Composite Wick

Abstract

A wick having a predominant material and a secondary material, for use in a vaping environment, makes use of characteristics of each of these materials to provide reliable wicking and a desired heat transfer characteristic. Many materials known to have good wicking characteristics act as insulators, which can result in a buildup of heat in the wick near a heater. This buildup of heat can result in the burning of one or both of the wick and the e-liquid carried by the wick. The inclusion of a secondary material having improved heat transfer characteristics allows for the wick to transport heat through at least one of the length and depth of the wick. In one embodiment, a cotton wick is supplemented by the addition of metal strands making up approximately 25% of the wick by volume.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This is the first application for the instant invention.

TECHNICAL FIELD

This application relates generally to a composite wick, and more particularly to a fiber-metal composite wick for use in conjunction with an electronic cigarette or vaporizer.

BACKGROUND

Electronic cigarettes and vaporizers are well regarded tools in smoking cessation. In some instances, these devices are also referred to as an electronic nicotine delivery system (ENDS). A nicotine based liquid solution, commonly referred to as e-liquid, often paired with a flavoring, is atomized in the ENDS for inhalation by a user. In some embodiments, e-liquid is stored in a cartridge or pod, which is a removable assembly having a reservoir from which the e-liquid is drawn towards a heating element by capillary action through a wick. In many such ENDS, the pod is removable, disposable, and is sold pre-filled.

In some ENDS, a refillable tank is provided, and a user can purchase a vaporizable solution with which to fill the tank. This refillable tank is often not removable, and is not intended for replacement. A fillable tank allows the user to control the fill level as desired. Disposable pods are typically designed to carry a fixed amount of vaporizable liquid, and are intended for disposal after consumption of the e-liquid. The ENDS cartridges, unlike the aforementioned tanks, are not typically designed to be refilled. Each cartridge stores a predefined quantity of e-liquid, often in the range of 0.5 to 3 ml. In ENDS systems, the e-liquid is typically composed of a combination of any of vegetable glycerine, propylene glycol, nicotine and flavorings. In systems designed for the delivery of other compounds, different compositions may be used.

In the manufacturing of the disposable cartridge, different techniques are used for different cartridge designs. Typically, the cartridge has a wick that allows e-liquid to be drawn from the e-liquid reservoir to an atomization chamber. In the atomization chamber, a heating element in communication with the wick is heated to encourage aerosolization of the e-liquid. The aerosolized e-liquid can be drawn through a defined air flow passage towards a user's mouth. Wicks are conventionally formed of a variety of different materials. A cotton wick is among the most common wicks. Cotton fibers are arranged to typically extend in a common direction, and are then formed into a wick. This encourages wicking along a common axis. Other natural fibers can be used in a similar fashion. Some wicks are formed of glass fibers. The use of a glass fiber reduces the possibility of burning, but this can come at the cost of reduced capillary draw and other such problems. Wicks are typically surrounded by a heating coil. The heating coil helps to both control how tight the wick is, but also allows for heating of the wick. Some wicks have been suggested using more exotic materials including carbon fiber and ceramic.

FIGS. 1A, 1B and 1C provide front, side and bottom views of an exemplary pod 50. Pod 50 is composed of a reservoir 52 having an air flow passage 54, and an end cap assembly 56 that is used to seal an open end of the reservoir 52. End cap assembly has wick feed lines 58 which allow e-liquid stored in reservoir 52 to be provided to a wick (not shown in FIG. 1). To ensure that e-liquid stored in reservoir 52 stays in the reservoir and does not seep or leak out, and to ensure that end cap assembly 56 remains in place after assembly, seals 60 can be used to ensure a more secure seating of the end cap assembly 56 in the reservoir 52. In the illustrated embodiment, seals 60 may be implemented through the use of o-rings.

As noted above, pod 50 includes a wick that is heated to atomize the e-liquid. To provide power to the wick heater, electrical contacts 62 are placed at the bottom of the pod 50. In the illustrated embodiment, the electrical contacts 62 are illustrated as circular. The particular shape of the electrical contacts 62 should be understood to not necessarily germane to the function of the pod 50.

Because an ENDS device is intended to allow a user to draw or inhale as part of the nicotine delivery path, an air inlet 64 is provided on the bottom of pod 50. Air inlet 64 allows air to flow into a pre-wick air path through end cap assembly 56. The air flow path extends through an atomization chamber and then through post wick air flow passage 54.

