High-frequency, low-temperature regenerative heat exchanger

Abstract

A high-frequency, low-temperature regenerator ( 12 ). The regenerator ( 12 ) includes a substrate ( 50 ) having rare earth material ( 52 ) disposed thereon. In a specific embodiment, the substrate ( 50 ) has channels or pores ( 54 ) therethrough or therein to facilitate gas flow through the regenerator ( 12 ). The substrate ( 50 ) is constructed from a material, such as polyimide, polyester, or stainless steel, which is sufficient to define the geometry of the regenerator ( 12 ). The rare earth material ( 52 ) is selected and deposited on the substrate ( 50 ) in a layer ( 52 ) having thermal penetration depth that is greater than the thickness of the layer ( 52 ). The thermal penetration depth is sufficiently high to enable all of the rare earth material ( 52 ) to contribute to thermal regeneration at an operating frequency of 30 Hz. In the illustrative embodiment, the thickness of the substrate ( 50 ) is less than or equal to approximately 0.001 inches. The layer of rare earth material ( 52 ) is approximately 0.0002 inches thick. The substrate ( 44, 50 ) includes a stack of plated substrates ( 44 ) that are stacked so that spaces ( 54 ) exist between the plated substrates ( 44 ), which result in a porosity of approximately 15 percent. Dimples, pleats, or other mechanisms in the plated substrates ( 44 ) preserve the spaces ( 54 ) between the plated substrates ( 44 ). In the specific embodiment, the spaces ( 54 ) are approximately 0.00025 inches wide, and the working gas is helium.

What is claimed is:  
     
         1 . A regenerator comprising: 
 a substrate and    rare earth material disposed on a surface of said substrate.    
     
     
         2 . The regenerator of  claim 1  wherein said substrate has channels or pores therethrough or therein.  
     
     
         3 . The regenerator of  claim 2  wherein said substrate is constructed from a material sufficient to define the geometry of said regenerator.  
     
     
         4 . The regenerator of  claim 3  wherein said substrate is constructed from a flexible material that is thermally inert below temperatures of 15 K, whereby the volumetric heat capacity of said flexible material is very low below 15 K.  
     
     
         5 . The regenerator of  claim 3  wherein said substrate includes polyimide or polyester.  
     
     
         6 . The regenerator of  claim 3  wherein said rare earth material is chosen and deposited on said substrate in a layer so that the thermal penetration depth of said layer of rare earth material is greater than the thickness of said layer.  
     
     
         7 . The regenerator of  claim 6  wherein said thermal penetration depth is sufficiently high so that approximately all of said rare earth material contributes to thermal regeneration at an operating frequency of 30 Hz.  
     
     
         8 . The regenerator of  claim 7  wherein said thermal penetration depth is approximately two orders of magnitude greater than the thickness of said layer of rare earth material.  
     
     
         9 . The regenerator of  claim 7  wherein said rare earth material includes an element, compound, or alloy containing one or more lanthanide elements.  
     
     
         10 . The regenerator of  claim 9  wherein said rare earth material is erbium.  
     
     
         11 . The regenerator of  claim 9  wherein the thickness of said substrate is less than or equal to approximately 0.001 inches.  
     
     
         12 . The regenerator of  claim 11  wherein said layer of rare earth material that is approximately greater than or equal to 0.0002 inches thick.  
     
     
         13 . The regenerator of  claim 13  wherein each of said plated substrate includes plural substrates having perforations therethrough, said substrates being stacked perpendicular to a flow of working gas in said regenerator.  
     
     
         14 . The regenerator of  claim 3  wherein said substrate includes a stack of plated substrates that are stacked so that spaces corresponding to said channels or pores occur between said plated substrates.  
     
     
         15 . The regenerator of  claim 14  wherein said stack of plated substrates is a matrix having a matrix porosity of approximately 15 percent.  
     
     
         16 . The regenerator of  claim 14  further including means for preserving said spaces between said plated substrates.  
     
     
         17 . The regenerator of  claim 16  wherein said means for preserving spaces includes dimples in said plated substrates.  
     
     
         18 . The regenerator of  claim 17  wherein said spaces are approximately 0.00025 inches wide.  
     
     
         19 . The regenerator of  claim 18  wherein said regenerator is adapted for use with helium gas.  
     
     
         20 . The regenerator of  claim 14  wherein said plated substrates are screens or other woven wire meshes, said screens or other woven wire meshes plated with sufficient rare earth material to fill spaces in said screens or other woven wire meshes  
     
     
         21 . A method for constructing an efficient regenerator comprising: 
 obtaining sheets of substrate material;    dimpling or pleating said substrate material;    employing deposition techniques to deposit a layer of rare earth materials on said sheets of substrate to yield plated sheets; and    stacking said plated sheets in a shape desired for said regenerator.    
     
     
         22 . The method of  claim 21  wherein said step of employing vapor deposition includes using highly-energetic plasma deposition techniques.  
     
