The invention disclosed herein relates generally to micro-vaporizers that heat a liquid to generate vapor. The invention particularly relates to resistive heating elements for micro-vaporizers.
Micro-vaporizers heat and vaporize small amounts of liquids or soluble solids, such as nicotine containing liquids, fragrances, flavored liquids, chemical agents, biochemical agents, essences, glues, waxes, resins, and saps. Micro-vaporizers typically vaporize fluids at a rate of less than 100 milliliters per hour (ml/h). Micro-vaporizers are applied in products such as: electronic cigarettes, home fragrance dispensers, personal and home dispensers of bug repellent, and medical treatment dispensers for inhalers. Micro-vaporizers are often applied in consumer products used by retail consumers with little or no training or instruction in the use of the product. Micro-vaporizers should be safe for consumer use, easy to operate, reliable, deliver vapor quickly and consistently upon demand by a consumer, require little or no training to operate, be inexpensive to manufacture, and be rugged to withstand shocks from falls and usage by consumer.
A micro-vaporizer has a heating element powered by a battery. The heating element is in contact with the liquid or soluble solid to be vaporized. Conventional heating elements are commonly electric heating coils or Positive Temperature Coefficient (PTC) heating elements. Conventional heating element are commonly immersed in a fluid filled chamber or surrounded by fluid adsorbent material in the micro-vaporizer.
Micro-vaporizers rapidly and repeatedly deliver vapor on demand to a consumer. The consumer may activate heating element by sucking on the end of the micro-vaporizer, pressing a button or otherwise commanding the vaporizer to generate vapor. The need for rapid and repeated generation of vapor has caused conventional heating elements to be configured to consume large amounts of electrical power. To supply the needed power, conventional micro-vaporizers tend to have high charge density batteries, such as lithium batteries and rechargeable batteries. These batteries are relatively expensive, large and unfriendly to the environment when the micro-vaporizer is disposed of. There is a need to avoid expensive and large batteries but still have a micro-vaporizer that rapidly and repeatedly delivers vapor.
A heating element for a micro-vaporizer has been conceived and is disclosed herein. The heating element is an electrically resistive element having a surface configured to be coated with a thin film of the liquid or solid to be vaporized. The heating element need only heat the thin film to produce vapor. Because only a thin film is being heated, the power consumed by the heating element is relatively small as compared to conventional heating elements that heat a larger volume of the fluid or solid.
The heating element may be adapted from a conventional electrical resistor circuit element. Electrical resistors are well-known, inexpensive and available in a large variety of resistance values. Conventional resistors are passive resistive elements used in electrical circuits. Each resistor has a maximum power rating which indicates the maximum electrical energy that the resistor may dissipate without overheating. Conventional resistors are operated such that the energy applied to the resistor is below the maximum power rating. Conventional wisdom is that operating a resistor above its maximum power rating will create excessive heat and damage the resistor.
In contrast to conventional wisdom and practice, a conventional resistor is operated above its maximum power rating to function as the heating element for a micro-vaporizer. Operating a resistor above its maximum power rating causes the resistor to heat sufficiently to vaporize a thin film of liquid or solid applied to a surface of the resistor. Operating the resistor above its maximum power rating creates an effective and inexpensive heating element for a micro-vaporizer.
Damage that might be caused to the resistor by operating it above its maximum power rating is suppressed by cooling the surface of the resistor with a thin film of a vaporizing fluid or solid and by applying electrical energy to the resistor for short periods, such as while a customer repeatedly inhales on a micro-vaporizer. Further, any damage caused to the resistor may be tolerated if the micro-vaporizer is disposed of after a relatively short period of use, such as less than a day, a week or month.
The embodiments of heating elements for micro-vaporizers disclosed here have benefits including relatively low power consumption, a surface configured to receive and vaporize a thin film of liquid or soluble solid, and may be powered by inexpensive alkaline dry-cell batteries, such as AAA batteries.
The heating elements for micro-vaporizers disclosed herein may be resistors configured to have a wettable surface and to be used in a micro-vaporizer. These types of heating elements can be beneficial by providing a steep temperature gradient that allows for rapid vaporization; being small and compact heating elements, providing a wettable surface to receive a thin film to be vaporized, and being a single-element that is easily mounted in the micro-vaporizer.
An exemplary embodiment of a heating element for a micro-vaporizer comprises a heating element, and a wetted surface on an outer surface of the heating element. Another exemplary embodiment of a heating element for a micro-vaporizer comprises a heating element, and a fluid storing membrane snugly fitted onto an outer surface of the heating element.
An exemplary embodiment of a micro-vaporizer cartridge for vaporization comprises a cartridge casing configured to house the heating element for vaporization that includes a heating element and a wetted surface or a fluid storing membrane snugly fitted onto an outer surface of the heating element.
