Method and apparatus for heat exchanging

Abstract

The subject invention pertains to a method and apparatus for heating exchanging. In various embodiments, the application of coating, plating, soldering, and brazing technologies can be used to create high performance heat exchangers. Specific embodiments of the subject heat exchanger can be lightweight and resistant or impervious to oxidation and/or corrosion. Specific embodiments of the subject heat exchanger can be highly manufacturable. Embodiments of the subject invention are directed to a heat exchanger that includes primarily, but not necessarily entirely, components or assemblies that are made from aluminum and/or aluminum alloys, and are coated or plated with a more oxidation and/or corrosion resistant metal. The coated or plated aluminum components or assemblies can be specifically resistant to corrosion or oxidation in the presence of water or water based solutions and mixtures. The metallic coating or plating materials can have excellent thermal conductivity so as to minimize the reduction of heat exchanger performance. Furthermore, these coated or plated components or assemblies can be highly assemblable and manufacturable as a result of the coating or plating process.

Description

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a cross section of a portion of an embodiment of a heat exchanger in accordance with the subject invention.

FIG. 2 shows a cross section of a portion of a heat exchanger in accordance with an embodiment of the subject invention.

FIG. 3 shows a cross section of a portion of a heat exchanger with plating or coating on the inside and outside surfaces, in accordance with an embodiment of the subject invention.

FIG. 4 shows a cross section of a portion of a heat exchanger with plating or coating on the inside surfaces, in accordance with an embodiment of the subject invention.

FIG. 5 shows an embodiment of a heat exchanger having a main body and a cover, in accordance with an embodiment of the subject invention.

FIG. 6 shows a cross section of an embodiment of a heat exchanger in accordance with an embodiment of the subject invention.

FIG. 7 shows a perspective cross section of an embodiment of a heat exchanger in accordance with an embodiment of the subject invention.

FIG. 8 shows a perspective cross section of an embodiment of a heat exchanger in accordance with an embodiment of the subject invention.

DETAILED DESCRIPTION

The subject invention pertains to a method and apparatus for heating exchanging. In various embodiments, the application of coating, plating, soldering, and brazing technologies can be used to create high performance heat exchangers. Specific embodiments of the subject heat exchanger can be lightweight and resistant or impervious to oxidation and/or corrosion. Specific embodiments of the subject heat exchanger can be highly manufacturable.

Embodiments of the subject invention are directed to a heat exchanger that includes primarily, but not necessarily entirely, components or assemblies that are made from aluminum and/or aluminum alloys, and are coated or plated with a more oxidation and/or corrosion resistant metal. The coated or plated aluminum components or assemblies can be specifically resistant to corrosion or oxidation in the presence of water or water based solutions and mixtures. The metallic coating or plating materials can have excellent thermal conductivity so as to minimize the reduction of heat exchanger performance. Furthermore, these coated or plated components or assemblies can be highly assemblable and manufacturable as a result of the coating or plating process.

Many processes for plating or coating over aluminum are well known in the art. Materials for plating or coating aluminum include, but are not limited to, the following: zinc, tin, lead, silver, gold, copper, cadmium, and nickel. Mixtures or alloys of these materials can also be utilized. The plating or coating processes can be, for example, electro-less or electrolytic. A single or multiple plating/coating process can be used to create the final plating or coating. Pre-processing and post-processing procedures utilized before and/or after the plating or coating process are well known in the art and can be utilized in accordance with the subject invention.

The plating or coating over the aluminum used in the heat exchanger can be applied to individual components of the heat exchanger prior to assembly, or the heat exchanger can be partially or completely assembled first. The plating or coating can be applied to the inside surfaces and/or_the outside surfaces of the heat exchanger components or assembly.

Many of the plating or coating materials are highly solderable and brazable, thus allowing heat exchangers that are made in accordance with specific embodiments of the subject invention to be easily and highly manufacturable. According to the American Welding Society (AWS), soldering is “a group of joining processes that produce coalescence of materials by heating them to the soldering temperature and by using a filler metal (solder) having a liquidus not exceeding 840° F. (450° C.), and below the solidus of the base metals”. Also, according to the AWS, “brazing joins materials by heating them in the presence of a filler metal having a liquidus above 840° F. (450° C.) but below the solidus of the base metal”. Many soldering and brazing filler materials, as well as the processes utilized to successfully solder and braze materials, are well documented and known in the art, and can be incorporated with various embodiments of the subject invention. Tin/silver soldering alloys have been found to work very well for joining plated or coated aluminum surfaces. Excellent solderability and brazability can allow for relatively simple and cost effective manufacturing of heat exchangers made in accordance with various embodiments of the subject invention.

