Low cost high performance laminate matrix

Abstract

A porous solid substrate suitable for forming heat exchange elements and method for fabricating the substrate are provided. The porous solid substrate is usable in a regenerator or heat exchanger for exchanging thermal energy with a fluid flowing through elements formed from the substrate. Elements formed from the substrate are especially suitable for use in a regenerator matrix used in deep refrigeration cryocoolers based on the Stirling refrigeration cycle. The porous solid element substrate is formed from a plurality of thin screen sheets of interwoven stands of fine wire with each sheet having a thickness of substantially three times the diameter of the wire stands. Sheets are arraigned one above another with surfaces of adjacent sheets in mechanical contact. The sheets sintered in a high temperature high-pressure environment to form a composite element having sintered contact points between adjacent sheets. The composite elements are more easily handled, less susceptible to damage during manufacturing and reduce the manufacturing cost of the heat exchanger.

What I claim:  
     
         1 . A heat exchange element for exchanging thermal energy with a fluid flowing there through comprising: 
 a plurality of individual elements each having an external surface for exchanging thermal energy with the fluid and wherein each of the plurality of individual elements is joined together with another of the plurality of individual elements by a sintered joint between contacting points of the external surfaces thereof for forming a composite element; and,    wherein the plurality of individual elements are formed to provide a void volume proximate to non-contacting points of the external surfaces, said void volume providing a path for the fluid to flow through and a convective mixing volume.    
     
     
         2 . The heat exchange element of  claim 1  wherein the plurality of individual elements comprises a plurality of thin screen sheets of interwoven wire strands with each of the sheets having substantially opposing top and bottom external surfaces, and wherein the sheets are stacked together with the top and the bottom surfaces of alternating sheets in mating contact and wherein the sheets are joined together at contact points formed between the top and the bottom surfaces of alternating sheets.  
     
     
         3 . The heat exchange element of  claim 2  wherein each of the thin screen sheets of interwoven wire strands comprises a plurality of substantially parallel first wire strands interwoven with a plurality of substantially parallel second wire strands.  
     
     
         4 . The heat exchange element of  claim 3  wherein the first wire strands and the second wire strands are substantially perpendicular.  
     
     
         5 . The heat exchange element of  claim 4  wherein the first and the second wire strands are interwoven in a plain pattern.  
     
     
         6 . The heat exchange element of  claim 4  wherein the first and the second wire strands are interwoven in a twill pattern.  
     
     
         7 . The heat exchange element of  claim 3  wherein the wire strands comprise metal wire strands.  
     
     
         8 . The heat exchange element of  claim 3  wherein the wire strands have a round cross-section.  
     
     
         9 . The heat exchange element of  claim 3  wherein the wire strands comprise stainless steel wire having a round cross-section.  
     
     
         10 . The heat exchange element of  claim 8  wherein the wire strands have a diameter in the range of 0.0005-0.002 inches.  
     
     
         11 . The heat exchange element of  claim 10  wherein said first and second wire strands are interwoven with a mesh in the range of 10 to 250 stands per inch.  
     
     
         12 . The heat exchange element of  claim 11  wherein said first and second wire strands are interwoven with the same mesh.  
     
     
         13 . The heat exchange element of  claim 11  wherein said first and second wire strands are interwoven with a different mesh.  
     
     
         14 . The heat exchange element of  claim 1  wherein each of plurality of individual elements is substantially identical.  
     
     
         15 . The heat exchange element of  claim 1  wherein each of the plurality of individual elements has a characteristic orientation that relates to the performance of the element for one of exchanging thermal energy with the fluid and providing flow resistance to the fluid and wherein the characteristic orientation of each of the plurality of elements is aligned along a desired axis.  
     
     
         16 . The heat exchange element of  claim 2  wherein the plurality of individual thin screen sheets comprises less than 25 substantially identical screen sheets formed from stainless steel wire having a round cross-section with a diameter in the range of 0.0005-0.002 inches and interwoven with a mesh in the range of 200-400 wire strands per inch.  
     
     
         17 . The heat exchange element of  claim 2  wherein each of the plurality of screen sheets has a characteristic orientation defined by a weave pattern and wherein the characteristic orientation affects the performance of the element for one of exchanging thermal energy with the fluid and providing flow resistance to the fluid and wherein the characteristic orientation of each of the plurality of elements is aligned along a first desired axis.  
     
     
         18 . The heat exchange element of  claim 2  wherein each of the plurality of screen sheets has a characteristic orientation defined by a weave pattern and wherein alternating sheets are stacked together with the characteristic orientation aligned along a first desired axis and a second desired axis separated from the first desired axis by an angle α.  
     
     
         19 . The heat exchange element of  claim 18  wherein the angle α is 45 degrees.  
     
     
         20 . A thermal energy exchange apparatus for exchanging thermal energy with a fluid comprising: 
 a hollow conduit for confining fluid flow therein;    a thermal energy exchange matrix contained within the hollow conduit for exchanging thermal energy with the fluid, said thermal energy exchange matrix comprising;    a plurality of individual elements each having an external surface for exchanging thermal energy with the fluid and wherein each of the plurality of individual elements is joined together with another of the plurality of individual elements by a sintered joint between contacting points of the external surfaces thereof for forming a composite element; and,    wherein the plurality of individual elements are formed to provide a void volume proximate to non-contacting points of the external surfaces, said void volume providing a path for the fluid to flow through and a convective mixing volume.    
     
