to impinge on the internal surfaces of the aerosol-generating system. As a result, aerosol condensation within the aerosol-generating system is less likely to occur.

[0014] The mean vapour discharge direction can be substantially perpendicular to the heating surface. As used herein, the term "substantially perpendicular" means 90 degrees ± 10 degrees, preferably ± 5 degrees.

[0015] The advantage of the mean vapour discharge direction being substantially perpendicular to the heating surface is that it makes it simple to orient the mean vapour discharge direction relative to the mean airflow direction, as the vapour will be discharged substantially perpendicular to the heating surface of the porous body. As a result, by angling the heater assembly appropriately relative to the airflow in the airflow path (or vice versa), a desired angle between the mean vapour discharge direction and the mean airflow direction can be achieved.

[0016] The heater assembly can be positioned at a location along the airflow path. The heating surface of the heater assembly can be in fluid communication with the airflow path. The heating surface can be arranged substantially parallel to the airflow path. The heating surface can be arranged substantially parallel to the average airflow direction. The heating surface can be arranged substantially perpendicular to the airflow path. The heating surface can be arranged substantially perpendicular to the average airflow direction. The heating surface can face in a downstream direction of the airflow path. The heater assembly can be arranged to one side of the airflow path. The heater assembly can be arranged within the airflow path. The airflow path can be split such that air flows past more than one surface of the heater assembly. The airflow path can comprise a first airflow channel arranged substantially parallel to the heating surface. The airflow path can comprise a second airflow channel arranged substantially perpendicular to the heating surface. The second airflow channel can begin at the heating surface.

[0017] The heater assembly and the airflow path can be arranged such that the angle between the average vapour discharge direction and the average airflow direction is less than 110 degrees, preferably less than 100 degrees.

[0018] The heater assembly and the airflow path can be arranged such that the angle between the average vapour discharge direction and the average airflow direction is about 90 degrees. This arrangement results in vapour being discharged at an angle substantially perpendicular to the average airflow direction. The average vapour discharge direction has no velocity or directional component opposite to the airflow direction and so any momentum loss of the airflow is reduced. This reduces the tendency for recirculation and turbulence to occur in the airflow path and vapour is less likely to impinge on internal surfaces of the aerosol-generating system. Furthermore, entrainment of vapour in the airflow is improved. As a result, condensation of aerosol within the aerosol-generating system is less likely to occur.

[0019] The heater assembly and the airflow path can be arranged such that the angle between the average vapour discharge direction and the average airflow direction is less than 90 degrees. In this arrangement, the average vapour discharge direction has no velocity or directional component opposite to the airflow direction and in fact has a velocity and directional component in the same direction as the average airflow direction. Thus, any momentum loss of the airflow is further reduced. This reduces the tendency for recirculation and turbulence to occur in the airflow path and vapour is less likely to impinge on internal surfaces of the aerosol-generating system. Furthermore, entrainment of vapour in the airflow is improved. As a result, condensation of aerosol within the aerosol-generating system is less likely to occur.

[0020] The heater assembly and the airflow path can be arranged such that the angle between the average vapour discharge direction and the average airflow direction is about 45 degrees. The heater assembly and the airflow path can be arranged such that the angle between the average vapour discharge direction and the average airflow direction is less than 45 degrees.

[0021] The heater assembly and airflow path can be arranged such that the average vapour discharge direction and the average airflow direction are substantially the same. In this arrangement, as the average vapour discharge direction and the average airflow direction are the same, there is effectively no loss of momentum of the airflow. This reduces the tendency for recirculation and turbulence to occur in the airflow path, and it is less likely that vapour will impinge on the internal surfaces of the aerosol-generating system. Furthermore, the entrainment of vapour in the airflow is improved. As a result, condensation of aerosol within the aerosol-generating system is less likely to occur.

[0022] The porous body can comprise at least one airflow guide to direct airflow towards the heating surface. Advantageously, this helps to direct airflow to the location where vapour is discharged to improve the entrainment of aerosol in the airflow.

[0023] The air inlet can be distal of the heater assembly. The air inlet can be in a region of the heater assembly, for example, the air inlet can be positioned at a location along the length of the aerosol-generating system that substantially corresponds to the location of the heater assembly.

[0024] The terms "distal", "proximal", "upstream" and "downstream" are used herein to describe the relative positions of components or component parts of the aerosol-generating system. The aerosol-generating system according to the present disclosure has a proximal end and an opposing distal end, through which, in use, aerosol exits the article or device for delivery to a user. The proximal end of the aerosol-generating system can also be referred to as the mouth end. In use, a user draws on the proximal end of the aerosol-generating system in order to inhale aerosol generated by the aerosol-generating system. The terms upstream and downstream are in relation to the direction of movement of airflow or aerosol through the aerosol-generating system when a user draws on the proximal end of the aerosol-generating system. The proximal end of the aerosol-generating system is downstream of the distal end of the aerosol-generating system.

[0025] The cross-sectional area of the airflow path in the region of the heater assembly can be configured such that, in use, the airflow velocity in the region of the heater assembly is between 0.1 and 2 metres per second, preferably between 0.5 and 1.5 metres per second, and more preferably about 1 metre per second. The cross-sectional area of the airflow path in the region of the heater assembly can be between 9.15 square millimetres and 183 square millimetres. This range of cross-sectional areas will provide airflow velocities in the region of the heater assembly in the range of between 0.1 and 2 metres per second in the case of a 55 millilitre (55 cubic centimetres) puff of 3 second duration based on a standard Coresta puff profile. Such a puff corresponds to a volumetric flow rate of 18.3 cubic centimetres per second through the airflow path. This range of airflow velocities has been found to effectively entrain vapour discharged from different designs of heating element without excessively cooling the heating element.

[0026] The porous body can comprise a plurality of interconnected open-cell pores. The porous material can have a porosity of between 20% and 80%.

[0027] The porous body can have any suitable geometry. For example, the porous body can be in the shape of a cube or cuboid, or it can have the shape of a disc or a cylinder, or a combination of the above. The heating surface of the porous body can be flat or curved. The liquid uptake surface of the porous body can be flat or curved. The liquid uptake surface of the porous body can have recesses or pores through which at least a portion of the liquid aerosol-forming substrate is taken up.

[0028] The porous body can be substantially incompressible. The porous body can be incompressible.

[0029] The porous body can be made of any suitable material. The porous body can be made of a material having a thermal conductivity of less than 150 W / mK, preferably less than 100 W / mK, and more preferably less than 60 W / mK. The porous body can be made of a non-conductive material.

[0030] The porous body can comprise a porous ceramic body. The porous body can comprise a ceramic. The porous body can comprise any suitable inert or biocompatible ceramic. Examples of suitable ceramics include, but are not limited to, AI2O3, Zr02, Si3N4, SiC, Ti3AlC2, BN, AIN, Si02, MgO, mica, diatomite, silicates, suicides, borides, glass, or combinations thereof. An advantage of using ceramic materials is that they are thermally stable at the temperatures at which the heater assembly is typically operated, and typically have a thermal decomposition temperature that is significantly higher than the thermal decomposition temperature of conventional wicks. This can help to reduce the risk of producing undesirable by-products during heating.

[0031] The porous body can comprise a porous glass body.

[0032] The porous body can comprise capillary materials that transport liquid through the material by capillary action. The porous body can have a fibrous or porous structure. The porous body can comprise a bundle of capillaries. For example, the porous body can comprise a plurality of fibres or threads or other capillary tubes. The porous body can comprise fibres or threads of cotton or treated cotton (e.g. acetylated cotton). Other suitable materials can also be used, for example ceramic or graphite based fibrous materials or materials made from spun, drawn or extruded fibres such as glass fibres, cellulose acetate or any suitable heat resistant polymer.

[0033] The porous body can be constructed from a monolithic material or a hybrid material.

[0034] The thickness of the porous body can be configured such that heat loss of the liquid held by the conduction to the liquid reservoir or liquid storage portion is negligible. The thickness of the porous body can vary depending on the material from which the porous body is made and the thermal properties of the liquid being transported by the porous body. The porous body can have a thickness of between 1 mm and 10 mm, preferably between 2 mm and 8 mm, and more preferably between 3 mm and 6 mm.

[0035] The heating element can be configured to have a vapor discharge velocity in the range of 0.1 to 1 meter per second. Keeping factors such as the power supplied to the heating element constant, the vapor discharge velocity can be adjusted by adjusting the form of the heating element, as discussed further below.

[0036] The heating element can comprise a non-porous heating element or a track. As discussed above, a non-porous heating element causes vapor pressure to build up under the heating element and results in a high vapor discharge velocity.

[0037] The heating element can be porous. The heating element can have a porosity of between 20% and 80%.

[0038] The heating element can comprise an electrically resistive heating element. The heating element can be made of any suitable electrically conductive material. Suitable materials include, but are not limited to: semiconductors (such as doped ceramics), electrically “conductive” ceramics (such as, for example, molybdenum disilicide), carbon, graphite, metals, metal alloys, and composites made of ceramic and metallic materials. Such composites can include doped or undoped ceramics. Examples of suitable doped ceramics include doped silicon carbides. Examples of suitable metals include titanium, zirconium, tantalum, and platinum group metals. Examples of suitable metal alloys include stainless steel; constantan; nickel-, cobalt-, chromium-, aluminum-, titanium-, zirconium-, hafnium-, niobium-, molybdenum-, tungsten-, tin-, gallium-, manganese- and iron-containing alloys; and super-alloys based on nickel, iron, cobalt; stainless steel, iron-aluminum based alloys, and iron-manganese-aluminum based alloys. TITANIUM® is a registered trademark of the Titanium Metals Corporation.

[0039] In one example, the heating element can be made of a metal alloy selected from one or more of: a Ni-Cr alloy, a NiCrAlY alloy, a FeCrAl alloy (e.g., Kanthal), a FeCrAlY alloy, a Fe3Al alloy, a Ni3Al alloy, a NiAl alloy, a CuNi alloy.

[0040] In another example, the heating element can be made of stainless steel, such as a 300 series stainless steel, such as AISI 304, 316, 304L, 316L.

[0041] In another example, the heating element can be made of an electroceramic including, but not limited to, MoSi2, doped SiC, indium tin oxide (ITO), lanthanum-doped strontium titanate (SLT), yttrium-doped strontium titanate, or a combination thereof.

[0042] The heating element can comprise a doped portion of the porous body. The porous body can be doped such that the portion of the porous body acting as the heating element is electrically conductive. Doping the porous body can be advantageous as it avoids altering the porosity of the porous body. This can be advantageous over other known techniques of forming a heating element which involve depositing the heating element by thin film or thick film techniques which can degrade the properties of the porous body, in particular the porosity. The thickness of the doped portion can be between 5 microns and 100 microns. The thickness of the doped portion can be increased in cases where the cross-sectional area of the heating element is small or where the required heating resistance is high. The dopant used to dope the porous body can be an n-type dopant or a p-type dopant. The dopant can be any one of, but is not limited to, nitrogen, phosphorus, aluminium or boron. The interface between the heating element and the porous body can comprise a portion of the partially doped porous material.

[0043] The heating element can comprise a porous layer of electrically conductive material. Advantageously, a heating element comprising a porous layer of electrically conductive material allows current to flow through the heating element such that the heating element can be resistively heated, and also allows vapour to travel through the heating element via the pores in its porous structure. Thus, vapour discharge through the porous heating element occurs. This avoids the build-up of vapour pressure underneath the heating element and high velocity vapour discharge at the sides of the heating element. The inventors have found that this arrangement results in a consistent vapour across the heating element, as well as a lower vapour discharge velocity of approximately 0.1 m / s. Such a low vapour discharge velocity means that the vapour is easily carried away by the airflow, thereby reducing the impact of the vapour on the internal walls of the aerosol-generating system.

