Patent Publication Number: US-2023146874-A1

Title: Controlled Bubble Nucleation

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is the first application for the instant invention. 
     TECHNICAL FIELD 
     This application relates generally to a heater for generating a controlled evaporation, and more particularly to a heater that makes use of surface features to encourage bubble nucleation at defined points to aid in the control of bubble size. 
     BACKGROUND 
     In any number of different fields, the efficiency of heat transfer to a liquid is important. Within a boiler system, heat is conventionally introduced through either a heater coil or a heating surface. In a boiling system, heat is applied through the heater and is absorbed by the adjacent liquid. If the heat is sufficient, the liquid nearest the heater may undergo a phase change and be converted to vapor. This may cause the creation of a bubble that can grow at the heater until a critical bubble size is reached. In a situation in which the heater is submerged in a sufficiently deep pool of liquid, the bubbles will detach from the heating surface and rise through the liquid, until they reach the surface. In a thin film situation, the bubbles will reach a critical size and will pop, with the vapor escaping and the liquid that formed the bubble surface being ejected as droplets of varying sizes. 
     The critical size of a bubble in both scenarios is dependent upon many different factors, including properties of the liquid such as the viscosity of the liquid, the amount of heat applied, and surface properties of the heater. 
     The manner in which heat is applied and bubbles are generated have been studied for over 100 years, with initial expressions representing the inertial controlled growth or collapse of bubbles in a steam kettle having been derived in 1917 by John William Strutt, 3rd Baron Rayleigh. It is understood that controlling the formation of bubbles in a heated liquid is a mechanism that can be used to improve heat transfer to the liquid. In one extreme example, the formation of a single bubble along the surface of the heater may create a vapor hotter than the boiling point of the liquid, but which does not do an effective job of heat transfer into the remaining liquid. Thus, it is important to control the effects of bubble generation in the heating of liquids. 
     In some research, it has been suggested that the effectiveness of heat transfer into a liquid may be a function of factors including the average diameter of a bubble departing (e.g. leaving the surface of the heater), the average frequency of bubble departure (i.e. how frequently bubbles separate from the heater), and the density of bubble nucleation. 
     It should be understood that some research papers have indicated that nucleation can be controlled through the use of coatings or building up features on a metal heater using ceramics, polymers and other such materials. The objective appears to be the facilitation of bubble nucleation to avoid superheating of the liquid, and to promote more efficient heat transfer through the creation of bubbles. However, it should be noted that although much of this work is focused on increasing the number of bubbles created, there is little focus on either increasing density of bubble nucleation, or in controlling the diameter of bubbles. 
     In a somewhat unrelated art, 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&#39;s mouth. 
       FIGS.  1 A,  1 B and  1 C  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.  1 B . This cross section of the device is shown with a complete (non-sectioned) wick  72  and heater  74 . 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  72  and heater  74 . 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  72 . 
     Typically the heater  74  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  74 . 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. 
     User experience of an ENDS is related to a number of factors including the delivery of nicotine and the flavor compounds in the e-liquid. The size of the droplets entrained by the airflow, after the bubble pops, is associated with a number of different experiences. Flavor compounds are best experienced by smaller particle sizes. Larger particles are less likely to impart flavour, and are associated with other negative experiences including an effect referred to as spitback. 
     Spitback is a term used to refer to the result of a large particle being entrained in the air flow and delivered with high velocity to the user. In different applications and different devices, there is a droplet threshold above which droplets are known to be associated with user complaints about spitback. In one example, in an ENDS device, droplets over 5 μm in diameter are typically considered to be the cause of user complaints about spitback. This threshold may vary from device to device. The mitigation of spitback can be achieved through the control of the size of the droplets entrained in the air flow. 
     In some conventional ENDS, a mouthpiece that sits atop the pod  50  can be used to modify the path of the airflow exiting air flow passage  54 . Because the droplets in questions are larger droplets, they tend to have greater momentum than the more desirable droplets. By controlling the placement of apertures in the mouthpiece, larger droplets can be kept from ingestion by the user. The laminar air flow in passage  54  will typically direct larger droplets in a straighter air flow. If the mouthpiece has air flow holes placed away from the center of air flow passage  54 , larger droplets will typically not be passed through to the user. 
