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A test sequence with two gas-loaded heat pipes of different geometry with external noncondensable gas reservoirs was performed in order to detect, analyze and classify conjugated and detached fluctuations of evaporator temperature, operating temperature and the position of the vapor/gas front after start-up. The fluctuations become noticeable at operation with more than half of the condenser open and gain force the more the front approaches the condenser end. It was found that amplitude, frequency and polarity of the fluctuations also depend on the magnitude of a heat load step change, the gas charge and the working fluid. A method is mentioned of how to dampen the fluctuations.

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.

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.