WET TURBOEXPANDER FOR CRYOCOOLERS OF SPACEBORNE SURVEILLANCE SENSORS

THE NEED FOR INCREASING THE SENSITIVITY OF SPACE-BORNE SENSORS WILL REQUIRE DEVELOPMENT OF LONG-LIFE, HIGHLY EFFICIENT HELIUM LIQUIFIERS. CONVENTIONAL HELIUM LIQUIFIERS EMPLOY A JOULE-THOMSON EXPANSION VALVE TO EXPAND THE HELIUM AT TEMPERATURES BELOW ABOUT 10 DEG K. IT HAS BEEN SHOWN THAT GAINS OF UP TO 30% IN OVERALL CYCLE EFFICIENCY CAN BE OBTAINED IF THE JOULE-THOMSON VALVE IS REPLACED BY AN EXPANSION ENGINE OR AN EXPANSION TURBINE. THIS EFFICIENCY GAIN TRANSLATES INTO A MAJOR REDUCTION IN COMPRESSOR POWER AND RADIATOR WEIGHT. BECAUSE OF RELIABILITY AND VIBRATION CONSIDERATIONS IT WOULD BE HIGHLY DESIREABLE TO USE MINIATURE "WET" TURBOEXPANDERS INSTEAD OF RECIPROCATING EXPANSION ENGINES. THIS PROPOSAL DESCRIBED PHASE I OF A PROJECT TO DEVELOP AND TEST A "WET" CRYOGENIC TURBOEXPANDER OPERATING IN GAS BEARINGS. THE PRINCIPAL FEATURES OF THE PROPOSED DESIGNS ARE SUPERIOR RELIABILITY AND HIGH EFFICIENCY. PHASE I OF THE PROGRAM WILL CONSIST OF ESTABLISHING SPECIFICATIONS FOR THE WET TURBOEXPANDERS AND PERFORMING PRELIMINARY FLUID DYNAMIC AND MECHANICAL DESIGNS IN ORDER TO DETERMINE THE TECHNICAL FEASIBILITY OF EMPLOYING A GAS BEARING TURBOEXPANDER AS A "WET" EXPANDER.