SMOKING SUBSTITUTE APPARATUS

Abstract

A smoking substitute apparatus is disclosed, comprising a housing comprising a base portion, a mouthpiece portion, and one or more walls extending longitudinally from the base portion towards the mouthpiece portion. An air inlet is formed in a wall of the housing and spaced longitudinally from the base portion. An outlet is formed in the mouthpiece portion. An airflow path extends from the air inlet to the outlet, the airflow path comprising a first portion downstream of the air inlet and extending longitudinally towards the base portion of the housing, and a transversely extending second portion that is downstream of the first portion. The apparatus has a vaporizer comprising a wick and a heating element for heating a heatable portion of the wick. The heatable portion of the wick is elongated in a direction substantially parallel to the direction of airflow in the second portion of the airflow path.

Claims

1. A smoking substitute apparatus comprising: a housing comprising a base portion, a mouthpiece portion, and one or more walls extending longitudinally from the base portion towards the mouthpiece portion; an air inlet formed in a wall of the housing and spaced longitudinally from the base portion; an outlet formed in the mouthpiece portion; an airflow path extending from the air inlet to the outlet, the airflow path comprising a first portion downstream of the air inlet and extending longitudinally towards the base portion of the housing, and a transversely extending second portion that is downstream of the first portion; and a vaporizer comprising a wick and a heating element for heating a heatable portion of the wick, the heatable portion of the wick being elongated in a direction substantially parallel to the direction of airflow in the second portion of the airflow path.

2. A smoking substitute apparatus according to claim 1 wherein the air inlet is longitudinally spaced from the base portion of the housing by a distance that is greater than 8 mm.

3. A smoking substitute apparatus according to claim 1 wherein the airflow path comprises a third portion extending longitudinally from the second portion to the outlet

4. A smoking substitute apparatus according to claim 3 wherein the second portion of the airflow path is substantially perpendicular to the first and/or third portions of the airflow path.

5. A smoking substitute apparatus according to claim 3 wherein a bypass air inlet is provided into the third portion of the airflow path.

6. A smoking substitute apparatus according to claim 1 wherein the airflow path is generally U-shaped

7. A smoking substitute apparatus according to claim 1 wherein the second portion of the airflow path has a length that is longer than the length of the heatable portion of the wick.

8. A smoking substitute apparatus according to claim 3 wherein the apparatus comprises a tank for housing an aerosol precursor disposed between the first and the third portions of the airflow path.

9. A smoking substitute apparatus according to claim 1 wherein the housing comprises a width, a length and a depth, the depth being smaller than each of the width and the length and the heatable portion of the wick being oriented in the direction of the width of the housing.

10. A smoking substitute system comprising a base unit and a smoking substitute apparatus, wherein the smoking substitute apparatus is removably engageable with the base unit and wherein the smoking substitute apparatus comprises: a housing comprising a base portion, a mouthpiece portion, and one or more walls extending longitudinally from the base portion towards the mouthpiece portion; an air inlet formed in a wall of the housing and spaced longitudinally from the base portion; an outlet formed in the mouthpiece portion; an airflow path extending from the air inlet to the outlet, the airflow path comprising a first portion downstream of the air inlet and extending longitudinally towards the base portion of the housing, and a transversely extending second portion that is downstream of the first portion; and a vaporizer comprising a wick and a heating element for heating a heatable portion of the wick, the heatable portion of the wick being elongated in a direction substantially parallel to the direction of airflow in the second portion of the airflow path.

11. A method of using a smoking substitute apparatus to generate an aerosol, the smoking substitute apparatus comprising: a housing comprising a base portion, a mouthpiece portion, and one or more walls extending longitudinally from the base portion towards the mouthpiece portion; an air inlet formed in a wall of the housing and spaced longitudinally from the base portion; an outlet formed in the mouthpiece portion; an airflow path extending from the air inlet to the outlet, the airflow path comprising a first portion downstream of the air inlet and extending longitudinally towards the base portion of the housing, and a transversely extending second portion that is downstream of the first portion; and a vaporizer comprising a wick and a heating element for heating a heatable portion of the wick, the heatable portion of the wick being elongated in a direction substantially parallel to the direction of airflow in the second portion of the airflow path.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0120] So that the disclosure may be understood, and so that further aspects and features thereof may be appreciated, embodiments illustrating the principles of the disclosure will now be discussed in further detail with reference to the accompanying figures, in which:

[0121] FIG. 1 illustrates a set of rectangular tubes for use in experiments to assess the effect of flow and cooling conditions at the wick on aerosol properties. Each tube has the same depth and length but different width.

[0122] FIG. 2 shows a schematic perspective longitudinal cross sectional view of an example rectangular tube with a wick and heater coil installed.

[0123] FIG. 3 shows a schematic transverse cross sectional view an example rectangular tube with a wick and heater coil installed. In this example, the internal width of the tube is 12 mm.

[0124] FIGS. 4A-4D show air flow streamlines in the four devices used in a turbulence study.

[0125] FIG. 5 shows the experimental set up to investigate the influence of inflow air temperature on aerosol particle size, in order to investigate the effect of vapor cooling rate on aerosol generation.

[0126] FIG. 6 shows a schematic longitudinal cross sectional view of a first smoking substitute apparatus (pod 1) used to assess influence of inflow air temperature on aerosol particle size.

[0127] FIG. 7 shows a schematic longitudinal cross sectional view of a second smoking substitute apparatus (pod 2) used to assess influence of inflow air temperature on aerosol particle size.

[0128] FIG. 8A shows a schematic longitudinal cross sectional view of a third smoking substitute apparatus (pod 3) used to assess influence of inflow air temperature on aerosol particle size.

[0129] FIG. 8B shows a schematic longitudinal cross sectional view of the same third smoking substitute apparatus (pod 3) in a direction orthogonal to the view taken in FIG. 8A.

[0130] FIG. 9 shows a plot of aerosol particle size (Dv50) experimental results against calculated air velocity.

[0131] FIG. 10 shows a plot of aerosol particle size (Dv50) experimental results against the flow rate through the apparatus for a calculated air velocity of 1 m/s.

[0132] FIG. 11 shows a plot of aerosol particle size (Dv50) experimental results against the average magnitude of the velocity in the vaporizer surface region, as obtained from CFD modelling.

[0133] FIG. 12 shows a plot of aerosol particle size (Dv50) experimental results against the maximum magnitude of the velocity in the vaporizer surface region, as obtained from CFD modelling.

[0134] FIG. 13 shows a plot of aerosol particle size (Dv50) experimental results against the turbulence intensity.

[0135] FIG. 14 shows a plot of aerosol particle size (Dv50) experimental results dependent on the temperature of the air and the heating state of the apparatus.

[0136] FIG. 15 shows a plot of aerosol particle size (Dv50) experimental results against vapor cooling rate to 50° C.

