Measurement of the working fluid distribution within a heat pipe wick

The longitudinal distribution of the working fluid in the wick of a heat pipe is studied with respect to the wick material, heat input, fill charge of the working fluid, and pipe inclination. The fluid distribution in rectangular (RHP) and cylindrical (CHP) heat pipes were measured using an electric capacitance technique for various values of the above parameters. Two types of wick were used for both the RHP and the CHP: packed glass spheres (mean diameter 0.15 mm) and crushed firebrick (0.2 mm). The RHP was operated in the horizontal mode only, while the angle was varied for the CHP. It is shown that in the horizontal operating mode the saturation in the heating section decreases steeply in spite of the uniform saturation in the adiabatic and cooling sections. In the tilt operation mode, gravity has a significant effect on the level of saturation in both the heating and cooling sections.