In an embodiment, aluminum alloys, which exhibit high tensile strength, can be utilized as a construction material for a heat exchanger. As less material can be used to design heat exchangers with specific force and pressure requirements, embodiments utilizing aluminum can be preferable. Less material translates to lighter weight heat exchangers, which is very desirable for some applications. Aluminum type 6061-T6 can be utilized as a heat exchanger construction material in the subject invention. In additional embodiments, aluminum types 5052, 7005, 7075, 7175, 7178, and 7475 can be utilized as a construction material.

The plating or coating process for aluminum can involve numerous processes and steps. In an embodiment, the process involves the following steps:

• • 1. Degreasing, to eliminate oils, greases, and dirt from the manufacturing processes used.
  • 2. Acid etching, to remove the aluminum oxide film, so as to improve adhesion of coating or plating materials.
  • 3. Zincate treatment, to remove any small amounts of aluminum oxide remaining from the acid etching, and to coat the aluminum surface with zinc to prevent the formation of additional aluminum oxide.
  • 4. Metal plating.

In an embodiment of the subject invention, the aluminum plating process can be modified to optimize plating adhesion, aluminum coverage, and enhanced endurance. Adhesion, coverage, and endurance are very important in certain applications, as breaches in the coating can result in a detrimental failure of the heat exchanger. Breaches in coating can be caused by a variety of reasons. As an example, the media in heat exchangers can flow with a significant velocity, which has the potential to harmfully erode coating or plating materials. Furthermore, the media in heat exchangers may contain particulate or contaminants that can abrade coated or plated surfaces, thus exposing the aluminum barrier material.

In embodiments of the subject invention, aluminum components are processed in the zincate treatment twice, to ensure the surfaces are free of all aluminum oxide and completely coated with zinc. Then, in specific embodiments, instead of proceeding directly to plating with the final desired metallic coating or plating, a layer of nickel is applied. This layer of nickel can be applied, utilizing, for example, an electroless process. In many cases, the layer of zinc is removed and replaced by the metal in the plating process. The layer of nickel can be between 0.0001″ and 0.010″ thick, but is commonly between 0.0005″ to 0.0015″ thick. The electroless nickel plating process provides a uniform and complete coating of nickel over even complex and small passageways and channels, as are very common in heat exchangers. After the layer of electroless nickel has been applied, other coating or plating materials can be applied.

Embodiments of the invention involve a refrigerant evaporator or condenser, which are specific types of heat exchangers. As used herein, a refrigerant is loosely defined as a substance that can provide a cooling effect. Any refrigerant can be used, including; but not necessarily limited to, nitrogen, helium, oxygen, water, air, carbon dioxide, ammonia, R-134a, R-410a, R-600, R-600a, R-407c R-22, R-404a, R507, R-12, perfluoropolyethers, perfluorocarbons, and hydrofluoroethers.

In a refrigerant evaporator, refrigerant is one of the two media used, and is considered the primary medium. The refrigerant evaporates, thus changing from a liquid state to a vapor state, thereby absorbing heat from the secondary medium in the heat exchanger. Any secondary medium can be used, including, but not necessarily limited to, another refrigerant, air, water, ethylene glycol, propylene glycol, oil, or alcohol.

In a refrigerant condenser, refrigerant is one of the two media used, and is considered the primary medium. The refrigerant condenses, thus changing from a vapor state to a liquid state, thereby giving heat to the secondary medium in the heat exchanger. Any secondary medium can be used, including, but not necessarily limited to, another refrigerant, air, water, ethylene glycol, propylene glycol, oil, or alcohol.

Embodiments of the invention are directed to a specialized refrigerant evaporator, which can be used to cool heat generating components directly without the use of a secondary medium.

FIG. 1 shows a cross section of an embodiment of a heat exchanger that can be used to directly cool heat generating objects. Refrigerant 100 enters the portion of a heat exchanger shown, removes heat 104 from the heat generating part 103, and exits 105 the portion of the heat exchanger shown. Refrigerant 100, 105 is used to cool the barrier 102 between it and the heat generating part 103. Heat transfers 104 from the heat generating part 103 to the refrigerant 100, 105. The heat generating component 103 can be, for example, a computer processor, a laser diode, solid-state laser system, resistor, electronic device or other heat generating device. In an embodiment, the barrier material 102 can be aluminum. The barrier material 102 can be plated or coated 101 to prevent or inhibit corrosion or oxidation on the inside surface. FIG. 2 shows a cross section of a portion of a simple heat exchanger with the plating or coating on the outside 109. Heat is transferred 112 from the secondary medium 110, 107 to the primary medium 106, 111. The barrier material 108 can be aluminum. This heat exchanger can have the plating or coating on the outside, so as to allow for assembly by soldering or brazing, and to provide corrosion and oxidation protection to the outside atmosphere.