[0044] The heating element can comprise a porous metal film. The porous metal film can comprise a thick film, i.e. the porous metal film can have a thickness of between 5 pm and 50 pm, preferably between 10 pm and 30 pm, more preferably between 15 pm and 25 pm. The porous metal film can comprise a thin film, i.e. the porous metal film can have a thickness of less than 5 pm, preferably less than 3 pm, more preferably less than 2 pm.

[0045] The heating element can comprise a metal foam. The metal foam can have a thickness of less than 100 pm, preferably less than 50 pm, more preferably less than 30 pm.

[0046] The heating element can define a heated region. The heated region can cover at least a portion of the heating surface. The heated region can substantially cover the entire heating surface. The heated region can have any suitable shape. The heated region can be square or rectangular, the heated region can be circular or elliptical. The heated region can be less than 30mm 2 , preferably less than 20mm 2 , more preferably less than 15mm 2 , even more preferably less than 10mm 2 .

[0047] The heating element can be configured to provide a power density between 0.3 W / mm 2 and 2 W / mm 2 and preferably between 0.5 W / mm 2 and 1.5 W / mm 2 . The heating element can be configured to provide a power density of at least 0.5 W / mm 2 and preferably at least 1 W / mm 2 .

[0048] The inventors have advantageously found that the power density applied to the heating element is a more important factor in determining the amount of aerosol generated than the power applied to the heating element itself. As used herein, the term "power density" refers to the amount of electrical power applied to the heating element per unit of heated region.

[0049] A first dimension of the heated region of the heating element can be in the range 2mm to 10mm. A second dimension of the heated region of the heating element can be in the range 2mm to 10mm. The dimensions of the heated region or heating surface of the heating element can be 5mm x 6mm, or 5mm x 4mm, or 5mm x 3mm, or 5mm x 2mm.

[0050] The heating element can have an electrical resistance at room temperature between 0.5Ω and 1.5Ω, between 0.7Ω and 1.3Ω or preferably about 1Ω.

[0051] The electrically heated element can comprise a discrete, solid, pre-formed component. The electrically heated element can have any suitable shape or form. Examples of suitable shapes and forms include, but are not limited to, a band, a ribbon, a filament, a wire, a mesh, a flat spiral coil, a fibre or a fabric.

[0052] The electrically heated element can be formed from an electrically conductive material deposited onto the heating surface. As used herein, the term "electrically conductive material" denotes a material having a conductivity of 1 x 10 -2A material having an electrical resistivity of Ωm or less. As used herein, the term "deposited" means applied as a layer or coating by a physical or chemical process, for example in the form of a liquid, plasma or vapour, which subsequently condenses or aggregates to form the electrical heating element, rather than simply laid on or fixed to the porous body as a solid, pre-formed component. The heating element can be deposited or patterned by thick film technology, such as screen printing, inkjet printing, aerosol jet printing, LDS (laser direct structuring). A template can be added in the heating element material which will be removed upon sintering to form a porous structure and enhance liquid evaporation and reduce vapour emission speed. The heating element can be deposited or patterned by thin film technology, such as PVD (physical vapour deposition) (e.g. evaporation or sputtering) or CVD (chemical vapour deposition) or similar technology.

[0053] The heater assembly can further comprise first and second electrical contacts connected to the heating element. Each electrical contact can be provided at an opposite side of the heating surface. The electrical heating element can extend between the electrical contacts. The electrical heating element can form an electrical connection therebetween.

[0054] The electrical contacts can be formed from any suitable material. Examples of materials suitable for use in the electrical contacts include, but are not limited to, copper, zinc and gold.

[0055] In one example, the first and second electrical contacts can be formed from an electrically conductive material deposited directly onto the heating surface of the porous body.

[0056] The heating element and the porous body can be integrally formed. Providing a heating element integrally formed with the porous body can advantageously provide a more robust and reliable connection between the heating element and the porous body. This can advantageously help to improve heat transfer between the heating element and the porous body.

[0057] Integrally forming the heating element with the porous body can also advantageously provide a heating element that is more easily and reliably manufactured, thus resulting in a more energy efficient heating element capable of generating a more consistent aerosol. This in turn can provide an improved and more enjoyable experience for a user of the aerosol-generating system. Such an arrangement can also help to reduce the likelihood of a user experiencing dry heating or dry draws.

[0058] The advantage of integrally forming the heating element with the porous body is that it helps to alleviate manufacturing tolerance issues experienced with wick and coil heaters and other arrangements in which the heating element is separate from the liquid transport element. The size and arrangement of the heating element relative to the porous body is also fixed, which helps to produce a more consistent aerosol. This is because the heating element is fixed to the porous body, which helps to supply the heating element with liquid aerosol-forming substrate. This also helps to prevent unwanted heat loss, which helps to improve energy efficiency.

[0059] By forming the heating element integrally with the porous body, the resulting aerosol- generating system can benefit from reduced material requirements. This is because the need for an intermediate component to secure the heating element relative to the porous body can be reduced or eliminated entirely. Material savings can result in cost savings for the overall aerosol-generating system. An additional advantage of reduced material requirements in the overall aerosol-generating system is to provide a more sustainable and environmentally friendly solution.

[0060] As the heating element is formed integrally with the porous body, the heating surface of the porous body can not be a clearly defined surface. The porous body and the heating element can be made from a single monolithic portion of porous material. In this case, the heating element can be a portion of the porous material that has been configured to generate heat. This can be achieved by, for example, doping a portion of the porous material or diffusing an electrically conductive material into the porous material, as described in more detail below. Thus, the heating surface of the porous body can represent the interface between the portion of the porous material configured to transport the liquid aerosol-forming substrate and the portion of the porous material configured to generate heat. Depending on the manner in which the heating element is formed, the heating surface of the porous body can be a gradual interface between the portion of the porous material configured to transport the liquid aerosol-forming substrate and the portion of the porous material configured to generate heat.

[0061] Alternatively, the porous body and the heating element can be formed as two separate parts that are assembled together.

[0062] The heating element can be bonded to the heating surface of the porous body. Providing a heater assembly in which the heating element is bonded to the heating surface of the porous ceramic body has the advantage that a robust and reliable connection can be established between the heating element and the porous ceramic body. This can advantageously help to improve heat transfer between the heating element and the porous ceramic body.

[0063] The heating element can have a tapered cross-sectional shape. The heating element can taper in a direction from the liquid uptake surface to the heating surface.

[0064] The liquid uptake surface of the porous body can have a different area to the area of the heating surface of the porous body.

[0065] A heater assembly whose heating surface has the same area as the liquid uptake surface can be inefficient due to heat generated by the heater not being used to vaporise the aerosol-forming substrate. An inefficient heater assembly provides a reduced throughput of aerosol.

[0066] Advantageously, providing a porous body in which the heating surface and the liquid uptake surface have different areas can improve the throughput of aerosol generated by the heater assembly compared to a heater assembly in which the heating surface has the same area as the liquid uptake surface.

[0067] For example, in a heater assembly in which the area of the heating surface of the porous body is less than the area of the liquid uptake surface of the porous body, heat flow from the heating element towards the liquid uptake surface and then to the liquid storage portion by conduction can be reduced. The relatively smaller heating surface provides a small heat transfer area through which heat is transferred from the heating element to the porous body and towards the liquid uptake surface by conduction.

[0068] Thus, reducing heat loss from the heating element to the bulk of the porous body can improve heating efficiency, as more thermal energy provided by the heating element can be used to vaporise the aerosol-forming substrate. Thus, a porous body shaped such that the heating surface has a smaller area than the liquid uptake surface can increase the throughput of aerosol generated by the heater assembly. For example, in a heater assembly in which the area of the liquid uptake surface of the porous body is less than the area of the heating surface of the porous body, the smaller area of the liquid uptake surface can cause a reduction in heat flow from the heating element to the liquid uptake surface through the aerosol-forming substrate via thermal conduction.

[0069] Thus, reducing heat flow from the heating surface to the liquid uptake surface can improve heating efficiency, as more thermal energy provided by the heating element can be used to vaporise the liquid aerosol-forming substrate. Thus, a porous body shaped such that the liquid uptake surface has a smaller area than the heating surface can provide increased heating efficiency, which can increase the throughput of aerosol generated by the heater assembly.

[0070] Improving heating efficiency can reduce power consumption during use of the heater assembly.

[0071] The area of the heating surface of the porous body can be less than the area of the liquid uptake surface of the porous body. The area of the liquid uptake surface of the porous body can be greater than the area of the heating surface of the porous body.

[0072] Advantageously, when the porous body has a shape such that the heating surface has a smaller area than the liquid uptake surface, heat flow from the heating element towards the liquid uptake surface and then to the liquid storage portion by conduction can be reduced. The relatively smaller heating surface provides a small heat transfer area through which heat is transferred from the heating element to the porous body and towards the liquid uptake surface by conduction.

[0073] Thus, reducing heat loss from the heating element to the bulk of the porous body can improve heating efficiency, as more thermal energy provided by the heating element can be used to vaporise the aerosol-forming substrate. Thus, a porous body shaped such that the heating surface has a smaller area than the liquid uptake surface can increase the throughput of aerosol generated by the heater assembly.

[0074] Advantageously, the shape of the porous body such that the heating surface has a smaller area than the liquid uptake surface can reduce the area of the heating surface that is close enough to the heating element to allow liquid aerosol-forming substrate to be transported to the heating surface for evaporation. In other words, the size and shape of the heating surface can be more closely matched to the size and shape of the heating element. As a result, more liquid aerosol-forming substrate can be transported from the liquid uptake surface to the region of the heating surface that is close to the heating element, which can result in more liquid aerosol-forming substrate being evaporated at the heating surface. More liquid aerosol-forming substrate evaporation can increase the throughput of aerosol generated by the heater assembly. Furthermore, this arrangement can allow the power density at the heating surface to be maximised, which also improves heating efficiency.

[0075] Advantageously, the liquid uptake surface having a larger area than the heating surface can allow the liquid uptake surface to receive a larger volume of liquid aerosol-forming substrate from the liquid storage portion. As a result of the relatively smaller area of the heating surface, the flow rate of liquid aerosol-forming substrate to the heating element can be higher when the liquid aerosol-forming substrate is transported through the porous body and towards the heating surface than in the case of a typical heater assembly. Higher flow rates of liquid aerosol-forming substrate at the heating element can increase the throughput of aerosol generated by the heater assembly.

[0076] The ratio of the area of the heating surface of the porous body to the area of the liquid uptake surface of the porous body can be less than or equal to 0.9. The ratio of the area of the heating surface of the porous body to the area of the liquid uptake surface of the porous body can be at least 0.1. The ratio of the area of the heating surface of the porous body to the area of the liquid uptake surface of the porous body can be between 0.1 and 0.9.

[0077] The area of the heating surface of the porous body can be greater than the area of the liquid uptake surface of the porous body. The area of the liquid uptake surface of the porous body can be less than the area of the heating surface of the porous body.

[0078] Advantageously, when the porous body has a shape such that the liquid uptake surface has a smaller area than the heating surface, the smaller area of the liquid uptake surface can result in a reduction in heat flow from the heating element to the liquid uptake surface via thermal conduction through the aerosol-forming substrate. As a result, reducing the heat flow from the heating surface to the liquid uptake surface can improve thermal efficiency, as more thermal energy provided by the heating element can be used to evaporate liquid aerosol-forming substrate. Therefore, the porous body having a shape such that the liquid uptake surface has a smaller area than the heating surface can provide increased heating efficiency, which can increase the throughput of aerosol generated by the heater assembly.