[0137] FIG. 16 shows a plot of aerosol particle size (Dv50) experimental results against vapor cooling rate to 75° C.

[0138] FIG. 17 is a schematic front view of a smoking substitute system, according to a reference arrangement, in an engaged position;

[0139] FIG. 18 is a schematic front view of the smoking substitute system of FIG. 17 in a disengaged position;

[0140] FIG. 19 is a schematic longitudinal cross sectional view of a smoking substitute apparatus of the reference arrangement;

[0141] FIG. 20 is an enlarged schematic cross sectional view of part of the air passage and vaporization chamber of the reference arrangement;

[0142] FIG. 21 is a schematic longitudinal cross sectional view of a smoking substitute apparatus according to a first embodiment;

[0143] FIG. 22 is a schematic longitudinal cross sectional view of a smoking substitute apparatus according to a second embodiment;

[0144] FIG. 23 shows the results of modelling on the velocity field of airflow and the volume fraction of vapor for a reference arrangement (left hand side) in which the air flow direction is perpendicular to the axis of the wick and for an embodiment (right hand side) in which the air flow direction is parallel to the axis of the wick.

DETAILED DESCRIPTION

[0145] Further background to the present disclosure and further aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. The contents of all documents mentioned in this text are incorporated herein by reference in their entirety.

[0146] FIGS. 17 and 18 illustrate a smoking substitute system in the form of an e-cigarette system 110. The system 110 comprises a main body 120 of the system 110, and a smoking substitute apparatus in the form of an e-cigarette consumable (or “pod”) 150. In the illustrated arrangement the consumable 150 (sometimes referred to herein as a smoking substitute apparatus) is removable from the main body 120, so as to be a replaceable component of the system 110. The e-cigarette system 110 is a closed system in the sense that it is not intended that the consumable should be refillable with e-liquid by a user.

[0147] As is apparent from FIGS. 17 and 18, the consumable 150 is configured to engage the main body 120. FIG. 17 shows the main body 120 and the consumable 150 in an engaged state, whilst FIG. 18 shows the main body 120 and the consumable 150 in a disengaged state. When engaged, a portion of the consumable 150 is received in a cavity of corresponding shape in the main body 120 and is retained in the engaged position by way of a snap-engagement mechanism. In other embodiments, the main body 120 and consumable 150 may be engaged by screwing one into (or onto) the other, or through a bayonet fitting, or by way of an interference fit.

[0148] The system 110 is configured to vaporize an aerosol precursor, which in the illustrated arrangement is in the form of a nicotine-based e-liquid 160. The e-liquid 160 comprises nicotine and a base liquid including propylene glycol and/or vegetable glycerin. In the present embodiment, the e-liquid 160 is flavored by a flavorant. In other embodiments, the e-liquid 160 may be flavorless and thus may not include any added flavorant.

[0149] FIG. 19 shows a schematic longitudinal cross sectional view of the smoking substitute apparatus forming part of the smoking substitute system shown in FIGS. 17 and 18. In FIG. 19, the e-liquid 160 is stored within a reservoir in the form of a tank 152 that forms part of the consumable 150. In the illustrated embodiment, the consumable 150 is a “single-use” consumable 150. That is, upon exhausting the e-liquid 160 in the tank 152, the intention is that the user disposes of the entire consumable 150. The term “single-use” does not necessarily mean the consumable is designed to be disposed of after a single smoking session. Rather, it defines the consumable 150 is not arranged to be refilled after the e-liquid contained in the tank 152 is depleted. The tank may include a vent (not shown) to allow ingress of air to replace e-liquid that has been used from the tank. The consumable 150 preferably includes a window 158 (see FIGS. 17 and 18), so that the amount of e-liquid in the tank 152 can be visually assessed. The main body 120 includes a slot 157 so that the window 158 of the consumable 150 can be seen whilst the rest of the tank 152 is obscured from view when the consumable 150 is received in the cavity of the main body 120. The consumable 150 may be referred to as a “clearomizer” when it includes a window 158, or a “cartomizer” when it does not.

[0150] In some arrangements, the e-liquid (i.e., aerosol precursor) may be the only part of the system that is truly “single-use”. That is, the tank may be refillable with e-liquid or the e-liquid may be stored in a non-consumable component of the system. For example, in such arrangements, the e-liquid may be stored in a tank located in the main body or stored in another component that is itself not single-use (e.g., a refillable cartomizer).

[0151] The external wall of tank 152 is provided by a casing of the consumable 150. The tank 152 annularly surrounds, and thus defines a portion of, a passage 170 that extends between a vaporizer inlet 172 and an outlet 174 at opposing ends of the consumable 150. In this respect, the passage 170 comprises an upstream end at the end of the consumable 150 that engages with the main body 120, and a downstream end at an opposing end of the consumable 150 that comprises a mouthpiece 154 of the system 110.

[0152] When the consumable 150 is received in the cavity of the main body 120 as shown in FIG. 19, a plurality of device air inlets 176 are formed at the boundary between the casing of the consumable and the casing of the main body. The device air inlets 176 are in fluid communication with the vaporizer inlet 172 through an inlet flow channel 178 formed in the cavity of the main body which is of corresponding shape to receive a part of the consumable 150. Air from outside of the system 110 can therefore be drawn into the passage 170 through the device air inlets 176 and the inlet flow channels 178.

[0153] When the consumable 150 is engaged with the main body 120, a user can inhale (i.e., take a puff) via the mouthpiece 154 so as to draw air through the passage 170, and so as to form an airflow (indicated by the dashed arrows in FIG. 3) in a direction from the vaporizer inlet 172 to the outlet 174. Although not illustrated, the passage 170 may be partially defined by a tube (e.g., a metal tube) extending through the consumable 150. In FIG. 3, for simplicity, the passage 170 is shown with a substantially circular cross-sectional profile with a constant diameter along its length. In other embodiments, the passage may have other cross-sectional profiles, such as oval shaped or polygonal shaped profiles. Further, in other embodiments, the cross sectional profile and the diameter (or hydraulic diameter) of the passage may vary along its longitudinal axis.

[0154] The smoking substitute system 110 is configured to vaporize the e-liquid 160 for inhalation by a user. To provide this operability, the consumable 150 comprises a heater having a porous wick 162 and a resistive heating element in the form of a heating filament 164 that is helically wound (in the form of a coil) around a portion of the porous wick 162. The porous wick 162 extends across the passage 170 (i.e., transverse to a longitudinal axis of the passage 170 and thus also transverse to the air flow along the passage 170 during use) and opposing ends of the wick 162 extend into the tank 152 (so as to be immersed in the e-liquid 160). In this way, e-liquid 160 contained in the tank 152 is conveyed from the opposing ends of the porous wick 162 to a central portion of the porous wick 162 so as to be exposed to the airflow in the passage 170.

