Study on the effects of the countercurrent flow interaction on the thermal performance of grooved wick heat pipes

Abstract

A one-dimensional mathematical model for a miniature heat pipe with a grooved wick structure has been developed to predict thermal performance characteristics including the effects of the shear stress at the liquid-vapor interface, the initial liquid charge, and the contact angle. From the proposed model, the governing equation for the steady-state operation is obtained and solved numerically. Because the liquid-vapor interfacial shear stress affects seriously the liquid flow and the maximum heat transport rate of the grooved wick heat pipe, an accurate modeling for the pressure drop characteristics of the liquid flow is required. In particular, a novel method called a modified Shah method is suggested and validated by experiment; this method is an essential feature of the proposed model and accounts for the effect of the liquid-vapor interfacial shear stress. An experimental apparatus for measuring non-dimensional friction factor (Po) of the liquid flow in open rectangular microchannels with the hydraulic diameters of 0.4mm, 0.43mm, 0.48mm is constructed in order to reproduce real situations in the grooved wick heat pipe. Analytic results from the modified Shah method are compared with the experimental data, and they show a close agreement with each other. In addition to measuring Po, visualization of the liquid flow in the open microchannels using micro-PlV (Particle Image Velocimetry) is performed. On the other hand, experiments for measuring the maximum heat transport rate and the total thermal resistance are conducted in order to verify the proposed mathematical model of the grooved wick heat pipe. The experimental data for the maximum heat transport rate considering heat loss from the experimental apparatus are shown to be in close agreement with numerical results. The proposed mathematical model is used for the thermal optimization of the wick structure with respect to the width and the height of groove. As a result of the optimization, it is estimated t...