[0079] Advantageously, the shape such that the liquid absorbing surface has a smaller area of the porous body than the heating surface can reduce the area of the heating surface that is not close enough to the heating element to allow liquid aerosol-forming substrate to be transported to the heating surface for vaporisation. In other words, the size and shape of the heating surface can be more closely matched to the size and shape of the heating element. As a result, more liquid aerosol-forming substrate can be transported from the liquid absorbing surface and reach the region of the heating surface proximate to the heating element, which can result in more liquid aerosol-forming substrate being vaporised at the heating surface. More liquid aerosol-forming substrate vaporisation can increase the throughput of aerosol generated by the heater assembly.

[0080] The heating surface of the porous body can be convex in one or both of the first lateral direction and the second lateral direction. The first lateral direction can be orthogonal to the second lateral direction.

[0081] Advantageously, by providing a porous body having a heating surface that is convex in one or both of the first lateral direction and the second lateral direction can enable the surface area of the heating surface to be increased without increasing the width of the heating surface. This can improve the efficiency of the aerosol-generating system in vaporising liquid aerosol-forming substrate, while helping to avoid the need to redesign other components of the aerosol-generating system to accommodate the porous ceramic body.

[0082] Providing a heating surface that is convex along one or both of the first lateral direction and the second lateral direction can help to avoid or minimise recirculation of the airflow proximate to the heater assembly. In particular, the convex heating surface can help to avoid or minimise recirculation of the airflow proximate to the central region of the heater assembly. This can reduce the level of turbulence in the airflow proximate to the heater assembly. As discussed above, reducing the level of turbulence in the airflow proximate to the heater assembly can improve the entrainment of vapour of the aerosol-forming substrate in the airflow. This can improve the quality of the aerosol generated by the aerosol-generating system.

[0083] Improving the entrainment of vapour in the airflow through the aerosol-generating system can avoid or reduce condensation of vapour to form large droplets of liquid aerosol-forming substrate. This can help to avoid an unpleasant and undesirable user experience.

[0084] Improving the entrainment of vapour in the airflow through the aerosol-generating system can avoid or reduce condensation of vapour on the internal surfaces of the aerosol-generating system. This can help to avoid or minimise damage to the aerosol-generating system, and can allow optimal functioning of the aerosol-generating system.

[0085] The heating surface of the porous body can be convex in a single lateral direction.

[0086] The heating surface of the porous body can be convex in both the first lateral direction and the second lateral direction.

[0087] The heating surface of the porous body can be convex in one or both of the first lateral direction and the second lateral direction, based on the configuration of the heater assembly relative to the one or more airflow paths of the aerosol-generating system. The heater assembly can be configured to minimise the level of turbulence in the airflow adjacent to the heater assembly. For example, it can be advantageous to arrange the heater assembly in the aerosol-generating system such that air drawn into the aerosol-generating system follows a curved path along at least a portion of the curved surface of the heater assembly.

[0088] The heating element can be convex in one or both of the first lateral direction and the second lateral direction.

[0089] The curvature of the heating element in the first lateral direction can be substantially the same as the curvature of the heating surface of the porous body in the first lateral direction. The curvature of the heating element in the second lateral direction can be substantially the same as the curvature of the heating surface of the porous body in the second lateral direction. The curvature of the heating element in both the first lateral direction and the second lateral direction can be substantially the same as the curvature of the heating surface of the porous body in both the first lateral direction and the second lateral direction, respectively.

[0090] The heater assembly can comprise a thermally insulating layer. The thermally insulating layer can have a lower thermal conductivity than the porous body. The thermally insulating layer can be disposed between the porous body and the heating element. The thermally insulating layer can be in contact with each of the porous body and the heating element. The thermally insulating layer can be configured to reduce heat transfer from the heating element to the porous body.

[0091] Advantageously, by providing a thermally insulating layer disposed between the porous body and the heating element, heat loss from the heating element to the porous body and the liquid within the porous body is reduced. This provides a more efficient heater assembly, in which the amount and number of uses of the device by a user before the device power source, such as a battery, is depleted can be increased. The inventors estimate that in known devices, approximately one third of the energy from the heating element is lost through conduction in the porous body and the liquid in the porous body. The remaining two thirds is used to generate an aerosol by heating the liquid aerosol-forming substrate. In the arrangements described herein, these energy losses are reduced. In particular, the thermally insulating layer reduces the propagation or conduction of heat from the heating element towards or through the porous body. This reduction in conduction can concentrate heat to the heating surface of the porous body, minimising heat dissipation and increasing the heating efficiency of the heater assembly.

[0092] The thermally insulating layer can comprise a thermally insulating material. The thermally insulating material can have a lower thermal conductivity than the porous body. The thermally insulating material can have a higher porosity than the porous body. This has the advantage of providing a thermally insulating layer which is particularly effective in reducing energy losses, whilst being easy to manufacture.

[0093] The thermal barrier layer can comprise a material having a thermal conductivity of less than 40 Watts per metre Kelvin. This has the advantage of providing a thermal barrier layer which is effective in reducing energy losses through the porous body. The thermal barrier layer can comprise a material having a thermal conductivity of less than 10 Watts per metre Kelvin. This has the advantage of providing a thermal barrier layer which is particularly effective in reducing energy losses through the porous body.

[0094] The thermal barrier layer can extend entirely between the porous body and the heating element. This has the advantage of providing a more effective barrier between the heating element and the porous body and thus is particularly effective in reducing energy losses through the porous body.

[0095] The thermal barrier layer can comprise one or more of: alumina, zirconia, zirconia with magnesium oxide, glass-ceramic, quartz, porous polymer. The porous polymer can be polyimide.

[0096] The thermal barrier layer can comprise alumina having a thermal conductivity of 20-40 Watts per metre Kelvin. The thermal barrier layer can comprise a material having a thermal conductivity of less than 10 Watts per metre Kelvin, such as zirconia with or without magnesium oxide, glass-ceramic, quartz. The use of alumina, zirconia with or without magnesium oxide, glass-ceramic, quartz is advantageous because these materials are compatible with manufacturing processes involving sintering and thus it is easier to manufacture a heater assembly having a thermal barrier layer of one of these materials.

[0097] The thermal barrier layer can have a thickness of between 0.1 mm and 2 mm. A thermal barrier layer having such a thickness is particularly suitable for reducing energy losses from the heating element to the porous body. Preferably, the thermal barrier layer has a thickness of between 0.5 mm and 1.5 mm. A thermal barrier layer having such a thickness is also suitable for reducing energy losses from the heating element to the porous body.

[0098] The average pore size of the porous body can vary between the liquid- absorbing surface and the heating surface.

[0099] Providing a porous body comprising a variation in pore size between the liquid-absorbing surface and the heating surface can advantageously help to control the delivery of liquid aerosol-forming substrate from a reservoir of liquid aerosol-forming substrate to the heating element. In particular, the variation in pore size between the liquid-absorbing surface and the heating surface can allow the porous body to provide a consistent supply of aerosol-forming substrate to the heating surface. This can advantageously avoid undesirable "dry heating". In addition, the porous body of the present application can also advantageously prevent leakage of liquid aerosol-forming substrate from the heating surface of the porous body.

[0100] The average pore size of the porous body can vary in any way between the liquid- absorbing surface and the heating surface. The average pore size can vary from relatively larger pores at the liquid-absorbing surface to relatively smaller pores at the heating surface.

[0101] Providing a porous body with a larger average pore size at the liquid uptake end and a smaller average pore size at the heating end can particularly facilitate efficient transfer of liquid aerosol-forming substrate from the liquid uptake end of the porous body to the heating end of the porous body without allowing leakage. In particular, the inventors of the present application have found that liquid aerosol-forming substrate is transferred from the liquid uptake end of the porous body to the heating end of the porous body by capillary action. The speed at which the liquid aerosol-forming substrate moves through the porous body depends on a number of factors including, but not limited to, the geometry of the pores, the surface tension between the liquid aerosol-forming substrate and the porous body, the viscosity of the liquid aerosol-forming substrate, the surface tension of the liquid aerosol-forming substrate. The inventors of the present application have found that a balance of these factors is required to provide efficient transfer of liquid aerosol-forming substrate to the heating surface of the porous body while preventing leakage of the liquid aerosol-forming substrate.

[0102] First, in order to provide efficient capillary flow of the liquid through the porous body, the capillary pressure must overcome the viscous resistance pressure. Second, in order to prevent leakage, the inertial force must not overcome the capillary pressure. These two requirements are achieved by providing a porous body with larger pores at the liquid uptake end and smaller pores at the heating end.

[0103] In particular, the inventors of the present application have recognised that the viscosity of the liquid aerosol-forming substrate varies with temperature. In particular, the viscosity of the liquid aerosol-forming substrate decreases as its temperature increases. As a result, the viscosity of the liquid aerosol-forming substrate decreases as it moves through the porous body from the liquid uptake surface to the heating surface. Since the liquid aerosol-forming substrate is transported through the porous body by capillary forces, the capillary forces need to overcome the viscous resistance of the liquid. The viscous resistance decreases as the viscosity decreases. As a result, the capillary forces required to move the liquid aerosol-forming substrate can be reduced towards the heating surface of the porous body while still maintaining the same flow rate. Therefore, the average pore size of the porous body can be reduced towards the heating surface without reducing the flow of the liquid aerosol-forming substrate through the porous body.

[0104] The heating element can comprise a plurality of tracks or track portions arranged electrically in parallel. The heating element resistance at room temperature can be between 0.5 Ohm and 1.5 Ohm, preferably between 0.7 Ohm and 1.3 Ohm, and more preferably 1 Ohm. The resistance of the heating element can be matched to the requirements of the control electronics.

[0105] The at least two electrically parallel heating tracks in the electrically parallel heating track can have similar electrical resistances to each other, or have the same electrical resistance to each other. Preferably, all electrically parallel heating tracks have similar or the same electrical resistance to each other. The electrically parallel arranged heating tracks can have different electrical resistances, which is particularly beneficial in a heater assembly where it is advantageous for a zone of the heating element to generate a different power level. For example, this can be the case to compensate for higher heat losses in an outer portion of the heating element. Thus, the heating tracks on the outer portion or outer portions of the heating element can be designed to have a lower electrical resistance (which can generate more heat) than the heating tracks in the center of the heating element.

[0106] The heating element can comprise a plurality of tracks or track portions. The plurality of tracks or track portions can be electrically parallel arranged. By electrically parallel arrangement, the current flow is split into separate parallel flow paths, which are then recombined.

[0107] The heating element can comprise a first connection pad and a second connection pad. The first connection pad or the second connection pad (or the first connection pad and the second connection pad) can be configured to allow connection to an external electrical circuit. An aperture or plurality of apertures in the heating element can separate each track or track portion. The heating element can comprise at least one diverging portion, in which the current flow is split from the first connection pad into the track portions. The track portions define electrically parallel paths. The heating element can comprise a converging portion. In the converging portion, the current flow is combined from the track portions defining electrically parallel paths into the second connection pad.

[0108] Various different arrangements of electrically parallel arranged tracks or track portions are possible. The heating element can comprise two, three, four or more track portions defining electrically parallel paths.

[0109] Advantageously, by providing electrically parallel arranged tracks or track portions, if one track portion is defective, the current flow can be redistributed and the heating element can still be flowed through, i.e. the electrical connection between the first connection pad and the second connection pad is not broken. In contrast, in a simple serpentine heater defining a single electrical path between the first connection pad and the second connection pad, if a portion of the serpentine heating element is broken or contains a defect, this can cause an increase in local electrical resistance, which in turn increases the power dissipation, which in turn increases the electrical resistance until the break.

