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A combined two-stage Stirling and Joule-Thomson cycle refrigerator has been developed for advanced celestial observation missions. The specified cooling capacity is 40 mW at the final 4 K stage and 200 mW at the second 20 K stage. The precooler compressor power amounts to about 100 W, most of which is thermally dissipated. This study has therefore been made to propose a most suitable method of the waste heat rejection. Proposed are a loop heat pipe (LHP) and a mechanical pump loop (MPL). Computational sizing procedures of the two are presented with mass estimate models. Also presented is an empirically obtained relation between the cooling efficiency and the ambient temperature. This algebraic expression is then used to find the required electrical power for the 20 K stage cooling. Numerical results of the LHP/MPL design calculations are displayed in the figures as a function of the ambient temperature ranging from 150 K to 310 K.

Investigated in this study are thermodynamic and transport properties of FC-72, -84, -77, -75, -40, -43, -70; FX-3250, -3300; PF-5050, -5060, -5070, -5080; and DF134a. All the fourteen are non-CFCs(non-chlorofluorocarbons), substitutable for commonly used coolants like Freons and not destroying ozon layers. The collected property data has mathematically been handled to reduce to proposed empirical formulas. Finally obtained are temperature-dependent algebraic expressions for the saturated vapor pressure, the saturated liquid density, the specific heat at constant pressure of liquid, the thermal conductivity of liquid, the kinematic viscosity of liquid, the surface tension of liquid, the latent heat of vaporization, the specific enthalpy of liquid, and that of vapor. All the coefficient values are listed in the tables along with applicable temperature ranges and prediction errors.