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Loop heat pipes (LHPs) are hermetically sealed heat-transfer devices, possessing a superflow thermal resistance and operating on a closed evaporation-condensation cycle with the use of a "capillary mechanism" for pumping the working fluid. LHPs are capable of transferring heat flows from several watts to several kilowatts at a different orientation in the gravity field and zero-g conditions without the use of any additional energy sources.
Advantages of LHPs:
At present LHPs are successfully used in systems of thermal regulation of space equipment.
(20 m in length, capacity of 1.7 kW)
LHP with a disk-shaped evaporator
(30 mm in diameter)
LHP in Tests
(2 m in length)
A high capacity copper-water LHP with the effective length of 310 mm was developed. This devise has a flat-oval evaporator which thickness is 7 mm and has the vapor and liquid lines with 6 mm diameter. The size of the evaporator active zone is 32 mm x 32 mm.
The tests of LHP were carried out with the heat sources which have 1 cm2 and 9 cm2 heat surfaces. The condenser was cooled by the running water under the temperature of 20C. The maximum heat flux in the heating area with 1 cm2 heat source was 998 W/cm2, and with 9 cm2 heat source it was 134 W/cm2. The minimal LHP thermal resistance of 0,044C/W was reached under the 1200W heat load and the heat source temperature of 143,5C.
Heat load dependence of the heat source temperature, obtained in tests of a copper-water loop heat pipe with the liquid condenser cooling at 20Ñ