[0110] The present inventors have also found that electrically parallel tracks or track portions have the surprising additional advantage. In such an arrangement, in the event of a break in one track portion, the heating element will still operate in a beneficial manner and can operate in a beneficial manner for an initial temporary period of time, as the break in one track or track portion will result in a higher energy density on the remaining tracks or track portions. In this case, the same power will still be provided, but over a smaller area, thus increasing the throughput of the aerosol- generating substrate. Such a break causing an increase in current on the unbroken tracks or track portions can ultimately affect the user experience. This can be mitigated by a mechanism to alert the user that the performance of the heater assembly can be below optimal in the future. Electrically parallel tracks have the advantage of increasing the number of puffs before the heater completely fails, and potentially increasing the heater lifetime to the lifetime of the device.

[0111] The heating element can comprise a plurality of tracks or track portions defining a path having at least one bend. The inner edge of the bend can be curved.

[0112] The inner edge of the bend being curved has the advantage of directing the flow of current around the at least one bend in a more evenly distributed manner. This reduces current concentration, which in turn limits hot spot generation.

[0113] The heating element can comprise a plurality of tracks or track portions having a gradient of electrical resistivity normal to the flow of current in one or more corners, such that the electrical resistivity is higher at an inner portion of the corner and lower at an outer portion of the corner. Such a gradient is beneficial in balancing localized high current density and reducing hot spot generation.

[0114] The aerosol-generating system can comprise an aerosol-generating device and a cartridge. The cartridge can be removably coupled to the aerosol-generating device. The cartridge can comprise any of the example heater assemblies described above. The cartridge can comprise a liquid storage portion or reservoir configured to hold a liquid aerosol-forming substrate. The liquid storage portion can be arranged at a side of the heater assembly opposite the heating surface. Alternatively, the aerosol-generating device can comprise any of the example heater assemblies described above.

[0115] As used herein, the term "aerosol-forming substrate" refers to a substrate capable of releasing volatile compounds that can form an aerosol. The volatile compounds can be released by heating a liquid aerosol-forming substrate.

[0116] The aerosol-forming substrate can be liquid at room temperature. The aerosol-forming substrate can comprise both a liquid component and a solid component. The liquid aerosol-forming substrate can comprise nicotine. The nicotine-containing liquid aerosol-forming substrate can be a nicotine salt substrate. The liquid aerosol-forming substrate can comprise plant-based material. The liquid aerosol-forming substrate can comprise tobacco. The liquid aerosol-forming substrate can comprise tobacco-containing material containing volatile tobacco flavour compounds that are released from the aerosol-forming substrate upon heating. The liquid aerosol-forming substrate can comprise homogenised tobacco material. The liquid aerosol-forming substrate can comprise non-tobacco-containing material. The liquid aerosol-forming substrate can comprise homogenised plant-based material.

[0117] The liquid aerosol-forming substrate can comprise one or more aerosol formers. An aerosol former is any suitable known compound or mixture of compounds which, in use, facilitates the formation of a dense and stable aerosol and is substantially resistant to thermal degradation at the operating temperature of the system. Examples of suitable aerosol formers include glycerol 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 glycerol; esters of polyhydric alcohols such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or poly-carboxylic acids such as dimethyl dodecanedioate and dimethyl tetradecanedioate. The liquid aerosol-forming substrate can include water, solvents, ethanol, plant extracts and natural or artificial flavours.

[0118] The liquid aerosol-forming substrate can comprise nicotine and at least one aerosol former. The aerosol former can be glycerol or propylene glycol. The aerosol former can comprise both glycerol and propylene glycol. The liquid aerosol-forming substrate can have a nicotine concentration of between about 0.5% to about 10%, for example about 2%.

[0119] The airflow pathway can pass through the liquid storage portion. For example, the liquid storage portion can have an annular cross-section defining an internal passageway or aerosol channel, and the airflow pathway can extend through the internal passageway or aerosol channel of the liquid storage portion.

[0120] The cartridge can comprise a cartridge housing. The cartridge housing can be formed from a durable material. The cartridge housing can be formed from a liquid-impermeable material. The cartridge housing can be formed from a mouldable plastics material such as polypropylene (PP) or polyethylene terephthalate (PET) or a copolymer such as Tritan TMThe copolymer is made from three monomers: dimethyl terephthalate (DMT), cyclohexanedimethanol (CHDM), and 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO). The cartridge housing can define a portion of the liquid storage portion or reservoir. The cartridge housing can define the liquid storage portion. The cartridge housing and the liquid storage portion can be integrally formed. Alternatively, the liquid storage portion can be formed separately from the outer housing and disposed in the outer housing.

[0121] The aerosol-generating device can comprise a power source for supplying power to the heater assembly. The aerosol-generating device can comprise control circuitry for controlling the supply of power from the power source to the heater assembly. The cartridge can be removably coupled to the aerosol-generating device.

[0122] The aerosol-generating device can comprise a housing. The housing can be elongate. The housing can comprise any suitable material or combination of materials. Examples of suitable materials include a metal, an alloy, a plastic, or a composite material containing one or more of the aforementioned materials, or a thermoplastic suitable for food or pharmaceutical applications, such as polypropylene, polyether ether ketone (PEEK), and polyethylene. Preferably, the material is lightweight and non-brittle.

[0123] The aerosol-generating device housing can define a cavity for receiving a portion of the cartridge. The aerosol-generating device can have a connection end configured to connect the aerosol-generating device to the cartridge. The connection end can comprise a cavity for receiving the cartridge.

[0124] The power source can be any suitable power source. Preferably, the power source is a DC power source. The power source can be a battery. The battery can be a lithium-based battery, such as a lithium cobalt battery, a lithium iron phosphate battery, a lithium titanate battery, or a lithium polymer battery. The battery can be a nickel metal hydride battery or a nickel cadmium battery. The power source can be another form of charge storage device, such as a capacitor. The power source can be rechargeable and configured for a number of charge-discharge cycles. The power source can have a capacity that allows for storage of sufficient energy for one or more user experiences of the aerosol-generating system; for example, the power source can have sufficient capacity to allow for continuous aerosol generation for a period of approximately six minutes, corresponding to the typical time taken to smoke a conventional cigarette, or for a period that is a multiple of six minutes. In another example, the power source can have sufficient capacity to allow for a predetermined number of puffs or discrete activations of the aerosol-generating system.

[0125] The control circuitry can comprise any suitable controller or electrical components. The controller can comprise a memory. Information for carrying out the above described method can be stored in the memory. The control circuitry can comprise a microprocessor. The microprocessor can be a programmable microprocessor, a microcontroller, or an application specific integrated chip (ASIC) or other electronic circuitry capable of providing control. The control circuitry can be configured to continuously supply power to the heating element after activation of the device, or can be configured to supply power intermittently, such as on a puff-by-puff basis. The power can be supplied to the heating element in the form of current pulses, for example by means of pulse width modulation (PWM).

[0126] Features described in relation to one of the above examples can equally apply to other examples of the disclosure.

[0127] The application is defined in the claims. However, a non-exhaustive list of non-limiting examples is provided below. Any one or more features of these examples can be combined with any one or more features of another example, embodiment or aspect described herein.

[0128] Example Ex1 : A heater assembly comprising a heating element for vaporising a liquid aerosol-forming substrate and a porous body for transporting the liquid aerosol-forming substrate to the heating element.

[0129] Example Ex2: The heater assembly according to example Ex1, wherein the porous body comprises a liquid absorbing surface and a heating surface.

[0130] Example Ex3: The heater assembly according to example Ex1 or Ex2, wherein the heating element is located on the heating surface of the porous body.

[0131] Example Ex4: The heater assembly according to any preceding example, wherein the heating element is fluid permeable.

[0132] Example Ex5: The heater assembly according to any preceding example, wherein the porous body comprises at least one airflow guide to direct airflow towards the heating element.

[0133] Example Ex6: The heater assembly according to any preceding example, wherein the heating element is porous.

[0134] Example Ex7: The heater assembly according to example Ex6, wherein the heating element has a porosity of between 20% and 80%.

[0135] Example Ex8: The heater assembly according to example Ex6 or Ex7, wherein the heating element comprises a porous layer of an electrically conductive material.

[0136] Example Ex9: The heater assembly according to Example Ex8, wherein the heating element comprises a porous metal film.

[0137] Example Ex10: The heater assembly according to Example Ex8, wherein the heating element comprises a metal foam.

[0138] Example Ex11 : The heater assembly according to any preceding example, wherein the heating element and the porous body are integrally formed.

[0139] Example Ex12: The heater assembly according to any preceding example, wherein the heating element comprises a doped portion of the porous body.

[0140] Example Ex13: The heater assembly according to any of Examples Ex1 to Ex10, wherein the porous body and heating element are formed as two separate parts that are assembled together.

[0141] Example Ex14: The heater assembly according to Example Ex13, wherein the heating element is bonded to a heating surface of the porous body.

[0142] Example Ex15: The heater assembly according to any preceding example, wherein the heating element has a tapered cross-sectional shape.

[0143] Example Ex16: The heater assembly according to Example Ex15, wherein the heating element tapers in a direction from the liquid absorption surface to the heating surface.

[0144] Example Ex17: The heater assembly according to Example Ex15 or Ex16, wherein a liquid absorption surface of the porous body has an area that is different from an area of a heating surface of the porous body.

[0145] Example Ex18: The heater assembly according to Example Ex17, wherein the area of the heating surface of the porous body is less than the area of the liquid absorption surface of the porous body.

[0146] Example Ex19: The heater assembly according to Example Ex17, wherein the area of the heating surface of the porous body is greater than the area of the liquid absorption surface of the porous body.

[0147] Example Ex20: The heater assembly according to any preceding example, wherein the heating surface of the porous body is convex in one or both of a first lateral direction and a second lateral direction, the first lateral direction being orthogonal to the second lateral direction.

[0148] Example Ex21 : The heater assembly according to any preceding example, wherein the heater assembly further comprises a thermal insulation layer configured to reduce heat transfer from the heating element to the porous body.

[0149] Example Ex22: A heater assembly according to Example Ex21, wherein the thermal barrier layer has a lower thermal conductivity than the porous body.

[0150] Example Ex23: A heater assembly according to Example Ex21 or Ex22, wherein the thermal barrier layer is disposed between the porous body and the heating element.

[0151] Example Ex24: A heater assembly according to Example Ex21 or Ex22, wherein the thermal barrier layer is in contact with each of the porous body and the heating element.

[0152] Example Ex25: A heater assembly according to any preceding example, wherein the average pore size of the porous body varies between the liquid uptake surface and the heating surface.

[0153] Example Ex26: A heater assembly according to Example Ex25, wherein the average pore size varies from relatively larger pores at the liquid uptake surface to relatively smaller pores at the heating surface.

[0154] Example Ex27: A heater assembly according to any preceding example, wherein the heating element comprises a plurality of tracks or track portions arranged in electrical parallel.

[0155] Example Ex28: A heater assembly according to any preceding example, wherein the heating element comprises a plurality of tracks or track portions defining a path having at least one bend, an inner edge of the bend being curved.

[0156] Example Ex29: An aerosol-generating system comprising a heater assembly according to any preceding example.

[0157] Example Ex30: An aerosol-generating system according to Example Ex29, wherein, in use, vapour is discharged from the heater assembly in an average vapour discharge direction.

[0158] Example Ex31 : An aerosol-generating system according to Example Ex29 or Ex30, wherein the aerosol-generating system further comprises an air inlet and an aerosol outlet, the air inlet being in fluid communication with the aerosol outlet to define an air flow path through the aerosol-generating system.

[0159] Example Ex32: An aerosol-generating system according to Example Ex31, wherein the heater assembly is arranged in fluid communication with the air flow path such that air flows through the heater assembly in an average air flow direction.

[0160] Example Ex33: An aerosol-generating system according to Example Ex32, wherein the heater assembly and the airflow pathway are arranged such that the angle between the average vapour discharge direction and the average airflow direction is less than 135 degrees.