FIG. 3 shows a simple heat exchanger with plating or coating on the inside and outside surfaces 113. Heat is transferred 120 from the secondary medium 118, 115 to the primary medium 114, 119. The barrier material 117 can be aluminum. This heat exchanger can have the plating or coating on the inside and outside surfaces 113. Having the plating or coating on the outside surface can allow for assembly of multiple sections by soldering or brazing and, provide corrosion protection from the outside atmosphere, having the plating or coating on the inside surfaces can provide corrosion protection from to the inside against corrosion or oxidation induced by the medium.

FIG. 4 shows a simple heat exchanger with plating or coating on the inside 124. Heat is transferred 127 from the secondary medium 125, 122 to the primary medium 121, 126. The barrier material 123 can be aluminum. This heat exchanger can have the plating or coating on the inside surfaces 124, which can provide corrosion protection against corrosion or oxidation induced by the medium.

In a specific embodiment, after nickel is applied to the surface of the aluminum, copper is plated on top of the electroless nickel layer on the aluminum. Copper is both corrosion resistant and highly solderable and brazable. Copper plating is an electrolytic process so the coating thickness is highly dependent on the geometry of the parts to be coated and dependent on the process, the technique, and the equipment used to apply the coating. In an embodiment, the copper thickness can be between 0.0001″ and 0.010″. In a further embodiment, the copper thickness is between 0.0005″ to 0.0015″ thick.

In an embodiment, the heat exchanger is used as an evaporator and the primary medium is a refrigerant. In a specific embodiment, the primary medium in the heat exchanger is R-134a and the secondary medium is water, or a water based solution or mixture. Without protection, the aluminum surfaces in contact with the water, or water based solution or mixture, would readily and nearly continuously oxidize. In addition, the unprotected aluminum surfaces would be more susceptible to galvanic, stress, and cavitation corrosion. Such oxidation and corrosion would likely reduce the heat transfer performance substantially and likely reduce the usable life of the heat exchanger as a reduction in barrier material wall thickness occurs. Plating or coating portions, or all, of the aluminum surfaces exposed to the water, or water based solution or mixture, reduces or eliminates such oxidation and/or corrosion. Plating or coating the portions, or all, of the aluminum surfaces in contact with the water base medium also helps maintain the quality of the water based medium, by reducing or eliminating, aluminum and aluminum oxide from entering the water and deteriorating the quality of the water. Aluminum and aluminum oxide are undesirable additions to the water, especially if the water would be used for human consumption (i.e. drinking water). The Maximum Contaminant Level (MCL) of aluminum in drinking water is regulated by NSF International, a company that provides standards for public drinking water quality.

Other secondary fluids can also be used where the subject invention provides corrosion and oxidation protection. These secondary fluids include solutions of water and ethylene glycol (0.1 to 55.0% by volume), water and propylene glycol (0.1 to 55.0% by volume). A wide variety of commercially available “inhibited” glycols can also be utilized in addition to, or in place of, pure ethylene and propylene glycols. The inhibited glycols contain beneficial additives, which can minimize the formation of foam and/or bubbles in the fluid, as well as potentially further reduce corrosion of metal surfaces.

In an embodiment, referring to FIG. 5, the subject heat exchanger is made from two individual components, a main body 129 and a cover 128. In a further specific embodiment, both a main body and the cover are made from type 6061-T6 aluminum. Both the main body and cover can be plated or coated in accordance with an embodiment of the subject invention. In a specific embodiment, the double zincate treatment, electroless nickel plating of 0.0005″ to 0.0015″ thickness, and copper plating of 0.0005″ to 0.0015″ thickness, can be applied. After the plating processes are complete for both the body and cover, the two can be attached. In an embodiment, the body and the cover can be soldered together. In a specific embodiment, the solder has 93-98% tin and 2-7% silver. Soldering or brazing is preferred, but not necessary, as refrigerants can be elusive, where elusive means that the refrigerants tend to leak, or escape, to some degree, through a wide variety of o-rings, gaskets, seals, and joints. Soldering or brazing is preferred as it can create a “hermetic”, or perfect, seal, between the two media and/or with respect to the outside atmosphere. A cross section of an embodiment of a heat exchanger is shown in FIG. 6. In this specific embodiment, the narrow channels 130 for one of the media are 0.050″ wide by 0.354″ tall. The primary medium enters the heat exchanger through a ¼ inch nominal hole 132, then enters numerous small diameter holes 131, and then enters the narrow channel 130.

