Patent Application
20110024037
This invention relates to a method for manufacturing heat exchangers, particularly heat exchangers comprising micro tubes.
Heat exchangers are used to transfer energy from one fluid to another. Heat exchangers are typically characterized by heat transfer rates between fluids and corresponding pressure drops of the fluid(s) across the heat exchanger. Examples of other performance metrics include volume, weight, cost, durability, and resistance to fouling. Micro tube heat exchangers are effectively shell and tube heat exchangers where the outer tube diameter is very small (diameters less than about 1.5 mm, and preferably less than 1.0 mm) compared to what has been used extensively in industry (outer tube diameters greater than 3 mm). Micro tube heat exchangers commonly utilize thousands, tens of thousands, or even millions of tubes. Micro tubes may be defined as tubes, each having an outer diameter of less than about 1.5 mm, and preferably less than one (1) mm.
There are advantages to using micro tubes which include more heat exchange area per unit volume, higher heat transfer coefficients, and an enhanced ratio of heat transfer/pressure drop associated with very low Reynolds numbers, all of which lead to greatly enhanced heat transfer/volume, heat transfer/weight (so called compact heat exchangers) and thermal performance. However, a challenging component in manufacturing micro tube heat exchangers is the manufacture of the header plates and/or mid plates. Each header plate and mid plate typically will contain an identical pattern of holes, numbering in the thousands, tens of thousands, or millions, corresponding to the thousands, tens of thousands, or even millions of tubes. The precision of the hole spacing and the diameter of the holes must be within tight enough tolerances such that the tubes easily can pass through the header plates and mid plates during the manufacture process, yet also provide a tight clearance (on the order of 0.001-0.004 inches (0.0025-0.01 mm) diametrical clearance) desired for the bonding/sealing process associated with either brazing, soldering, or adhesive gluing. The thickness of the header plates is typically much thicker than the mid plates, since the structural loads imposed on header plates are much greater. One known method to manufacture header plates and mid plates is to drill the appropriate hole pattern in each plate. This process has been used successfully to fabricate heat exchangers, but it is expensive since the time and resources required to drill thousands to millions of holes in each of the header plates and mid plates is significant. Furthermore, when structural loads dictate that the header must be relatively thick (greater than about five times the hole diameter), the process to drill holes becomes substantially longer. If the application requires hard-to-drill materials such as 304 stainless steel, a nickel alloy such as INCONEL®, or titanium (as opposed to an easy-to-drill material such as many aluminum alloys), hole drilling is even more expensive and time consuming.
Another challenging component in manufacturing micro tube heat exchangers is the process of joining the thousands, tens of thousands, or millions of micro tubes to the header plates. While micro tube heat exchangers are typically more compact than heat exchangers using tubes with larger diameter, the number of tubes is typically much greater for a given application. Because the number of tubes in a micro tube heat exchanger can number tens of thousands, even millions, it is important that the process used to join the tubes to the header plates be extremely reliable. A preferable joint provides structural integrity and prevents leakage of one fluid stream into the other. A success rate far above 99.99% is typically required. For example, if a tube-to-header plate joining process with a 99.5% success rate is used to join tubes to header plate on a product with 100,000 tubes, then each of the two header plates will have 500 leaks. Even if the success rate is 99.9%, each header will have 100 leaks. A success rate of 99.99% would still result in 10 leaks in each header. Similarly, a heat exchanger with one million tubes and a success rate of 99.99% would have 100 leaks in each header. Identifying and patching tens or hundreds of leaks would be time consuming and expensive. An approach that results in zero, one, or two leaks would allow the manufacturer to produce the product much more inexpensively. A heat exchanger with 100,000 tubes (200,000 header plate-tube joints) with one leak will produce a success rate equal to 99.9995%. Of course, zero leaks is far more preferable than even one leak. Regarding micro tube heat exchangers, achieving such a success rate in excess of 99.9995% is important and may impact the commercial viability of the micro tube heat exchanger.
Still yet another challenging component of the manufacture of micro tube heat exchangers is the process by which tubes are inserted. Normally tube heat exchangers involve hundreds or even thousands of tubes, and it may be important to control the costs associated with tube insertion. For the case of micro tube heat exchangers, the problem associated with tube insertion cost is magnified greatly because the number of tubes is extremely high, even for relatively small, mass produced products. For at least the foregoing reasons, it has now become apparent that a need exists for a method to manufacture micro tube heat exchanger that allows for the quick and inexpensive insertion of thousands to millions of tubes through the header and/or mid plates, as well as facile methods of fabricating the header plates and of joining the tubes to header plate(s) so as to form substantially leak-free seals therebetween.