[0161] Example Ex34: An aerosol-generating system according to any one of Examples Ex30 to Ex33, wherein the average vapour discharge direction is substantially perpendicular to the heating surface.

[0162] Example Ex35: An aerosol-generating system according to Example Ex33 or Ex34, wherein the heater assembly and the airflow pathway are arranged such that the angle between the average vapour discharge direction and the average airflow direction is about 90 degrees.

[0163] Example Ex36: An aerosol-generating system according to Example Ex33 or Ex34, wherein the heater assembly and the airflow pathway are arranged such that the angle between the average vapour discharge direction and the average airflow direction is less than 90 degrees.

[0164] Example Ex37: An aerosol-generating system according to Example Ex36, wherein the heater assembly and the airflow pathway are arranged such that the average vapour discharge direction and the average airflow direction are substantially the same.

[0165] Example Ex38: An aerosol-generating system according to any one of Examples Ex31 to Ex37, wherein the air inlet is distal of the heater assembly.

[0166] Example Ex39: An aerosol-generating system according to any one of Examples Ex31 to Ex38, wherein the cross-sectional area of the airflow pathway in the region of the heater assembly is configured such that, in use, the airflow velocity is between 0.1 and 2 metres per second.

[0167] Example Ex40: A method of manufacturing a heater assembly for use in an aerosol-generating system, the method comprising: forming a porous ceramic body for conveying a liquid aerosol-forming substrate, the porous ceramic body having a liquid uptake surface and a heating surface; and providing a heating element for evaporating a liquid aerosol-forming substrate, the heating element being located on the heating surface of the porous ceramic body.

[0168] Example Ex41 : A method according to Example Ex40, wherein the heating element is bonded to the heating surface of the porous body.

[0169] Example Ex42: A method according to Example Ex40, wherein the step of providing a heating element comprises depositing a porous layer of electrically conductive material on the heating surface of the porous ceramic body.

[0170] Example Ex43: A method according to Example Ex42, wherein the heating element is deposited or patterned by thick film technology selected from one or more of screen printing, inkjet printing, aerosol jet printing and laser direct structuring (LDS).

[0171] Example Ex44: A method according to Example Ex42, wherein the heating element is deposited or patterned by thin film technology selected from one or more of physical vapour deposition (PVD) techniques such as evaporation or sputtering and chemical vapour deposition (CVD).

[0172] Example Ex45: A method according to Example Ex40, wherein the heating element and the porous body are integrally formed.

[0173] Example Ex46: A method according to Example Ex45, wherein the step of providing the heating element comprises doping a portion of the porous ceramic body to form a heating portion for vaporising a liquid aerosol generating substrate. BRIEF DESCRIPTION OF DRAWINGS

[0174] Examples will now be further described with reference to the drawings in which:

[0175] Figure 1 is a schematic cross-sectional view of a heater assembly 1 of a known type arranged in an air flow path.

[0176] Figure 2 is a schematic plan view of a heater assembly according to an example of the disclosure.

[0177] Figure 3 is a schematic cross-sectional view of the heater assembly of Figure 2

[0178] Figure 4 is a schematic view of the interior of an aerosol-generating system according to an example of the disclosure.

[0179] Figure 5 is a schematic cross-sectional view of a portion of an aerosol-generating system according to another example of the disclosure, showing an arrangement of a heater assembly relative to an air flow path within the aerosol-generating system.

[0180] Figure 6 is a schematic cross-sectional view of a portion of another aerosol-generating system according to another example of the disclosure, showing another arrangement of a heater assembly relative to an air flow path within the aerosol-generating system.

[0181] Figure 7 is a schematic perspective view of a heater assembly according to another example of the disclosure;

[0182] Figure 8 is a schematic perspective view of a heater assembly according to another example of the disclosure; Figure 7 ​a schematic side view of a heater assembly according to another example of the disclosure;

[0183] Figure 9 a schematic plan view of a heater assembly according to another example of the disclosure;

[0184] Figure 10 a schematic perspective view of a heater assembly according to another example of the disclosure;

[0185] Figure 11 a schematic cross-sectional view through a heater assembly according to another example of the disclosure;

[0186] Figure 12 a schematic cross-sectional view through a heater assembly according to another example of the disclosure;

[0187] Figures 13a to 13c is a schematic diagram of three heating elements for an aerosol-generating system; and

[0188] Figure 14a and Figure 14b is a schematic diagram depicting the flow of current around the corners of a heating element track. DETAILED DESCRIPTION

[0189] It will be appreciated that at least some of the figures in this application are schematic and have been simplified for clarity. Thus, some features can have been omitted and features are not necessarily drawn to scale.

[0190] In describing features of the disclosure, reference is made to mentions of orientation such as vertical, horizontal, upward, downward, upper and lower, etc. These are not intended to imply any limitation on the orientation of the features, but merely to show the relative spatial arrangement of the features, particularly with reference to the drawings or the relative spatial arrangement in a normal use case. It will be appreciated that features of the disclosure can have different orientations in use.

[0191] With reference to Figure 2 , a heater assembly 100 is shown, which comprises a heating element 104 for vaporising a liquid aerosol-forming substrate and a porous body 102 for supplying liquid aerosol-forming substrate from a reservoir or liquid storage portion (not shown) to the heating element 104. The porous body 102 has a liquid- absorbing surface (not shown) and a heating surface 102a. The heating element 104 is arranged on the heating surface 102a of the porous body 102.

[0192] The heating element 104 is formed from a layer of an electrically conductive material, such that an electric current can be passed through the heating element 104 to heat the heating element 104 by resistive or Joule heating. The heating element 104 is also porous, such that it is fluid permeable and vapour can pass through the heating element from the heating surface 102a of the porous body 102. Thus, in use, liquid aerosol-forming substrate is supplied from the reservoir to the heating surface 102a of the porous body 102. The liquid aerosol-forming substrate is drawn through the porous body 102 and the heating element 104 by capillary action. The liquid aerosol-forming substrate is heated by the heating element 104 to form a vapour, which is drawn through the heating element 104 and into a user's mouth.Figure 2 In the heater assembly 100, vapor emission occurs via a heating element 104. The heating element 104 may include a thin metal layer or film having pores extending through its thickness. Alternatively, the heating element may include a metal foam having interconnected open pores extending through its thickness. In this example, the porous body 102 comprises a porous ceramic body formed of a suitable ceramic material, such as Al2O3. Furthermore, the heating element 104 has been deposited on the porous ceramic body 102 using a suitable physical or chemical vapor deposition process.

[0193] The heater assembly 100 also includes electrical contacts 106 electrically connected to the heating element 12. The electrical contacts 106 are arranged on and near opposite ends of the heating surface 102a. The heating element 104 extends between the electrical contacts 106. The electrical contacts 106 are arranged to connect to a control circuitry for controlling the power supply to the heating element. The electrical contacts 106 are formed of a material with higher conductivity than heating elements such as copper, gold, or zinc, but other suitable materials can be used. This avoids the generation of excessive, wasted heat in the electrical contacts.

[0194] Figure 3 It shows Figure 2 A schematic cross-sectional view of the heater assembly 100. For clarity and simplicity, [the following text is missing]. Figure 2 The electrical contact 106 in Figure 1 is omitted, and the features are not drawn to scale. The liquid-absorbing surface 102b is... Figure 3 The lower surface of the porous body 102 is shown in the diagram, and the heating surface 102a is also shown as the lower surface of the porous body 102. However, it should be understood that the orientation of these surfaces may differ during use or once the heater assembly 100 is installed in the aerosol generating apparatus. Liquid stored in a liquid reservoir or liquid storage section (not shown) contacts the liquid absorption surface 102b, and as... Figure 3 As indicated by arrow E, the liquid aerosol forming matrix is ​​conveyed through the porous body 102 to the heating surface 102a. A porous heating element 104 is arranged on the heating surface 102a of the porous body 102 and heats the liquid aerosol forming matrix conveyed thereto, causing the liquid aerosol forming matrix to boil and generate vapor. The porous heating element 104 has a plurality of pores 108 extending from the heating surface 102a through the thickness of the heating element to the exterior of the heater assembly 100.

[0195] Because the heating element 104 is porous, the vapor generated during heating of the heating element 104 can pass through the pores 108 of the heating element 104, and as... Figure 3from the heating surface 102a, as indicated by arrows F. The heating element does not have any impermeable sections that prevent vapor release and cause accumulation of vapor pressure underneath the heating element. This reduces the speed of vapor emission from the heating element 104 compared to conventional impermeable track heating elements. Table 1 below shows the average vapor emission speed of vapor emitted from various different configurations of heating elements. The heated area of all heating elements in Table 1 is approximately 5 mm x 3 mm.

[0196] As can be seen from Table 1 below, all heating elements achieve a relatively low vapor emission speed, i.e. a vapor emission speed of less than 1 meter per second. Such a low vapor emission speed means that the vapor can easily be carried away by the airflow in the airflow path without impinging on the inner walls of the airflow path and causing condensation. The average vapor emission direction is substantially perpendicular to the heating surface 102a of the porous body 102, as indicated by arrows F, and the vapor is emitted uniformly across the surface of the heating element.

[0197]

[0198] Table 1

[0199] Figure 4 is a schematic view of the interior of an aerosol-generating system 200 according to an example of the disclosure. The aerosol-generating system comprises two main components, a cartridge 202 and a main body portion or aerosol-generating device 204. A connection end 202a of the cartridge 202 is removably connected to a corresponding connection end 204a of the aerosol-generating device 204. The connection end 202a of the cartridge 202 and the connection end 204a of the aerosol-generating device 204 each have electrical contacts or connections (not shown) arranged to cooperate to provide an electrical connection between the cartridge 202 and the aerosol-generating device 204. The aerosol-generating device 204 comprises a device housing 209 which houses a power supply in the form of a battery 206 (which in this example is a rechargeable lithium-ion battery) and control circuitry 208. The aerosol-generating system 200 is portable and has a size comparable to a conventional cigar or cigarette. A mouthpiece 210 is arranged at a mouth end 202b of the cartridge 202. The mouth end 202b is positioned opposite the connection end 202a of the cartridge 202.

[0200] The cartridge 202 comprises a cartridge housing 212 which houses the heater assembly 100 and a liquid reservoir or liquid storage portion 218 for holding a liquid aerosol-forming substrate. Figure 4 The heater assembly 100 in Figure 2 has a similar configuration to that of Figure 3 but with the Figure 2 and Figure 3The orientation in Figure 1 is inverted compared to that in Figure 2, such that the liquid uptake surface 102b faces upwards and is in fluid communication with the liquid storage portion 218, and the heating surface 102a carrying the heating element (not shown) faces downwards. Liquid aerosol-forming substrate is transported from the liquid uptake surface 102b through the porous body 102 downwards to the heating element, and vapourised aerosol-forming substrate is discharged from the heating surface 102a when electrical power is supplied to the heating element. As indicated by arrow F in Figure 1, the average vapour discharge direction is substantially perpendicular to the heating surface 102a of the porous body 102.