     
         23 . The method of  claim 21  wherein said substrate includes a polyimide sheet, a polyester sheet, and/or a woven wire mesh.  
     
     
         24 . The method of  claim 21  wherein said plated sheets are stacked parallel to the direction of flow of cryogen through said regenerator.  
     
     
         25 . A method for constructing an efficient regenerator comprising the steps of: 
 obtaining sheets of substrate material of predetermined dimensions, said sheets having a structure such that when said sheets are stacked, uniform channels exist between said sheets;    depositing a high specific heat material of a predetermined thickness on said sheets to yield plated sheets in response thereto, said high specific heat material not thick enough to completely fill said uniform channels;    stacking said sheets to yield a stack of plated sheets; and    placing said stack of plated sheets into a pressure vessel or regenerator sleeve.    
     
     
         26 . The method of  claim 25  wherein said sheets are polyimide sheets.  
     
     
         27 . The method of  claim 25  wherein said sheets are screens.  
     
     
         28 . The method of  claim 25  wherein said substrate material is polyimide or stainless steel.  
     
     
         29 . The method of  claim 28  wherein in said step of depositing, enough high specific heat material is deposited on said screens to fill in spaces in said screens to yield solid plated sheets.  
     
     
         30 . The method of  claim 28  wherein in said step of depositing, sufficient high specific heat material is deposited on said screens to partially in spaces in said screens to yield plated sheets having perforations therethrough.  
     
     
         31 . The regenerator of  claim 25  further including the step of cutting said stack of plated sheets to accommodate said pressure vessel.  
     
     
         32 . The method of  claim 25  wherein said step of depositing includes using plasma deposition techniques.  
     
     
         33 . The method of  claim 25  wherein said channels are uniform channels.  
     
     
         34 . The method of  claim 25  wherein said thickness of said high specific heat material is sufficient to accommodate a desired operational frequency of said regenerator.  
     
     
         35 . The method of  claim 34  wherein said high specific heat material has a sufficiently high specific heat to enable high frequency operation of an accompanying cryocooler beyond 30 Hz at cryogenic temperatures below 35 K.  
     
     
         36 . The method of  claim 35  wherein said high specific heat material includes one or more rare earth materials.  
     
     
         37 . A pulse tube cryocooler comprising: 
 first means for generating a pressure wave through a cryogenic fluid;    second means coupled to said first means for implementing regenerative heat exchange with said cryogenic fluid, said second means including a heat exchange structure having rare earth materials disposed thereon or therein; and    third means coupled to said second means for harnessing a temperature differential resulting from said pressure wave and facilitated by said second means.    
     
     
         38 . The pulse tube cryocooler of  claim 37  wherein said first means includes a compressor or pressure wave generator.  
     
     
         39 . The pulse tube cryocooler of  claim 38  wherein said second means includes a first stage regenerator in gaseous communication with said compressor.  
     
     
         40 . The pulse tube cryocooler of  claim 39  wherein a first warm-end heat exchanger is connected between said first stage regenerator and said compressor, said first heat exchanger positioned at a warm end of said cryocooler.  
     
     
         41 . The pulse tube cryocooler of  claim 40  wherein said first stage regenerator is coupled to a cold end of a first stage pulse tube at a cool portion of said cryocooler and is coupled to a second stage regenerator at said cool portion.  
     
     
         42 . The pulse tube cryocooler of  claim 41  wherein a cool-end heat exchanger is connected between said first stage pulse tube and said first stage regenerator at said cool portion of said cryocooler.  
     
     
         43 . The pulse tube cryocooler of  claim 42  wherein said first stage pulse tube is coupled to a surge volume at said warm end of said cryocooler, and wherein a second warm-end heat exchanger is positioned between said second stage pulse tube and said surge volume at said warm end of said cryocooler.  
     
     
         44 . The pulse tube cryocooler of  claim 43  wherein said second stage regenerator includes sheets of rare earth material stacked so that predetermined spacing exists between said sheets.  
     
     
         45 . The pulse tube cryocooler of  claim 44  wherein said rare earth material and said predetermined spacing are sufficient to enable high-frequency operation of said cryocooler at or beyond 30 Hz and cooling to below 35 K.  
     
     
         46 . The pulse tube cryocooler of  claim 45  wherein said second stage regenerator is coupled to a second stage pulse tube at a cold end of said cryocooler.  
     
     
         47 . The regenerator of  claim 46  further including a cold end heat exchanger connected between said second stage regenerator and said second stage pulse tube at said cold end of said cryocooler, said cold end producing temperatures below 10 K.  
     
     
         48 . The pulse tube cryocooler of  claim 47  wherein said second stage pulse tube is coupled to said surge reservoir at said warm end of said cryocooler, and wherein a third warm-end heat exchanger is connected between said second stage pulse tube and said surge volume.