Abstract:
An apparatus and method for efficient heating fluid by using electromagnetic energy, The fluid is passed into a channeling structure within a region of space illuminated with electromagnetic energy uniformly, equally and simultaneously for rapid heating. Electromagnetic energy penetrates the fluid and causes it to heat. Structure in close proximity to the fluid in the channeling structure efficiently converts electromagnetic energy to heat to further heat the fluid to obtain a substantially homogeneous final desired temperature. The fluid is moved through the channeling structure creating turbulent to maximize the transfer of electromagnetic energy to the fluid.

Description:
PRIORITY CLAIM  
       [0001]     This application claims priority of U.S. patent application Ser. No. 10/860,379 filed 3 Jun. 2004. 
     
    
     TECHNICAL FIELD OF THE INVENTION  
       [0002]     The present invention relates to fluid heating systems, particularly to tankless fluid heating systems, and more particularly to tankless microwave-heated water systems.  
       BACKGROUND OF THE INVENTION  
       [0003]     In the field of fluid heating systems for domestic, commercial and industrial use of heated fluid, there are fluid-tank heaters and tankless fluid heaters. For example, water-tank heating systems, such as those found in many homes throughout the world, provide hot water by heating a large volume of water in a water tank. This is wasteful since such a large volume of hot water is needed only intermittently. Tankless water heaters seek efficiency by heating water on demand. Typically, in a tankless system, heat is concentrated about a section of conduit through which the water flows from the water source to the water use point. The section of conduit may be coiled to allow more water to be heated at a time as the water passes through the region of space heated by the heat source. The heat source may be electrical, flame, or microwave.  
         [0004]     There are many types of tankless water heater systems and microwave water heaters described in the art. For example U.S. Pat. No. 5,387,780 discloses a “microwave powered boiler” for heating water. A first cabinet is provided that surrounds and protects a second cabinet made of a material such as steel that reflects microwave energy. In the interior space between the first and second cabinet is a thermal insulating material. Enclosed within the second cabinet is a third cabinet that forms a tank where the water is heated. A microwave source coupled to wave guiding structure feeds microwave energy to the region between the second and third cabinet. The wall of the third cabinet allows microwave energy to penetrate there through to heat the water enclosed thereby. A thermostat control system is provided so that when the water temperature in the tank is lower than the set point, the magnetron microwave source is initiated to generate microwave energy to heat the water until the set point is reached.  
         [0005]     An example of a tankless water heater system that uses a microwave source and a coiled conduit section is provided by Electro Silica, a provider of water heating systems. Their website on the World Wide Web is electrosilica.com. There is shown a system wherein cold water received from a water source flows generally downward through a coiled conduit section that is enclosed within a stainless steel tank. The coil is disposed against the interior wall of the tank. Above the coil and above or at the top of the region enclosed by the tank, is a set of magnetrons that produce microwave energy at 2450 Mega-Hertz (MHz). The coil is flexible and made of a silica-based substance that enables microwaves to penetrate there through and heat the water therein. The metal tank shaped, purportedly to prevent “generation of refraction and diffraction waves.” The base of the chamber formed by the tank serves as a reflecting dish to direct energy upward towards the silica based flexible coil in the chamber. As demand for water is made, the magnetron sources initiate to produce microwave energy that propagates in the chamber. Some of this energy propagates into the water in the coiled conduit and is absorbed by the water to generate heat. At the bottom of the steel chamber is an outlet to supply water that has been heated within the chamber.  
         [0006]     One problem presented by tankless and microwave heaters is the relative inefficiency of energy transfer. Ideally, one would want all of the generated energy to be converted to heat only the fluid as it passes through a well-defined region. In practice, some energy generated by the source will not heat the fluid, but rather, will be dissipated and conducted away by structure exterior to the fluid. In the case of microwave-heated systems, some microwave energy never enters the water, but is reflected away by the boundary of the water-carrying conduit section. This further reduces efficiency.  
         [0007]     For at least these reasons, there is a need for a more efficient electromagnetic-energy-heated tankless water heater.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention provides a method for efficient heating of fluid by electromagnetic energy. According to an aspect of the present invention, an electromagnetic energy source is coupled to an enclosure to produce electromagnetic energy within the enclosure. Within the enclosure, structure channels fluid through the enclosure and substantially converts electromagnetic energy to heat in the proximity of the fluid within the enclosure to add substantial heat to the fluid.  
