Large Capacity, Multi-Cylinder Cryocooler for High Temperature Superconductor (HTS) Applications

High Temperature Superconductor (HTS) technologies, currently under development by DOE and its partners, offer high efficiency power generation and transmission. Cryocoolers, a critical enabler for HTS products, are underdeveloped for this application, being too small, unreliable, costly, and inefficient. The lack of a more suitable cryocooler could impede the commercialization of HTS products. This project will develop a multi-cylinder, free-piston Stirling cryocooler expressly to suit the needs of HTS products. The approach will build on previously developed technology for Stirling cycle engines and cryocoolers, in which the size and efficiency advantages of kinematic machines were combined with the high-reliability and low-maintenance characteristics of free-piston machines. In Phase I, detailed analytical modelng will be performed, and extensive evaluations (of piston, bearing, seal, and linear motor configurations) will be conducted. A detailed conceptual design for a complete multi-cylinder, free-piston, Stirling cryocooler system, which can be packaged as a turn-key solution for HTS integrators, also will be developed. The design will be targeted to provide 300 W of heat lift at 65K, with under 3.5 kW electrical input. In Phase II, a full-scale prototype will be demonstrated. Commercial Applications and Other Benefits as described by the awardee: The multi-cylinder, free-piston Stirling cryocooler should be a differentiated product for HTS integrators due to its compact size, maintenance-free reliability, and high efficiency. Additional applications include small-scale gas liquefaction, large zero-boil-off systems, and military uses.