Patent Publication Number: US-2010108780-A1

Title: Liquid atomization device and method

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent App. No. 61/110,315 filed on Oct. 31, 2008 and entitled APPARATUS AND METHOD FOR ATOMIZING A LIQUID. This application further claims priority to U.S. Provisional Patent App. No. 61/238,596 filed on Aug. 31, 2009 and entitled METHOD AND DEVICE FOR VAPORIZATION OF A LIQUID. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to delivery devices, and more particularly to devices and methods for atomizing a liquid to facilitate delivery to a target zone. 
     2. Background 
     Many beneficial substances, such as deodorizers, fragrances, insect repellants, insecticides, and the like, are commercially available in liquid form. Often, such liquids are packaged in containers such as spray bottles or aerosol cans so the liquids can be converted to a fine mist or spray. This allows the liquids to be finely dispersed over a large target zone to provide a beneficial effect. 
     Various delivery devices aim to maximize the beneficial effects of such a liquid over an extended period of time. For example, automatic air fresheners may be designed to periodically spray a predetermined amount of fragrance into the air over time via a pressurized pump. These systems, however, are generally mechanically complex, requiring numerous moving parts and associated expense. 
     Other delivery techniques involve automatically or periodically heating a container over time to atomize its beneficial liquid contents. Indeed, some beneficial liquids require a thermal input to provide the energy needed for them to rise to a temperature where atomization readily occurs, and may require additional thermal input for the “heat of vaporization,” which carries the liquid into a vapor phase. 
     Many fragrances and other beneficial liquids, however, become particularly volatile when exposed to heat and may decompose on heat transfer surfaces. As a result, extended heating periods may prematurely denature the beneficial liquid, initially producing a highly potent effect that quickly diminishes. Intermittent heating periods, however, may be inefficient with respect to the amount of energy required to effectuate liquid atomization. Intermittent heating periods may also prove largely ineffective due to slow vaporization response times resulting from inefficiencies in heat transfer from the container to the liquid. 
     In view of the foregoing, what is needed is a device and method to efficiently atomize a liquid for delivery to a target zone. Beneficially, such a device and method would effectuate a fast vaporization response time, minimize the amount of energy needed to atomize the liquid, and enable simple and inexpensive manufacture and use. Such a device and method are disclosed and claimed herein. 
     SUMMARY 
     The invention has been developed in response to the present state of the art and, in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available devices and methods. Accordingly, the invention has been developed to provide a device and method for atomizing a liquid that overcomes various shortcomings of the prior art. The features and advantages of the invention will become more fully apparent from the following description and appended claims, or may be learned by practice of the invention as set forth hereinafter. 
     Consistent with the foregoing, a liquid atomization device in accordance with the invention may include a liquid reservoir to contain a liquid, and a liquid pathway to receive at least a portion of the liquid from the liquid reservoir. The liquid pathway may include one end communicating with the liquid reservoir, and another end communicating with a target zone. Two electrodes may be placed in the liquid pathway to accommodate the liquid therebetween. An AC power source may be connected to each of the electrodes to generate an alternating current through the liquid, thereby atomizing at least a portion of the liquid for delivery to the target zone. 
     A corresponding method is also disclosed and claimed herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through use of the accompanying drawings in which: 
         FIG. 1  is a cross-sectional side view of one embodiment of a liquid atomization device in accordance with the invention; 
         FIG. 2A  is a cross-sectional top view of one embodiment of a liquid pathway that may be included in a liquid atomization device in accordance with the invention; 
         FIG. 2B  is a cross-sectional side view of the liquid pathway illustrated in  FIG. 2A ; 
         FIG. 3A  is a cross-sectional top view of another embodiment of a liquid pathway in accordance with the invention; 
         FIG. 3B  is a cross-sectional side view of the liquid pathway illustrated in  FIG. 3A ; 
         FIG. 4A  is a cross-sectional top view of yet another embodiment of a liquid pathway in accordance with the invention; 
         FIG. 4B  is a cross-sectional side view of the liquid pathway illustrated in  FIG. 4A ; 
         FIG. 5  is a cross-sectional side view of a liquid atomization device constructed and used for testing purposes; 
         FIG. 6  is a graphical representation of a thermogravimetric analysis and a differential thermal analysis experimentally obtained for the liquid atomization device illustrated in  FIG. 5 ; 
         FIG. 7  is a graphical representation of fragrance delivery rates experimentally obtained for the liquid atomization device illustrated in  FIG. 5 ; 
         FIG. 8  is a cross-sectional side view of another liquid atomization device constructed and used for testing purposes; 
         FIG. 9  is a graphical representation of fragrance delivery rates experimentally obtained for the liquid atomization device illustrated in  FIG. 8 ; and 
         FIG. 10  is a graphical representation of hypothetical fragrance delivery data for an embodiment of a liquid atomization device incorporating three fragrances in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the invention, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of certain examples of presently contemplated embodiments in accordance with the invention. The presently described embodiments will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. 
