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Circumferentially grooved heat pipes have been studied as capillary pumps to be used in two-phase heat transfer loops. Experimental results up to 1.7 W/cm2 were found for Freon 11 as the working fluid. To improve the knowledge of the performance of these capillary pumps, some design parameters are now studied. The heat transport capability and the capillary pumping pressure are analyzed for different values of the groove width, groove opening angle and inner radius of the capillary pump. Theoretical results indicates somewhat better performance for capillary pumps with rectangular grooves than with trapezoidal grooves. Fine groove widths and small values of inner radius are also desirable.

This paper is related to the theoretical investigation of a space radiator with integrated multiple variable conductance heat pipes. Such a radiator is desirable to keep temperature variations of sensitive amplifiers in communication satellites within a few degrees, independent on their heat dissipation. For the purpose of dynamic studies of this kind of cooling system three aluminum/acetone heat pipes controlled by argon gas are thermally coupled in the evaporator and condenser area. A finite difference analysis is applied to study the system's response in case of failure of one of the heat pipes. The effects of change of spacing between the heat pipes and slitting of the radiator are mentioned.

Circumferentially grooved heat pipe evaporators have been proposed as an alternative solution to obtain high capillary pressure and large liquid cross sections to reduce the viscous pressure losses in the liquid flow. Such evaporators have been employed in a capillary pumped two-phase loop and first results have been reported for loop operation in the mechanical pump assisted mode. Additional tests have been carried out in order to determine the performance of the loop also in the capillary pumped mode. Using freon 11 as the working fluid, heat fluxes up to 12 kW/m2 have been measured. For ammonia, the corresponding value is estimated to be about 78 kW/m2. A theoretical analysis is also presented in order to understand differing performances of the individual capillary pumps.

The dynamic behavior of a space radiator that is driven by gas-loaded heat pipes with external reservoirs is dependent on the interactions between the neighboring heat pipes and on those between each pipe and its respective reservoir. To get an insight into these phenomena a thermal vacuum test program with a 3-GLHP radiator was performed with varying gas masses and heat loads and also in the configuration where the radiating sheets were segmented. The heat pipes are axially grooved, with acetone as working fluid and argon as control gas. The test results are contrasted with results from a numerical simulation that is based on a flat front type vapor space model. Special interest is directed to operation near and at overload and to the thermal response to the failure of one outside heat pipe.