High Effectiveness Heat Exchanger for Cryogenic Refrigerators

We propose an innovative high performance cryogenic heat exchanger manufactured of titanium by photo-etching and diffusion bonding. This is a parallel plate design of thin laminated titanium foils. Titanium is used because of it low thermal conductivity which allows more compact heat exchangers with lower parasitic heat loss. Photo-etched patterns in the foils create the flow passages for the hot and cold flows with solid barrier foils separating the streams. A difficult problem with high performance heat exchangers is balancing the mass flow rate between multiple flow passages required for all but the smallest levels of cooling; this problem can degrade exchanger ineffectiveness by factors of more then 3. Our manufacturing technique allows us to include flow balancing features within the flow passages to automatically balance the flow rates. Recuperative cycle cryocoolers, such as reverse Brayton, Joule-Thomson or their hybrids, require high effectiveness heat exchangers to reach cryogenic temperatures. Higher effectiveness leads directly to improved system efficiency or allows lower temperatures to be reached. Improved heat exchanger performance will directly lead to lower input power cryocoolers particularly for the 4-10 K temperature range where cryocooler system efficiencies are very low.