Size limits for Stirling cycle refrigerators and cryocoolers

This paper explores the lower size limit placed on regenerative coolers by thermodynamics and heat transfer. Information derived in this paper has direct relevance to the development of small-scale refrigerators and cryocoolers that are based on standard gas cycles employing regeneration. A model is developed for the Stirling cycle incorporating a regenerator effectiveness and a regenerator axial conduction term, both of which are dependent on the length scale of the device. The coefficient of performance for the cooler is set to zero in order to explore the no-heat load condition. Results from this study suggest that a cryocooler fabricated from a low thermal conductivity material can be made with a length scale under one centimeter. Stainless steel or other similar material would be suitable for the design.