       FIG.  3    illustrates an alternate embodiment of a pod  50  of the existing art. In addition to the above described features, pod  50  includes an airflow feature  78  within the post wick airflow passage  54  designed to filter out larger droplets. The inclusion of a blunt body airflow feature  78  can aid in the disruption of laminar flow after the airflow passes over wick  72  and heater  74 . The disruption of laminar flow can result in the creation of vortices that effectively push droplets above a weight threshold into the sidewalls of post wick airflow passage  54 . This vortex generation feature  78  acts as a filter to aid in removing droplets above a defined size from the airflow, which can aid in the removal of droplets associated with spitback. 
       FIG.  4    illustrates the wick  72  and heater  74  of an ENDS pod in more detail. Wick  72  is often formed from a material such as cotton, with other common materials including other fabrics such as linen, nylon, other polymer based materials, wool, cellulose and hemp, but also extending to glass or carbon fibers. Typically a wick  72  has at least one end immersed in the e-liquid, and the e-liquid is then drawn across the wick through capillary action. The heater  74  helps to volatilize the e-liquid so that as bubbles form and rupture the droplets of e-liquid are entrained within the airflow passing over the wick. Due to the size and placement of the heater  74 , e-liquid  80  drawn through wick  72  covers the heater  74 . The portion of the coating e-liquid  80  adjacent heater  74  is the liquid that is subjected to volatilization. As this e-liquid is depleted, the capillary action of wick  72  draws in new e-liquid to replenish the e-liquid depleted. As noted above, the popping or rupturing of a bubble created in the heated e-liquid allows for the generation of the e-liquid droplets that are used to carry both flavoring and nicotine to the user. 
     Through many techniques and physical structures, the above ENDS prior art has attempted to mitigate the transmission of droplets associated with spitback, however none of these techniques have been successful in completely eliminating spitback, which remains a problem to many users. It should be noted that mitigation of spitback has typically relied upon physical filtering of an airflow to remove droplets of a particular size. In other arts, heat transfer into a liquid to promote boiling does not provide control over nucleation nor over the size of the bubbles created. This can result in both an inefficient heating of the liquid, and a more chaotic surface, which may result in loss of the heated liquid when bubble rupture at the surface. 
     It would therefore be beneficial to have a mechanism to control the generation of bubbles to a particular size to either improve heat transfer efficiency, or to control the size of the droplets created. 
     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 heater for heating a liquid. The liquid being heated has a set of physical characteristics including both a viscosity and a boiling point. In some embodiments, the set of physical characteristics of interest will also include a specific heat capacity. The heater comprises a heating surface with first and second aberrations. The heating surface of the heater allow for the transfer of heat from the heater into the liquid. The first and second aberrations are spaced apart from each other by a distance determined in accordance with at least one of the set of physical characteristics and a heating objective. 
     In an embodiment of the first aspect, the heating surface is planar. In another embodiment, the first and second aberrations are contained within a set of aberrations. In a further embodiment, aberrations within the set of aberrations are spaced apart from each other by at least the determined distance. In further embodiments, the location of each aberration within the set of aberrations corresponds to the center of a circle having a radius of half the determined distance, and having a distance to the nearest next aberration of the determined distance. In another embodiment, the location of each aberration within the set of aberrations corresponds to the centre of a hexagon, and each hexagon corresponding to an aberration within the set of aberrations is tiled across the heating surface. In some embodiments, the heater of the first aspect is an element within a boiler system. 
     In an embodiment of the first aspect, at least one of the first and second aberrations is machined into the heating surface. In another embodiment, at least one of the first and second aberrations is created on the heating surface through at least one of perforating the heating surface, stamping the heating surface, etching the heating surface, forging the heating surface with at least one aberration, and additively manufacturing the at least one aberration. In some embodiments, the heater comprises at least one of the following materials: aluminium, copper; steel, titanium and nickel. 