     As used herein, the term “AC power supply” refers to an energy storage element that generates an electric current or voltage that reverses direction at regularly recurring intervals. The term “atomize” is used to refer to a process of converting a liquid to minute particles or a fine spray that may be entrained in a gas. 
       FIG. 1  illustrates one embodiment of a liquid atomization device  100  in accordance with the invention. The liquid atomization device  100  may include a liquid reservoir  102  to contain a liquid prior to atomization and dispersal, and a liquid pathway  104  to receive a beneficial liquid, atomize at least a portion of the liquid, and direct the atomized liquid to an external target zone. A beneficial liquid may include, for example, a fragrance, an insect repellant, an insecticide, or any other liquid imparting a beneficial effect known to those in the art. In some embodiments, the liquid reservoir  102  and/or liquid pathway  104  may be substantially encased within a housing  106 . 
     The liquid reservoir  102  may include at least one opening  108  communicating with an end  110  of the liquid pathway  104 . In certain embodiments, the liquid reservoir  102  may include substantially rigid walls  112 , and may be vented to permit liquid contained therein to passively flow from the reservoir  102  to the liquid pathway  104  under the influence of gravity. Alternatively, the walls  112  of the liquid reservoir  102  may be substantially elastic, such that the reservoir  102  has a collapsible, variable volume. In this manner, embodiments of the invention may avoid a partial vacuum that may otherwise result in the reservoir  102  as liquid volume is drawn out of the liquid pathway  104  through the vaporizing and atomizing process. 
     Of course, one skilled in the art will recognize that a flow of liquid from the liquid reservoir  102  to the liquid pathway  104  may be accomplished by various means, including for example, a diaphragm pump, a centrifugal pump, a gas-generation pump, or by any other suitable means known to those in the art. In any case, as liquid mass is expelled from an open end  114  of the liquid pathway  104 , additional liquid may enter the pathway  104  through the end  110 , thus continuing the atomizing and dispersal process. 
     The liquid pathway  104  may be substantially elongate, and may be oriented such that the opening or end  114  communicating with the target zone may be hydraulically higher than the opening or end  110  communicating with the liquid reservoir  102 . Further, in some embodiments, the surface area of the opening or end  114  communicating with the target zone may be small relative to the volume of liquid contained in the pathway  104 , thereby limiting passive liquid evaporation resulting from exposure to the ambient environment. 
     In order to atomize the liquid passing therethrough, two or more electrodes  116   a ,  116   b  may be positioned within the liquid pathway  104 . The electrodes  116   a ,  116   b  may be made of metals, carbides, conductive polymers, conductive ceramics, or other materials that are electrically conductive and stable in the presence of the beneficial liquid. 
     During operation, liquid may be received into the liquid pathway  104  from the opening  108  in the liquid reservoir  102 . Power may be applied to the electrodes  116   a ,  116   b  by an AC power supply  126  and attached leads  120   a ,  120   b  to produce an alternating current through the liquid. Depending on the specific characteristics of the liquid and the voltage and frequency of the AC signal, a corona may form in the liquid resulting in resistive heating and vaporization. The rate of heat generation from resistive heating or corona may depend on the resistance of the liquid, the voltage and frequency of the AC signal, and geometric factors such as electrode spacing and electrode area. As the liquid temperature rises, a portion of the liquid may vaporize. Buoyancy or volume expansion may cause the vaporized liquid  122  to rise through the liquid pathway  104  to its open end  114 . As the vapor  122  is expelled, a portion of the liquid may be carried with the vapor in the form of atomized droplets. 
     The liquid atomization device  100  may use AC power as opposed to DC power to atomize the liquid for several reasons. First, many liquids may not be electrically or ionically conductive and therefore may not readily conduct DC current. Second, in cases where the liquids do conduct DC current, the DC current can cause decomposition reactions at the electrodes, resulting in fouling of the electrodes  116   a ,  116   b  and reduced currents due to reduced conductivity through the decomposition products. As a result, the liquid atomization device  100  may utilize an AC power supply  126  to generate an alternating current through the liquid. 