FIG. 2 illustrates a cross section taken along line A in FIG. 1B. This cross section of the device is shown with a complete (non-sectioned) wick 66 and heater 68. End cap assembly 56 resiliently mounts to an end of air flow passage 54 in a manner that allows air inlet 64 to form a complete air path through pod 50. This connection allows airflow from air inlet 64 to connect to the post air flow path through passage 54 through atomization chamber 70. Within atomization chamber 70 is both wick 66 and heater 68. When power is applied to contacts 62, the temperature of the heater increases and allows for the volatilization of e-liquid that is drawn across wick 66.

Typically the heater 68 reaches temperatures well in excess of the vaporization temperature of the e-liquid. This allows for the rapid creation of a vapor bubble next to the heater 68. As power continues to be applied the vapor bubble increases in size, and reduces the thickness of the bubble wall. At the point at which the vapor pressure exceeds the surface tension the bubble will burst and release a mix of the vapor and the e-liquid that formed the wall of the bubble. The e-liquid is released in the form of aerosolized particles and droplets of varying sizes. These particles are drawn into the air flow and into post wick air flow passage 54 and towards the user.

Management of the heat in the wick is often simply regarded as a matter of limiting the power delivered by the heater into the wick. Heating of the wick is typically restricted to the surface of the wick, nearest to the heater. When saturated, the heat introduced by the heater is at least partially absorbed by the surrounding e-liquid. Some of the e-liquid provides a larger cooling effect through its evaporation. Excess heat delivered to the wick can result in burning of either of the wick and the e-liquid within the wick. Typically, wicks are selected for their ability to draw e-liquid, and not for their heat transfer characteristics. As such, the ability of a wick to move heat is limited, and its ability to either prevent or mitigate the burning of either the e-liquid or the wick is insufficient.

While cotton wicks are considered desirable for, among other reasons, their ability to wick e-liquid from the reservoir to the atomization chamber, they are more susceptible to burning. Alternatives like glass fiber are less likely to burn, but are more expensive and some users complain about a muting of flavors. Although glass fiber itself is less likely to burn, localized heating can result in burning of compounds within the e-liquid. Other more exotic wicking materials include ceramics (which are expensive for use in disposable pods), stainless steel meshes (which have a reputation for poor wicking) and a variety of other materials such as hemp, rayon, flax and linen. Each of these materials have advantages and disadvantages, but for disposable pod based ENDS, cotton has a number of advantages in material properties that extend past its low cost.

In unrelated art, U.S. Pat. No. 8,926,781 to Cagle et al. teaches the use of a hybrid wick, where both cotton and wood are used to create a candle wick that cleanly bums but has some of the rigidity of wood. This hybridization is designed to provide a clean burning wick, while the capillary flow associated with the actual wicking action is not a focus. It should be noted that in an ENDS system, one of the intentions is the creation of a wick that does not burn, as opposed to a wax-based candle wick, where the intention is to burn the wick as a means of liberating sufficient wax to act as a fuel for burning.

In U.S. Pat. No. 10,258,089 to Sears et al. a wick with a heating wire woven through the wick is disclosed. In describing the wick, there is an indication that the wick could be made of metals, ceramics and carbonized filaments. It should be understood that metal mesh wicks are known in the field, and it is commonly suggested that they be saturated with e-liquid and then be exposed to heat to create an electrically non-conductive carbonized layer at the surface to avoid electrical conductivity with the heater. There is also a reference to the wick being made of one or more natural or synthetic fibers such as cotton, cellulose, polyesters, polyamides, polylactic acids, and glass fibers. Many of these fibers have similar issues as cotton, in that they may have capillary wicking properties, but they are poor at heat transfer, and are susceptible to burning.

The ability of a wicking material to resist burning is a health and safety issue. Although heater control can be applied to help mitigate this problem, the manner in which ENDS and other vaping devices function requires the rapid heating of the e-liquid, which in turn requires the application of power to generate high heat for limited amounts of time. While this does result in the vaporization and atomization of e-liquid atop the heating coil, it also results in a localized heat transfer into the wick on the opposite side of the heating coil. As the wick is often an insulator, it does not transfer the heat generated by the heating coil. Exotic wicking materials like metals and carbonized filaments tend to have inferior wicking properties when compared to cotton and other such materials, and additionally these exotic wicking materials are often electrically conductive, so care has to be taken to ensure that the heater provides heat and not electricity to the wick, lest the entire wick become a heater.

