Patent Application
20140076517
A heat pipe can conduct heat from a heat source such as from an electronic device through vapor heat transfer. Typically, the heat pipe includes a working fluid, an evaporator section, and a condenser section. The working fluid is vaporized at the evaporator section. The vapor is received at the condenser section, whereupon the vapor is condensed to form a liquid working fluid. Capillary action and/or gravity returns the condensed working fluid to the evaporator section, thereby completing a cycle.
In many applications, heat pipes of various shapes and sizes are clamped to other elements (e.g., a device or structure generating heat to be removed by the heat pipes) in order to increase the efficiency of heat transfer to and/or from the heat pipes. For example, a plurality of heat pipes can be used in a switching unit for a motor drive. Motor drives are power conversion systems that provide power to electric motors in a controlled fashion. In a switching unit for a motor drive, semiconductor switching devices can be positioned between heat pipes, abutting the evaporator sections of the heat pipes. The assembly of switching devices and heat pipes is clamped together to maintain good electrical and thermal conduction therebetween. Other examples of heat pipe clamping applications and clamping devices exist.
Despite the advantages of clamping heat pipes to other structures as described above, in many cases the preferred clamping forces can damage some heat pipes, such as heat pipes comprising material, dimensions, and/or shapes that make the heat pipes less resistant to deformation under high clamping loads. With reference to switching units as described above, clamping forces can be as high as 20 kN.
As an example of a heat pipe feature that renders the heat pipe less able to withstand desired clamping forces without immediate deformation or deformation (i.e., “creep”) over a period of time, some heat pipes are made of annealed copper, which can be relatively soft. The copper can be annealed for a variety of reasons, such as by being exposed to high temperatures needed to sinter wick material on inside surfaces of the heat pipe. In any case, high desired clamping forces may distort and potentially damage such heat pipes. A distorted heat pipe may degrade heat transfer from the semiconductor devices, and may even damage the devices.
Thus, there has developed a need for a heat transfer device more capable of resisting clamp loads exerted on one or more surfaces of the device, as well as heat transfer and heat clamping systems in which such heat transfer devices are used.
In some embodiments, a heat-transfer system is provided for conducting heat from a heat source, and includes a plurality of serially coupled evaporators for generating a respective vapor, at least one reinforcement element interposed between adjacent evaporators, and a condenser in fluid communication with the evaporator.
In other embodiments, an evaporator is provided for generating a vapor, and includes an enclosed vapor chamber having a wall, the wall defining a recess; and a reinforcement element located at least partially within the recess.
Some embodiments of the present invention provide a heat transfer system, the heat transfer system including a plurality of serially coupled evaporators for generating a respective vapor, at least one of the evaporators including an enclosed vapor chamber having a wall; a reinforcement element adjacent to the wall, the reinforcement element including an outer surface; a condenser in fluid communication with the evaporator; and a clamp for compressing the evaporators together, the clamp including two end plates and a coupling member extending between the end plates.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “mounted,” “connected” and “coupled” are used broadly and encompass both direct and indirect mounting, connecting and coupling. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect.
Each heat-transfer device 40 includes a working fluid (not shown), an evaporator 50 for generating a vapor from the working fluid, and a condenser 60 in fluid communication with the evaporator 50. In the illustrated embodiment, and with reference to
The working fluid resides within the vapor chamber. Any number of fluids can be suitable as a working fluid so long as they have a liquid phase and a vapor phase. Suitable working fluids include, but are not limited to, water, ammonia, Freon® (E. I. du Pont de Nemours and Company), acetone, ethane, ethanol, heptane, methanol, potassium, sodium, hydrocarbons, fluorocarbons, methyl chloride, liquid metals such as cesium, lead, lithium, mercury, rubidium, and silver, cryogenic fluids such as helium and nitrogen, and other fabricated working fluids. The particular working fluid can be chosen depending on the operating temperature requirements or other preferences for the particular heat-transfer system 10.
