Drawn-polymer microchannel heat exchangers with application to recuperative cryocoolers

Abstract

Polymer microchannel heat exchangers for use in cryocooler applications have been developed. These heat exchangers are manufactured using a thermal drawing process where a bulk polymer preform is heated and stretched. The thermal drawing process results in microchannels with a characteristic dimension of 50–100 µm with an overall length of many meters. The drawn heat exchangers are lightweight, flexible, and have a large surface-area-to-volume ratio. Proof of concept design and testing of a nitrogen and hydrogen Joule-Thomson cryocooler utilizing a Polyetherimide (PEI) drawn-polymer recuperative heat exchanger is presented. These heat exchangers operated leak free at cryogenic temperatures under pressures up to 11 MPa. With a 95 % effective drawn polymer recuperator, the hydrogen cryocooler reached a saturation temperature of 20.5 K and demonstrated a cooling power of 28 mW. Mass flow maldistribution has been identified as a barrier to higher effectiveness performance. Suggestions for improvements and future development are discussed.