It would therefore be beneficial to have a mechanism to further manage heating of the wick.

SUMMARY

It is an object of the aspects of the present invention to obviate or mitigate the problems of the above-discussed prior art.

In a first aspect of the present invention, there is provided a wick. The wick can be used to draw an atomizable liquid from a reservoir towards a heater. The wick comprises both a predominant material and a secondary material. The predominant material is typically responsible for providing much of the wicking capacity of the wick, and in some embodiments it is one of a synthetic fibrous material and a natural fibrous material. In some embodiments, a synthetic fibrous material may include polyesters and glass fibers, while a natural fibrous material may include cotton, hemp, linen, wool, rayon, cellulose and wood fiber. The second material is typically responsible for providing heat transfer between locations within the wick, and comprises at least one of: a metal, graphite, carbon fiber, a doped silicon and a carbonized filament.

In an embodiment of the first aspect, the atomizable liquid is an e-liquid comprising at least one of propylene glycol, vegetable glycerin, nicotine and a flavoring. The metal may be one of aluminium, copper, silver, titanium and stainless steel. The predominant material may be a combination of two or more materials, and may optionally be an insulator. The secondary material may be better at transferring heat than the predominant material. The predominant material may have higher wicking capacity with respect to the atomizable liquid than the secondary material.

In an embodiment, the predominant material is cotton and the secondary material is a metal, such as aluminium which optionally makes up between 20% and 30% of the wick by volume. In another embodiment, the predominant material is cotton and the secondary material is carbon fiber which optionally makes up between 45% and 55% of the wick by volume.

In further embodiments, the wick is surrounded by a heater coil comprised of a metal that is optionally different than the secondary material, and in some embodiments may be one of nichrome, stainless steel, and kanthal.

In a second aspect of the present invention, there is provide a wick for drawing at atomizable liquid from a reservoir towards a heater. The wick comprises a predominant material and a secondary material. The predominant material has a permeability coefficient of approximately 2.25×10⁻¹³ m². The secondary material has a thermal conductivity of at least approximately 100 W/m K.

In an embodiment of the second aspect, the atomizable liquid is an e-liquid comprising at least one of propylene glycol, vegetable glycerin, nicotine and a flavoring. In another embodiment, the predominant material comprises at least one of: cotton, hemp, linen, wool, rayon, polyester, glass fiber, cellulose and wood fiber. In some embodiments, the secondary material comprises at least one of: a metal, graphite, carbon fiber, a doped silicon and a carbonized filament. In some embodiments, the predominant material includes cotton and the secondary material is a metal making up between 20% and 30% of the wick by volume. In another embodiment, the predominant material is cotton and the secondary material is carbon fiber making up between 45% and 55% of the wick by volume.

In a third aspect of the present invention, there is provided a pod for use in a vaporizer system, such as an ENDS. The pod comprises a reservoir for storing an atomizable liquid, and a wick positioned within an atomization chamber situated within an airflow path through the pod. The pod further comprises a heater connected to electrical leads for heating the wick and atomizing the stored atomizable liquid carried by the wick. The wick is comprised of a predominant material and a secondary material.

In one embodiment, the predominant material is comprised of at least one of a natural or synthetic fibrous material. The natural fibrous materials may be selected from cotton, hemp, linen, wool, rayon, cellulose and wood fiber, while the synthetic fibrous material may be selected from a list comprising polyester and glass fiber. In some embodiments, the secondary material is comprised of a metal, graphite, carbon fiber, a doped silicon and a carbonized filament. The metal may be one of aluminium, copper and silver.

In another embodiment, the predominant material has a permeability coefficient of approximately 2.25×10⁻³ m². The secondary material may have a thermal conductivity of at least approximately 100 W/m K.

