Hampson’s type cryocoolers with distributed Joule–Thomson effect for mixed refrigerants closed cycle

•It is an experimental study of mixed coolants Joule–Thomson (JT) cryocooling, of a Hampson’s type heat exchanger.•A uniqueness of these cryocoolers: the capillary tubes of the heat exchanger serve also as the throttling devices.•The JT effect is distributed along the high pressure channel of the heat exchanger is also the sole throttling device.•Previous studies used long Linde’s tube-in-tube type heat exchangers and a concentrated throttles at the cold end.•Four configurations tested; each with two mixtures, and each with two compressors of different displacements.

Most previous studies on Joule–Thomson cryocoolers of mixed refrigerants in a closed cycle focus on the Linde kind recuperator. The present study focuses on four constructions of Hampson’s kind miniature Joule–Thomson cryocoolers based on finned capillary tubes. The frictional pressure drop along the tubes plays the role of distributed Joule–Thomson expansion so that an additional orifice or any throttle at the cold end is eliminated. The high pressure tube is a throttle and a channel of recuperation at the same time. These coolers are tested within two closed cycle systems of different compressors and different compositions of mixed coolants. All tests were driven by the same level of discharge pressure (2.9 MPa) while the associated suction pressures and the associated reached temperatures are dependent on each particular cryocooler and on the closed cycle system. The mixture of higher specific cooling capacity cannot reach temperatures below 80 K when driven by the smaller compressor. The other mixture of lower specific cooling capacity driven by the larger compressor reaches lower temperatures. The examined parameters are the cooldown period and the reachable temperatures by each cryocooler.