The ultimate temperature and cooling power of both the superfluid Stirling refrigerator (SSR) and the ~3He-~4He dilution refrigerator depend largely on the efficiency of their counterflow heat exchangers. This efficiency is limited mainly by the Kapitza boundary resistance at low temperatures. The usual method of overcoming this problem has been to increase the surface area of the heat exchangers. A different approach is to make the heat exchangers out of materials that have low Kapitza boundary resistance such as plastics. This article describes the design, construction, and performance of plastic heat exchangers that have been successfully used in our SSRs. Specifically, the paper includes a detailed description of our heat exchangers, step-by-step instructions on the construction of a plastic heat exchanger, and simple calculations of the performance of the heat exchanger under typical SSR operating conditions.
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