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The paper is devoted to discussing the problems of serviceability of capillary pumped loops (CPL) in startup and stationary modes of operation. It gives the results of experimental investigation of a CPL with a length of the transportation zone of about 5 m and high-pressure capillary pumps creating a head up to 40 kPa on ammonia and 20 kPa on freon-152A, which have been tested as working fluids. On the basis of the experimental data and analysis of the CPL operating cycle the paper gives the determination of serviceability conditions connected with the required degree of subcooling of the working fluid that is supplied into capillary pumps.

Loop heat pipes (LHP) are controllable heat transfer devices that may operate in different regimes. When there is a possibility of redistribution of liquid between the evaporator and condenser, the regime of autoregulation is realized. Such a regime produces a performance characteristic of a specific form and makes it possible to implement control over an LHP temperature within a certain range of variation of heat load by means of corresponding selection of the constructive parameters. Active control is more reliable and precise. It is realized by means of thermal action on the returning flow of a working liquid. It was shown in the experiments that active control provides practically constant temperature within the control range.

Loop heat pipes (LHP) are a special kind of two-phase heat-transfer devices with a capillary pumping of a working liquid. Owing to its construction, special fine-pored wick structures and the method of operation these devices can ensure an efficient heat transfer at any orientation in a gravity field. In the most severe evaporator-above-condenser regime the heat-transfer distance may be several metres. These qualities create good prospects for using LHPs in the thermal control systems of various apparatus, which in the process of tests or operation change their orientation in space or undergo inertial overloads.