     In an embodiment of the first aspect, the heater is a linear heating element. In another embodiment, the heater is wound around a wick that is optionally comprised of at least one of cotton, linen, nylon, other polymer based materials, hemp, wool, cellulose, glass fibers and carbon fibers. In another embodiment, the heater further comprises a third aberration, and the first and second aberrations are spaced apart by the determined distance, and the second and third aberrations are spaced apart by the determined distance. In a further embodiment, the first, second and third aberrations are spaced apart to form a line. In another embodiment, the liquid is an e-liquid comprising at least one of vegetable glycerine, propylene glycol, nicotine and a flavoring. In further embodiments, the liquid is an e-liquid comprising a cannabinoid. In other embodiments, the heating objective is to constrain production of droplets over a threshold diameter to below a defined quantity, where optionally the threshold diameter is 10 microns. 
     In a second aspect of the present invention, there is provided a pod for storing an atomizable liquid which has a set of physical characteristics. The pod is for use in a vaping device and has an airflow passage. The pod comprises a reservoir, a wick, and a heater. The reservoir is for storing the atomizable liquid. The wick is held within the pod so that it can be in fluid communication with the reservoir so that it can draw atomizable liquid from the reservoir across its length through capillary action. The heater is in contact with the wick and aligned with the airflow passage to allow for atomization of the atomizable liquid when power is delivered across the heater. The heater itself comprises a heating surface and first and second aberrations. The heating surface allows for transfer of heat from the heater into the atomizable e-liquid. This transfer of heat allows for the atomization of the e-liquid that is drawn across the wick. The first and second aberrations on the heating surface are spaced apart from each other by a distance determined in accordance with at least one of the set of physical characteristics and a heating objective. 
     It should be understood that the embodiments described above may be applied to any of the disclosed aspects, and may be used in isolation or in combination with other disclosed embodiments, where appropriate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described in further detail by way of example only with reference to the accompanying figure in which: 
         FIG.  1 A  is a front view of a prior art pod for use in an electronic nicotine delivery system; 
         FIG.  1 B  is a side view of the pod of  FIG.  1 A ; 
         FIG.  1 C  is a bottom view of the pod of  FIG.  1 A ; 
         FIG.  2    is a cross section of the pod of  FIGS.  1 A and  1 B  along cut line A in  FIG.  1 B ; 
         FIG.  3    is a cross section of an alternate pod design; 
         FIG.  4    is a side view of a conventional horizontal heater and wick assembly for use in an ENDS; 
         FIG.  5 A  is a side view of a linear heater according to an embodiment of the present invention; 
         FIG.  5 B  is a side view of the linear heater of  FIG.  5 A  illustrating bubble creation; 
         FIG.  6    is a perspective view of a planar heater according to an embodiment of the present invention for use in a boiler-style heater; 
         FIG.  7    illustrates an example of the configuration of a planar heater such as the one illustrated in  FIG.  6   ; and 
         FIG.  8    is a side view of a linear heater according to embodiments of the present invention as applied to a linear heater within a heater and wick assembly. 
     
    
    
     In the above described figures like elements have been described with like numbers where possible. 
     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. 
     In the above-described prior art, heating a liquid to a boiling point is done through the application of heat to the liquid, typically by passing an electric current through a heating element to generate heat. Liquids will convert to a gas phase when heated past their boiling point. Typically, a liquid will somewhat uniformly increase in temperature and driving the heater to a higher temperature will result in a greater overall temperature (a higher average temperature), but the temperature of the liquid will not exceed the boiling point until (almost) all the liquid has approached the boiling point. This can be observed in a kettle, where the application of more heat will result in the liquid approaching the boiling point faster, but will not cause the temperature of the liquid to exceed the boiling point. However, on a more local scale, boiling of the liquid nearest the heater may occur without bringing the temperature of all the liquid to the boiling point. Because the generation of vapor bubbles is part of the heat transfer process, the size of the generated bubbles can have an effect on the efficiency of the heat transfer process. 