[0155] The helical filament 164 is wound about the exposed central portion of the porous wick 162 and is electrically connected to an electrical interface in the form of electrical contacts 156 mounted at the end of the consumable that is proximate the main body 120 (when the consumable and the main body are engaged). When the consumable 150 is engaged with the main body 120, electrical contacts 156 make contact with corresponding electrical contacts (not shown) of the main body 120. The main body electrical contacts are electrically connectable to a power source (not shown) of the main body 120, such that (in the engaged position) the filament 164 is electrically connectable to the power source. In this way, power can be supplied by the main body 120 to the filament 164 in order to heat the filament 164. This heats the porous wick 162 which causes e-liquid 160 conveyed by the porous wick 162 to vaporize and thus to be released from the porous wick 162. The vaporized e-liquid becomes entrained in the airflow and, as it cools in the airflow (between the heated wick and the outlet 174 of the passage 170), condenses to form an aerosol. This aerosol is then inhaled, via the mouthpiece 154, by a user of the system 110. As e-liquid is lost from the heated portion of the wick, further e-liquid is drawn along the wick from the tank to replace the e-liquid lost from the heated portion of the wick.

[0156] The filament 164 and the exposed central portion of the porous wick 162 are positioned across the passage 170. More specifically, the part of passage that contains the filament 164 and the exposed portion of the porous wick 162 forms a vaporization chamber. In the illustrated example, the vaporization chamber has the same cross-sectional diameter as the passage 170. However, in some arrangements the vaporization chamber may have a different cross sectional profile compared with the passage 170. For example, the vaporization chamber may have a larger cross sectional diameter than at least some of the downstream part of the passage 170 so as to enable a longer residence time for the air inside the vaporization chamber.

[0157] FIG. 20 illustrates in more detail the vaporization chamber and therefore the region of the consumable 150 around the wick 162 and filament 164. The helical filament 164 is wound around a central portion of the porous wick 162. The porous wick extends across passage 170. E-liquid 160 contained within the tank 152 is conveyed as illustrated schematically by arrows 401, i.e., from the tank and towards the central portion of the porous wick 162.

[0158] When the user inhales, air is drawn from through the inlets 176 shown in FIG. 19, along inlet flow channel 178 to vaporization chamber inlet 172 and into the vaporization chamber containing porous wick 162. The porous wick 162 extends substantially transverse to the airflow direction. The airflow passes around the porous wick, at least a portion of the airflow substantially following the surface of the porous wick 162. In examples where the porous wick has a cylindrical cross-sectional profile, the airflow may follow a curved path around an outer periphery of the porous wick 162.

[0159] At substantially the same time as the airflow passes around the porous wick 162, the filament 164 is heated so as to vaporize the e-liquid which has been wicked into the porous wick. The airflow passing around the porous wick 162 picks up this vaporized e-liquid, and the vapor-containing airflow is drawn in direction 403 further down passage 170.

[0160] The power source of the main body 120 may be in the form of a battery (e.g., a rechargeable battery such as a lithium-ion battery). The main body 120 may comprise a connector in the form of, e.g., a USB port for recharging this battery. The main body 120 may also comprise a controller that controls the supply of power from the power source to the main body electrical contacts (and thus to the filament 164). That is, the controller may be configured to control a voltage applied across the main body electrical contacts, and thus the voltage applied across the filament 164. In this way, the filament 164 may only be heated under certain conditions (e.g., during a puff and/or only when the system is in an active state). In this respect, the main body 120 may include a puff sensor (not shown) that is configured to detect a puff (i.e., inhalation). The puff sensor may be operatively connected to the controller so as to be able to provide a signal, to the controller, which is indicative of a puff state (i.e., puffing or not puffing). The puff sensor may, for example, be in the form of a pressure sensor or an acoustic sensor.

[0161] Although not shown, the main body 120 and consumable 150 may comprise a further interface which may, for example, be in the form of an RFID reader, a barcode or QR code reader. This interface may be able to identify a characteristic (e.g., a type) of a consumable 150 engaged with the main body 120. In this respect, the consumable 150 may include any one or more of an RFID chip, a barcode or QR code, or memory within which is an identifier and which can be interrogated via the interface.

[0162] In the reference arrangements described above based on FIGS. 17-20, the heatable portion of the wick is arranged transversely to the direction of the airflow in the vaporizer (vaporization chamber). However, the present inventors have realized that there are advantages to arranging the airflow path and the orientation of the heatable portion of the wick differently.

[0163] FIG. 21 shows a longitudinal cross sectional view of a smoking substitute apparatus 500 according to a first aspect. The drawing is schematic. It is intended that this apparatus is configured for use with a main body substantially as shown in FIGS. 17 and 18. Air flow through the apparatus is illustrated using straight arrows.

[0164] The air inlet 502 of the apparatus 500 is in the form of an aperture formed in the first side wall 504 of the housing 506. In particular, the air inlet 502 is spaced along the first side wall 504 (in a longitudinal direction) from the base 508 of the housing 506 so as to be partway along the first side wall 504 from the base 508. The outlet 510 is formed in the mouthpiece 512 and an airflow path extends from the air inlet 502 to the outlet 510, such that a user can draw air through the airflow path by inhaling at the outlet 510. As will be described in more detail below, the airflow path follows a generally U-shaped path through the apparatus 500.

[0165] The airflow path comprises first, second and third airflow path portions. The first airflow path portion is defined by a first passage 514 extending longitudinally from the air inlet 502 towards the base 508 of the apparatus 500. This first passage 514 is defined between a first tank wall 516 that is laterally spaced from the first side wall 504 (in which the air inlet 502 is formed) and that extends generally parallel to the first side wall 504.

[0166] The third airflow path is similarly defined by a third passage 520 that is formed between a second tank wall 522 and the second side wall 518. The second tank wall 522 is laterally spaced from and generally parallel to the second side wall 518. Both the first 516 and second 522 tank walls span the front and rear walls (not shown) of the housing 506. In this way, the tank 524 is partly defined between the first and second tank walls 516, 522, an upper wall 526 and the front and rear walls.

[0167] The second airflow path portion is in the form of a vaporizing chamber 528 that extends transversely across the lower part of the housing 506 so as to connect lower ends of the first 514 and second 520 airflow passages. Thus, upon inhalation by a user, air may flow into the air inlet 502, through the first passage 514, through the vaporizing chamber 528 (where vapor may be entrained in the air) and subsequently through the third passage 520 and on to where it is discharged (into a user's mouth) from the outlet 510 at the mouthpiece 512, in communication with an upper end of the third passage 520. Thus, the airflow path comprises at least two turns (at the air inlet 502 and the connection between the vaporizing chamber 528 and the first passage 514) between the vaporizer chamber 528 and the air inlet 502. This may reduce the propensity for leakage of e-liquid out of the air inlet 502 (i.e., from the vaporizing chamber 528).

