EXPERIMENTS AND ANALYSES OF FLAT MINIATURE HEAT PIPES

Two flat copper-water axially grooved miniature heat pipes are fabrica ted employing the electric-discharge-machining (EDM) wire-cutting meth od. Because of the advantage of the EDM method, axial grooves are prov ided around the entire interior perimeters of the miniature heat pipes , The two miniature heat pipes are tested under different heat inputs, cooling temperatures, and orientations, The maximum heat transfer rat e for the heat pipes tested is about 40 W, and the maximum heat flux a chieved is about 20 W/cm(2), based on the outer surface of the evapora tor, The effective thermal conductance of the heat pipe is on the orde r of 40 times that of copper based on the external cross-sectional are a of the miniature heat pipe, If the effective thermal conductance is evaluated based on the interior cross-sectional area of the heat pipe, it can be 100 times higher than the thermal conductivity of copper. A nalyses for heat-pipe limitations are also pel formed based on certain analytical relations, It is found that the capillary limit is the dom inant heat transfer limitation for the miniature heat pipes tested in this paper, To improve the accuracy of the analytical model, the hydra ulic radius in the capillary limit is corrected using the exact two-di mensional solutions found in the literature, and the expression for th e friction factor that takes into account the shear stress at the liqu id/vapor interface is adopted, The analytical results based on these m odifications are compared with corresponding experimental results with good agreement.