The present invention is deemed to meet the foregoing need, amongst others, by providing manufacturing methods to greatly reduce the cost and time of manufacturing micro tube heat exchangers. Specifically, at least one embodiment of the invention addresses one or more of the three manufacturing issues (header and mid plate manufacture, highly reliable bonding of tubes to the headers, and tube insertion) that are important components of overall cost and efficiency.
An embodiment of this invention is a method comprising disposing a first end plate adjacent to a second end plate, wherein the first end plate and second end plate each define a pattern of apertures. The first end plate is aligned with the second end plate such that the pattern of apertures in the first end plate is substantially aligned with the pattern of apertures in the second end plate. The method further comprises placing an end portion of each of a plurality of micro tubes in contact with the first end plate, the micro tubes being substantially vertically disposed and substantially perpendicular to a top surface of the first end plate, so as to place the micro tubes on the first end plate, and vibrating at least one of the micro tubes while the micro tubes are on the first end plate, thereby causing the micro tubes to insert into and through respective aligned apertures of the patterns of apertures in the first end plate and the second end plate. The method further comprises separating the first end plate from the second end plate while the micro tubes extend therethrough, until the first end plate and the second end plate are disposed proximate to respective end portions of the micro tubes extending therethrough, and affixing each end portion of the micro tubes to a respective end plate, thereby forming a pathway in a micro tube heat exchanger component for the flow of an internal fluid to be heated or cooled by external flow of an external fluid. It will be appreciated that, as used throughout this disclosure, the term vibrating means to cause to move to and fro, side to side and/or up and down.
Another embodiment of this invention is a method comprising disposing at least one mid plate adjacent to a first end plate and a second end plate thereby forming a stack, wherein the mid plate, the first end plate, and the second end plate each define a pattern of apertures. The mid plate, the first end plate, and the second end plate are aligned such that the pattern of apertures in each of the mid plate, the first end plate, and the second end plate is substantially aligned in the stack. The method further comprises placing an end portion of each of a plurality of micro tubes in contact with the first end plate, the micro tubes being substantially vertically disposed and substantially perpendicular to a top surface of the first end plate, so as to place the micro tubes on the first end plate, and vibrating at least one of the micro tubes while the micro tubes are on the first end plate, thereby causing the micro tubes to insert into and through respective aligned apertures of the patterns of apertures in the stack. The method further comprises separating the stack while the micro tubes extend therethrough, until the first end plate and the second end plate are each disposed proximate to respective end portions of the micro tubes extending therethrough and the mid plate is disposed at a selected location between the first end plate and the second end plate, and affixing each end portion of the micro tubes to a respective end plate, thereby forming a pathway in a micro tube heat exchanger component for the flow of an internal fluid to be heated or cooled by external flow of an external fluid.
In another aspect of the invention there is provided a method for fabricating a heat exchanger header while sealing a plurality of microtubes thereto. The method comprises
providing a stack of a plurality of lamina each of which defines a pattern of lamina apertures, the apertures being substantially alignable in the stack;
disposing a plurality of microtubes through respective aligned lamina apertures extending through and defined by the stack of lamina so as to form a subassembly, a clearance existing between each of the microtubes and their respective aligned apertures when the microtubes are so disposed; and
adhering together the lamina in the stack and the plurality of microtubes so disposed while forming a seal at the clearances.
Still another aspect of the invention provides a method of fabricating a heat exchanger, comprising
threading a plurality of microtubes through respective, substantially aligned apertures formed by adjacent, stacked lamina, the microtubes and the lamina through which they are thread defining clearances;
separating at least some of the stacked lamina to form separate groups of one or more header lamina and one or more support lamina while the microtubes remain threaded therethrough, and disposing one or more of the support lamina at different respective points along a length of the microtubes; and
adhering the header lamina to the plurality of microtubes threaded therethrough while forming a seal at the clearances
These and other embodiments, advantages and features of this invention will be still further apparent from the ensuing detailed description, drawings and appended claims.
In each of the above figures, like numerals are used to refer to like or functionally like parts among the several figures.