[0168] The vaporizer is located in the vaporizing chamber 528 and comprises a porous wick 530 and a heater filament 532 coiled around the porous wick 530. The heatable portion of the wick 530 (i.e., that part of the wick that has the heater filament 532 coiled around it) extends along the vaporizing chamber 528 (substantially parallel to the direction of airflow through the vaporizing chamber 528). That is, the wick 530 extends in the width direction of the housing 506.

[0169] The vaporizing chamber 528 is bounded at its upper limit by a base wall of the tank and at its lower limit by the base 508 of the housing 506.

[0170] The ends of the wick 530 are inserted through apertures in the base wall of the tank in order to allow the wick to be saturated with aerosol precursor (e-liquid) for communication along the wick to the heatable portion of the wick. In this way, the ends of the wick 530 are in contact with aerosol precursor (e-liquid) stored in the tank 524. This e-liquid is transported along the wick 530 (e.g., by capillary action) to the heatable portion of the wick 530 that is exposed to airflow flowing through the vaporizing chamber 528. The transported e-liquid is heated by the heater filament 532 (when activated, e.g., by detection of inhalation), which causes the e-liquid to be vaporized and to be entrained in air flowing along the wick 530. This vaporized liquid may cool to form an aerosol in the vaporizing chamber 528, or in the third passage 520, which may then be inhaled by a user.

[0171] The base of the apparatus accommodates the electrical interface of the apparatus. The electrical interface comprises two electrical contacts that are electrically connected to the heating filament 532. In this way, when the apparatus is engaged with the main body, power can be supplied from the power source of the main body to the heating filament 532.

[0172] FIG. 22 shows a second embodiment, which is a modification of FIG. 21. The features of FIG. 22 corresponding to those in FIG. 21 are not described again. In FIG. 22, there is provided a bypass air inlet, through the second side wall 517 into the third passage 520. The provision of a bypass airflow allows the air flow in the vaporization chamber to be more gentle (and therefore less turbulent and with lower velocity) for a particular total flow rate through the device than for FIG. 21. This permits the generation of an aerosol with a larger particle size and with a tighter particle size distribution.

[0173] In the description above, it is explained that the shape and orientation of the first passage combined with the vaporization chamber reduces the risk of e-liquid leakage. The shape of the third passage combined with the vaporization chamber has corresponding advantages. In particular, there is a risk of e-liquid spitting from the heated wick. There is no straight line path from the wick to the outlet and therefore any drops of e-liquid emitted in this way should hit an internal wall of the apparatus rather than reach the outlet. Spitting and condensed e-liquid flow down to accumulate below the wick. This reduces the chance of the air inlet and/or outlet becoming blocked. E-liquid below the wick evaporates during operation of the apparatus due to radiative heat from the heater.

[0174] The inventors have considered the effect of the relative orientation of the heatable portion of the wick and the airflow direction in the vaporization chamber. FIG. 23 shows the results of modelling on the velocity field of airflow and the volume fraction of vapor for a reference arrangement (left hand side) in which the air flow direction is perpendicular to the axis of the wick and for an embodiment (right hand side) in which the air flow direction is parallel to the axis of the wick.

[0175] Where the airflow direction is perpendicular to the wick (as shown on the left in FIG. 23), there is a significant difference in conditions at the leading face of the wick compared to the trailing face of the wick. At the leading face, the vapor volume fraction is low, indicating that the vapor has condensed into an aerosol quickly as it is carried away from the wick. At the trailing face, the vapor volume fraction is high, indicating that the vapor is more slowly condensing into the aerosol. This modelling therefore shows that the cooling rate experienced by the vapor is significantly different at different parts of the wick. It is considered that cooling rate has a very significant effect on the particle size and particle size distribution of the aerosol. Therefore, these differences in cooling rate are expected to lead to a broad particle size distribution.

[0176] Where the airflow direction is parallel to the wick (as shown on the right in FIG. 23), conditions at the parts of the wick emitting vapor are more uniform. As can be seen, the vapor volume fraction is spatially relatively uniform along the wick. Therefore, the vapor condenses relatively uniformly, independent of position along the wick. This modelling therefore shows that the cooling rate experienced by the vapor is relatively uniform at different parts of the wick. This is therefore considered to lead to a narrow particle size distribution. The heating and flow conditions in the vaporization chamber can furthermore be controlled (in part by the use of a bypass if necessary) in order to generate an aerosol with a relatively large particle size, for example with dv50 in the range 2-3 μm.

EXAMPLES

[0177] There now follows a disclosure of certain examples of experimental work undertaken to determine the effects of certain conditions in the smoking substitute apparatus on the particle size of the generated aerosol. However, the present disclosure is to be understood to not be limited in its application to the specific experimentation, results, and laboratory procedures disclosed herein after. Rather, the Examples are simply provided as one of various embodiments and are meant to be exemplary, not exhaustive.

[0178] The experimental work described in these examples has relevance to one or more of the embodiments disclosed above, for example in view of the effects demonstrated on the particle size of the generated aerosol based on control of the flow conditions at the wick, such as when a bypass airflow is implemented.

[0179] Introduction

[0180] Aerosol droplet size is a considered to be an important characteristic for smoking substitution devices. Droplets in the range of 2-5 μmare preferred in order to achieve improved nicotine delivery efficiency and to minimize the hazard of second-hand smoking. However, at the time of writing (September 2019), commercial EVP devices typically deliver aerosols with droplet size averaged around 0.5 μm, and to the knowledge of the inventors not a single commercially available device can deliver an aerosol with an average particle size exceeding 1 μm.

[0181] The present inventors speculate, without themselves wishing to be bound by theory, that there has to date been a lack of understanding in the mechanisms of e-liquid evaporation, nucleation and droplet growth in the context of aerosol generation in smoking substitute devices. The present inventors have therefore studied these issues in order to provide insight into mechanisms for the generation of aerosols with larger particles. The present inventors have carried out experimental and modelling work alongside theoretical investigations shown in the examples below, leading to significant achievements as now reported.

[0182] This disclosure considers the roles of air velocity, air turbulence and vapor cooling rate in affecting aerosol particle size.

[0183] Experiments

[0184] In these examples, a Malvern PANalytical Spraytec laser diffraction system was employed for the particle size measurement. In order to limit the number of variables, the same coil and wick (1.5 ohms Ni—Cr coil, 1.8 mm Y07 cotton wick), the same e-liquid (1.6% freebase nicotine, 65:35 propylene glycol (PG)/vegetable glycerin (VG) ratio, no added flavor) and the same input power (10 W) were used in all experiments. Y07 represents the grade of cotton wick, meaning that the cotton has a linear density of 0.7 grams per meter.

[0185] Particle sizes were measured in accordance with ISO 13320:2009(E), which is an international standard on laser diffraction methods for particle size analysis. This is particularly well suited to aerosols, because there is an assumption in this standard that the particles are spherical (which is a good assumption for liquid-based aerosols). The standard is stated to be suitable for particle sizes in the range 0.1 micron to 3 mm.

