Development and Results of Testing of a Long Loop Heat Pipe with Flexible Elements

The paper presents the results of development, hydrodynamic analysis, and thermal testing of a stainless-steel loop heat pipe of length 4.56 m with a cylindrical capillary pump-evaporator of diameter 12 mm, which was equipped with a fine-pored wick. The vapor line and the liquid line of the device of diameter 2 mm had inserts in the form of tubular spirals ensuring additional flexibility and permitting the variation of the effective length of the loop heat pipe. As the working fluid, ammonia was used. Thermal tests were carried out under the standard conditions in the horizontal position, as well as in unfavorable positions when the evaporator was 1.1 and 2 m higher than the condenser. The heat pipe condenser was cooled by running temperature-stabilized liquid with a temperature of 20°С. A nominal heat load of 100 W was achieved in all positions of the device. The heat source temperature remained between 46.5 and 48.7°C, and the thermal resistance of the “heat source–cooling liquid” system varied from 0.26 to 0.28°C/W.