         [0009]     According to another aspect of the invention, a membrane is provided that enables substantial penetration of electromagnetic energy through the membrane. A fluid channeling structure is provided that channels fluid through the enclosure from an inlet to an outlet. Electromagnetic energy from a source penetrates the membrane and heats the fluid in the channeling structure. Either the channeling structure or structure in close proximity thereto is comprised of a material that generates heat in response to electromagnetic energy. Thus, structure is provided to channel the fluid through the enclosure and that substantially converts electromagnetic energy to heat in proximity to the fluid.  
         [0010]     The foregoing has outlined rather broadly aspects, features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional aspects, features and advantages of the invention will be described hereinafter. It should be appreciated by those skilled in the art that the disclosure provided herein may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Persons of skill in the art will realize that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims, and that not all objects attainable by the present invention need be attained in each and every embodiment that falls within the scope of the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:  
         [0012]      FIG. 1  is a side view of a preferred embodiment of the present invention.  
         [0013]      FIG. 2  is a top view of a fluid channeling structure.  
         [0014]      FIG. 3  is a circuit for control of a magnetron.  
         [0015]      FIG. 4  is a side view of an alternative embodiment of a fluid channeling structure.  
         [0016]      FIG. 5  is a side cross-sectional view of a dual chamber configuration. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]      FIG. 1  illustrates a side view of a preferred embodiment of the present invention. An enclosure  1000  comprising a first section  1010  and a second  1020  is provided. The first and second sections,  1010  and  1020 , are brought together so that a fluid flow channeling structure  1050  is captured within the cavity formed by joining the first and second sections. An electromagnetic energy source  1080 , such as a magnetron or a klystron, is positioned and coupled to the cavity. The walls of sections  1010  and  1020  are preferably metallic to confine the electromagnetic energy there within.  
         [0018]     As shown in  FIG. 1 , fluid flow channeling structure  1050  has a flange with bolt holes so that bolts  1040  can be inserted there through. First section  1010  also exhibits a flange with holes that align with the holes in the flange of channeling structure  1050 . Placed between first section  1010  and channeling structure  1050  is a membrane  1060 . Membrane  1060  has holes around its outer periphery that align with the holes of the flanges of first section  1010  and channeling structure  1050 . Second section  1020  also has a flange with holes aligned with the holes in channeling structure  1050 . Bolts  1040  thereby pass through the flange of second section  1020 , through channeling structure  1050 , through membrane  1060 , and through the flange of first section  1010 , wherein the bolts  1040  are secured by nuts  1045 .  
         [0019]     At a side of first section  1010  provision is made for a circulation fan motor  1070  and fan blade  1075  to distribute electromagnetic energy evenly in the enclosure  1000 . If the fan blade  1075  is made of a low-loss, low-dielectric constant material, it will cause less perturbation of the electromagnetic fields in the cavity than a fan blade that is metallic. A metal fan blade will reflect electromagnetic energy waves and substantially affect the field distribution in the cavity.  
         [0020]     A top view of fluid flow channeling structure  1050  is shown in  FIG. 2 . A fluid inlet  2010  is connected to a cold fluid source using standard fittings. A flow sensor or switch  2040  is provided to measure whether a threshold level of fluid is passing through inlet  2010  to determine the level of instantaneous demand. Fluid inlet  2010  directs fluid into a series of parallel channels  2000  formed by partitions  2005 . An outer perimeter of structure  1050  can be treated with a electromagnetic energy reflecting material to prevent leakage of electromagnetic energy from the enclosure. The channels are connected sequentially so that fluid flows first in one direction then in another direction in a raster pattern to substantially increase the volume of fluid being heated in the enclosure at any instant of time. The channel structure of the illustrated embodiment is exemplary. Other patterns for channeling the fluid may be implemented. For a household water heating application, the channeling structure may be of outside dimensions of 10 inches by 10 inches, and 1 inch thick with the source operating at 2.45 Giga-Hertz (GHz) with a free space wavelength of about 4.82 inches.  
         [0021]     Note that unlike a coil, channels  2000  create turbulent, as opposed to laminar, fluid flow to maximize the transfer of electromagnetic energy to the molecules of the fluid. A hot fluid outlet  2020  is provided at an end of the channeling structure to communicate heated fluid to one or more use points. A temperature probe  2030  is provided at outlet  2020  to measure the temperature of the fluid that exits channeling structure  1050 .  
