The heat transfer capability prediction of heat pipes based on capillary rise test of wicks

Abstract

In this study, the capillary limit of heat pipe is predicted on the basis of capillary rise test. Firstly, porous wicks and cylindrical heat pipes are fabricated utilizing copper powders with identical diameters but different shapes. The pore structures and capillary performances of wicks are characterized, and thermal performances of heat pipes are also measured. Results show that high temperature sintering causes wick shrinkage towards the pipe wall, and the shrinkage degree increases with increase of powder irregularity, which results in decrease of wick cross-sectional area and thickness. A curve fitting equation describing capillary rise test is obtained and the capillary performance of the wick also increases with increase of powder irregularity. Fitting results show that the capillary pressure of irregular powders decreases nearly 30% comparing with that of spherical powders, but its permeability increases 533%. The experimental capillary limits of heat pipes sintered with spherical, sphere-like, dendritic and irregular copper powders are 18 W, 20 W, 44 W and 42 W, respectively. Furthermore, the predicted capillary limits at working temperatures are about 7∼11 W smaller than experimental values. Finally, the experimental capillary limit is employed to correct the prediction equation of capillary limit at different working temperatures.