In some embodiments, the atomizable liquid is an e-liquid comprising at least one of propylene glycol, vegetable glycerin, nicotine and a flavoring.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

FIG. 1A is a front view of a pod, according to the prior art, for use with a vaporizer system;

FIG. 1B is a side view of the pod of FIG. 1A;

FIG. 1C is a bottom view of the pod of FIGS. 1A and 1B;

FIG. 2 is a sectioned view of the pod of FIG. 1A along section line A in FIG. 1B;

FIG. 3 is a sectioned view of a pod according to an embodiment of the present invention;

FIG. 4 is an illustration of a wick according to an embodiment of the present invention; and

FIG. 5 is a sectioned view of a pod according to an embodiment of the present invention.

It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

DETAILED DESCRIPTION

In the instant description, and in the accompanying figures, reference to dimensions may be made. These dimensions are provided for the enablement of a single embodiment and should not be considered to be limiting or essential. Disclosure of numerical range should be understood to not be a reference to an absolute value unless otherwise indicated. Use of the terms about or substantively with regard to a number should be understood to be indicative of an acceptable variation of up to ±10% unless otherwise noted.

Although presented below in the context of use in an electronic nicotine delivery system such as an electronic cigarette (e-cig) or a vaporizer (vape) it should be understood that the scope of protection need not be limited to this space, and instead the scope of protection is delimited by the scope of the claims. Embodiments of the present invention are anticipated to be applicable in areas other than ENDS, including (but not limited to) other vaporizing applications.

To address issues associated with burning of the wick, embodiments of the present invention provide a wick that has improved heat transfer characteristics in comparison to conventional cotton wicks. By improving the heat transfer characteristic of a wick, the heat generated by the heater can still be used to atomize the e-liquid, but the wick can be protected from burning. Localised burning of a wick may be associated with breaking or otherwise interrupting long fibers within the wick resulting in a reduction in the capillary action of the wick. A possible reduction in the amount of e-liquid that can be carried by the wick may reduce the heat transfer ability of the wick, resulting in more burning and creating a spiraling problem. Due to the insulting nature of a natural fiber wick, heat in the wick does not dissipate quickly, which may result in adverse effects on the e-liquid carried by the wick, including burning of the e-liquid (independent of the burning of the wick itself).

Accordingly, an improvement in the heat transfer characteristics of a wick in an ENDS pod may provide benefits. However, improving the heat transfer characteristics by changing the material of the wick may have other adverse effects. These effects, as discussed above, may include a reduction in the capillary draw of the wick. By reducing the capillary effect of the wick, less e-liquid is available to the heater, and the vaping sensation is impaired.

FIG. 3 illustrates a sectioned view of pod 100 for use in an ENDS or other such vaping system. Pod 100 is shown without the mouthpiece shown in earlier figures as it is not germane to the novelty of pod 100. Pod 100 comprises reservoir 102 and end cap 106, much as earlier figures. Reservoir 102 is designed for the storage of e-liquid and it defines a post-wick air flow passage 104 through which the atomized e-liquid passes when the user draws on the device. End cap 106 defines wick feed lines 108 which allow e-liquid to pass from the reservoir 102 into the end cap 106 where it can come into contact with wick 116. End cap 106 is secured in reservoir 102 through the use of a seal such as O-ring 110. Electrical contacts 112 provide an electrical connection to the ENDS device, and deliver power to heater 118.

When a user draws on the device, an airflow is generated extending along the air flow path from pre-wick air flow passage 114 into atomization chamber 120 and then to post-wick air flow passage 104. Residing within atomization chamber 120 is the wick 116 and heater 118. When power is applied across the heater, e-liquid carried to the heater by wick 116 is atomized and released into the airflow path. This allows the atomized e-liquid to be delivered to the user.

Where in the previously illustrated figures, the wick was composed of a material such as cotton, polyester, rayon, hemp, linen or another such wicking material, wick 116 is illustrated as having inclusions. This is better illustrated in FIG. 4.

FIG. 4 illustrates wick 116, heater 118 and the connection to electrical contact 112. As noted, where prior art wicks were rather homogeneous in appearance and characteristics, wick 116 is formed predominantly of a first material 122 and a second material that appears as inclusions 124. Wick 116 is shown from both front and side views, with the front view illustrating a cut on the right side to show an interior view of wick 116. Heater 118 is shown on the left side of wick 116 as in the illustrated embodiment, heater 118 is only present on the surface of wick 116. It should be noted that in some prior art embodiments, a heater is woven into the wick, and such an embodiment is believed to be compatible with the wick 116 of the illustrated embodiment.