     As a bubble forms and expands, the heater can increase the temperature of the vapor above the boiling point of the liquid, which causes the size of the bubble to increase. This may not have an effect on the temperature of the liquid outside the bubble. Accordingly, when trying to improve the efficiency of heat transfer into a liquid, there may be an optimal size of bubble. Bubbles smaller than this size may not transfer sufficient heat to the rest of the liquid as they travel through the liquid (possibly a function of a bubble with an insufficiently small surface area), and bubbles above this size may not have the efficiency of a set of smaller bubbles at absorbing heat and creating vapor from the liquid. Furthermore, in thin-film heating applications where the liquid being heated takes the form of a thin film across the heater, the size of the bubble generated has a relationship to the size of the droplets created during the rupturing of the bubbles. In some applications, this may result in a messy boiling process, and in others, such as those related to ENDS it may result in the generation of sub-optimal droplet sizes. 
       FIG.  5 A  illustrates a linear heating element  100  according to one embodiment of the present invention. Where in prior art implementations, surface defects within a heater may create irregularities, in the illustrated embodiments intentional aberrations  102  are formed within the surface of heater  100 . In some embodiments the aberrations  102  are less than 1 mm in size. In the illustrated embodiment, the aberrations  102  form peaks, and create a crevice  106  with the rest of the surface of heater  100 . In some embodiments, this can be formed by cutting or slicing into the heater  100 . The height and the angle at which the aberration  102  leaves from the heater  100  can vary between embodiments. As shown on heater  100 , there are a plurality of aberrations, each one spaced apart from a previous aberration  102  by a distance  104 . In some embodiments the distance  104  between aberrations  102  may be between 60 microns and 2 mm. It should be understood that the distance  104  acts as a regulator on the maximum size of the bubble produced, and the size of the bubble (in conjunction with the properties of the liquid being heated) will define the expected distribution of droplet sizes created from the rupturing of the bubble. The distance  104 , the height of the aberration  102  and its angle of departure from the heater  100  may all vary in accordance with properties of the liquid to be heated, including a viscosity, the specific heat capacity of the liquid, the desired maximum size of bubble and other such properties. 
     As shown in  FIG.  5 B , as heat is applied through heater  100 , a bubble  108  will form around aberration  102 . This may be related to the crevice  106  providing heating on multiple sides, or it may be related to other requirements for nucleation. As two adjacent bubbles  108  form, spaced apart by distance  104 , they will come into contact with each other when the distance  110  between their centers is approximately the inter-aberration distance  104 . It should be apparent from  FIG.  5 B , that the bubbles will each have a radius that is approximately half of the distance  104 . 
     As bubbles  108  come into contact with each other, they provide an impediment to continued growth. This will encourage either the departure of the bubbles  108  from the surface of the heater, or it will encourage the rupturing of the bubbles  108 . The difference between these two situations is largely associated with whether the liquid is a thin film or a boiler-like setup. Those skilled in the art will appreciate that the distance  104  between aberrations  102  may be selected in accordance with a desired bubble size. This bubble size may be associated with physical characteristics of a liquid being heated, such as the viscosity of the liquid, the boiling point of the liquid, the specific heat capacity of the liquid, and other such physical characteristics. The heat to which the heater  100  is heated may also be taken into account in determining the bubble size, as may be the rate at which the heater  100  itself is heated. A heating objective may also be considered. In some embodiments, the heating objective may be to minimize the time or power required to heat the liquid to a specific temperature or state. In other embodiments, the manner in which a bubble ruptures may be taken into account when setting a heating objective. If different sizes of bubbles create different distributions of droplet sizes when they rupture, a desired droplet size, or a desired profile of droplet sizes may define the heating objective. In one example, in an ENDS system, droplets of a diameter in excess of 10 microns may be associated with spitback, so a heating objective may be to create a bubble that ruptures to minimize production of droplets in excess of 10 microns. It should be understood that different liquids may require different bubble sizes to satisfy the same final objective, so the heating objective may be associated with physical properties of the liquid. It should also be understood that the above description of a 10 micron spitback threshold may be based on properties of a specific e-liquid, and for other e-liquids a different spitback threshold may be required. 
