| Abstract: | Several processes are candidates for use in a microminiature cryocooler. They are an adiabatic demagnetization cycle, a surface heat pumping cycle, and a cycle based on Joule-Thomson expansion. The later is chosen for further investigation because it is the most feasible and useful process. The heat exchanger that is necessary for the Joule-Thomson expansion cycle to operate is analyzed in detail using fundamentals of fluid flow and heat transfer. A steady-state analysis indicates that the gas flow is laminar and that the pressure drop along the length of the heat exchanger is negligible. A transient analysis, using a computer program, indicates that the temperature of the substrate must be taken into account. Also, the mass flow rate and the length of the heat exchanger have dramatic effects on the operation of the heat exchanger. The transient analysis can serve as the basis for a more accurate model of the transient and steady-state conditions of the heat exchanger, which will allow the design of an actual microminiature cryocooler. |
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