[0201] The cartridge 202 comprises one or more air inlets 222 formed in the cartridge housing 212 at a location along the length of the cartridge 202 corresponding to the location of the heating surface 102a of the heater assembly 100. An aerosol outlet 226 is located in the mouthpiece 210 at the mouth end 202b of the cartridge 202. The one or more air inlets 222 are in fluid communication with the aerosol outlet 226 to define an airflow path 220 through the cartridge 202 of the aerosol-generating system 200. The airflow path 220 flows from the one or more air inlets 222 to the heater assembly 100 in an airflow channel 223. The heater assembly 100 is arranged in fluid communication with the airflow path 220 in the airflow channel 223. As indicated by arrow I in Figure 2, air enters the one or more air inlets 222 and flows through the airflow channel 223 past the heater assembly 100 in the average airflow direction. As can be seen in Figure 2, the heater assembly 100 and the airflow path 220 in the airflow channel 223 are arranged such that the angle between the average vapour discharge direction F and the average airflow direction I is approximately 90 degrees (that is, angled substantially perpendicular to the average airflow direction I). The average vapour discharge direction F has no velocity or directional component opposite to the average airflow direction I, and so any momentum loss of vapour is reduced. This reduces the tendency for vapour to recirculate and turbulent flow in the airflow path 220, and vapour is less likely to impinge on the inner surface of the airflow channel 223. Figure 4 Figure 4

[0202] In the example of Figure 2, the liquid storage portion 218 has a cross-section that is annular, and is arranged around the central sealed aerosol channel 224. Once the airflow path 220 reaches the heater assembly 100, the airflow path is diverted upwards around the side of the heater assembly 100, and flows through the aerosol channel 224 to the aerosol outlet 226. It will be appreciated that other arrangements of the liquid storage portion and the airflow path can be implemented, such as the arrangements discussed below in relation to Figures 3 to 5. Figure 4 Figure 5 Figure 6

[0203] ​​​​​The aerosol-generating system 200 is configured so that a user can draw or puff on the mouthpiece 210 of the cartridge 202 to draw aerosol through the aerosol outlet 226 into their mouth. In operation, when a user draws on the mouthpiece 210, air is drawn in through one or more air inlets 222, along the airflow path 220 through the airflow passage 223, past and around the heater assembly 100, and along the airflow path 220 through the aerosol passage 224 to the aerosol outlet 226. When the system is activated, the control circuitry 208 controls the supply of electrical power from the battery 206 to the cartridge 202. This in turn controls the amount and nature of vapour generated by the heater assembly 100. The control circuitry 208 can comprise an airflow sensor (not shown) and the control circuitry 208 can supply power to the heater assembly 100 when the airflow sensor detects a user draw. This type of control arrangement has been used for many years in aerosol-generating systems such as inhalers and e-cigarettes. When a user draws on the mouthpiece 210 of the cartridge 202, the heater assembly 100 is activated and generates vapour which is entrained in the airflow path 220. The vapour cools within the airflow path 220 to form an aerosol which is then drawn through the aerosol outlet 226 into the user’s mouth.

[0204] Figure 5 is a schematic cross-sectional view of part of an aerosol-generating system 300 according to another example of the disclosure, showing the arrangement of the heater assembly 100 relative to an airflow path 320 within the aerosol-generating system 300. For simplicity, other components of the aerosol-generating system have been omitted from Figure 5 Figure 5 The heater assembly 100 of Figure 2 and Figure 3 is the same as the heater assembly 100 ofThe aerosol-generating system 300 comprises a liquid storage portion 322 which holds a liquid aerosol-forming substrate in contact with the liquid-absorbing surface 102b of the porous body 102. As indicated by arrow E, the liquid aerosol-forming substrate is transported from the liquid storage portion 322 through the porous body 102 to the heating surface 102a. Vaporised aerosol-forming substrate is discharged from the heating surface 102a through the porous heating element 104. As indicated by arrow F, the average vapour discharge direction is substantially perpendicular to the heating surface 102a of the porous body 102.

[0205] In the example of Figure 5 the heater assembly 100 is arranged below or to one side of an airflow passage or path 320 defined by airflow passage walls 324. As Figure 5The left-hand end of the visible portion of the airflow path 320 receives airflow from an air inlet (not shown) and the right-hand end of the visible portion of the airflow path delivers airflow to an aerosol outlet (not shown), viewed in cross-section. The heating surface 102a of the porous body 102 is arranged parallel to and facing the airflow path 320. The heater assembly 100 is in fluid communication with the airflow path such that airflow in the airflow path flows past the heater assembly 100 in an average airflow direction, as indicated by arrow G. The heater assembly 100 and the airflow path 320 are arranged such that the angle Θ between the average vapour discharge direction F and the average airflow direction G is about 90 degrees (that is, angled substantially perpendicularly to the average airflow direction G). The average vapour discharge direction F has no velocity or directional component opposite to the average airflow direction G and so any momentum loss of the airflow is reduced. This reduces the tendency for recirculation and turbulence to occur in the airflow path 320 and it is less likely that vapour will impinge on the inner surface of the airflow passage wall 324.

[0206] Figure 6 is a schematic cross-sectional view of a portion of an aerosol-generating system 400 according to another example of the disclosure, showing a further arrangement of the heater assembly 100 relative to an airflow path 420 within the aerosol-generating system 400. For simplicity, other components of the aerosol-generating system have been omitted from Figure 6 the view. Figure 6 The heater assembly 100 of Figure 2 and Figure 3 is the same as the heater assembly 100 of The aerosol-generating system 400 comprises a liquid storage portion 422 holding a liquid aerosol-forming substrate in contact with the liquid absorbent surface 102b of the porous body 102. The liquid aerosol-forming substrate is transported from the liquid storage portion 422 through the porous body 102 to the heating surface 102a, as indicated by arrow E. Vaporised aerosol-forming substrate is discharged from the heating surface 102a through the porous heating element 104. The average vapour discharge direction is substantially perpendicular to the heating surface 102a of the porous body 102, as indicated by arrow F.

[0207] In Figure 6In the example of Figure 4, the airflow passage or path 420 divides into first and second airflow path sections 420a, 420b that pass either side of the heater assembly 100. The first and second airflow path sections 420a, 420b combine downstream of the heater assembly 100 into a third airflow path section 420c. The first and second airflow path sections 420a, 420b receive airflow from one or more air inlets (not shown) and the third airflow path section 420c delivers the airflow to an aerosol outlet (not shown). The airflow path 420 is defined by airflow passage walls 424. The heating surface 102a of the porous body 102 is arranged substantially perpendicular to the airflow path 420 and faces in a downstream direction of the airflow path 420. The heater assembly 100 is in fluid communication with the airflow path such that airflow in the airflow path flows past the heater assembly 100 in an average airflow direction as indicated by arrow G.

[0208] The heater assembly 100 and the airflow path 120 are arranged such that the angle Θ between the average vapour discharge direction F and the average airflow direction G is less than 90 degrees. Upstream of the heating surface 102a of the porous body 102, the average airflow direction G past the heater assembly 100 is substantially the same as the vapour discharge direction F. At a point along the airflow path 420 corresponding to the heating surface 102a, the airflow path 420 begins to narrow or taper inwards, at which point the average airflow direction G past the heater assembly 100 changes to an angle Θ of approximately 45 degrees relative to the vapour discharge direction F. Downstream of the heating surface 102a of the porous body 102 in the third airflow path section 420c, the average airflow direction G of the combined airflow is again substantially the same as the vapour discharge direction F. It will be appreciated that the narrowing or tapering of the airflow path 420 can be omitted. In that case, the average airflow direction G past the heater assembly 100 will be substantially the same as the vapour discharge direction F.

[0209] Figure 4 、 Figure 5 and Figure 6 The cross-sectional area of the airflow paths 220, 320 and 420 in the aerosol-generating devices of Figures 2 to 4 is designed such that sufficient vapour from the liquid aerosol-forming substrate is brought into the airflow once discharged from the heater assembly 100. The airflow velocity is preferably higher than the vapour discharge velocity of the vapour discharged from the heater assembly to ensure proper entrainment of the vapour in the airflow paths 320 and 420. For example, for a vapour discharge velocity of 0.1 to 0.7 m / s, an airflow velocity of approximately 1 m / s is desirable. A 55 ml (55 cm3) puff of 3 seconds duration corresponds to a volumetric flow rate of 18.3 cm3 / s according to the standard Coresta puff curve. Since the airflow velocity is the ratio of the volumetric flow rate and the cross-sectional area, an airflow path with a cross-sectional area of 18.3 mm2 3 corresponds to an airflow velocity of 1 m / s. The cross-sectional area of the airflow paths 220, 320 and 420 is therefore designed to be less than 18.3 mm2. 3 Since the airflow velocity is the ratio of the volumetric flow rate and the cross-sectional area, an airflow path with a cross-sectional area of 18.3 mm22 of 1 meter per second. It will be appreciated that, in the aerosol-generating device of Figure 5 of 1 meter per second. It will be appreciated that, in the aerosol-generating device of

[0210] It has been found that a cross-sectional area X of 18.3 cm2 3 of 1 meter per second. It will be appreciated that, in the aerosol-generating device of

[0211] Figure 7 and Figure 8 A schematic diagram of an example heater assembly 500 for an aerosol-generating system is shown. The heater assembly 500 comprises a heating element 510 and a porous body 520. The heating element 510 is configured to vaporise an aerosol-forming substrate, such as a liquid aerosol-forming substrate, to form an aerosol. The heating element 510 is configured to convert electrical energy into heat energy by material resistance of the heating element 510 to an electrical current.

[0212] The porous body 520 is configured to transport liquid aerosol-forming substrate to the heating element 510. In other words, the porous body 520 supplies liquid aerosol-forming substrate to the heating element 510. The porous body 520 has a first end face and an opposing second end face. The first end face is a liquid absorption surface 530 and the second end face is a heating surface 540. In this example, both the liquid absorption surface 530 and the heating surface 540 are substantially planar surfaces. The porous body 520 also has a plurality of lateral faces extending between the liquid absorption surface 530 and the heating surface 540. In this example, as will be discussed in more detail below, the porous body 520 has a first lateral face 550 opposite a second lateral face 560 and a third lateral face 570 opposite a fourth lateral face 580.

[0213] The porous body 520 comprises a plurality of pores. The plurality of pores are interconnected to provide a fluid path for liquid aerosol-forming substrate through the porous body 520 from the liquid absorption surface 530 to the heating surface 540. The porous body 520 is formed from a material that does not chemically interact with the liquid aerosol-forming substrate. In this example, the porous body 520 is a porous ceramic body and can be formed from, for example, Ca2Si03 or Si02 (or Ca2Si03 and Si02). In another example, the porous body 520 can be, for example, a porous glass body.

[0214] The heating element 510 is located on the heating surface 540 of the porous body 520. In Figure 7 and Figure 8 In the example, the heating element 510 is a porous membrane extending across substantially all of the heating surface 540.

[0215] The liquid absorption surface 530 of the porous body 520 has an area that is different from the area of the heating surface 540 of the porous body 520. In particular, in Figure 7 and Figure 8 In the example, the area of the heating surface 540 is smaller than the area of the liquid absorption surface 530.

[0216] In the example, the heating surface 540 has a smaller area than the liquid absorption surface 530 because the length of the heating surface 540 is smaller than the length of the liquid absorption surface 530. Additionally or alternatively, in another example, the heating surface 540 can have a smaller area than the liquid absorption surface 530 because the width of the heating surface 540 is smaller than the width of the liquid absorption surface 530. Figure 7 Figure 8 In the example, the heating surface 540 has a smaller area than the liquid absorption surface 530 because the length of the heating surface 540 is smaller than the length of the liquid absorption surface 530. Additionally or alternatively, in another example, the heating surface 540 can have a smaller area than the liquid absorption surface 530 because the width of the heating surface 540 is smaller than the width of the liquid absorption surface 530.

