Development and investigation of a loop heat pipe with a high heat-transfer capacity

Highlights: • An ammonia LHP 21 m long has been developed and tested. • Tests were conducted at a horizontal orientation and heat sink temperatures of 4 °C and 20 °C. • The LHP demonstrated serviceability in the range of heat loads from 200 to 1700 W. • The minimum value of the "heat source – heat sink" thermal resistance was at a level of 0.034 °C/W. - Abstract: Loop heat pipes (LHPs) are passive heat-transfer devices which may be used in energy-efficient systems of recovery of low-potential heat, for heat transfer from renewable energy sources, and also in systems of thermal regulation of different equipment with remote heat sinks or sources. The paper shows the results of development and thermal tests of an LHP 21 m long made of stainless steel with ammonia as a working fluid. The device had a cylindrical evaporator 24 mm in diameter with an active zone length of 188 mm equipped with a nickel wick with an effective pore radius of 1.05 µm and a porosity of 70%. The LHP condenser made in the form of a pipe-in-pipe heat exchanger 310 mm long was cooled by running water with a temperature of 4 °C and 20 °C. Tests were conducted at a horizontal orientation of the device. At a cooling temperature of 20 °C a maximum heat load of 1700 W (12 W/cm²) was achieved at a vapor temperature of 62 °C, which corresponded to a heat source temperature of 89 °C. In this case the thermal resistance of the "heat source – cooling liquid" system was equal to 0.034 °C/W.