Miniaturization of Components for Low Capacity Reverse Brayton Cryocoolers
Developments are being carried out to extend the practical use of turbomachine-based reverse Brayton cycle cryocooler technology to lower capacity applications. These developments focus primarily on cooling loads in the range of 0.5 W to 2 W at temperatures from about 40 K to 70 K in a single stage cycle with neon. With some modification, the technology can also be applied to multi-stage helium cycles for cooling loads as low as 100 mW at temperatures as low as 5 K. The goal is to produce systems incorporating vibration-free turbomachines with performance characteristics comparable to those that have been demonstrated for larger cycles — i.e., the 5 W 65 K single stage reverse Brayton cycle cryocooler. These efforts, if successful, should result in turbomachine based cryocoolers with input powers of about 100 W or less.
The critical components for a low capacity reverse Brayton cycle cryocooler include the expansion turbine and the turbo-compressor. This paper describes a novel turbine design that is currently under development and discusses developments associated with a high-performance miniature compressor. The expansion turbine drives an AC generator at cryogenic temperatures to extract shaft work with minimal parasitic heat leak to the cold end. Options for the compressor include magnetic bearings to reduce drag losses, and a new motor design using basic features of the expansion turbine’s AC generator.
KeywordsCryogenic Temperature Journal Bearing Magnetic Bearing Cooling Load Small Business Innovation Research
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