     
         21 . The thermal energy exchange apparatus of  claim 20  wherein the number of individual elements is selected to provide one composite element filing the hollow conduit.  
     
     
         22 . The thermal energy exchange apparatus of  claim 20  wherein the number of individual elements is selected to provide a plurality of separate composite elements stacked together to substantially fill the hollow conduit.  
     
     
         23 . The thermal energy exchange apparatus of  claim 22  wherein each of the plurality of separate composite elements is substantially identical.  
     
     
         24 . The thermal energy exchange apparatus of  claim 20  wherein each of the plurality of individual elements has a characteristic surface area and a characteristic void volume that affect the thermal energy exchange characteristic and the flow resistance of the composite element formed thereby and wherein the thermal energy exchange matrix comprises a plurality of composite elements and wherein at least a portion of the composite elements comprises individual elements having a different characteristic surface area and a different characteristic void volume.  
     
     
         25 . The thermal energy exchange apparatus of  claim 24  wherein the flow resistance of each composite element is selected in accordance with a local viscosity of the fluid within the conduit.  
     
     
         26 . The thermal energy exchange apparatus of  claim 22  wherein: 
 each of the plurality of composite elements is formed with less than 20 substantially identical individual screen elements; and,  
 each of the individual screens comprises interwoven round stainless steel wire strands having a diameter in the range of 0.0005-0.002 inches and a mesh in the range of 200-400 wire strands per inch.  
 
     
     
         27 . The thermal energy exchange apparatus of  claim 22  wherein: 
 the hollow conduit comprises a cylindrical element with an inside tube diameter of less than 0.25 inches; and,  
 wherein each of the plurality of composite elements are cylindrical with an outside diameter sized to provide a slight clearance fit with the inside diameter of the tube and wherein each of the plurality of individual elements joined together to form each composite element comprises a screen formed from interwoven stainless steel wire strands having a round cross-section with a diameter of less than 0.002 inches, said screens each having a substantially identical weave pattern of parallel first wire strands interwoven with parallel second wire strands, with said first and said second wire strands being substantially perpendicular, and with said first and said second wire strands having a mesh of more than 100 wires per inch.  
 
     
     
         28 . A method for exchanging thermal energy with a fluid flowing in a conduit comprising: 
 forming a plurality of individual elements with surface area for exchanging thermal energy with the fluid and void volume proximate to the surface area;    arranging each of the plurality of individual elements in a position for contacting at least one other of the plurality of individual elements at contacting points of the surface area thereof;    sintering the individual elements into contact thereby forming a composite element comprising all of the plurality of individual elements, said composite element comprising a void volume proximate to non-contacting points of the surface area, said void volume providing a path for the fluid to flow through and a convective mixing volume;    forming the composite element to a shape and size for installation within the conduit; and,    forcing the fluid through the conduit and the void volume such that the fluid exchanges thermal energy with the composite element.    
     
     
         29 . The method of  claim 28  wherein the composite element size and shape are selected to substantially fill the conduit with one composite element.  
     
     
         30 . The method of  claim 28  wherein the composite element size and shape are selected to substantially fill the conduit with a stack of a plurality of composite elements.  
     
     
         31 . The method of  claim 30  further comprising the steps of: 
 forming a plurality of types of composite elements each with a different fluid flow resistance; and,  
 arranging the types of composite elements in the tube in accordance with a local fluid viscosity in the tube.  
 
     
     
         32 . The method of  claim 30  further comprising the step of roughening contacting surfaces of each of the plurality of composite elements in the stack to increase conductive thermal resistance between adjacent elements in the stack.  
     
     
         33 . A refrigeration unit for cyclically compressing and expanding a refrigeration gas in accordance with a Stirling cycle comprising: 
 a compressor for providing a variable working volume within a compression cylinder thereof for compressing the refrigeration gas therein;    a hollow cylindrical cold well tube in fluid communication with the compression cylinder, said cold well tube being sealed at a cold end thereof;    a regenerator piston movably supported within the hollow portion of the cold well tube for providing an expansion space for expanding the refrigeration gas at said sealed cold end in response to partially withdrawing the regenerator piston from the cold well tube, said regenerator piston comprising a hollow regenerator tube filled with a regenerator matrix for exchanging thermal energy with the refrigeration gas as the gas flows through hollow portion of the regenerator piston; and,    wherein at least a portion of the regenerator matrix comprises a plurality of individual screen elements sintered into physical contact to form a composite element.    
     
     
         34 . The refrigeration unit of  claim 33  wherein the composite element comprises less than 25 substantially identical individual screen elements comprising stainless steel wire having a round cross-section with a diameter in the range of 0.0005-0.002 inches and interwoven with a mesh in the range of 200-400 wire strands per inch.  
     
     
         35 . The refrigeration unit of  claim 33  wherein composite element types having different flow resistance characteristics are formed using different individual screen elements and further wherein the flow resistance of a portion of the plurality of composite elements is selected in accordance with a local fluid viscosity within the regenerator tube.