Patent Application
20070246193
1. Field of the Invention
The subject invention relates to a heat exchanger assembly for cooling an electronic device.
2. Description of the Prior Art
The operating speed of computers is constantly being improved to create faster computers. With this, comes an increase in heat generation and a need to effectively dissipate that heat.
Heat exchangers and heat sink assemblies have been used that apply natural or forced convection cooling methods to dissipate heat from electronic devices that are highly concentrated heat sources such as microprocessors and computer chips; however, air has a relatively low heat capacity. Thus, liquid-cooled units called LCUs employing a cold plate in conjunction with high heat capacity fluids have been used to remove heat from these types of heat sources. Although LCUs are satisfactory for moderate heat flux, increasing computing speeds have required more effective heat sink assemblies.
Accordingly, thermosiphon cooling units (TCUs) have been used for cooling electronic devices having a high heat flux. A typical TCU absorbs heat generated by the electronic device by vaporizing a working fluid housed on the boiler plate of the unit. The boiling of the working fluid constitutes a phase change from liquid-to-vapor state and as such the working fluid of the TCU is considered to be a two-phase fluid. Vapor generated during boiling of the working fluid is then transferred to a condenser, where it is liquefied by the process of film condensation over the condensing surface of the TCU. The heat is rejected into ambient air flowing over the condenser and fins are commonly employed on the condenser to increase the heat transferred from the vapor. The condensed liquid is returned back to the boiler plate by gravity to continue the boiling-condensing cycle.
Examples of such thermosiphons include PCT Patent Application WO 02/081996A2 to Joshi et al. and U.S. Pat. No. 6,085,831 to DiGiacomo et al.
The Joshi patent discloses an assembly for cooling an electronic device including a housing having a lower portion holding a refrigerant and an upper portion having condensing tubes extending upwardly from the lower portion of the housing. Air heat transfer fins extend between adjacent condensing tubes. The condensing tubes extend parallel to one another and thus, the air fins between two adjacent condensing tubes are of equal length.
The DiGiacomo patent is a thermosiphon including a housing having a lower portion for holding a refrigerant and an upper portion including a plurality of condensing tubes extending upwardly and outwardly along a single vertical plane from the lower portion of the housing. Boiler heat transfer fins extend into the upper portion of the housing to enhance heat transfer from the vapor boiled off of the refrigerant to the upper portion of the housing. The condensing tubes are formed out of a condensing chamber having plate-like fins extending into the chamber from the upper portion of the housing.
Although the prior art effectively dissipates heat from electronic devices, there is a continuing need for alternative designs for effectively dissipating heat from electronic devices. Specifically, there is a need for alternative designs for orientation insensitive thermosiphons.
The invention provides a heat exchanger assembly for cooling an electronic device comprising a housing. The housing includes an upper portion and a lower portion extending along a primary axis wherein the upper portion of the housing includes a plurality of condensing tubes spaced from one another transversely to the axis. The condensing tubes extend axially with each condensing tube extending upwardly from a bottom end at the lower portion of the housing to distal and spaced top ends. A refrigerant is disposed in the lower portion of the housing for undergoing a liquid-to-vapor-to-condensate cycle within the housing. A plurality of air heat transfer fins zigzag transversely to the axis between adjacent ones of the condensing tubes for dissipating heat from the condensing tubes while vapor is boiled off of the refrigerant. At least two next adjacent condensing tubes of the plurality diverge upwardly from the bottom ends toward the distal ends thereof. Accordingly, the space containing the air heat transfer fins between the two next adjacent condensing tubes is greater at the top distal ends than at the bottom ends of the condensing tubes.
The invention provides an alternative design for a compact heat exchanger for cooling an electronic device able to operate in a vertical position, a horizontal position or at any angle of tilt therebetween. The invention provides a constant cross section such that it can be manufactured by extrusion methods thereby lower the cost of manufacturing.
Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, a heat exchanger assembly 20 is generally shown for cooling an electronic device 22.
The assembly 20 includes a housing 24 generally indicated having an upper portion 26 and a lower portion 28 extending along a primary axis A, and having a front end 30 and a back end 32. The lower portion 28 of the housing 24 includes a floor 34, a top wall 36, and diverging side walls 38 extending outwardly and upwardly from the floor 34 to the top wall 36. The upper portion 26 of the housing 24 includes a plurality of condensing tubes 40, 42 extending axially and spaced from one another transversely to the axis. Each condensing tube extends upwardly from a bottom end 44 at the lower portion 28 of the housing 24 to distal and spaced top ends 46.
In the embodiment shown in
A pair of endplates 48 is secured to the housing 24 wherein one endplate 48 is disposed on the front end 30 and the other endplate 48 is disposed on the back end 32. The endplates 48 are thin plates that are brazed and cover the cross section of the housing 24 that includes all of the condensing tubes 40, 42 and the lower portion 28 of the housing 24 between the planes of the endplates 48. The endplates 48 do not cover the spaces between adjacent condensing tubes 40, 42 wherein the fins 50, 52 are disposed, so that air can be moved through the spaces and over the air fins 50.
A refrigerant 54 is disposed in the lower portion 28 of the housing 24 for undergoing a liquid-to-vapor-to-condensate cycle within the housing 24. A plurality of boiler heat transfer fins 52 are disposed in the lower portion 28 for transferring heat from the electronic device 22 to the refrigerant 54. The boiler heat transfer fins 52 extend axially along the floor 34 of the lower portion 28 of the housing 24.
The housing 24 and the boiler heat transfer fins 52 disposed in the lower portion 28 of the housing 24 are extruded and thereafter cut into sections of a predetermined length. The endplates 48 are subsequently secured to the front end 30 and back end 32 of the housing 24 thereby lowering the cost of manufacturing the invention as compared to conventional methods of manufacturing.
A plurality of air heat transfer fins 50 are included and zigzag transversely to the primary axis A between adjacent ones of the condensing tubes 40, 42 for dissipating heat from the condensing tubes 40, 42 as vapor is boiled off of the refrigerant 54. The air heat transfer fins 50 extend axially along the entire length of the condensing tubes 40, 42 between opposite ends thereof.
The assembly 20 is distinguished by at least two next adjacent condensing tubes 40, 42 of the plurality diverging upwardly from the bottom ends 44 toward the distal ends 46 thereof. The two next adjacent condensing tubes 40, 42 are the center two of the plurality. The air heat transfer fins 50 extend between the two next adjacent condensing tubes 40, 42 and the space between the two next adjacent condensing tubes 40, 42 is greater at the top distal ends 46 than at the bottom ends 44 of the condensing tubes 40, 42, i.e., the space containing the air fins 50. As illustrated in both embodiments, the air fins 50 zigzag between evenly spaced fin apexes from top to bottom between the condensing tubes 40, 42. Alternatively, the air fins 50 that zigzag between apexes can be stretched to vary the distance vertically between apexes so that the air fins 50 are denser at the top of the diverging condensing tubes 40, 42.
In the embodiment shown in
The two next adjacent condensing tubes 40 extend vertically along parallel tube axes and at least one of the remaining condensing tubes 40 (all of them as illustrated) extends along a tube axis parallel to each of the tube axes of the two next adjacent condensing tubes 40.
In the embodiment shown in
In operation, the electronic device 22 generates heat which is transferred to the boiler heat transfer fins 52, causing the refrigerant 54 to boil. Vapor boiled off of the refrigerant 54 then rises due to gravity into the condensing tubes 40, 42. In a vertical position, shown in
Obviously, many modifications and variations of the present invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.