The predominant material 122 of wick 116 is typically a fibrous material allowing for wicking. Both natural and synthetic fibrous materials can be used and, in one embodiment, the predominant material is a standard cotton. The fibers of the cotton 122 are largely aligned with each other to create a wick 116 that allows for capillary action to draw e-liquid across the wick 116. The use of cotton or another such material for the predominant material 122 in wick 116 allows for the wicking characteristics of wick 116 to be maintained. To improve the overall heat transfer characteristics of wick 116, the second material 124 is added. In the illustrated embodiment, metal elements, such as metal threads or ribbons are included as the second material 124 in wick 116. In the illustrated embodiment, second material 124 can be added without a large concern about the direction of the fibers. In the illustrated embodiment, some metal threads are aligned with the cotton fibers, while others are otherwise oriented. The metal threads are selected for the second material 124 due to their heat transfer characteristics. By adding the metal threads to the cotton, a heat transfer pathway is established. This allows heat to be drawn from near the heater 118 to other parts of the wick 116 that would otherwise not have as high a temperature. This effectively reduces the temperature in the hot spots near the heater 118, and reduces the potential for burning. By having fibers of second material 124 running in a number of different directions, heat transfer can be directed along each of the fibers to many parts of the wick.

Just as materials other than cotton (such as hemp, linen, rayon, wool, etc.) could be used as the predominant material 122 in wick 116, a variety of different materials could be used as the second material 124. A variety of metals could be used, as could other materials that have good heat conductivity, such as strands of carbon fiber. In some embodiments more than one heat conducting material could be used as the secondary material. Because there is generally an overlap between materials that conduct heat well and materials that conduct electricity well, and there may be a desire to avoid allowing strands of the second material 124 to bridge between windings of heater 116. To accomplish this, one or both of the heater 116 and the strands of second material 124 may be encapsulated. In some embodiments this may be a natural encapsulation of the wires caused, for example, by oxidation of the surface of the metal. In other embodiments, encapsulation may be done using a different material, such as a thin polymer coating that prevents electrical connections, but still allows for heat transfer. The selection of a metal for use as the second material 124 can be done using knowledge of toxicity information to reduce or eliminate the possibility that the second material 124 would be the source of toxicity to the user. It should be understood that additional materials may be included other than the predominant and secondary materials.

In some embodiments, fibers of the second material 124 are selected in advance for their length. This allows for a preferential arrangement of the second material 124 based on fiber length. In such an example, longer fibers would be arranged to be generally in line with the fibers of the wick 116, allowing for heat transfer along the length of wick 116, while shorter fibers could be arranged to allow for heat transfer into the wick 116. This would allow wick 116 to absorb and transfer heat both along its length and into its core, which is typically the furthest location from the heater 118.

While some prior art solutions have taught that a heater could be woven through a wick, this is a complex manufacturing process. The effect of such a prior art solution is to obtain a more even heating profile through the length and profile of a wick. In the embodiments discussed above, a similar effect can be achieved without needing the complex manufacturing process required by the prior art. Instead, a composite wick comprised of a predominant material, such as cotton, and a secondary material such as aluminium, copper, silver or another such metal, can be treated as any other wick. The wrapping of such a composite wick in a heating coil made up of a metal such as nichrome, kanthal, stainless steel or titanium, can be done using a conventional winding process that is common in the art. Thus improved heat transfer characteristics of the wick can be achieved at a lower cost and complexity than prior art solutions. None of the above should be taken as meaning that the composite wick could not be used in conjunction with a process that integrates a heater within the wick.

In some embodiments, a wick can be made in several layers, each layer having different patterns of inclusion of the secondary material 124. Using such a manufacturing technique, the outermost layer of wick 116 can have a large number of fibers of the secondary material aligned with the predominant material 122. This allows for heat transfer along the length of the wick 116, with the interior of the wick 116 having fibers arranged to promote heat transfer across the profile of the wick 116.

