VISUALIZATION EXPERIMENTS ON OPERATIONAL CHARACTERISTICS OF A CENTERED-WICK HEAT PIPE (EFFECT OF LIQUID VOLUME)

This paper describes visualization experiments on the fluid flow and heat transfer characteristics in a centered-wick heat pipe. In recent years, many studies have been conducted on this type of heat pipe for thermal management of thin electronic devices; however, the working phenomena in the centered-wick heat pipe have not been fully understood. Two kinds of heat pipes with the vapor channel heigh of 0.5 and 1.0 mm were fabricated. The heat pipe casing was made of semi-transparent polymer for visualization. Sintered copper powder was installed as a wick, and water was used as a working fluid. In experiment, an evaporator section of the heat pipe was heated with a heater while a condenser section was cooled using a water-cooling jacket. Temporal temperature variations of the heat pipe were measured with thermocouples, and fluid flow phenomena in the heat pipe were captured with a camera. The experiments were conducted by changing the amount of the working fluid in the heat pipe. From the experimental results, it was confirmed that an additional working fluid was required to avoid an unnecessary increase in the thermal resistance of the heat pipe. Moreover, it was also confirmed that there existed an optimum value for the additional working fluid. The optimum value for the heat pipe with 0.5-mm-high vapor channel was 20%, and that for the heat pipe with 1.0-mm-high vapor channel was 30%.