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This contribution presents an approach for a mathematical model which is based on a detailed experimental characterization of a heat transport system as used in common satellite applications. The heat transported is being emitted from the electrical consumers inside the satellite. The present heat transport system consists of two loop heat pipes (LHP), which transport the heat obtained from four arterial heat pipes (AHP) to the heat sink outside the satellite using ammonia as a working fluid. Due to nonconstant operation parameters, e.g. the thermal load and temperature of the heat sink, unwanted oscillations of the saturation temperature can be observed, which have a great impact on the operation temperature of the electrical consumers. In order to eliminate these oscillations and to ensure an optimal operation temperature an additional heat source, e.g. a heating film located on the compensation chamber of the LHPs, is being introduced into the system. This approach requires a fundamental knowledge of the thermal characteristics as well as a reliable control of the heating film. Therefore a mathematical model has been set up based on available concepts in literature and validated using experimental data from a novel test facility. This procedure allows the description of unknown thermal properties by setting up steady state test conditions within the heat transport system. In a second step effects concerning the thermal capacity of the system as well as of the surroundings can be quantified and included into the numerical description of the system. Present results for both, the experimental characterization and the mathematical description, will be presented and compared in detail. Furthermore a brief summary of the knowledge gained from both concepts will be given.

This paper presents results of an experimental investigation on pressure drop and heat transfer for a wide range of Reynolds and Prandtl numbers ranging from 8 < Pr < 60 and 40 < Re < 3500, for flat tubes without and with passive inserts. For three different kinds of passive insert designs, the impact on heat and momentum transfer due to coaction of the total set of passive inserts with different shape and amount was investigated. Experimental results were analyzed regarding two main aspects: Heat transfer mechanisms and pressure drop induced by friction and form drag forces due to the presence of different shapes. After heat and momentum transfer mechanisms for each passive insert design were analyzed, heat transfer and pressure drop enhancement were compared to each other, leading to an efficiency discussion. Different concepts for efficiency evaluation, which are cited in literature, were applied to the presented experimental data. Pros and cons of the different concepts are discussed. Finally, we propose an equation for evaluation of total performance, which fully respects the energetic and exergetic aspects of heat transfer and pressure drop enhancement.