FIG. 5 illustrates an alternate configuration of a pod 200. Pod 200 comprises reservoir 202 having a post-wick air flow passage 204, and an end cap assembly 206. End cap assembly 206 includes wick feed lines 208, electrical contacts 210, an air inlet forming a pre-wick air flow passage 212, an atomization chamber 214 housing wick 216 and heater 218 (which is connected to electrical contacts 210). To seal end cap assembly 206 with reservoir 202, so that e-liquid cannot cannot leak or seep out of reservoir 202, and to keep end cap assembly 206 mounted within reservoir 202, and in place of the previously described O-ring, is a resilient cover or top cap 220. Resilient top cap 220 may be formed of any number of different resilient materials including silicone.

Wick 216 is comprised of a predominant material 222, and a secondary material 224 such as strands or fibers of metal, carbon fiber, or a doped silicon. The predominant material 222 can be either a natural fibrous material such as cotton, hemp, linen, rayon, wool, cellulose, silk, derivatives of wood pulp and other such natural fibers, or a synthetic fibrous material, such as polyester, glass fibers, and other such synthetic materials. As before, the predominant material 222 is typically relied upon for its wicking characteristics, while secondary material 224 is relied upon for its heat transfer characteristics. It should be understood by those skilled in the art that the selection of a predominant material may be made to select a material that resists burning in the short exposures to high temperature and has good wicking properties. This may be characterized as having poor heat transfer characteristics and good e-liquid transfer characteristics. If such a selection is made, then the secondary material can be selected to provide the heat transfer characteristics missing in the predominant material. The selection of both the predominant and secondary materials should be done with considerations given to health and safety information about the materials. Thus, for example, although a material may tolerate high heat and provide wicking characteristics it may not make a good choice if it is toxic to the user. Similarly, it may be advantageous in some embodiments to avoid secondary materials that are not stable in the temperature ranges at which ENDS products operate. As illustrated in FIG. 5, the strands of secondary material 224 visible from the surface of wick 216 are largely aligned with the fibers of the predominant material 222 to encourage even heat transfer along the length of the wick 216.

Those skilled in the art will appreciate that the ratio between the predominant material 222 and the secondary material 224 may vary based on the desired characteristics of the wick 216, and the characteristics of each material. Each wick is typically comprised of filaments of these different materials. As noted above, various natural or synthetic materials can be used in the wick. Typically these materials are the predominant material in the wick, and may include cotton, hemp, linen, rayon, a variety of different polyesters or other natural fibers, and glass fibers. It should be understood that the predominant material may be a combination of one of more of these materials. The predominant material is typically selected based on wicking characteristics of the material with respect to the e-liquid. The secondary material is typically selected for its heat transfer characteristics, and may include any of a number of different metals, carbonized filaments such as strands or fibers of graphite, carbon fiber or a doped silicon. Those skilled in the art will appreciate that although many silicon structures act as insulators, a doped silicon can act as a suitable heat transfer agent. Accordingly other materials known to be semiconductors may also be usable as the secondary materials given the right doping and operations environments. In one embodiment, the predominant material may be cotton, while the secondary material is aluminium wire or strips, with the aluminium making up between 20% and 30% of the wick (by volume). In an embodiment, the aluminium makes up approximately 25% of the wick. In another embodiment, the predominant material may be cotton, while the secondary material is carbon fiber strips making up between 35% and 50% of the wick (by volume). In another embodiment, the predominant material is a natural fibrous material such as wool or a combination of wool and cotton, and the secondary material is a metal such as copper or silver, in a ratio of 70-80% fibrous material to 20-30% metal.

Variations in the makeup of the wick will be understood to result in different wicking and heat transfer characteristics, and may have an effect on the life of the wick. Thus, with differing objectives different combinations of the predominant materials and the secondary material can be used with different usage ratios. It should also be noted that either of the predominant material and the secondary material may be made of a combination of more than one material. For example, the predominant material may be a mix of cotton and hemp, and the second material may be strands of carbon fiber. In such an arrangement, it may be possible for the quantity of carbon fiber (by volume) to exceed the volume of cotton or the volume of hemp.