     In certain embodiments, the AC power supply  126  may be configured to generate a high frequency alternating current (“HFAC”) through the liquid between electrodes  116   a ,  116   b . In such embodiments, the electrodes  116   a ,  116   b  may be spaced relatively close together, creating a limited electrode zone or area between electrodes  116   a ,  116   b . The use of HFAC may enable current to pass through non-conductive liquids that may otherwise act as insulators for DC current. For example, in an experiment performed by the instant inventors, it was discovered that a DC current was not able to pass through a citrus liquid fragrance manufactured by Fragrance Oil Ltd., but a high frequency current of 43.6 kHz was able to be successfully conducted through the same liquid. 
     In certain embodiments, a controller  124  may be provided to control one or more parameters of the AC power supply  126  responsible for generating a current between the electrodes  116   a ,  116   b . Such parameters may affect, for example, the voltage or frequency of the AC signal, a duty cycle of the power supply  126 , an on/off period of the power supply  126 , or the like. For example, in one embodiment, the controller  124  may control the liquid dispensing rate by applying AC power to the electrodes  116   a ,  116   b  in periodic intervals (as with a duty cycle). In other embodiments, the controller  124  may control the liquid dispensing rate by adjusting the frequency and/or voltage of the AC signal. 
     Referring now to  FIGS. 2A and 2B , in certain embodiments, a liquid pathway  104  for use with the liquid atomization device  100  may include two independent and electrically isolated electrodes  116   a ,  116   b  positioned within an outer casing  202 . As shown, the electrodes  116   a ,  116   b  may be positioned within the liquid pathway  104  and oriented substantially parallel relative to one another. One skilled in the art will recognize, however, that the electrodes  116   a ,  116   b  may be oriented in various ways and positioned in various locations within the liquid pathway  104 , and that the present invention is not limited to the configuration shown. For example, in certain embodiments, one electrode  116   a  may be positioned at or near one end  114  of the liquid pathway  104  and the other electrode  116   b  may be positioned at or near the opposite end  110  of the liquid pathway  104 , thereby increasing the length of the current path through the liquid. 
     During operation, liquid may be received into an annulus or channel  200  between the two electrodes  116   a ,  116   b , thereby providing a conductive or semi-conductive medium through which a current may pass. In some embodiments, the liquid may act as a dielectric material directly exposed to the electrodes  116   a ,  116   b  within the liquid pathway  104 . As sufficient voltage is applied to the liquid at an appropriate frequency and exceeding the breakdown voltage, a corona may form within the liquid. The current or corona may generate heat, which may vaporize a portion of the liquid. The vapor exiting the liquid pathway  104  may entrain atomized liquid. 
       FIGS. 3A and 3B  illustrate an embodiment of the invention having one electrode  116   a  forming the outer wall or periphery of the liquid pathway  104 . Specifically, in the illustrated embodiment, the electrodes  116   a ,  116   b  may be positioned substantially concentrically relative to one another, such that one electrode  116   a  forms the outer wall or periphery of the liquid pathway  104 , while the other electrode  116   b  forms its core. An annulus  200  to accommodate a flow of liquid may be formed therebetween. In certain embodiments, insulating spacers (not shown) may be placed at the ends  110 ,  114  of the pathway  104  to center the core electrode  116   b  with respect to the outer electrode  116   a.    
     Referring now to  FIGS. 4A and 4B , another embodiment of a liquid pathway  104  may include a casing  202  surrounding an outer electrode  116   a . As shown, the electrodes  116   a ,  116   b  are arranged substantially concentrically relative to one another. In certain embodiments, the casing  202  may be constructed from a thermally and/or electronically insulating material, such as polypropylene, polyethylene, polytetrafluoroethylene (“PTFE”), oxide ceramic, nitride ceramic, glass, or the like. In certain embodiments, the casing  202  may be substantially impermeable to liquid, thereby enabling utilization of one or more substantially porous electrodes  116   a ,  116   b . Such a casing  202  may also prevent heat loss from the liquid and may demonstrate low thermal mass. As a result, the liquid may heat more quickly when power is applied to the electrodes  116   a ,  116   b , thereby providing faster activation response. In addition, the reduced heat loss and thermal mass may reduce the amount of energy needed to vaporize the liquid. This may create a liquid atomization device  100  that is more energy efficient and, in some embodiments, may reduce the size and weight of a battery used to operate the liquid atomization device  100 . 
     The following are two non-limiting examples of devices that were made and tested in accordance with embodiments of the invention. 