[0186] The results presented here concentrate on the volume-based median particle size Dv50. This is to be taken to be the same as the parameter d50 used above. cl First Example

Rectangular Tube Testing

[0187] The work reported in a first example based on the inventors' insight that aerosol particle size might be related to: 1) air velocity; 2) flow rate; and 3) Reynolds number. In a given EVP device, these three parameters are inter-linked to each other, making it difficult to draw conclusions on the roles of each individual factor. In order to decouple these factors, experiments were carried out using a set of rectangular tubes having different dimensions in the first example.

[0188] These were manufactured by 3D printing. The rectangular tubes were 3D printed in an MJP 2500 3D printer. FIG. 1 illustrates the set of rectangular tubes. Each tube has the same depth and length but different width. Each tube has an integral end plate in order to provide a seal against air flow outside the tube. Each tube also has holes formed in opposing side walls in order to accommodate a wick.

[0189] FIG. 2 shows a schematic perspective longitudinal cross sectional view of an example rectangular tube 1170 with a wick 1162 and heater coil 1164 installed. The location of the wick is about half way along the length of the tube. This is intended to allow the flow of air along the tube to settle before reaching the wick.

[0190] FIG. 3 shows a schematic transverse cross sectional view an example rectangular tube 1170 with a wick 1162 and heater coil 1164 installed. In this example, the internal width of the tube is 12 mm

[0191] The rectangular tubes were manufactured to have same internal depth of 6 mm in order to accommodate the standardized coil and wick, however the tube internal width varied from 4.5 mm to 50 mm. In this disclosure, the “tube size” is referred to as the internal width of rectangular tubes.

[0192] The rectangular tubes with different dimensions were used to generate aerosols that were tested for particle size in a Malvern PANalytical Spraytec laser diffraction system. An external digital power supply was dialled to 2.6 A constant current to supply 10 W power to the heater coil in all experiments described in the first example. Between two runs, the wick was saturated manually by applying one drop of e-liquid on each side of the wick.

[0193] Three groups of experiments were carried out in this study: [0194] 1. 1.3 lpm (litres per minute, L min.sup.−1 or LPM) constant flow rate on different size tubes [0195] 2. 2.0 lpm constant flow rate on different size tubes [0196] 3. 1 m/s constant air velocity on 3 tubes: i) 5 mm tube at 1.4 lpm flow rate; ii) 8 mm tube at 2.8 lpm flow rate; and iii) 20 mm tube at 8.6 lpm flow rate.

[0197] Table 1 shows a list of experiments in this study. The values in “calculated air velocity” column were obtained by simply dividing the flow rate by the intersection area at the center plane of wick. Reynolds numbers (Re) were calculated through the following equation:

[00001]$\mathrm{Re}=\frac{\rho \mathrm{vL}}{\mu }$

[0198] where: p is the density of air (1.225 kg/m.sup.3); v is the calculated air velocity in table 1; μ is the viscosity of air (1.48×10.sup.−s m.sup.2/s); L is the characteristic length calculated by:

[00002]$L=\frac{4P}{A}$

[0199] where: P is the perimeter of the flow path's intersection, and A is the area of the flow path's intersection.

TABLE-US-00001 TABLE 1 List of experiments in the rectangular tube study first example Calculated air Tube size Flow rate Reynolds velocity [mm] [Ipm] number [m/s] 1.3 Ipm 4.5 1.3 153 1.17 constant flow 6 1.3 142 0.71 rate 7 1.3 136 0.56 8 1.3 130 0.47 10 1.3 120 0.35 12 1.3 111 0.28 20 1.3 86 0.15 50 1.3 47 0.06 2.0 Ipm 4.5 2.0 236 1.81 constant flow 5 2.0 230 1.48 rate 6 2.0 219 1.09 8 2.0 200 0.72 12 2.0 171 0.42 20 2.0 132 0.23 50 2.0 72 0.09 1.0 m/s 5.0 1.4 155 1.00 constant air 8 2.8 279 1.00 velocity 20 8.6 566 1.00

[0200] Five repetition runs were carried out for each tube size and flow rate combination. Between adjacent runs there were at least 5 minutes wait time for the Spraytec system to be purged. In each run, real time particle size distributions were measured in the Spraytec laser diffraction system at a sampling rate of 2500 per second, the volume distribution median (Dv50) was averaged over a puff duration of 4 seconds. Measurement results were averaged and the standard deviations were calculated to indicate errors as shown below.

Second Example

Turbulence Tube Testing

[0201] The Reynolds numbers in Table 1 are all well below 1000, therefore, it is considered fair to assume all the experiments in the first example would be under conditions of laminar flow. Further experiments were carried out and reported in a second example to investigate the role of turbulence.

[0202] Turbulence intensity was introduced as a quantitative parameter to assess the level of turbulence. The definition and simulation of turbulence intensity is discussed below.

[0203] Different device designs were considered in order to introduce turbulence. In the experiments reported in the second example, jetting panels were added in the existing 12 mm rectangular tubes upstream of the wick. This approach enables direct comparison between different devices as they all have highly similar geometry, with turbulence intensity being the only variable.

[0204] FIGS. 4A-4D show air flow streamlines in the four devices used in this turbulence study. FIG. 4A is a standard 12 mm rectangular tube with wick and coil installed as explained in the first example, with no jetting panel. FIG. 4B has a jetting panel located 10 mm below (upstream from) the wick. FIG. 4C has the same jetting panel 5 mm below the wick. FIG. 4D has the same jetting panel 2.5 mm below the wick. As can be seen from FIGS. 4B-4D, the jetting panel has an arrangement of apertures shaped and directed in order to promote jetting from the downstream face of the panel and therefore to promote turbulent flow. Accordingly, the jetting panel can introduce turbulence downstream, and the panel causes higher level of turbulence near the wick when it is positioned closer to the wick. As shown in FIGS. 4A-4D, the four geometries gave turbulence intensities of 0.55%, 0.77%, 1.06% and 1.34%, respectively, with FIG. 4A being the least turbulent, and FIG. 4D being the most turbulent.

[0205] For each of FIGS. 4A-4D, there are shown three modelling images. The image on the left shows the original image (color in the original), the central image shows a greyscale version of the image and the right-hand image shows a black and white version of the image. As will be appreciated, each version of the image highlights slightly different features of the flow. Together, they give a reasonable picture of the flow conditions at the wick.

[0206] These four devices were operated to generate aerosols following the procedure explained above regarding the first example using a flow rate of 1.3 lpm and the generated aerosols were tested for particle size in the Spraytec laser diffraction system.

Third Example

High Temperature Testing

[0207] This experiment described in the third example is aimed to investigate the influence of inflow air temperature on aerosol particle size, in order to investigate the effect of vapor cooling rate on aerosol generation.