[0217] In the example, the porous body 520 is shaped as a trapezoidal prism. In the case that the porous body 520 has a trapezoidal prism shape, both the first lateral face 550 and the second lateral face 560 have a trapezoidal shape, in particular an isosceles trapezoid, both the third lateral face 570 and the fourth lateral face 580 have a rectangular shape, and both the liquid absorption surface 530 and the heating surface 540 have a rectangular shape. In another example, the liquid absorption surface 530 and the heating surface 540 can have a square shape. Figure 7 Figure 8 The porous body 520 tapers from the liquid absorption surface 530 towards the heating surface 540. In other words, the cross-sectional area of the porous body 520 gradually decreases from the liquid absorption surface 530 towards the heating surface 540. In and

[0218] In the example, the length of the porous body 520 decreases from the liquid absorption surface 530 towards the heating surface 540, which causes the tapering. Figure 7 Figure 8 In one example, the porous body 520 is formed of a sintered ceramic, such as silicon carbide. The porous body 520 comprises open pores. The open pores are longitudinal pores that extend substantially from the liquid absorption surface 530 to the heating surface 540 of the porous body 520. The pore diameter of the pores in the porous body 520 varies between the liquid absorption surface 530 and the heating surface 540.

[0219] In one example, the porous body 520 is formed of a sintered ceramic, such as silicon carbide. The porous body 520 comprises open pores. The open pores are longitudinal pores that extend substantially from the liquid absorption surface 530 to the heating surface 540 of the porous body 520. The pore diameter of the pores in the porous body 520 varies between the liquid absorption surface 530 and the heating surface 540.

[0220] ​​The porous body 520 includes a heating end and a liquid absorption end. A heating surface 540 is disposed at the heating end, and a liquid absorption surface 530 is disposed at the liquid absorption end. The porous body 520 includes a first average pore diameter at the liquid absorption end and a second average pore diameter at the heating end. The first average pore diameter is larger than the second average pore diameter.

[0221] The first pore size at the liquid absorption end is approximately 150 micrometers. The second pore size at the heating end is approximately 20 micrometers. The pore size varies linearly between the first and second pore sizes to provide a pore size gradient between the liquid absorption end and the heating end of the porous body 520.

[0222] The pore structure and pore size gradient in the porous body 520 are achieved by etching pores in a portion of silicon carbide.

[0223] Figure 9 A schematic plan view of an exemplary heater assembly 600 for an aerosol generation system is shown. The heater assembly 600 includes a heating element 610 and a porous body 620. The porous body 620 may be made of any suitable ceramic material (such as those discussed in any of the examples above). The heating element 610 is located on the heating surface 612 of the porous body 620. Figure 9 In this example, the heating element 610 is serpentine in shape and located on the heating surface 612. Similar to... Figure 7 and Figure 8 The exemplary heater assembly 500 in the example, Figure 9 The heater assembly 600 has a tapered shape such that the area of ​​the heating surface 612 is smaller than the area of ​​the liquid absorption surface (invisible), the liquid absorption surface being... Figure 9 The view shown is located on the lower side of the porous body 620. Both the liquid absorption surface and the heating surface 612 are square. In this way, the porous body 620 of the heater assembly 600 has a truncated pyramidal shape. The four longitudinal surfaces 613 of the porous body 620 each have a trapezoidal shape of equal size.

[0224] The porous body 620 of the heater assembly 600 also includes a plurality of airflow guides 614 for guiding airflow toward the heating surface 612. Each of the four longitudinal surfaces 613 includes an airflow guide disposed in the surface 613 in the form of a longitudinal groove or slit. Each of the airflow guides 614 extends from the liquid absorption surface (not visible) to the heating surface 612. The airflow guides 614 help improve the efficiency of airflow in the region of the heater assembly 600. This arrangement is particularly advantageous when the airflow is substantially aligned with the vapor emission direction of the vaporized aerosol matrix from the heating surface 612.

[0225] Figure 10A heater assembly 700 for use in an aerosol-generating system is shown. The heater assembly 700 comprises a heating element 710 for vaporising a liquid aerosol-forming substrate. The heater assembly 700 further comprises a porous body 720 for delivering the liquid aerosol-forming substrate to the heating element 710. The porous body 720 has a liquid- absorbing surface 721 and an opposing heating surface 722. The heating element 710 is located on the heating surface 722 of the porous body 720. The porous body 720 can be made of any suitable ceramic material, such as the materials discussed in any of the examples above.

[0226] The heating surface 722 of the porous body 720 is curved. In particular, the heating surface 722 of the porous body 720 is convexly curved in a single lateral direction (first lateral direction).

[0227] The porous body 720 is prism-shaped. When looking at a longitudinal cross-section perpendicular to the direction of curvature of the porous body 720, the heating surface 722 of the porous body 720 is shown as an arc. The porous body 720 has two longitudinal planes of symmetry.

[0228] The heating surface 722 of the porous body 720 has a width 723 in the first lateral direction which is substantially the same as the width of the porous body 720 in the first lateral direction and substantially the same as the width of the heater assembly 700 in the first lateral direction. The heating surface 720 of the porous body 720 has a width of about 5 millimetres in the first lateral direction.

[0229] The heating surface 722 of the porous body 720 has a length or thickness 724 of about 1 millimetre. The porous body 720 has a length or thickness 725 of about 3 millimetres.

[0230] The heating surface 722 of the porous body has a curvature of about 3.6 millimetres. The heating surface 722 of the porous body has a surface area of about 28 square millimetres.

[0231] The porous body 720 comprises four longitudinal surfaces or side walls extending from the liquid-absorbing surface 721 to the heating surface 722. The four side walls are substantially perpendicular to the substantially planar liquid-absorbing surface 721. The liquid-absorbing surface 721 is square-shaped.

[0232] The heating element 710 is an electrically resistive heating element 710 and is curved. In particular, the curvature of the heating element 710 is substantially the same as the curvature of the heating surface 722 of the porous body 720. Thus, the heating element 710 is also convexly curved in a single lateral direction.

[0233] The heating element 710 is positioned directly on the heating surface 722 of the porous body 720. The heating element 710 extends across a substantial portion of the heating surface 722 of the porous body 720. Substantially the entire heating element 710 is in contact with the heating surface 722 of the porous body 720.

[0234] Figure 11 A schematic cross-sectional view of a heater assembly 800 for an aerosol-generating system is shown. The heater assembly 800 comprises a heating element 810, a thermal barrier 820, and a porous body 830. The porous body 830 is configured to supply liquid aerosol-forming substrate to the heating element 810. In particular, the porous body 830 is configured to transport liquid aerosol-forming substrate from a liquid reservoir (not shown) to the heating element 810. The porous body 830 is configured to store some liquid aerosol-forming substrate prior to aerosolization by the heating element 810.

[0235] The porous body 830 is a rectangular block and has a first end face and an opposing second end face. The first end face is a liquid absorption surface 834 and the second end face is a heating surface 833. In this example, both the liquid absorption surface 834 and the heating surface 833 are substantially planar surfaces. The porous body 830 also has a plurality of lateral faces extending between the liquid absorption surface 834 and the heating surface 833. The porous body 830 has a first lateral face 831 opposite a second lateral face 832 and a third lateral face (not shown) opposite a fourth lateral face (not shown). The porous body 830 has a thickness defined between the liquid absorption surface 834 and the heating surface 833.

[0236] The porous body 830 comprises a plurality of open pores. The plurality of open pores are interconnected to provide a fluid path for aerosol-generating liquid through the porous ceramic body 830. The heater assembly 800 can be configured such that liquid can pass through the fluid path of the porous body 830 to the heating element 810 as depicted by arrow 870. The porous body 830 is configured for fluid 870 to pass from the liquid absorption side 834 to the heating surface 833. The porous body 830 comprises a material that does not chemically interact with the liquid aerosol-forming substrate. The porous body 830 comprises a ceramic. The porous body 830 comprises a porous ceramic such as, but not limited to, one or more of: AI2O3, Zr02, Si3N4, SiC, Ti3AlC2, BN, AIN, Si02, MgO, mica, diatomite, silicates, suicides, borides. Alternatively, the porous body 830 can comprise a porous glass. It will be appreciated that the porous body 830 can have a different shape or comprise a different material.

[0237] The heating element 810 is configured to heat the liquid aerosol-forming substrate to form an aerosol. The heating element 810 is configured to convert electrical energy into heat energy by material resistance of the heating element 810 to an electrical current.

[0238] The heating element 810 includes tracks defining a path of the heating surface 823 across the thermal barrier 820. The heating element 810 defines a serpentine or electrically parallel track shape of the heating surface 823 across the thermal barrier 820. Three cross sections through portions of the tracks of the heating element 810 are shown in Figure 11 The plurality of track portions are arranged with a distance between at least two of the plurality of track portions 818, 819 in the range of 200 to 300 micrometers. The track portions are evenly spaced apart. It will be appreciated that the distance between at least two of the plurality of track portions 818, 819 can not be equal.

[0239] The heating element 810 is elongated and comprises a metal such as, but not limited to, stainless steel, a Ni-Cr alloy, a NiCrAlY alloy, a FeCrAl alloy (e.g. Kanthal), a FeCrAlY alloy, a Fe3Al alloy, a Ni3Al alloy, a NiAl alloy, and a CuNi alloy. It will be appreciated that the heating element 810 can have a different shape or comprise a different material.

[0240] The heating element 810 is arranged along an outer surface of the thermal barrier 820. The heating element 810 is in direct contact with the thermal barrier 820. The thermal barrier 820 is arranged to enhance thermal isolation between the heating element 810 and the porous body 830. The thermal barrier 820 is arranged to extend across at least a portion of the heating element 810 to thermally isolate the heating element 810 from the porous body 830. The thermal barrier 820 is configured to reduce heat dissipation through the porous body 830 in order to improve energy efficiency by reducing energy loss.

[0241] The thermal barrier 820 is planar and has a size and shape configured to extend across the electric heating element 810. The thermal barrier 820 is configured to extend completely across the surface of the heating element 810. The thermal barrier 820 is configured to substantially cover the porous body 830 underneath the thermal barrier 120.

[0242] The thermal barrier 820 has a first end face 824 and an opposite second end face 823. In this example, both the first end face 824 and the second end face 823 are substantially planar surfaces. The first end face 824 of the thermal barrier 820 is in direct contact with the porous ceramic body 830. The second end face 823 of the thermal barrier 820 is in direct contact with the heating element 810.

[0243] The thermal barrier 820 has a thickness defined between the first end face 824 and the second end face 823. The thickness of the thermal barrier 820 is smaller than the thickness of the porous body 830. The thermal barrier 820 can have a thickness between 0.1 mm and 2 mm, preferably between 0.5 mm and 1.5 mm.

[0244] The thermal barrier 820 comprises a material having a low thermal conductivity. The thermal barrier 820 comprises or consists of a material having a lower thermal conductivity than the porous ceramic body 830. The thermal barrier 820 can have a higher porosity than the porous ceramic body 830. The thermal barrier 820 can comprise a material such as one or more of: alumina, zirconia, zirconia with magnesium oxide, glass-ceramic, quartz, porous polymer. It will be appreciated that the thermal barrier 820 can have a different shape or comprise a different material.

[0245] Figure 12 A schematic cross-sectional view of another example heater assembly 801 for an aerosol-generating system is shown. The heater assembly 801 is the same as the heater assembly 800 of Figure 12 Figure 11 The heater assembly 801 is the same as the heater assembly 800 of Figure 11

[0246] The heating element 815 extends to cover the area of the second end face 823 of the thermal barrier 820. The heating element 815 has a liquid absorption surface 814 and a heating surface 813. In this example, both the liquid absorption surface 814 of the heating element 815 and the heating surface 813 of the heating element 815 are substantially planar surfaces. The liquid absorption surface 814 of the heating element 815 is in direct contact with the thermal barrier 120.

[0247] Figures 13a to 13c Schematic diagrams of different heating elements 910a-c for an aerosol-generating system are shown. Each heating element 910a-c comprises a plurality of tracks or track portions 917 arranged in electrical parallel. By being arranged in electrical parallel, the current flow is split into separate parallel flow paths. The flow paths are then recombined.

