Performance of cylindrical and flattened heat pipes at various inclinations including repeatability in anti-gravity - A comparative study

A comparative study of cylindrical and flattened heat pipes having different screen mesh size wicks is conducted at various inclinations (−90° to +90°) for a heat load range of 10-60 W. The effect of flattening of heat pipes having same screen mesh wick at various inclinations are also analysed. Anti-gravity (−90°) tests are also repeated at different time intervals to analyze the reliability of these heat pipes if they have to remain idle for a certain period. Experiment results show that the thermal performance of the heat pipes are influenced by inclination angle, mesh size of the wick, cross section of the heat pipe and heat input. The inclination at which the maximum heat transfer occurs is not the same for three heat pipes tested. The lowermost thermal resistance witnessed is 0.46 K/W, for cylindrical heat pipe, at an inclination of −45° for an applied heat input of 60 W. The maximum evaporator and condenser heat transfer coefficient values observed are 3876 W/m2 K and 1698 W/m2 K respectively. The anti-gravity repeatability tests shows that these heat pipe works well even after some idle period and the variation in evaporator temperature is found to be less than ±7.5%.