[0208] The experimental set up is shown in FIG. 5. The testing used a Carbolite Gero EHA 12300B tube furnace 3210 with a quartz tube 3220 to heat up the air. Hot air in the tube furnace was then led into a transparent housing 3158 that contains the EVP device 3150 to be tested. A thermocouple meter 3410 was used to assess the temperature of the air pulled into the EVP device. Once the EVP device was activated, the aerosol was pulled into the Spraytec laser diffraction system 3310 via a silicone connector 3320 for particle size measurement.

[0209] Three smoking substitute apparatuses (referred to as “pods”) were tested in the study: pod 1 is the commercially available “myblu optimised” pod (FIG. 6); pod 2 is a pod featuring an extended inflow path upstream of the wick (FIG. 7); and pod 3 is pod with the wick located in a stagnant vaporization chamber and the inlet air bypassing the vaporization chamber but entraining the vapor from an outlet of the vaporization chamber (FIGS. 8A and 8B).

[0210] Pod 1, shown in longitudinal cross sectional view (in the width plane) in FIG. 6, has a main housing that defines a tank 160x holding an e-liquid aerosol precursor. Mouthpiece 154x is formed at the upper part of the pod. Electrical contacts 156x are formed at the lower end of the pod. Wick 162x is held in a vaporization chamber. The air flow direction is shown using arrows.

[0211] Pod 2, shown in longitudinal cross sectional view (in the width plane) in FIG. 7, has a main housing that defines a tank 160y holding an e-liquid aerosol precursor. Mouthpiece 154y is formed at the upper part of the pod. Electrical contacts 156y are formed at the lower end of the pod. Wick 162y is held in a vaporization chamber. The air flow direction is shown using arrows. Pod 2 has an extended inflow path (plenum chamber 157y) with a flow conditioning element 159y, configured to promote reduced turbulence at the wick 162y.

[0212] FIG. 8A shows a schematic longitudinal cross sectional view of pod 3. FIG. 8B shows a schematic longitudinal cross sectional view of the same pod 3 in a direction orthogonal to the view taken in FIG. 8A. Pod 3 has a main housing that defines a tank 160z holding an e-liquid aerosol precursor. Mouthpiece 154z is formed at the upper part of the pod. Electrical contacts 156z are formed at the lower end of the pod. Wick 162z is held in a vaporization chamber. The air flow direction is shown using arrows. Pod 3 uses a stagnant vaporizer chamber, with the air inlets bypassing the wick and picking up the vapor/aerosol downstream of the wick.

[0213] All three pods were filled with the same e-liquid (1.6% freebase nicotine, 65:35 PG/VG ratio, no added flavor). Three experiments were carried out for each pod: 1) standard measurement in ambient temperature; 2) only the inlet air was heated to 50° C.; and 3) both the inlet air and the pods were heated to 50° C. Five repetition runs were carried out for each experiment and the Dv50 results were taken and averaged.

[0214] Modelling Work

[0215] In the following examples, modelling work was performed using COMSOL Multiphysics 5.4, engaged physics include: 1) laminar single-phase flow; 2) turbulent single-phase flow; 3) laminar two-phase flow; 4) heat transfer in fluids; and (5) particle tracing. Data analysis and data visualization were mostly completed in MATLAB R2019a.

Fourth Example

Velocity Modelling

[0216] Air velocity in the vicinity of the wick is believed to play an important role in affecting particle size. In the first example, the air velocity was calculated by dividing the flow rate by the intersection area, which is referred to as “calculated velocity” in this work. This involves a very crude simplification that assumes velocity distribution to be homogeneous across the intersection area.

[0217] In order to increase reliability of the work, computational fluid dynamics (CFD) modelling was performed to obtain more accurate velocity values: [0218] 1) The average velocity in the vicinity of the wick (defined as a volume from the wick surface to 1 mm away from the wick surface) [0219] 2) The maximum velocity in the vicinity of the wick (defined as a volume from the wick surface to 1 mm away from the wick surface)

TABLE-US-00002 TABLE 2 Average and maximum velocity in the vicinity of wick surface obtained from CFD modelling Calculated Average Maximum Tube size Flow rate velocity* velocity** Velocity** [mm] [Ipm] [m/s] [m/s] [m/s] 1.3 Ipm 4.5 1.3 1.17 0.99 1.80 constant 6 1.3 0.71 0.66 1.22 flow rate 7 1.3 0.56 0.54 1.01 8 1.3 0.47 0.46 0.86 10 1.3 0.35 0.35 0.66 12 1.3 0.28 0.27 0.54 20 1.3 0.15 0.15 0.32 50 1.3 0.06 0.05 0.12 2.0 Ipm 4.5 2.0 1.81 1.52 2.73 constant 5 2.0 1.48 1.31 2.39 flow rate 6 2.0 1.09 1.02 1.87 8 2.0 0.72 0.71 1.31 12 2.0 0.42 0.44 0.83 20 2.0 0.23 0.24 0.49 50 2.0 0.09 0.08 0.19 *Calculated by dividing flow rate with intersection area **Obtained from CFD modelling

[0220] The CFD model of the fourth example uses a laminar single-phase flow setup. For each experiment, the outlet was configured to a corresponding flowrate, the inlet was configured to be pressure-controlled, the wall conditions were set as “no slip”. A 1 mm wide ring-shaped domain (wick vicinity) was created around the wick surface, and domain probes were implemented to assess the average and maximum magnitudes of velocity in this ring-shaped wick vicinity domain.

[0221] The CFD model outputs the average velocity and maximum velocity in the vicinity of the wick for each set of experiments carried out in section 2.1. The outcomes are reported in Table 2.

Fifth Example

Turbulence Modelling

[0222] Turbulence intensity (I) is a quantitative value that represents the level of turbulence in a fluid flow system. It is defined as the ratio between the root-mean-square of velocity fluctuations, u′, and the Reynolds-averaged mean flow velocity, U:

[00003]$I=\frac{u^{\prime }}{U}=\frac{\sqrt{\frac{1}{3}\left(u_x^{\mathrm{\prime 2}}+u_y^{\mathrm{\prime 2}}+u_z^{\mathrm{\prime 2}}\right)}}{\sqrt{{\stackrel{\_}{u_x}}^2+{\stackrel{\_}{u_y}}^2+{\stackrel{\_}{u_z}}^2}}=\frac{\sqrt{\frac{1}{3}\left[{\left(u_x-\stackrel{\_}{u_x}\right)}^2+{\left(u_y-\stackrel{\_}{u_y}\right)}^2++{\left(u_z-\stackrel{\_}{u_z}\right)}^2\right]}}{\sqrt{{\stackrel{\_}{u_x}}^2+{\stackrel{\_}{u_y}}^2+{\stackrel{\_}{u_z}}^2}}$

[0223] where u.sub.x, u.sub.y and u.sub.z are the x-, y- and z-components of the velocity vector, u.sub.x, u.sub.y, and u.sub.z represent the average velocities along three directions.

