High-Efficiency Joule-Thomson Cryocoolers Incorporating an Ejector

Joule-Thomson (JT) cryocoolers have no moving parts and therefore are vibration-free. These are attractive for cooling small optical detectors in space for earth observation missions. JT cryocoolers produce cooling by expanding high-pressure gas through a JT restriction. This, however, is a highly irreversible entropy-generating process. If work could be extracted during the expansion process, the efficiency of the cooling cycle would be significantly improved. In this paper, a JT cooling cycle with an additional ejector is proposed. The high-pressure gas, as the primary fluid of the ejector, is used to compress the low-pressure gas leaving the evaporator, thus reducing the coldend temperature or/and the input power of the compressor. Compared to a basic JT cycle, the improvement in the COP of the cycle with an ideal ejector is analyzed. The effects of frictional and mixing losses on the real performance of an ejector are estimated through numerical simulations, which aids the understanding of ejector theory and provides information for optimizing the ejector under certain operating conditions.