With continued reference to
A clamp 130 is provided for compressing the evaporators 50 and switching devices 20 together so as to maintain a good electrical and thermal conduction therebetween. The clamp 130 includes two end plates 140, 150 and one or more coupling members 160 extending between the end plates 140, 150. In the illustrated embodiment, each end plate 140, 150 is generally X-shaped. In other embodiments, however, the end plates 140, 150 are not necessarily generally X-shaped. For example, the shape of one or both of the end plates 140, 150 may be a polygon, a circle, an oval, an ellipse, or a combination thereof. In the illustrated embodiment, four coupling members 160 extend between the end plates 140, 150. Each coupling member 160 includes on one end a respective fastener 170 that is threaded to secure the end plate 150 thereto. In other embodiments, one or more of the coupling members 160 may include fasteners 170 on both ends to the secure the end plates 140, 150 thereto. In still other embodiments, one or more of the coupling members 160 may be secured to the end plates 140, 150 using other suitable mechanisms that provide a compressive force. Although in the illustrated embodiment a surface of the evaporator 50 is clamped to a heat source 20 for a particular application, the invention finds application in any other case in which clamping force is used between an evaporator 50 and a heat source 20. Moreover, the use of any other clamping device or structure suitable for clamping one or more heat sources 20 to the evaporator 50 of one or more heat-transfer device 40 is contemplated herein and falls within the spirit and scope of the present invention.
The heat-transfer devices 40 optionally include a wick (not shown) disposed on at least a portion of the interior surfaces of the pipes 110. In some embodiments, the evaporator 50 is at least partially hollow, and a wick is disposed on inside surfaces of the evaporator 50. In embodiments that do not include the wick, the working fluid may be returned through the outlet pipe 110 via gravity. The wick may be formed by any materials so as to suitably provide a capillary action that returns the condensed working fluid to the evaporator 50. Suitable wick materials include, but are not limited to, a sintered or brazed metal structure, screen metal mesh, and longitudinal or spiral grooves. Sintering or brazing requires heating the heat-transfer device 40 with the wick structure to above 450° C.-1000° C. Such heat treatment can anneal the material (e.g., copper) from which the heat-transfer device 40 is formed, thereby substantially softening the material. As described above, a softened heat-transfer device 40 may undesirably distort and potentially become damaged under a high clamping force, either instantly or over some time.
Referring to
In particular embodiments, the reinforcement element 180 is made from metals such as copper, brass, aluminum, stainless steel, and the like, or alloys thereof such as MONEL® (nickel-copper alloy), copper-molybdenum alloys, clad materials such as copper/molt', molybdenum, KOVAR®, INVAR®, K-CORE®, tungsten, stainless steel, dispersion strength copper such as GLIDCOP® (copper alloy containing aluminum oxide ceramic particles), dispersion-hardened (or -strengthened) copper, or other solderable metals or alloys.
In some embodiments the heat sources 20 may be adhered to the reinforcement element 180, e.g. using welding, brazing, or adhesives, or the heat source 20 may be very tightly compressed against the reinforcement element 180. In these and other embodiments, it may be advantageous to use a material for the reinforcement element 180 which has a coefficient of thermal expansion (CTE) that is suitably matched to the properties of the heat source 20 (which may include electronic components which include silicon) and the evaporator 50 (which may be copper or another thermally conductive metal) to minimize stress between the adjacent parts that would otherwise result from heating and cooling cycles. In these embodiments, the reinforcement element 180 may suitably be made of a CTE-matched material such as KOVAR®, INVAR®, K-CORE®, or various clad materials. Use and selection of CTE-matched materials is known to those skilled in the art and is disclosed in US Patent Application Publication US 2011/0176276, which is incorporated herein by reference in its entirety.