FIG. 7 shows a perspective view of the cross section of the secondary medium inlet region. The secondary medium 134 enters through the ¼ inch nominal hole 133, then enters a larger perpendicular cutout 135, and then enters the narrow channel 136. The secondary medium flows in the spiral shaped narrow channel as the spiral shaped narrow channel spiral around, until the secondary medium reaches numerous small holes near the outlet port.

As shown in FIG. 8, the secondary medium 138 flows from the narrow channel 136 through numerous small diameter holes 137 that are perpendicular to the channel. From the small diameter holes 137, the secondary medium flows to the ¼ inch diameter nominal outlet port 139. The primary medium flows through a passage that is shaped identically to the passage for the secondary medium. In this embodiment, the two media flow in a counter flow pattern to optimize heat transfer between them. In an alternative embodiment, a parallel flow pattern can be utilized. In this embodiment, the overall size of the heat exchanger is 2.50 inches wide by 4.22 inches long by 0.75 inches high. Thin wall (0.001 inch to 0.025 inch) fin type material can be inserted into the primary and/or the secondary to enhance heat transfer. Fin stock of a variety of materials and geometries can be used, and is widely known in the art.

In an alternative embodiment, the main body and cover can be first joined by common aluminum brazing processes, which are well known in the art. The aluminum brazing process can, for example, involve a dip brazing process or a vacuum brazing process. In an embodiment, the two components shown in FIG. 6, the body 129 and cover 128, can be joined by an aluminum brazing process prior to plating, and then processed and plated or coated with one of the various plating or coating processes in accordance with the subject invention. In an embodiment, after the aluminum brazing process, the acid etching, the double zincate treatment, and the electroless nickel plating process can be applied. The solutions and chemicals used during the plating process may be pumped through the heat exchanger to ensure adequate and complete contact and coverage of the barrier material. Electrolytic plating on outside surfaces can then be accomplished. Preferably, the internal components are electrolytically plated prior to the cover being installed.

In a specific embodiment, a heat exchanger used as an evaporator may be utilized in a small chiller. A chiller can be loosely defined as a device that cools fluids. The subject chiller can be used to cool fluids, including those previously mentioned as secondary media. In this embodiment, the primary medium in the evaporator can be a refrigerant, such as R-134a. The evaporator can be manufactured and then processed in accordance with one or more of the processing techniques described in the subject application. In this embodiment, the cooled secondary medium can be used to cool a person or people. In a specific embodiment, commercially available heat transfer garments can be incorporated with the chiller to cool one or more people. This “personal cooling” device is preferably compact and lightweight, with the subject invention allowing for substantial weight savings. The weight savings for the evaporator shown in FIG. 6 is shown in Table II.

TABLE II
Evaporator Weight Comparison
Plated aluminum versus copper
		Copper (lbs)	Plated Aluminum (lbs)
	Evaporator	0.75	0.23
	Cover	0.1	0.03
	Total	0.85	0.26
Savings, when Plated aluminum is used
	Weight (lbs)	0.59
	Percentage	69%

The weight savings of 0.59 lbs is substantial for a small chiller product, in which the entire system can typically weigh between 1.0 and 25.0 lbs. Note that a competitive, commercially available evaporator sized for this application, and made from stainless steel and copper, would weigh at least 2.5 lbs. In an embodiment, an evaporator for use in a small chiller, and made according to the processes described in the subject application weighs about 0.26 lbs. The heat transfer rate between the primary and secondary media, or what is typically characterized as the device “cooling capacity”, can range between 50 and 1000 Watts. The secondary medium outlet temperature can range between 40 degrees Fahrenheit to 90 degrees Fahrenheit, and preferably range between 65 degrees Fahrenheit to 75 degrees Fahrenheit. In an embodiment, the shape of the chiller can be cylindrical, as previously described by U.S. Pat. No. 7,010,936 B2 (Rini Technologies, Inc., Mar. 14, 2006), which is hereby incorporated by reference in its entirety, or the chiller can have, for example, a square or rectangular box shape.

All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.

It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.