       FIG.  6    illustrates a boiler  120  making use of a heater  122  to heat a liquid within walls  126 . To allow for the improved heat transfer offered by a heater having controlled aberrations, the planar heater  122  has a series of aberrations  124 , similar to aberrations  102  on linear heater  100 . Aberrations  124  are spaced apart from each other so that, similarly to the spacings  104  on linear heater  100 , they are approximately equidistant to each neighbor. Those skilled in the art will appreciate that any one of a number of different arrangements of aberrations  124  on the heater surface  122  can be used, and that maintaining equidistance between closest neighbors is neither necessary nor essential in each embodiment. 
     In operation, liquid is contained within walls  126  of the boiler  120 , and heat is applied through the heater  122 . As the liquid heats, aberrations  124  serve as nucleation points for the bubble to form. The bubbles, once formed, will grow outwards from the aberrations. As the bubbles encounter each other, each bubble will restrain the growth of the adjacent bubbles. If there is sufficient liquid within boiler  120  to ensure that the bubbles are fully submerged when they reach this size, they will separate from the heater and rise through the liquid. As noted earlier, heat transfer can occur through having these bubbles break from the heater  122 , and rise through the liquid. By placing the aberrations in specific locations, the size of these bubbles can be largely controlled. It should be understood that due to a number of different factors, the nucleation process may not be completely regular, and as such, not every aberration will serve as a nucleation point starting at the same time. As such, some bubbles may form with a larger or a smaller radius, but the differences in these bubble sizes will be bounded by the location of other aberration locations. 
       FIG.  7    will be used in an explanation of how aberrations can be located on the surface of a heater to control bubble size. As will be apparent, it may not be feasible to arrange each aberration to be the nucleation point of a spherical bubble equidistant to the nucleation point of all neighboring bubbles. This would require the effective tiling of circles on a flat plane. Although it is possible to lay the circles beside each other with no overlap, there will be regions outside these circles. To maximize the placement of the aberrations, it may be preferred to replace the circle associated with the radius of a bubble, with a corresponding hexagon as shown in  FIG.  7   . In one embodiment, each of the hexagons  122 ,  124  could have at its center an aberration to allow for the creation of a simple tiling that allows for bubbles of a defined size. In another embodiment, the heater  122  has aberrations only within hexagons labelled  124 . Each of these hexagons  124  is surrounded by a heater hexagon  122  that has no aberration. This grouping of 7 hexagons is then tiled. This is a geometric arrangement used in a number of other fields, including in the determination of the placement of base stations in mobile networks, to create roughly circular cells. Those skilled in the art will appreciate that the particular tiling geometry used can be varied, with the understanding that the size of the bubbles created will largely depend on the distance between the heater cells  124  that have an aberration. 
     By heating heater  122  with a given power, and thus given temperature, it is possible to encourage nucleation to occur at defined points in the surface of heater  122  corresponding to the location of a surface aberration  124 . This allows for a heating surface with regularly spaced aberrations designed to promote nucleation. The aberrations can take a number of different forms, just as they can be tiled in a number of different ways. In the illustrated embodiments, the aberrations can be formed by cutting or slicing into the heater creating a crevice that allows for heating of the liquid from more than one surface at a given time. In other embodiments, the aberrations can be perforations in the surface of the heater, while in other various machining techniques can be used to create the aberrations. In some embodiments, chemical or laser etching can be applied to the surface of the heater to create aberrations that can be used to encourage nucleation. In some embodiments, a roughened patterning can be applied to a smooth heating surface to create regions that act as surface aberrations that act as nucleation sites. In such an embodiment, it may be desirable to restrict the size of the roughened region so that there is greater consistency in the sizing of the bubbles that are created. In other embodiments, a heater can be formed with the aberrations present, such as through a forging or stamping process. In further embodiments the aberrations can be formed through techniques such as additive manufacturing where the aberrations are built in layers upon the heating surface. 
     Although the above discussion has largely centered on a heater having a substantially planar heating surface, these teachings can also be applied to linear heaters, and to heaters designed to heat thin films of liquids, not just pools of liquid. 
