Experimental study of the thermal characteristics of a heat pipe

The performance of a cylindrical heat pipe under various operating conditions was experimentally analyzed. The heat pipe consists of a copper tube with a diameter of 12.7 mm and 4 layers of copper screen mesh act as the wick. The heat pipe was equipped with a vacuum ball valve in order to charge the heat pipe with different amounts of working fluid. The effect of the working fluid fill volume, inclination angle, and heat input on the equivalent thermal resistance of the heat pipe were investigated. The results showed that in gravity-assisted orientations (condenser located above evaporator), the inclination angle has a negligible effect on the performance of the heat pipe. However, for gravity-opposed orientations (evaporator above condenser), as the inclination angle increases, the temperature difference between the evaporator and condensation increases which results in a higher thermal resistance. It was also found that if the working fluid in the heat pipe is under-filled, the capillary limit of the heat pipe decreases dramatically. However, overfilling of the heat pipe degrades the heat pipe performance due to excess liquid interfering with the evaporation-condensation mechanism. The results obtained from this experiment were also used to verify a previously developed numerical model. Very good agreement between the numerically predicted results and those from the experiment were obtained, thus validating the numerical technique developed and reported in authors' previous papers.