         [0022]     Electronics for controlling a magnetron in response to signals from a temperature-setting device  3050 , temperature probe  2030 , and flow switch or sensor  2040  are shown in  FIG. 3 . A step up transformer  3010  provides power to the magnetron  3020  when the Triac or Power Relay device  3030  is activated by power control circuit  3040 . Power control circuit  3040  receives signals from probe  2030  and flow switch or sensor  2040 . According to one implementation, if flow switch or sensor  2040  detects that fluid is flowing within the preset flow rate, then no demand for hot fluid exists, and the fluid is not heated. If fluid exceeding the preset flow rate of the flow switch or sensor  2040  does flow, then the fluid is heated to maintain a constant temperature at the outlet as measured by temperature probe  2030 . A constant temperature is user-selected by way of the temperature-setting device  3050 .  
         [0023]     Returning to  FIG. 1 , electromagnetic energy source  1080  generates electromagnetic energy in a frequency band for which the fluid strongly absorbs electromagnetic energy. For example, several frequency bands for which water is an especially strong microwave absorber are known. The electromagnetic energy generated by electromagnetic energy source  1080  enters the cavity of enclosure  1000  containing channeling structure  1050 . This energy propagates and impinges upon membrane  1060 . Membrane  1060  is ideally a rigid low-loss dielectric material that allows electromagnetic energy impinging upon it to pass through it into the water. Channeling structure  1050  is made of a high loss material that absorbs electromagnetic energy at the source frequency rather efficiently and generates substantial heat in response. A high electromagnetic energy susceptor material with these properties is silicon carbide.  
         [0024]     Thus, electromagnetic energy penetrates membrane  1060 , enters the fluid, and is partially absorbed by the fluid to generate heat. Energy not absorbed by the fluid enters the electromagnetic-energy-absorbing fluid channeling structure and is at least partially absorbed thereby to generate heat. This heat from the channeling structure is absorbed by the fluid, thereby raising the temperature of the fluid further. Note that electromagnetic energy entering the electromagnetic-energy-absorbing channeling structure is rapidly attenuated so that a substantial portion of the energy entering the structure is absorbed therein. Any energy penetrating through the channeling structure will reflect from an interior surface of enclosure  1000  back to the channeling structure to be absorbed thereby.  
         [0025]     Unlike the prior art, where the fluid channeling structure is intentionally made of a low-loss material that enables substantial penetration without substantial absorption, of electromagnetic energy, the present invention provides: (1) structure that enables penetration of electromagnetic energy into the fluid and (2) structure in proximity to the flowing fluid that substantially converts electromagnetic energy to heat. Note that the structure that enables penetration of electromagnetic energy into the fluid may itself be a electromagnetic energy absorbing structure. Thus, for example, membrane  1060  may be comprised of a thin layer of silicon carbide. The membrane then allows some electromagnetic energy to penetrate into the water, while converting some electromagnetic energy to heat that is conducted to the water.  
         [0026]     The enclosure containing an electromagnetic-energy-absorbing structure as described herein can be viewed as a loaded electromagnetic cavity, with the fluid-filled channeling structure as the load. Clearly, an ideal rectangular cavity can sustain an electric field distribution that is zero at the top and bottom and maximum in the middle. Thus, one may position the channeling structure about halfway between the top and bottom of the enclosure. Alternatively, since the ideal rectangular cavity can sustain a field that is zero at the bottom and is maximum one-quarter wavelength from the bottom, one may position the channeling structure about one-quarter wavelength from the bottom. The position of the channeling structure within the enclosure that produces maximum transfer of electromagnetic energy to fluid heat can be determined by experimentation.  
         [0027]     Shown in  FIG. 4  is an alternative embodiment of fluid flow channeling structure  1050 . A grill-like channeling structure  1055  has on top an upper sheet of material  1061  and on bottom a lower sheet of material  1062 . The parts are assembled by passing bolts through bolt holes  1042  positioned around the periphery of the assembly. Grill-like channeling structure  1055  comprises partitions  2005  forming channels  2000  for fluid to flow from inlet  2010  to outlet  2020 . By forming the structure from separate pieces assembled together, each piece can be made of a material chosen for its response to electromagnetic energy.  
