Cryocooler Heat Exchangers Using Layered Structures with Anisotropic Conductance

Anisotropic Conductance HX Concept

DC cryogenic flow systems require very high effectiveness heat exchangers to reduce input power, while also requiring the heat exchangers to have low size, weight, power, and cost (SWaP-C). Cryocoolers for applications well below 20 K, such as superconducting digital electronics and space-based cosmic background detectors, demand very high efficiencies. In cryogenic heat exchangers, heat transfer is ideally accomplished through the transverse conduction of heat through the heat exchanger walls from the hot side to the cold side. However, cryogenic heat exchangers are inherently susceptible to performance penalties associated with parasitic heat conduction within the plane of the heat exchanger walls.

In an attempt to leverage the high effectiveness of microplate heat exchangers while minimizing parasitic losses, Micro Cooling Concepts (MC2), in cooperation with Ceramatec and Ball Aerospace, developed a concept that utilizes laminates with highly anisotropic thermal conductance to fabricate a cryogenic microplate heat exchanger with operating temperatures in the 4-16 K range. This work was funded by the US Navy under the Small Business Innovation Research (SBIR) program.

The cryogenic heat exchanger developed in the Navy Phase I SBIR effort utilized a composite assembly of lightweight ceramic (Pyrex) substrate with metal (silicon) vias. This approach had the advantages of increased heat exchanger effectiveness, reduced in-plane parasitic conduction losses, and a design and fabrication methodology applicable over a wide array of applications and temperature ranges.

The improved thermal performance, combined with the lower density of Pyrex and silicon, mean that heat exchanger weight reductions of 4X – 8X can be achieved while maintaining extremely low core pressure losses. The heat exchange density of the MC2/Ceramatec cryogenic heat exchanger concept exceeds that of several other designs in the literature (Zhu and Creare) by up to 5X.