A miniature reverse-Brayton cycle cryocooler and its key components: High effectiveness heat recuperator and miniature centrifugal compressor

Miniature reverse turbo Brayton cycle (RTBC) cryocooler can provide reliable low power (20W) cooling ability at liquid nitrogen temperature with a compact size and high thermal efficiency. Its applications include sensors, gas liquefaction, and superconductor cooling.; There are some key enabling technologies for a high efficiency RTBC cryocooler, including high effectiveness heat recuperator, miniature compressor/turbo-expander, high efficiency motor, and oil-free non-contact bearing. In this dissertation, an overall system design is proposed, with research on a micro-channel heat recuperator and a miniature centrifugal neon compressor. The system design demonstrates that a 99% effectiveness heat recuperator is essential to a high COP cryocooler. A micro-channel heat recuperator is proposed to achieve the performance. A design of single material and double material lamination build-up structure is modeled and numerically simulated. A design strategy is found based on the numerical research.; The low cooling power and low mass flow rate of the miniature cryocooler requires a miniature centrifugal neon compressor, which spins at 450,000 RPM. A scaled-up model is designed to test the compressor performance based on the turbomachinery similarity principle. This centrifugal compressor features a 150,000 RPM impeller and an axial diffuser. Radial inlet guide vane (IGV) is employed to produce a pre-swirl to improve efficiency and reduce size. Because of the low mass flow rate, the impeller uses low-height axial blades and 3-D twisted blades. A 3-D CFD simulation of the compressor is performed using a commercial CFD code FLUENTRTM1. An open-air compressor testing is performed to test the pressure rise performance of the compressor2. Testing and simulation results indicated that the radial IGV and axial-radial mixed impeller perform well, while axial diffuser has poor performance due to the large tangential velocity. The results show that the basic compressor layout design is successful for low mass flow rate, high-speed compressor. Because of the high rotational speed, future work on a special diffuser is needed to improve the compressor performance.; 13-D CFD simulation work is done by Xiaoyi Li. 2Testing work is done by Kevin Finney and Brian Gulliver.