Counter flow heat exchanger for a miniature joule-thomson cryocooler

Abstract

A counter flow heat exchanger comprising a body formed of stacked, fused, ceramic sheets. The sheets comprising: a bottom sheet, a second sheet, a third sheet, a fourth sheet and a top sheet. The sheets have punched holes such that when the sheets are aligned there is an inlet hole spanning from the top sheet to the fourth sheet, an outlet hole spanning from the top sheet to the second sheet, and an inflow hole spanning from the fourth sheet to the second sheet. Within the second sheet, a low pressure flow channel connects the outlet hole with the inflow hole. Within the fourth sheet, the inlet hole flows into a high pressure flow channel which flows into a narrow flow path which then empties into the inflow hole. The high pressure flow channel is aligned with the low pressure flow channel to allow for heat exchange.

1 . A counter flow heat exchanger for a miniature Joule-Thompson cryocooler, the heat exchanger comprising a body formed of a bottom sheet, a second sheet, a third sheet, a fourth sheet and a top sheet, all the sheets being made of low temperature cofired ceramics and stacked one above another and fused together, the second sheet comprising a low pressure flow channel along the length thereof terminating in an inflow hole at one end thereof and in an outlet hole at the other end thereof, the third sheet comprising an inflow hole at one end thereof corresponding to and matching with the inflow hole in the second sheet and an outlet hole at the other end thereof corresponding to and matching with the outlet hole in the second sheet, the fourth sheet comprising a high pressure flow channel along the length thereof, an inflow hole at one end thereof corresponding to and matching with the inflow hole in the third sheet and spaced apart from corresponding one end of the high pressure flow channel, an inlet hole terminating at the inception of the high pressure flow channel and an outlet hole corresponding to and matching with the outlet hole in the third sheet and spaced apart from the inlet hole in the fourth sheet, the top sheet comprising an inlet hole corresponding to and matching with the inlet hole in the fourth sheet and an outlet hole corresponding to and matching with the outlet hole in the fourth sheet and a narrow flow path between the fourth sheet and top sheet communicating with said one end of the high pressure flow channel and the inflow hole in the fourth sheet. 
     
     
         2 . The heat exchanger as claimed in  claim 1 , wherein the sheets are ‘green tape 951’. 
     
     
         3 . A method of manufacturing a counter flow heat exchanger for a miniature Joule-Thompson cryocooler, the heat exchanger comprising a body formed of a bottom sheet, a second sheet, a third sheet, a fourth sheet and a top sheet, all the sheets being made of low temperature cofired ceramics and stacked one above another and fused together, the method comprising punching a low pressure flow channel along the length of the second sheet with an inflow hole at one end thereof and an outlet hole at the other end thereof, punching an inflow hole and an outlet hole in the third sheet corresponding to and matching with the inflow hole and the outlet hole in the second sheet respectively, punching a high pressure flow channel along the length of the fourth sheet, punching an inflow hole at one end of the fourth sheet corresponding to and matching with the inflow hole in the third sheet and in spaced apart relationship with one end of the high pressure flow channel, punching an inlet hole at the other end of the high pressure flow channel and punching an outlet hole in the fourth sheet corresponding to and matching with the outlet hole in the third sheet and spaced apart from the inlet hole in the fourth sheet, punching an inlet hole and an outlet hole in the top sheet corresponding to and matching with the inlet hole and outlet hole in the fourth sheet respectively, filling the low pressure flow channel, high pressure flow channel, inflow holes, inlet holes and outlet holes with a sacrificial material and forming thin layer of a sacrificial material between the inflow hole and corresponding said one end of the high pressure flow channel in the fourth sheet, stacking the sheets one above another, cutting the sheets to size, compacting the sheets and fusing the sheets together by sintering at 30 to 900° C. with simultaneous formation of a narrow flow path in the fourth sheet and top sheet between the inflow hole in the fourth sheet and corresponding said one end of the high pressure flow channel in the fourth sheet. 
     
     
         4 . The method as claimed in  claim 3 , wherein the sheets are cut to size in a shearing machine. 
     
     
         5 . The method as claimed in  claim 3 , wherein the sheets are compacted by isostatic compression. 
     
     
         6 . The method as claimed in  claim 3 , wherein the sacrificial material comprises carbon paste. 
     
     
         7 . The method as claimed in  claim 3 , wherein the sheets are ‘green tape 951’. 
     
     
         8 . A miniature Joule-Thompson cryocooler comprising a counter flow heat exchanger as claimed in  claim 1 . 
     
     
         9 . The cryocooler as claimed in  claim 8 , which is a closed cycle miniature Joule-Thompson cryocooler. 
     
     
         10 . The cryocooler as claimed in  claim 8 , which is an open cycle miniature Joule-Thompson cryocooler. 
     
     
         11 . The method as claimed in  claim 4 , wherein the sheets are compacted by isostatic compression. 
     
     
         12 . The method as claimed in  claim 4 , wherein the sacrificial material comprises carbon paste. 
     
     
         13 . The method as claimed in  claim 5 , wherein the sacrificial material comprises carbon paste. 
     
     
         14 . The method as claimed in  claim 4 , wherein the sheets are ‘green tape 951’. 
     
     
         15 . The method as claimed in  claim 5 , wherein the sheets are ‘green tape 951’. 
     
     
         16 . The method as claimed in  claim 6 , wherein the sheets are ‘green tape 951’. 
     
     
         17 . A miniature Joule-Thompson cryocooler comprising a counter flow heat exchanger as claimed in  claim 2 .