High Effectiveness Heat Exchanger for Cryogenic Refrigerators

Cryocoolers are small-scale cryogenic refrigerators with refrigeration capacities ranging from a few milli-Watts to several 10's of Watts. The two main classes of cryocoolers are regenerative and recuperative, with the distinction being made by the majorheat exchanger type required. Within the recuperative cryocoolers, the two major types are Joule-Thomson (JT) and Brayton. Both types are based on a DC flow of the working fluid from a high pressure to a lower pressure, where the low pressure stream isused to precool the high pressure stream using a recuperative heat exchanger. The JT cycle is based on an isenthalpic expansion while the Brayton cycle is an isentropic expansion.Important for space applied cryogenic coolers is their ability to perform over long periods of time. This dictates that the cooler be essentially hermetically sealed with extremely small if any leaks. These leak rates should be on the order of 1x10-9cc/min or less. This program will develop the technology to fabricate highly efficient cryocoolers which are structurally sound and leak free. The first Phase of the program will focus on demonstrating the hermetic sealing of the HXs while developing newcryogenic HX designs for further investigation during a Phase II effort. This program will develop highly efficient cryogenic heat exchangers with lower packaging volumes, longer lifetimes, and lower weights. These heat exchangers would benefit both military and commercial cryogenic systems.