         [0028]     For example, upper sheet  1061  can be chosen to be a low-loss membrane that allows substantial penetration of electromagnetic energy there through without substantial electromagnetic energy absorption. Alternatively, for example, upper sheet  1061  can be chosen to allow substantial electromagnetic energy penetration, yet with some absorption within the upper sheet. This would create an upper hot plate to heat the fluid while still allowing substantial electromagnetic energy to penetrate into the fluid. Lower sheet  1062  will be chosen as a high loss material efficient at converting electromagnetic energy into heat. Such a material, as mentioned, is silicon carbide, which can be manufactured in a wide variety of shapes and absorption capacities, as is well known in the art. Finally, structure  1055  is also preferably made of a high efficiency converter such as silicon carbide that generates substantial heat in response to electromagnetic excitation. Note that the configuration can be sealed to prevent fluid leakage by means known in the art such as epoxy embedding.  
         [0029]     Although, a major application for the present invention is the heating of water for household, commercial and industrial applications, the invention may be employed to heat fluid other than water for a variety of applications. The size, and indeed the shape, of the enclosure and channeling structure, may be adapted to the application. Silicon carbide, as noted, can be formed in a variety of shapes. For micro-heating applications, small channels can be etched into a flat sheet of silicon carbide using methods known in the semi-conductor industry. Thus the channeling structure and microwave enclosure can be made of any practical size from very small to very large.  
         [0030]     The size of the enclosure will be dependent in part on the volume of fluid that must be heating within the enclosure at an instant of time for a given flow rate and fluid temperature to be achieved. Also, the field distribution in the enclosure is substantially affected by its dimensions. For example, in a particular application the cavity of the enclosure may be dimensioned to be resonant at a given frequency. Then with the cavity loaded by the fluid and channeling structure the electromagnetic energy source may be operated at, above, or below the resonant frequency of the cavity in a frequency range that coincides with a frequency range for which the fluid and structure in proximity to the fluid strongly absorbs microwave energy.  
         [0031]     In the alternative to enclosing the channeling structure within a metallic cavity, the channeling structure could be positioned in a region of space that is illuminated with an electromagnetic energy source such as a directional antenna. Although such a configuration is contemplated, a lack of confinement of the electromagnetic energy would be inappropriate for many applications.  
         [0032]      FIG. 5  shows a side view of an alternative embodiment of the present invention. A dual-feed chamber  5000  is provided with two electromagnetic energy sources  5080  and  5081 . Chamber  5000  comprises a first section  5010  and a second section  5020  that is the mirror image, cross-sectionally, of first section  5010 . Similar to the configuration of  FIG. 1 , within section  5010  is a circulation fan  5075  driven by motor  5070 . Section  5020  also has a circulation fan  5076  driven by motor  5071 .  
         [0033]     Enclosed between sections  5010  and  5020  is a fluid channeling and heating structure  5050 . The assembly of sections  5010 ,  5020  and  5050  is accomplished with bolts  5040  secured by nuts  5045  around the periphery of structure  5050 . Structure  5050  comprises two membranes  5060  and  5061 , one on each side of structure  5050 . These membranes allow substantial penetration of electromagnetic energy there through. The membranes may be made of a low loss dielectric or a thin layer of high loss material such as silicon carbide.  
         [0034]     Structure  5050  is comprised of a first set of channels  7000  formed by a first set of partitions  7005  and a second set of channels  7001  formed by a second set of partitions  7006 . Fluid enters channels  7001  through fluid inlet  7010 . Fluid exits channels  7000  through fluid outlet  7020 . Fluid in channels  7001  is communicated to fluid in channels  7000  by a partial open section at the very end of common channel region  7003 . When both sources  5080  and  5081  are operating, the fluid flowing through channels  7000  is heated predominately by the energy generated by source  5080 , and the fluid flowing through channels  7001  is heated predominately by the energy generated by source  5081 .  
         [0035]     The configuration of  FIG. 5  presents several advantages. If one of the sources,  5080  or  5081 , fails, the other source can still function to generate energy to heat the fluid to a desired degree. Indeed, the system can be operated with one source at a time. Also, the dual-level channeling structure  5050  allows about twice the volume of fluid to be in the region of heat generation as the embodiment of  FIG. 1 .  
         [0036]     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. The invention achieves multiple objectives and because the invention can be used in different applications for different purposes, not every embodiment falling within the scope of the attached claims will achieve every objective. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.