Illustrative embodiments of the invention are described below as they might be employed in the method of manufacturing a heat exchanger according to the present invention. It will be of course appreciated that in the development of an actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
Turning now to the Figures, one embodiment of the present invention includes a method for manufacturing a heat exchanger component 20 as shown in
As illustrated in
In one embodiment, the aligned first end plate and second plate are disposed in an assembly device comprising a first end portion and a second end portion, wherein the aligned first end plate and second end plate are retained proximate the first end portion of the assembly device. In an alternate embodiment illustrated in
In one embodiment, the assembly device may be an assembly jig comprising a first end portion, a second end portion spaced and opposite the first end portion, and at least two support members, wherein the support members support the first end portion and the second end portion and provide the spacing between the end portions. In one embodiment illustrated in
As shown in
In one embodiment, the receptacle may comprise a plurality of alignment members, wherein the alignment members may extend into the internal cavity of the receptacle. The alignment members allow for the positioning of the plurality of micro tubes in a substantially vertically disposed manner in the receptacle. The alignment members may be placed in a variety of locations in the receptacle, the locations depending, amongst other factors, on the number of micro tubes fed into the receptacle and the size and configuration of the receptacle. In at least one embodiment, the alignment members may be metal prongs extending into the cavity of the hopper, wherein the prongs function to dispose the micro tubes substantially vertically in the hopper.
As shown in
In certain embodiments, each of the plurality of micro tubes may not be inserted into and through a respective aperture in the pattern of apertures by the force of gravity or the additional vibration applied directly or indirectly to the micro tube. In at least one embodiment, at least one micro tube is manually inserted into and through a respective aperture in the pattern of apertures in the aligned first end plate and second end plate or stack. It should be appreciated that manually inserting the micro tubes may be accomplished by guiding each tube through a respective aperture by hand or other convenient method apparent to those of skill in the art.
As illustrated in
The plurality of micro tubes will be substantially parallel to each other and may be substantially perpendicular to a planar surface of the first end plate and second end plate and, optionally, the mid plates once the plates have been separated. In at least one embodiment, the micro tubes are substantially parallel to each other and substantially perpendicular to a planar surface of the separated plates.
In at least one embodiment, end plates are formed from one or more lamina 64 as shown in
Both end plates and mid plates may be made of one or more lamina of thin sheets, either metal or polymer, each having the desired hole pattern. These lamina are made via lithographic etching, or stamping, or drilling and either process can produce the required lamina from a variety of metal alloys, e.g., steel, nickel alloy, aluminum, titanium or the like, or from a polymer.
The lamina that are used to make the header plate and mid plates can be made lithographically by selective etching. Typically, the allowable thickness of lithographically etched sheet is on the order of one half of a hole diameter. If the thickness of the sheet is much greater than half of the hole diameter, then side wall taper will be excessive and control of hole quality is lost. Typical micro tube diameters are 0.5 millimeters in diameter, so the allowable thickness of the etched sheets is about 0.25 millimeters (which is about 0.010 inches).
In certain embodiments, end plates may comprise a plurality of lamina (whose thickness is on the order of 0.010 inches (0.25 mm)). Accordingly, in certain embodiments, mid plates may also comprise one or a plurality of lamina. Stacks of lamina 64, either for mid plates 30 or end plates are aligned, then joined together in one or more of a multiple of ways, e.g., rivets, spot welding, brazing, adhering, and the like as illustrated in
End plates and, when present, mid plates, each define a pattern of apertures. The patterns of apertures in each of the end plates used in a heat exchanger may be substantially identical. In embodiments including a mid plate, the pattern of apertures defined by the mid plate may be substantially identical to the pattern of apertures defined by the end plates. The pattern of apertures defines the spacing/position of the micro tubes in the heat exchanger. The pattern of apertures may vary. Nonlimiting examples of patterns include serpentine patterns, rectangular arrays, square arrays, and random patterns. As described below, each aperture typically will be circular and substantially geometrically equivalent to every other aperture in the pattern. However, other aperture shapes may be contemplated and remain within the scope of the present invention.
Etched and stamped parts allow for lithographically defining a non-circular hole as a circular hole. The ability to etch non circular holes becomes useful when the cross section of the micro tubes is non circular. Typically, the shape of the micro tubes will dictate the shape of each aperture in the pattern of apertures. However, the dimensions of the apertures in the pattern of apertures may define the dimensions of the micro tubes used. While circular micro tubes may be beneficial due to availability and cost, the fact that header and spacer plates can easily be manufactured which accommodate other tube cross section shapes means that tube cross section is a choice the designer will select, but is not a parameter by itself that uniquely differentiates micro tube heat exchangers.