     EXAMPLE 1 
     A liquid atomization device (similar to that shown in  FIG. 5 ) was made by fabricating a device  100  with two concentric electrodes  116   a ,  116   b , spaced apart from each other by an insulating nylon line. The outer electrode  116   a  area measured 3.534 square inches, while the inner electrode  116   a  area measured 2.356 square inches. The area of the outlet where liquid is exposed to the atmosphere was 0.06135 square inches. Fragrance was the liquid selected for delivery. The power supply  126  was a 15V DC power supply connected to a circuit that converted the signal to HFAC, and the frequency was set at 43.57 kHz. Standard thermogravimetric and differential thermo analysis tests were performed on a Simultaneous Thermal Analysis  409  (“STA  409 ”) manufactured by Netzsch. The results of these tests are shown in  FIG. 6 . 
     Particularly,  FIG. 6  is a plot (shown by the solid line  600 ) of fragrance weight percent not vaporized versus temperature as the fragrance was heated at a rate of 5° C. per minute, and a plot (shown by the broken line  602 ) of temperature difference between the sample and a control pan with no sample with respect to temperature. The plots show that approximately ten percent (10%) of the fragrance vaporizes exothermically below 140° C. Above that temperature, heat must be applied for the remaining ninety percent (90%) of the fragrance to be delivered via vaporization and atomization. 
     When 15V DC power was applied to the electrodes  116   a ,  116   b , there was no appreciable current through the liquid. As a result, there was a negligible difference between the fragrance delivery (determined by weight loss) with the 15V DC power applied, and a control when the power was off. On the other hand, when 15V DC power was applied through a set of circuits designed to convert DC power to HFAC, the fragrance delivery rate increased from a baseline to a level more than ten times above the baseline, as shown in  FIG. 7 . 
     EXAMPLE 2 
     As shown in  FIG. 8 , a liquid atomization device  100  was made by fabricating a device  100  having a variable volume liquid reservoir  102 , in this case a syringe with a moving piston  800 . The device  100  included a liquid pathway  104  defined by a housing  802  constructed of a polymer. The liquid pathway  104  was in liquid communication with the liquid reservoir  102  and a vapor outlet  804 . The open area of the vapor outlet  804  was 0.0475 square inches. Two electrodes  116   a ,  116   b  (having an electrode area of 0.345 square inches each) were exposed to liquid flow between the reservoir  102  and the outlet  804 . Each electrode was connected to a 12V DC power supply  126  connected to a circuit that converts the signal to HFAC. Fragrance was the liquid selected for delivery, and was contained in a variable volume reservoir  102  in fluid communication with the electrodes  116   a ,  116   b.    
     The experiment was conducted in the same manner as Example 1, with the frequency set at 43.57 kHz. The resulting delivery rates are shown in  FIG. 9 . 
     Referring now to  FIG. 10 , some embodiments of a liquid atomization device  100  in accordance with the invention may include more than one liquid reservoir  102 , thereby enabling atomization of more than one liquid and/or providing an additional supply of a particular liquid for delivery. 
     In one embodiment, a liquid atomization device  100  in accordance with the invention may include multiple liquid reservoirs  102 , each containing a different beneficial liquid. Each reservoir  102  may be connected to a unique liquid pathway  104  leading to a unique grouping of electrodes  116 , or “electrode zone,” and outlet. A controller  124  may communicate with the power supply  126  to alternate power from one electrode zone to another. In this manner, one liquid may be delivered for one period of time, and other liquids may be delivered for subsequent periods of time. In certain embodiments, the duration of the on/off periods or duty cycle may be adjusted as desired. In cases where the beneficial liquids are fragrances, such an embodiment may prevent a user from developing a fragrance tolerance that may otherwise develop where a single fragrance is delivered substantially continuously. 
     This type of cyclical or periodic delivery of different fragrances or beneficial liquids may be facilitated by the heating efficiencies and quick response of liquid atomization devices  100  and methods in accordance with the present invention. Indeed, directly heating the liquid via an alternating current may avoid a lag time between the time that electrical power is applied and the time that atomizing delivery begins. Likewise, direct heating combined with limited exposure of the beneficial liquid to the external environment may facilitate quick shut-off and limit unintended liquid loss due to evaporation. These features may enable cyclical or periodic delivery of various fragrances with limited fragrance overlap and waste. 
     A hypothetical example of this type of liquid atomization device  100  is illustrated in  FIG. 10 . In this exemplary embodiment, the liquid atomization device  100  includes three liquid reservoirs  102  retaining three different liquid fragrances. Power may be cycled from one electrode zone to another, such that one fragrance  1000  may be delivered for one period of time, followed by delivery of a second fragrance  1002  for a second period of time, and delivery of a third fragrance  1004  for a third period of time. 
     The present invention may be embodied in other specific forms without departing from its basic principles or essential characteristics. The described embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.