       FIG.  8    illustrates the application of the above described inventive concepts to a heater for use in conjunction with a wicking substrate in an ENDS or other vaporizer system. A wick  150  is in contact with a heater  152  and draws e-liquid  154  from a reservoir across the wick  150  so that it is in contact with heater  152 . Heater  152  may be referred to as a linear heater as its width is relatively minor in comparison to its length. In some embodiments, a linear heater may be a wire, whose length dominates its width or diameter. The heater  152  may be a metal wire, such as a copper wire, an aluminium wire, a steel wire, a titanium wire, a nickel wire or wire of other such materials. As noted in earlier discussions, this creates a surface film of e-liquid  154  that covers heater  152 . When power is applied across heater  152 , it increases in temperature to cause the volatilization of the thin film of e-liquid  154  atop the heater  152 . The e-liquid lost to the volatilization process is replaced by wick  150  typically through capillary action. 
     As shown in the magnification within  FIG.  8   , heater  152  has regularly spaced aberrations  156  that create a crevice  158  between the aberration  156  and the heater  152 . As heat is applied, the e-liquid within crevice  158  will be heated by both heater  152  and the aberration  156 . This may increase the likelihood of bubble nucleation at this location. Those skilled in the art will appreciate that this will increase the likelihood of bubbles forming at the interface between each of the aberrations  156  with the heater  152 . The regular spacing of the aberrations will result in bubbles forming much as shown in  FIG.  5 B . The spacing of the aberrations  156  result in bubbles that will rupture after contacting each other as the formed bubbles will generally be larger in diameter than the depth of the e-liquid film. However, one skilled in the art will note this depends on capillary action replenishing the surface, viscosity, and surface tension of the liquid to be heated. 
     Those skilled in the art will appreciate that by controlling the size of the bubbles within a vaporizer system, the size of droplets created by the rupturing of the bubbles can be constrained. These droplets are entrained within the airflow for delivery to the user. By controlling the size of droplets formed, effects such as spitback can be reduced, if not avoided, not by filtering out droplets of a given size, but instead by preventing the creation of many of these droplets. As noted earlier, there are many techniques that can be used for spitback mitigation and often they are used in conjunction with each other. By applying a mechanism to reduce the creation of spitback sized droplets, other known spitback mitigation techniques can be used if there is concern that in given environments spitback sized droplets may still be generated. 
     Those skilled in the art will appreciate that the above teaching can be applied in a variety of different styles of vaporizer devices including those with either horizontal or vertical wicks, and those that use conventional reservoirs or those that make use of reservoirs that are filled with a so-called cartomizer matrix used to hold the e-liquid in a sponge like element. Although discussed in the context of a nicotine based e-liquid, it should be understood that e-liquids used to deliver cannabinoids like one or both of Cannabidiol (CBD) and tetrahydrocannabinol (THC) also exhibit this tendency. It should be understood that there is often a wide variation in the thickness or viscosity of e-liquids held within a cartomizer based ENDS pod and the e-liquids used to deliver cannabinoids. Different e-liquids with different compositions may have different spitback thresholds. Different e-liquid compositions thus may require different spacings between the aberrations in the surface of the heater. Similarly, a change in the design of a vaping pod may also necessitate a change in the inter-aberration spacing. It should also be understood that in addition to the location of the aberrations on the heater, the size and shape of the aberrations may also require modification with changes in the design of the pod or the properties of the liquids in question. It should also be understood that the temperature to which the heater is heated may also be an input factor in selecting the size and shape of the aberrations. 
     In the ENDS embodiments discussed above, the e-liquid is stored in a replaceable pod that stores the e-liquid and draws the e-liquid from a reservoir into a wick, and then through the wick to a heater. It should be understood that in some embodiments, the wick may be vertically oriented, that is parallel (and possibly co-axial) with the direction of airflow through the pod. In other embodiments the reservoir may contain a cartomizer matrix that holds the e-liquid within the pod for delivery to the wick. In further embodiments, the reservoir storing the e-liquid, the heater and the wick may be integrally formed with the device. In such embodiments, the reservoir may be sealed so that the vaping device is a one-time use device. In other embodiments the reservoir may provide a port through which a user can refill the reservoir, and where at least one of the wick and heater may be replaceable by a user. 
     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.