In at least one embodiment, a plurality of micro tubes 44 will be provided as illustrated in
In one embodiment, the micro tubes are resized, wherein the micro tubes are cut to an appropriate length for a desired dimension of the micro tube heat exchanger component. the micro tubes may come in original form wrapped around a spool, wherein the length of the micro tubes may need to be modified to an appropriate size based on the dimensions of the desired heat exchanger. It should be appreciated that the micro tubes may be cut by any manner known in the art.
The micro tubes are affixed to the end plates and, optionally, the mid plates. The micro tubes should be joined to the end plates and, optionally, the mid plates via a sealant to prevent flow through the gap between each of the tubes and their respective aperture of the pattern of apertures. In one embodiment illustrated in
In another embodiment illustrated in
In another embodiment, illustrated for example in
For those embodiments of the invention employing an epoxy bonding material and/or a silicone sealant material, examples of potentially suitable epoxies include ARATHANE 5753 from CIBA Specialty Chemicals Corp., New York, N.Y.; AREMCO BOND 2315 from Aremco Products, Inc., Valley Cottage, N.Y.; epoxies available from National Adhesives such as BONDMASTER ESP-308 and ESP-309; Emerson & Cuming's ECCOBOND A-359 and A-410-5P; epoxies available from Cotronics, such as DURALCO 4525, 4538, 4540 and 4700, DURABOND 455, 7025, 7032, 950, 950FS and 954, and RESBOND 989; epoxies from Loctite such as HYSOL 3141/3163, E-214HP, E-40HT, E-60NC and U-05FL (Urethane); JB-WELD epoxy; MASTERBOND EP29LPSP; Plastech-Weld epoxies such as MAX 5000 and RAD-120; and epoxies from Scotch-Weld such DP-8010, EC-2214, EC-2216 and EC-3710. Examples of potentially suitable candidate silicone material include DOW CORNING 734, 736, 832, 1-2577 and 9-1363; General Electric's RTV-157; Loctite's 587 BLUE 598, BLACK 5606, 5607, 5699, 5900, 5910, 2577 and SUPERFLEX #2 Gasket Sealant; and Momentive's RTV-100, 106, 116, 118 and 159, and Silicone Solutions' SS-6604.
Once the micro tubes are sealingly attached to the end plates, a heat exchanger core is formed and a pathway is formed in the micro tube heat exchanger component 20 for the flow of an internal fluid A to be heated or cooled by external flow of an external fluid B. As illustrated in
In at least one embodiment, the heat exchanger is fabricated using polymer micro tubes, and may be fabricated using polymer mid plates, end plates, side plates, and manifolds. The end plates and mid plates may be metal or polymer. In the case where metal end plates are used, an adhesive is used to seal the micro tubes to the header plate. Preferably, the end plates and mid plates are made of a polymer if polymer micro tubes are used. A solvent or heat may be added to ensure that a chemical bond is established between the end plates, mid plate, and each micro tube.
The internal and external fluids may be a liquid or a gas. Depending on the operating conditions, particularly the temperature of the fluid to be cooled or heated, various external fluids may be used. It is to be understood that the chosen external or internal fluids should not degrade the heat exchanger component.
Except as may be expressly otherwise indicated, the article “a” or “an” if and as used herein is not intended to limit, and should not be construed as limiting, the description or a claim to a single element to which the article refers. Rather, the article “a” or “an” if and as used herein is intended to cover one or more such elements, unless the text expressly indicates otherwise.
This invention is susceptible to considerable variation within the spirit and scope of the appended claims.
A claim is made to the benefit of the priorities of co-pending U.S. Patent Appl. No. 61/156,385, filed on Feb. 27, 2009, and co-pending U.S. Patent Appl. No. 61/224,002 filed on Jul. 8, 2009, the disclosures of which are incorporated herein by reference.
The U.S. Government has provided support for the making of, and has certain rights in, this invention as provided for by the terms of Contract No. N68335-08-C-0127 awarded by the U.S. Department of the Navy.
| Number | Date | Country | |
|---|---|---|---|
| 61156385 | Feb 2009 | US | |
| 61224002 | Jul 2009 | US |