An exemplary method to vaporize fluids using a heating element comprises steps of applying a fluid onto a wetted surface or a fluid storing membrane that is fitted snugly onto an external surface of a heating element, supplying a current to the heating element that is higher than an inherent power rating of the heating element to generate heat, and vaporizing the fluid on the wetted surface or the fluid storing membrane using the heat generated by the heating element.
The wettable surface 109 may be formed of a plastic material commonly used to form the casing for electrical resistors. The wettable surface may have a texture, e.g., smooth, knurled, roughened or with capillary grooves, to promote distribution of a thin film on the surface. The wettable surface may be coated, e.g., painted, with a material that does not mix with the fluid or soluble solid. The wettable surface may hygroscopic to adsorb a liquid. For example, the wettable surface may be formed of polymers such as any or allow of nylon, ABS, polycarbonate, cellulose, poly(methyl methacrylate), polyethylene and polystyrene.
The wetted surface 109 may be wetted by liquid 107 supplied by a liquid applicator 108. The heating element 101 may receive a supply of current that is higher than a maximum power rating of the heating element 101 to cause heating of an outer surface of the heating element. The temperature produced by the heating element 101 may be high enough to damage the heating element 101.
Vaporization occurs by wetting the surface 109 of a resistive heating element 101 and heating the wetted surface. Electricity is applied to the resistive heating element 101 sufficient to heat the wetted surface 109 to a temperature sufficient to vaporize the liquid on the surface. The temperature is achieved as the energy in the electricity is dissipated as heat energy in the resistive heating element.
Conventional resistive elements, such as resistors in electronic circuits, are inexpensive, commercially available in various sizes and resistance values, and easily incorporated into an electrical circuit. However, resistors for electronic circuits are designed to resist current and are not intended to be a heating element. Nevertheless, current passing through a resistor will dissipate electrical energy into the resistor and thereby heat the resistor. The amount of current dissipated as heat into the resistor depends on the structure of the resistor and the current passing through the resistor.
Resistors are not intended to receive current that overheats the resistor. Resistors are typically assigned a Resistor Power Rating that specifies the electrical power in watts that the resistor is designed to safely dissipate. The Resistor Power Rating is an effective maximum power rating for a resistor and depends on the physical size, surface area and material of the resistor. The Resistor Power Rating defines the upper power limit for resistor. It is conventional practice to operate resistors at power levels below the Resistor Power Rating. It would defy conventional wisdom to operate resistor about the Resistor Power Rating.
Operating a resistor beyond the Resistor Power Rating allows the resistor to serve as a heating element for a micro-vaporizer, especially for a disposable micro-vaporizer. When operated beyond its Resistor Power Rating, the surface of the resistor becomes hot enough to vaporize a liquid or solid applied to the surface.
The power applied to a resistor used as a heating element may be characterized by equation (1) presented below:
WX=Wg+Wa Equation (1)
In Equation (1), Wx is the actual required wattage, Wa is the Resistor Power Rating of the resistor, and Wg is the wattage that exceeds the Resistor Power Rating. The amount of heat generated by the resistor is directly related to the Wg value.
When the temperature of a heating element reaches the maximum working temperature (Tmax), the heating element will become unstable and/or damaged and/or inoperable. With the constant supply of liquid, it may be possible to operate above Tmax of the heating element. Preferably, Tmax may not be reached using the embodiment. Therefore, an embodiment may have a resulting temperature due to the Wg value that is lower than Tmax of the particular heating element used. Because most of the fluids desired to be used in a micro-vaporizer may be vaporized between about 120-230° C., a suitable heating element to be used may preferably have a heat capacity of at least 200° C. A suitable heating element may also be flame retardant, and may not produce any type of smell or gas when operating within both the normal working temperature range and at Tmax.
When an electronic element, such as a resistor, receives a current higher than its power rating, the electronic element rapidly becomes hot. The higher the current supplied beyond the rated capacity, the hotter the electronic element becomes and the element may become unstable and/or damaged and/or inoperable. A micro-vaporizer is disclosed to utilize the heat generated by an electronic element that is given a higher-than-rated-capacity current to vaporize liquids. The liquid applied to the surface of the hot element quickly vaporizes. The vaporization cools the element and thereby prevents heat induced damage to the element.
The power or capacity rating mentioned herein is the basic parameter given by the factory to each electronic element. It is the upper limit of the power capacity that the elements can handle as designed. If used beyond the indicated ratings, the elements might become unstable and/or inoperable and/or damaged.