[0224] Higher turbulence intensity values represent higher levels of turbulence. As a rule of thumb, turbulence intensity below 1% represents a low-turbulence case, turbulence intensity between 1% and 5% represents a medium-turbulence case, and turbulence intensity above 5% represents a high-turbulence case.

[0225] In this study of the fifth example, turbulence intensity was obtained from CFD simulation using turbulent single-phase setup in COMSOL Multiphysics. For each of the four experiments explained in in the second example above, the outlet was set to 1.3 lpm, the inlet was set to be pressure-controlled, and all wall conditions were set to be “no slip”.

[0226] Turbulence intensity was assessed within the volume up to 1 mm away from the wick surface (defined as the wick vicinity domain). For the four experiments explained in the second example, the turbulence intensities are 0.55%, 0.77%, 1.06% and 1.34%, respectively, as also shown in FIGS. 4A-4D.

Sixth Example

Cooling Rate Modelling

[0227] The cooling rate modelling involves three coupling models in COMSOL Multiphysics: 1) laminar two-phase flow; 2) heat transfer in fluids, and 3) particle tracing. The model is setup in three steps:

[0228] (1) Set Up Two Phase Flow Model

[0229] Laminar mixture flow physics was selected in this study. The outlet was configured in the same way as in the fourth example. However, this model includes two fluid phases released from two separate inlets: the first one is the vapor released from wick surface, at an initial velocity of 2.84 cm/s (calculated based on 5 mg total particulate mass over 3 seconds puff duration) with initial velocity direction normal to the wick surface; the second inlet is air influx from the base of tube, the rate of which is pressure-controlled.

[0230] (2) Set Up Two-Way Coupling with Heat Transfer Physics

[0231] The inflow and outflow settings in heat transfer physics was configured in the same way as in the two-phase flow model. The air inflow was set to 25° C., and the vapor inflow was set to 209° C. (boiling temperature of the e-liquid formulation). In the end, the heat transfer physics is configured to be two-way coupled with the laminar mixture flow physics. The above model reaches steady state after approximately 0.2 second with a step size of 0.001 second.

[0232] (3) Set Up Particle Tracing

[0233] A wave of 2000 particles were release from wick surface at t=0.3 second after the two-phase flow and heat transfer model has stabilized. The particle tracing physics has one-way coupling with the previous model, which means the fluid flow exerts dragging force on the particles, whereas the particles do not exert counterforce on the fluid flow. Therefore, the particles function as moving probes to output vapor temperature at each timestep.

[0234] The model outputs average vapor temperature at each time steps. A MATLAB script was then created to find the time step when the vapor cools to a target temperature (50° C. or 75° C.), based on which the vapor cooling rates were obtained (Table 3).

TABLE-US-00003 TABLE 3 Average vapor cooling rate obtained from Multiphysics modelling Cooling rate to Cooling rate to Tube size Flow rate 50° C. 75° C. [mm] [Ipm] [° C./ms] [° C./ms] 1.3 Ipm 4.5 1.3 11.4 44.7 constant flow 6 1.3 5.48 14.9 rate 7 1.3 3.46 7.88 8 1.3 2.24 5.15 10 1.3 1.31 2.85 12 1.3 0.841 1.81 20 1.3 0*  0.536 50 1.3 0 0 2.0 Ipm 4.5 2.0 19.9 670 constant flow 5 2.0 13.3 67 rate 6 2.0 8.83 26.8 8 2.0 3.61 8.93 12 2.0 1.45 3.19 20 2.0 0.395 0.761 50 2.0 0 0 *Zero cooling rate when the average vapor temperature is still above target temperature after 0.5 second

[0235] Results and Discussions

[0236] Particle size measurement results for the rectangular tube testing are shown in Table 4. For every tube size and flow rate combination, five repetition runs were carried out in the

[0237] Spraytec laser diffraction system. The Dv50 values from five repetition runs were averaged, and the standard deviations were calculated to indicate errors, as shown in Table 4.

[0238] In this example, the roles of different factors affecting aerosol particle size will be discussed based on experimental and modelling results.

TABLE-US-00004 TABLE 4 Particle size measurement results for the rectangular tube testing Dv50 standard Tube size Flow rate Dv50 average deviation [mm] [Ipm] [μm] [μm] 1.3 Ipm 4.5 1.3 0.971 0.125 constant flow 6 1.3 1.697 0.341 rate 7 1.3 2.570 0.237 8 1.3 2.705 0.207 10 1.3 2.783 0.184 12 1.3 3.051 0.325 20 1.3 3.116 0.354 50 1.3 3.161 0.157 2.0 Ipm 4.5 2.0 0.568 0.039 constant flow 5 2.0 0.967 0.315 rate 6 2.0 1.541 0.272 8 2.0 1.646 0.363 12 2.0 3.062 0.153 20 2.0 3.566 0.260 50 2.0 3.082 0.440 1.0 m/s 5.0 1.4 1.302 0.187 constant air 8 2.8 1.303 0.468 velocity 20 8.6 1.463 0.413

[0239] Decouple the Factors Affecting Particle Size

[0240] The particle size (Dv50) experimental results of the above examples are plotted against calculated air velocity in FIG. 9. The graph shows a strong correlation between particle size and air velocity.

[0241] Different size tubes were tested at two flow rates: 1.3 lpm and 2.0 lpm. Both groups of data show the same trend that slower air velocity leads to larger particle size. The conclusion was made more convincing by the fact that these two groups of data overlap well in FIG. 9: for example, the 6 mm tube delivered an average Dv50 of 1.697 μm when tested at 1.3 lpm flow rate, and the 8 mm tube delivered a highly similar average Dv50 of 1.646 μm when tested at 2.0 lpm flow rate, as they have similar air velocity of 0.71 and 0.72 m/s, respectively.

[0242] In addition, FIG. 10 shows the results of three experiments with highly different setup arrangements: 1) 5mm tube measured at 1.4 lpm flow rate with Reynolds number of 155; 2) 8mm tube measured at 2.8 lpm flow rate with Reynolds number of 279; and 3) 20 mm tube measured at 8.6 lpm flow rate with Reynolds number of 566. It is relevant that these setup arrangements have one similarity: the air velocities are all calculated to be 1 m/s. FIG. 10 shows that, although these three sets of experiments have different tube sizes, flow rates and Reynolds numbers, they all delivered similar particle sizes, as the air velocity was kept constant. These three data points were also plotted out in FIG. 9 (1 m/s data with star marks) and they tie in nicely into particle size-air velocity trendline.

[0243] The above results lead to a strong conclusion that air velocity is an important factor affecting the particle size of EVP devices. Relatively large particles are generated when the air travels with slower velocity around the wick. It can also be concluded that flow rate, tube size and Reynolds number are not necessarily independently relevant to particle size, providing the air velocity is controlled in the vicinity of the wick.

