LIQUID HELIUM COMPOSITE REGENERATOR MATERIAL

IT IS PROPOSED TO PERFORM HEAT TRANSFER TESTS ON A NOVEL CRYOGENIC COMPOSITE MATERIAL DESIGNED FOR APPLICATION TO GAPREGENERATORS IN CRYOCOOLERS OPERATING NEAR 4.2 K. THE MATERIAL TO BE CONSTRUCTED FOR TESTING IS A COMPOSITE OF LIQUID HELIUM SELF-LOADED INTO A METALLIC EXTENDED SURFACE STRUCTURE WHOSE DISPERSION FORM IS DETERMINED BY THE THERMALFLUX AND FREQUENCY REQUIREMENTS OF SMALL CRYOCOOLERS. IT ISDESIGNED TO HAVE BOTH HIGH EFFECTIVE HEAT CAPACITY IN THE 3 K TO 6 K RANGE - DUE TO THE HELIUM VAPORIZATION AND RECONDENSATION - AND HIGH UNIAXIAL THERMAL CONDUCTIVITY DUE TO THE METALLIC COMPONENT. DURING THE REGENERATION CYCLE A VAPOR BUBBLE GROWS AND COLLAPSES COMPLETELY WITHIN THE STRUCTURE WHICH IS APPROXIMATELY 1 MM THICK. HEAT-TRANSFER EXPERIMENTS ARE PROPOSED TO MEASURE THE THERMAL PENETRATION INTO THE COMPOSITE MATERIAL AND TO TEST THE VALIDITY OF A MODEL WHICH HAS BEEN SHOWN TO APPLY TO METAL/PHASE-CHANGE-MATERIAL COMPOSITES NEAR ROOM TEMPERATURE. PHASE I TASKS WILL INCLUDE: (1) ANALYSIS AND MODELING OF THECOMPOSITE MATERIAL, (2) FABRICATION OF TEST SAMPLES, AND (3) THERMAL PENETRATION TESTS IN A HELIUM CRYOSTAT.