An exemplary heating element 101 in
A conventional rod-shaped resistor, as shown in
Another exemplary heating element may include using a semiconductor as a heating element. The semiconductor may be used as a heating element by applying a higher-than-capacity current through the positive node on the p-n junction in a semiconductor to generate heat. When designing the semiconductor chip, it may be desirable to use a chip with a series of p-n junctions depending on the desired power source and current, and not to use a current limiting resistor. It may be desirable to limit the liquid resistivity to less than 1 kΩ. Advantages of using a semiconductor as a heating element may include that the surface area, M value, may be less than 0.5 mm2, which may increase the thermal efficiency of the process.
Yet another embodiment for a heating element may be to use an automated MEMS module as a heating element. The heating method and usage may be similar to a semiconductor heating element. Additionally, the automated MEMS module may be able to reduce the time needed to heat up and cool down a heating element by detecting the ambient temperature to increase or decrease current required to heat up and cool down to desired temperatures. An automated MEMS module may have a long usage life because of its ability to control current and temperature automatically.
The heating element may be powered by any type of power source, such as a battery 105 shown in
An exemplary embodiment of a fluid storing membrane 102 used on a heating element 101 may have a snug fit on the heating element 101 to ensure maximum and uniform surface coverage between the heating element 101 and the fluid storing membrane 102. If a semiconductor is used as a heating element 101, it may be preferable to apply the fluid storing membrane 102 directly and snuggly onto the semiconductor chip, without a semiconductor casing in between the chip and the fluid storing membrane 102.
The fluid storing membrane 102 may be a non-woven or woven material, such as a paper, a cloth, or other absorbent material or coating. The fluid storing membrane 102 may supply a constant flow of fluids onto the surface of the heating element 101 by penetration of fluids through the membrane 102. The fluid storing membrane 102 may possess characteristics to endure at least the maximum temperature to be generated by the heating element 101, preferably at least three times the maximum temperature, to absorb aqueous and oil-based fluids, being flame retardant, and not to emit smells during the vaporization process. However, the membrane 102 may not be immersed in a liquid. Thickness of the fluid storing membrane 102 may be adjusted to modify the amount of vapors to be emitted.
In an embodiment, during the vaporization process, fluids stored in the fluid storing membrane 102 may be vaporized due to a Wg value applied to a heating element, and the membrane 102 may be configured to replenish fluids constantly as the fluids penetrate through the membrane and vaporize. The process may generate desired rate of vaporization by achieving a temperature gradient exchange equilibrium between the heating element 101 and the fluid storing membrane 102 such that the micro-vaporizer works continuously. The Wg and Wa values may achieve a difference of up to about thirty times when an equilibrium in the process is attained. The rate of vaporization may be optimized when the Wg value is close to but not over Tmax value of the heating element.
Required wattage Wx to achieve an equilibrium in the vaporization process may be approximately proportional to the amount of vaporization desired, and they may be calculated using the following equation:
WxαLαM*T*1/η Equation (2)
where Wx is the required wattage in the process, L is the amount of vaporization, M is the heating element surface area, T is the vaporization temperature, and η is the thermal efficiency that is proportional to the spacing between the fluid to be vaporized and the surface of the heating element 101. Equation 2 represents that Wx is proportional to L and is proportional to the product of M, T and 1/η.
To obtain a desired L value, while maintaining the fluid characteristics, it may be preferable to obtain a decrease in M value while T value increases. Such preference may obtain the advantages of reducing heat transfer loss and acquiring efficient fluid replenishment. For the same reasons, it may also be advantageous to obtain a minimum M value when L value is constant and minimal.
The advantages described may be shown in the exemplary test results below. Table 1 shows the values of M, T and Wx obtained on three types of exemplary heating elements when L=0.1 mg/h.
Table 1 compares differences in required wattage between the conventionally used heating coil and PTC elements, and a 1/16 W resistor as an exemplary heating element 101 used in the embodiments. It can be seen that the resistor requires the least wattage and generates the highest temperature.
An exemplary cartridge 700 using an exemplary heating element 101 is shown in
The cartridge 700 may be used as a standalone micro-vaporizer, as a singular and independent cartridge inside a micro-vaporizer product, or in conjunction with other cartridges in a micro-vaporizer product, and be applied to any type of micro-vaporizer products. The cartridge 700 may be configured to encompass different types of liquids desirable for micro-vaporization, including oils, aqueous fluids, and different types of soluble solids, including waxes and resins. The cartridge 700 may be configured to connect to or house a power source to power the heating element 101.
The cartridge 700 may be made of a material that has a heat capacity of at least the maximum temperature to be generated by the heating element 101, preferably at least three times the maximum temperature, the same heat capacity as described for the fluid storing membrane 102. The heating element 101 used in the cartridge 700 may also have a wetted surface. The cartridge 700 may be made into a single structure using a single material, such as from a mold, or be made using different types of materials for the different compartments inside the cartridge 700. In an embodiment, the cartridge 700 may be further enclosed by a heat resistant or insulating material to ensure the heating element 101 does not also heat up the outside of the cartridge 700.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.