Hydrodynamic and Heat Transfer Characteristics of Miniature Stirling Cryocooler Regenerators — A Review

Miniature Stirling coolers are preferred to provide cryogenic cooling for infra-red (IR) sensors used for communication, military, and space applications. They provide 0.25–1.5[Formula: see text]W of cooling effect at 60–80[Formula: see text]K. Miniature Stirling coolers used for space applications are time tested, reliable, and have the maximum COP compared to other types of coolers. Helium is used as the working fluid because of its low boiling point, high thermal conductivity, high ratio of specific heat, and inert gas properties. A regenerator is the primary heat exchanger in the system, which periodically exchanges heat with the cold and hot gases passing through the regenerator material. The effectiveness of the regenerator is the most important parameter influencing the cooling effect produced by the system. For the optimum performance of the cryocooler, the regenerator should have maximum heat transfer area, minimum void volume, minimum pressure drop, large heat capacity ratio between the matrix material and gas, and minimum longitudinal conduction. Since some of these requirements are conflicting in nature, the design of the regenerator becomes a challenge in the overall design of the cooler. A state-of-the-art review of regenerator materials, designs, and operation is presented in this study. The different sources of regenerator losses and the issues related to regenerator design and optimization are discussed in detail. Results of various experimental and numerical investigations conducted on a Stirling regenerator are discussed and the recent developments in material selection and design are highlighted.