Measurement of internal pressure and thermal performance in a closed-loop oscillating heat-pipe with check valves (CLOHP/CV)

The internal pressure and the thermal performance as characteristic parameters in a closed-loop oscillating heat-pipe with check valves (CLOHP/CV) under the normal operating condition have been investigated experimentally. The test CLOHP/CV was made of a copper capillary tube with various inner diameters. The inclination angle and the working temperature have been varied in the experiments. The working fluids of distilled water, ethanol and R123 were used with a filling ratio 50% of the total internal tube volume; the number of meandering turns was 40 and the number of check valves was 2. The lengths of the evaporator, adiabatic and condenser sections are all the same. The evaporator section was heated by electric strip heaters. The heat was removed from the condenser section by forced convective flow of ambient air blowing through the sections. The adiabatic section was well insulated by foam insulation. The thermal performance of the CLOHP/CV was evaluated by calculating the rate of heat transferred from the condenser to ambient air. It was found that the thermal performance of the CLOHP/CV has been improved by increasing the working temperature, the inclination angle and the inner diameter. The best performance of all the test CLOHP/CVs occurred for the case of R123 as working fluid, 2.03 mm inner diameter, 90 inclination angle and the working temperature of 200 degrees C, where the maximum internal pressure was 7.53 MPa and the minimum thermal resistance was 0.048 degrees C/W.