[0244] Further Consideration of Velocity

[0245] In FIG. 9 the “calculated velocity” was obtained by dividing the flow rate by the intersection area, which is a crude simplification that assumes a uniform velocity field. In order to increase reliability of the work, CFD modelling has been performed to assess the average and maximum velocities in the vicinity of the wick. In this study, the “vicinity” was defined as a volume from the wick surface up to 1 mm away from the wick surface.

[0246] The particle size measurement data were plotted against the average velocity (FIG. 11) and maximum velocity (FIG. 12) in the vicinity of the wick, as obtained from CFD modelling.

[0247] The data in these two graphs indicates that in order to obtain an aerosol with Dv50 larger than 1 μm, the average velocity should be less than or equal to 1.2 m/s in the vicinity of the wick and the maximum velocity should be less than or equal to 2.0 m/s in the vicinity of the wick.

[0248] Furthermore, in order to obtain an aerosol with Dv50 of 2 μm or larger, the average velocity should be less than or equal to 0.6 m/s in the vicinity of the wick and the maximum velocity should be less than or equal to 1.2 m/s in the vicinity of the wick.

[0249] It is considered that typical commercial EVP devices deliver aerosols with Dv50 around 0.5 μm, and there is no commercially available device that can deliver aerosol with Dv50 exceeding 1 μm. It is considered that typical commercial EVP devices have average velocity of 1.5-2.0 m/s in the vicinity of the wick.

Seventh Example

The Role of Turbulence

[0250] The role of turbulence has been investigated in terms of turbulence intensity, which is a quantitative characteristic that indicates the level of turbulence. In the seventh example, four tubes of different turbulence intensities were used to general aerosols which were measured in the Spraytec laser diffraction system. The particle size (Dv50) experimental results of the seventh example are plotted against turbulence intensity in FIG. 13.

[0251] The graph suggests a correlation between particle size and turbulence intensity, that lower turbulence intensity is beneficial for obtaining larger particle size. It is noted that when turbulence intensity is above 1% (medium-turbulence case), there are relatively large measurement fluctuations. In FIG. 13, the tube with a jetting panel 10mm below the wick has the largest error bar, because air jets become unpredictable near the wick after traveling through a long distance.

[0252] The results of the seventh example clearly indicate that laminar air flow is favorable for the generation of aerosols with larger particles, and that the generation of large particle sizes is jeopardized by introducing turbulence. In FIG. 13, the 12 mm standard rectangular tube (without jetting panel) delivers above 3 μm particle size (Dv50). The particle size values reduced by at least a half when jetting panels were added to introduce turbulence.

Eighth Example

Vapor Cooling Rate

[0253] FIG. 14 shows the high temperature testing results. Larger particle sizes were observed from all 3 pods when the temperature of inlet air increased from room temperature (23° C.) to 50° C. When the pods were heated as well, two of the three pods saw even larger particle size measurement results, while pod 2 was unable to be measured due to significant amount of leakage.

[0254] Without wishing to be bound by theory, the results of the eighth example are in line with the inventors' insight that control over the vapor cooling rate provides an important degree of control over the particle size of the aerosol. As reported above, the use of a slow air velocity can have the result of the formation of an aerosol with large Dv50. It is considered that this is due to slower air velocity allowing a slower cooling rate of the vapor.

[0255] Another conclusion related to laminar flow can also be explained by a cooling rate theory: laminar flow allows slow and gradual mixing between cold air and hot vapor, which means the vapor can cool down in slower rate when the airflow is laminar, resulting in larger particle size.

[0256] The results in FIG. 14 further validate this cooling rate theory: when the inlet air has higher temperature, the temperature difference between hot vapor and cold air becomes smaller, which allows the vapor to cool down at a slower rate, resulting in larger particle size; when the pods were heated as well, this mechanism was exaggerated even more, leading to an even slower cooling rate and an even larger particle size.

[0257] Further Consideration of Vapor Cooling Rate

[0258] In the sixth example, above, the vapor cooling rates for each tube size and flow rate combination were obtained via multiphysics simulation. In FIG. 15 and FIG. 16, the particle size measurement results were plotted against vapor cooling rate to 50° C. and 75° C., respectively.

[0259] The data in these graphs indicates that in order to obtain an aerosol with Dv50 larger than 1 μm, the apparatus should be operable to require more than 16 ms for the vapor to cool to 50° C., or an equivalent (simplified to an assumed linear) cooling rate being slower than 10° C./ms. From an alternative viewpoint, in order to obtain an aerosol with Dv50 larger than 1 μm, the apparatus should be operable to require more than 4.5 ms for the vapor to cool to 75° C., or an equivalent (simplified to an assumed linear) cooling rate slower than 30° C./ms.

[0260] Furthermore, in order to obtain an aerosol with Dv50 of 2 μm or larger, the apparatus should be operable to require more than 32 ms for the vapor to cool to 50° C., or an equivalent (simplified to an assumed linear) cooling rate being slower than 5° C./ms. From an alternative viewpoint, in order to obtain an aerosol with Dv50 of 2 μm or larger, the apparatus should be operable to require more than 13 ms for the vapor to cool to 75° C., or an equivalent (simplified to an assumed linear) cooling rate slower than 10° C./ms.

[0261] Conclusions of particle size experimental work of the above examples

[0262] In the above examples, particle size (Dv50) of aerosols generated in a set of rectangular tubes was studied in order to decouple different factors (flow rate, air velocity, Reynolds number, tube size) affecting aerosol particle size. It is considered that air velocity is an important factor affecting particle size—slower air velocity leads to larger particle size. When air velocity was kept constant, the other factors (flow rate, Reynolds number, tube size) has low influence on particle size.

[0263] The role of turbulence was also investigated. It is considered that laminar air flow favors generation of large particles, and introducing turbulence deteriorates (reduces) the particle size.

[0264] Modelling methods were used to simulate the average air velocity, the maximum air velocity, and the turbulence intensity in the vicinity of the wick. A COMSOL model with three coupled physics has also been developed to obtain the vapor cooling rate.

[0265] All experimental and modelling results of the above examples support a cooling rate theory that slower vapor cooling rate is a significant factor in ensuring larger particle size. Slower air velocity, laminar air flow and higher inlet air temperature lead to larger particle size, because they all allow vapor to cool down at slower rates.

[0266] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, of in the above examples, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilized for realizing the disclosure in diverse forms thereof.

[0267] While the disclosure has been described in conjunction with the exemplary embodiments and examples described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the disclosure and various examples set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the disclosure.

[0268] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0269] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0270] Throughout this specification, including the claims which follow, unless the context requires otherwise, the words “have”, “comprise”, and “include”, and variations such as “having”, “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0271] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means, for example, +/− 10%.

[0272] The words “preferred” and “preferably” are used herein refer to embodiments of the disclosure that may provide certain benefits under some circumstances. It is to be appreciated, however, that other embodiments may also be preferred under the same or different circumstances. The recitation of one or more preferred embodiments therefore does not mean or imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the disclosure, or from the scope of the claims.