[0248] In the heating elements 910a-c of Figures 13a to 13c Each heating element 910a-c comprises a first connection pad 913 and a second connection pad 914. The first and second connection pads 913, 914 are configured to allow connection to an external electrical circuit. An aperture or plurality of apertures 915 in the heating element 910a-c separates each track 917. Each heating element 910a-c comprises a diverging portion in which current is split from the first connection pad 913 into the tracks 917 defining an electrical parallel path. Each heating element 910a-c comprises a converging portion in which current is combined from the tracks 917 defining an electrical parallel path into the second connection pad 914.

[0249] Figures 13a to 13c ​​Three different arrangements of electrically parallel arranged tracks or track portions are shown. In Figure 13a , four tracks 917 are separated by three apertures 915 to define four electrically parallel paths. In Figure 13b , six track portions 917 are separated by one aperture 915 to define two electrically parallel paths. In Figure 13b , each electrically parallel path defines a serpentine path between a first connection pad 913 and a second connection pad 914. In Figure 13c , eight track portions 917 are separated by four apertures 915 to define four pairs of electrically parallel paths. Figure 13c Each pair of electrically parallel paths is separated by an intermediate connection 916, three intermediate connections are shown in Figure 13c

[0250] By arranging the tracks or track portions electrically in parallel, if one track portion is defective, the current can be redistributed and still flow through the heating element 910a to 910c, i.e. the electrical connection between the first connection pad 913 and the second connection pad 914 is not broken. This has the advantage of increasing the number of puffs before the heater is completely dead and potentially increasing the heater life to the life of the device. In contrast, in a simple serpentine heater defining a single electrical path between the first connection pad 913 and the second connection pad 914, if a part of the serpentine heating element is broken, the heating element will stop working due to the increase in local resistance at the point of break or defect. A defect in a simple serpentine heater causes an increase in local resistance. The increase in local resistance increases the power dissipation. The increase in power dissipation in turn increases the resistance until the break.

[0251] The inventors have also found that the parallel tracks or track portions of the electrically parallel arrangement explained with reference to Figures 13a to 13c have a surprising additional advantage. In such an arrangement, in the event of a break in one track portion, the heating element will still operate in a beneficial manner and can operate in a beneficial manner for an initial temporary period, as the break in one track or track portion will result in a higher energy density on the remaining tracks or track portions. In this case, the same power will still be provided but over a smaller area and therefore the throughput will be increased. Whilst such a break causing an increase in current on the unbroken tracks or track portions can ultimately reduce the user experience, the device or cartridge can comprise a mechanism to alert the user that the performance of the heater assembly can be below optimal in the future.

[0252] Such a mechanism relies on the following principle. The total resistance of the heating element depends on the following factors:

[0253] 1) the number of parallel heating tracks (more parallel tracks reduce the total resistance);

[0254] ​2) Cross-sectional area (width or thickness (or width and thickness)) of the parallel heating tracks (higher cross-sectional area results in lower electrical resistance);

[0255] 3) Length of the parallel heating tracks (longer tracks have higher electrical resistance);

[0256] 4) If the heating element is porous, adjust the porosity of the heating element (higher porosity increases electrical resistance);

[0257] 5) Specific chemical or material composition (e.g. alloyed by doping).

[0258] The overall total heating element resistance R of the arrangement of multiple heating tracks or track portions (i) tot , which are arranged in parallel such that the electrical current in at least two adjacent tracks or track portions flows in the same direction, R i is set forth in equation 1 :

[0259]

[0260] where n is the total number of heating tracks arranged in electrical parallel.

[0261] The behavior of a parallel track heating element when one heating track fails can be considered with reference to a heating element with 4 parallel heating tracks as shown for example in Figure 13a Each heating track has an electrical resistance of 3 Ohms. Using equation 1, the total electrical resistance of the heating element is 0.75 Ohms.

[0262] When one heating track starts to fail, the resistance of the failing heating track increases. The total resistance of the heating element also starts to increase in a linear relationship with the failing heating track resistance. However, as the heating track resistance continues to increase, the heating element resistance asymptotes to a constant resistance value. At this constant resistance value, the effect of the failing heating track on the heating element resistance is limited. In this example where each of the non-failed heating tracks has a resistance of 3 Ohms, the total resistance of the heating element asymptotes to 1 Ohm when the failing track can be considered an open circuit (i.e. no more current can flow through it). In this example, when one track fails, only three tracks remain to calculate the total heating element resistance.

[0263] To consider this behavior of such a heating element, consider a supply voltage of 3.5 Volts and a target power of 5.5 Watts. In this example, the non-failed parallel heating tracks maintain their initial resistance of 3 Ohms. In the failing track, the total maximum current decreases as the resistance increases. In the failing track, once it fails, the current decreases to zero. The current through the non-failed parallel tracks remains substantially constant as the resistance of the failing track increases (if resistance changes due to temperature increases are ignored).

[0264] For maximum power generation, a similar behavior is observed. Once a heating track has failed, less total power is generated. However, in this example, the maximum power is still above the target of 5.5 Watts, despite one of the heating tracks being failed.

[0265] In contrast to a heating element comprising a film, the overall heating element resistance increase can be monitored by the control electronics for a parallel track heating element. In a film heating element, the damaged area can widen over time until failure occurs, as the current density across the film heating element (perpendicular to the current flow) increases at the damaged area, generating more power, which increases the local temperature. This locally increases the resistance of the film heating element, further increasing the temperature until breakdown (i.e. positive feedback). In contrast, in a parallel track heating element, the overall heating element resistance increase can be monitored by the control electronics. The aerosol-generating system can be configured such that when a predetermined threshold is reached, the device or system informs the user through the user interface that the heater assembly should be replaced.

[0266] The aerosol-generating system can also be configured to prolong the life of the parallel track heating element. The aerosol-generating system can comprise control circuitry configured to adjust the power fed to the heater after a failure of a heating track is detected, for example, by a feedback loop. The control circuitry can be configured to provide a pulse width modulation (“PWM”) signal to control the power fed to the heater. The control circuitry can adjust the power fed to the heater by adjusting the duty cycle of the pulse width modulation signal. In an example, the control circuitry can be configured to have a duty cycle of 33.7% when the heating tracks are in a normal state. When one of the heating tracks has failed, the duty cycle can be increased to 44.9%. When one of the heating tracks fails, the power density (heating power generated by surface area) increases, enhancing the thermal efficiency of the heater body. Thus, the proper operation of the heater is not jeopardized by one failed heating track. A similar result occurs if a second heating track breaks. The control circuitry can be configured such that the duty cycle is further increased (to 67.4% in the current example). Thus, even if two of the heating tracks break, a heating element having four parallel heating tracks can still operate under nominal conditions of 5.5 Watts, as the duty cycle remains below 100%.

[0267] The control circuitry can be configured such that, once a parallel heating track has failed, based on the change in the nominal total resistance of the heating element, it is possible for the control circuitry to assess the state of the heating element (i.e. the number of failed heating tracks). The control circuitry can be configured such that, after a predefined number of heating track(s) has failed, the device can inform the user that the heater assembly should be replaced.

[0268] Figure 14a and Figure 14b A schematic of current flow 909 around a corner of a heating element track is shown. Figure 14a is a schematic of current flow 909a around a known heating element track, where a track portion 917a defines a path having a bend with an inner edge of the bend having a sharp corner. In such a track portion 917a, the current flow depicted by arrows 909a following the path of least resistance is concentrated (i.e., current density is increased). This concentration occurs at the inner edge of the corner. The current concentration can increase the local temperature, and can result in the presence of a hot spot at the corner. Hot spots are disadvantageous as they can affect the efficiency and reliability of the heating element. Although the local resistivity of the heater track material can increase due to the increase in local temperature (which would direct the current flow to a path of lower resistance), a hot spot still occurs.

[0269] Figure 14b is a schematic of current flow 909b around a heating element track, where a track portion 917b defines a path having a bend with an inner edge of the bend being curved. In this track portion 917b, the current flow 909b does not form a local hot spot.

[0270] Compared to the track shape shown in Figure 14a , the more smoothly curved track portion 917b shown in Figure 14b , the current flow 909b remains more evenly distributed across the heating track 917b, as depicted by the dotted arrows 909b. The current flow 909b is directed to flow more evenly to avoid concentration of current at any point. This in turn limits the creation of hot spots. The heater track 917b can have a resistivity gradient perpendicular to the current flow in one or more corners, such that the resistivity is higher at an inner portion of the corner and lower at an outer portion of the corner. Such a gradient is beneficial to balance the localized high current density and reduce hot spot creation.

[0271] For purposes of this specification and appended claims, unless 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, unless otherwise indicated. Accordingly, in this context, a number A is understood as A ± 5% of A. In this context, a number A can be considered to include values within the general standard error of a measurement of a property modified by the number A. In certain instances in the appended claims, the number A can deviate from the percentage listed above, provided that the amount by which A deviates does not materially affect the basic characteristics and novel features of the claimed application. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges, unless otherwise indicated.

Claims

1. An aerosol-generating system comprising: a heater assembly comprising: a heating element for vaporising a liquid aerosol-forming substrate, and a porous body for conveying the liquid aerosol-forming substrate to the heating element, the porous body having a liquid uptake surface and a heating surface, the heating element being located on the heating surface of the porous body; wherein the heating element is fluid permeable such that, in use, vapour is emitted from the heater assembly in an average vapour emission direction; wherein the aerosol-generating system further comprises an air inlet and an aerosol outlet, the air inlet being in fluid communication with the aerosol outlet to define an airflow path through the aerosol-generating system; wherein the heater assembly is arranged in fluid communication with the airflow path such that air flows in an average airflow direction past the heater assembly, wherein the heater assembly and the airflow path are arranged such that the angle between the average vapour emission direction and the average airflow direction is less than 90 degrees.

2. An aerosol-generating system according to claim 1, wherein the average vapour emission direction is substantially perpendicular to the heating surface.

3. An aerosol-generating system according to claim 1 or 2, wherein the heater assembly and the airflow path are arranged such that the average vapour emission direction and the average airflow direction are substantially the same.

4. An aerosol-generating system according to any preceding claim, wherein the porous body comprises at least one airflow guide to direct airflow towards the heating element.

5. An aerosol-generating system according to any preceding claim, wherein the air inlet is distal of the heater assembly.

6. An aerosol-generating system according to any preceding claim, wherein the cross-sectional area of the airflow path in the region of the heater assembly is between 9.15 mm2 and 183 mm2.

7. An aerosol-generating system according to any preceding claim, wherein the heating element comprises a porous layer of electrically conductive material.

8. An aerosol-generating system according to any preceding claim, wherein the heating element and the porous body are integrally formed.

9. An aerosol-generating system according to any of claims 1 to 7, wherein the heating element is bonded to the heating surface of the porous body.

10. An aerosol-generating system according to any preceding claim, wherein the heating element has a tapered cross-sectional shape.

11. An aerosol-generating system according to any preceding claim, wherein the heating surface of the porous body is convex in one or both of a first lateral direction and a second lateral direction, the first lateral direction being orthogonal to the second lateral direction.

12. An aerosol-generating system according to any preceding claim, wherein the heater assembly further comprises a thermally insulating layer having a lower thermal conductivity than the porous body, wherein the thermally insulating layer is disposed between and in contact with each of the porous body and the heating element, and the thermally insulating layer is configured to reduce heat transfer from the heating element to the porous body.

13. An aerosol-generating system according to any preceding claim, wherein the heating element comprises a doped portion of the porous body.

14. An aerosol-generating system according to any preceding claim, wherein the average pore size of the porous body varies between the liquid- absorbing surface and the heating surface.

15. An aerosol-generating system according to any preceding claim, wherein the heating element comprises a plurality of tracks or track portions arranged electrically in parallel.

Images