Claims

1. An apparatus for exchanging heat, comprising: one or more components having an aluminum and/or aluminum alloy barrier, wherein at least a portion of the aluminum and/or aluminum alloy barrier is coated with a metal coating such that the metal coated surface is in contact with a first medium during operation of the apparatus, wherein the metal coated surface is more oxidation and/or corrosion resistant to the first medium than a surface of the uncoated aluminum and/or aluminum alloy barrier.

2. The apparatus according to claim 1, wherein at least one of the one or more components is in thermal contact with a heat source such that heat is transferred from the heat source to the first medium through the aluminum and/or aluminum alloy barrier and the metal coating of the at least one of the one or more components.

3. The apparatus according to claim 2, wherein the one or more components form a first channel for the first medium to flow through, wherein a first interior surface of the first channel is the metal coated surface of the aluminum and/or aluminum alloy barriers of at least one of the one or more components.

4. The apparatus according to claim 3, wherein the one or more components form a second channel for a second medium to flow through, wherein the second medium is the heat source, wherein heat is transferred from the second medium to the first medium.

5. The apparatus according to claim 4, wherein a second interior surface of the second channel is the metal coated surface of the aluminum and/or aluminum alloy barriers of a second at least one of the one or more components, wherein the second interior surface is more oxidation and/or corrosion resistant to the second medium than the surface of the uncoated aluminum and/or aluminum alloy barrier.

6. The apparatus according to claim 1, wherein the metal is selected from the following group: zinc, tin, lead, silver, gold, copper, cadmium, nickel, and mixtures or alloys thereof.

7. The apparatus according to claim 1, wherein the metal is copper.

8. The apparatus according to claim 1, wherein the first medium is a refrigerant.

9. The apparatus according to claim 1, wherein the first medium is water or a water-based solution.

10. The apparatus according to claim 4, wherein the first medium and the second medium flow in a counter flow pattern.

11. The apparatus according to claim 4, wherein the first medium and the second medium flow in a parallel flow pattern.

12. The apparatus according to claim 4, wherein the first medium is a refrigerant.

13. The apparatus according to claim 8, wherein the apparatus is a refrigerant condenser.

14. The apparatus according to claim 8, wherein the apparatus is a refrigerant evaporator.

15. A method for manufacturing a heat exchanger, comprising: providing one or more components having an aluminum and/or aluminum alloy barrier, wherein the one or more components form a first channel for a first medium to flow through;locating a heat source in thermal contact with the one or more components such that heat is transferred from the heat source to the first medium through the aluminum and/or aluminum alloy barrier of at least one of the one or more components;coating at least a portion of the aluminum and/or aluminum alloy barrier with a metal coating such that the metal coated surface is in contact with a first medium, wherein the metal coated surface is more oxidation and/or corrosion resistant to the first medium than a surface of the uncoated aluminum and/or aluminum alloy barrier.

16. The method according to claim 15, wherein coating at least a portion of the aluminum and/or aluminum alloy barrier comprises: performing a zincate treatment to the at least a portion of the aluminum and/or aluminum alloy barrier to form a coat of zinc;plating the zinc coated at least a portion of the aluminum and/or aluminum alloy barrier with the metal.

17. The method according to claim 15, wherein coating at least a portion of the aluminum and/or aluminum alloy barrier further comprises acid etching the at least a portion of the aluminum and/or aluminum alloy barrier prior to performing the zincate treatment.

18. The method according to claim 17, wherein the metal is selected from the following group: zinc, tin, lead, silver, gold, copper, cadmium, nickel, and mixtures or alloys thereof.

19. The method according to claim 17, wherein the metal is copper.

20. The method according to claim 19, further comprising: applying a layer of nickel before metal plating with copper.

21. The method according to claim 20, wherein the layer of nickel is between 0.0001 inches and 0.01 inches thick.

22. The method according to claim 16, wherein plating with the metal comprises electrolytically depositing the metal.

23. The method according to claim 16, wherein the first medium is a refrigerant.

24. The method according to claim 16, wherein the first medium is water or a water-based solution.

25. The apparatus according to claim 3, wherein the metal is copper.

26. The apparatus according to claim 25, wherein the first medium is water or a water-based solution.

27. An apparatus for exchanging heat, comprising: at least two components each having an aluminum and/or aluminum alloy surface that are soldered or brazed to another of the at least two components, wherein at least a portion of the aluminum and/or alloy surface of each of the at least two components that is soldered or brazed to another of the at least two components is coated with a metal coating, wherein the metal coated surface is more solderable or brazable respectively, than the aluminum and/or aluminum alloy surface.