In some embodiments, the predominant material is selected for its ability to wick the e-liquid from the reservoir towards the heater, while the secondary material is selected for its ability to move heat through the wick. One measure of the wicking ability of a material is the permeability coefficient associated with that material, while a measure of the ability of a material to transfer heat through the wick is the thermal conductivity of the material. The permeability coefficient of a material is often classified in the context of Kozeny-Carman equations which were based on the flow of a liquid through a packed bed. Those skilled in the art will appreciate that when a predominant material has a higher thermal conductivity, the thermal conductivity of the secondary material does not need to be as high as it otherwise would need. The particular values of these metrics may vary based on the design of the pod in which the wick is placed, the composition of the particular e-liquid in use, the temperature to which the heater heats the e-liquid and wick, the duration of the heating cycle provided by the heater, and many other such design decisions. It should also be understood that the permeability coefficient associated with the material is also affected by the compression of the wick. In an embodiment where the predominant material is cotton, and the secondary material is a metal such as aluminium, a target lower end target for thermal conductivity for the secondary material may be approximately 100 W/m K. Other metals that may provide sufficient thermal conductivity may include copper and silver. The target permeability coefficient of the predominant material, in such an example may be approximately 2.25×10⁻¹³ m². Those skilled in the art will appreciate that these values may vary in different embodiments. For example, the permeability coefficient of a wick can typically only be determined experimentally, as different packing densities (caused for example by changing in the winding process used to wind a heater around a wick) would change the permeability of the wick in comparison to an otherwise identical wick. Accordingly, it should be understood that the targets for both the thermal conductivity and the permeability coefficient can vary.

In the instant description, and in the accompanying figures, reference to dimensions may be made. These dimensions are provided for the enablement of a single embodiment and should not be considered to be limiting or essential. The sizes and dimensions provided in the drawings are provided for exemplary purposes and should not be considered limiting of the scope of the invention, which is defined solely in the claims.

Claims

1. A wick, for drawing an atomizable liquid from a reservoir towards a heater, the wick comprising:

a predominant material comprising at least one of a natural fibrous material and a synthetic fibrous material; and

a secondary material comprising at least one of: a metal, graphite, carbon fiber, a doped silicon and a carbonized filament.

2. The pod of claim 1 wherein the atomizable liquid is an e-liquid comprising at least one of propylene glycol, vegetable glycerin, nicotine and a flavoring.

3. The wick of claim 1 wherein the metal is one of aluminium, copper, silver, and stainless steel.

4. The wick of claim 1 wherein the natural fibrous material comprises at least one of: cotton, hemp, linen, wool, rayon, silk, cellulose and wood fiber

5. The wick of claim 1 wherein the synthetic fibrous material comprises at least one of a polyester and a glass fiber.

6. The wick of claim 1 wherein the predominant material is a combination of two or more materials.

7. The wick of claim 1 wherein the predominant material is an insulator.

8. The wick of claim 1 wherein the secondary material has higher heat transfer capacity than the predominant material.

9. The wick of claim 1 wherein the predominant material has higher wicking capacity with respect to the atomizable liquid than the secondary material.

10. The wick of claim 1 wherein the predominant material is cotton and the secondary material is a metal.

11. The wick of claim 10 wherein the secondary material makes up between 20% and 30% of the wick by volume.

12. The wick of claim 1 wherein the predominant material is cotton and the secondary material is carbon fiber.

13. The wick of claim 12 wherein the secondary material makes up between 45% and 55% of the wick by volume.

14. The wick of claim 1 further comprising a heater coil wrapped around the first and second materials, the heater coil comprised of a metal and the heater coil and the secondary material are different materials.

15. A wick, for drawing an atomizable liquid from a reservoir towards a heater, the wick comprising:

a predominant material having a permeability coefficient of approximately 2.25×10−13 m2; and

a secondary material having thermal conductivity of at least approximately 100 W/m K.

16. The wick of claim 15 wherein the atomizable liquid is an e-liquid comprising at least one of propylene glycol, vegetable glycerin, nicotine and a flavoring.

17. The wick of claim 15 wherein the predominant material comprises at least one of: cotton, hemp, linen, wool, rayon, polyester, glass fiber, cellulose and wood fiber.

18. The wick of claim 15 wherein the secondary material comprises at least one of: a metal, graphite, carbon fiber, a doped silicon and a carbonized filament.

19. The wick of claim 15 wherein the predominant material is cotton and the secondary material is a metal making up between 20% and 30% of the wick by volume.

20. The wick of claim 15 wherein the predominant material is cotton and the secondary material is carbon fiber making up between 45% and 55% of the wick by volume.