In various embodiments, the reinforcement element 180 is a plate having a thickness of about 0.5 mm, about 1.0 mm, about 2.0 mm, about 3.0 mm, about 4.0 mm, about 5.0 mm, about 10 mm, about 13 mm, about 20 mm, about 30 mm, about 40 mm, about 50 mm, about 75 mm, or about 100 mm thick. In certain embodiments, the reinforcement element 180 covers about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, about 99%, or about 100% of the wall 80 of the evaporator 50. The thermal conductivity k of the reinforcement element 180, as well as the material(s) used to secure the reinforcement element 180 to the evaporator 50, may range from about 10 to about 500 W/(m.K) (e.g. copper has a thermal conductivity of about 400 W/(m.K)). The Mohs hardness of the reinforcement element 180 may be about 1.0, about 2.0, about 3.0, about 4.0, about 5.0, about 6.0, about 7.0, about 8.0, or about 9.0. Using a material with greater hardness has an advantage of making the reinforcement element 180 more resistant to marring, denting, and scratching.
In some embodiments the wall 80 of the evaporator 50 is relatively soft, which in some embodiments may be equivalent to H00 Cold-Rolled ⅛ Hard or 060 Soft (Table 1), while the reinforcement element 180 is harder, which in some embodiments may be H02 Half Hard or harder (Table 1). Other levels of hardness for the wall 80 and the reinforcement element 180 are also possible, provided that the reinforcement element 180 has a greater hardness than the wall 80.
In various embodiments, the reinforcement element 180 has a material yield strength of at least 50 MPa, at least 70 MPa, at least 100 MPa, at least 150 MPa, at least 200 MPa, at least 250 MPa, at least 300 MPa, at least 400 MPa, at least 500 MPa, or at least 1000 MPa. In general, the reinforcement element 180 is selected so that it has a material yield strength that is greater than the material yield strength of the evaporator 50.
In the illustrated embodiment, the wall 80 has a first stiffness, which may be determined, e.g., using a suitable ASTM test specimen, and has a first Vickers hardness number associated therewith. The reinforcement element 180 has a second stiffness, which may also be determined, e.g. using a suitable ASTM test specimen, and has a second Vickers hardness number associated therewith. In some embodiments, the second stiffness is higher than the first stiffness. In some embodiments, the second Vickers hardness number is higher than the first Vickers hardness number. Further, in various embodiments the hardness and stiffness of the wall 80 and the reinforcement element 180 may be determined and expressed using other measures such as the Brinell hardness scale.
In the illustrated embodiment (
In manufacturing the heat-transfer system 10, one or more evaporator bodies 55 are formed of metal, with a recess 190 machined or otherwise suitably formed on the wall 80. The evaporator body 55 may be at least partially hollow, and a wick material may be disposed on inside surfaces of the evaporator body 55. The wick material may be sintered or brazed by heating the evaporator body 50 with the wick structure to above 450° C.-1000° C. The evaporator body 55 is then charged with a working fluid. Separately formed cooling fins 120 are connected to the evaporator body 55 through one or more pipes 110. The reinforcement element 180 is formed of a material having a stiffness, hardness, or resistance to deformation greater than that of the evaporator body 55. The reinforcement element 180 may be soldered to the recess 190, or otherwise suitably coupled to the recess 190, e.g., via welding or adhesives.
An illustrative embodiment of the evaporator 50 is described in greater detail below.
The evaporator 50 can be a generally H-shaped block comprising a pair of walls 80 that are substantially parallel to each other and extending along the longitudinal axis 90. Each wall 80 in this particular example can include a respective recess 190 that measures 8.4 cm in the longitudinal direction and 2 mm in depth substantially perpendicular to the longitudinal direction. The evaporator 50 can be positioned on the power cage 30 or other support structure. Each recess 190 can be configured to start at a position spaced 3 mm from the support structure 30, extending upwardly and away from the support structure. Reinforcement elements 180 can be soldered to each recess 190. The wall 80 in this particular example is completely annealed (e.g. 060 Soft, Table 1) whereas the reinforcement element 180 in this particular example is H02 Half Hard (Table 1). Thus, the reinforcement element 180 has a hardness that is higher than that of the wall 80.
Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described.
This application claims priority to U.S. Provisional Patent Application No. 61/703,534 filed Sep. 20, 2012, the content of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61703534 | Sep 2012 | US |
