Capillary Evaporation in Microchanneled Polymer Films

Abstract

The capillary-driven evaporation heat transfer and the resulting fluid flow mechanisms occurring in a microchanneled, flexible polymer microfilm were investigated to better understand the operation and improve the design process of two-phase flexible membrane heat pipe devices. Experimental tests were conducted to evaluate the capillary evaporation heat transfer limit in a polymer microfilm with 26-μm-wide capillary grooves. The experimental results indicated that the microchanneled polymer film could create a capillary force sufficient to function adequately when used with wettable working fluids such as methanol or ethanol. The maximum evaporation heat transport capacity was found to decrease significantly as the effective length of the polymer microfilm increased. In addition to the experimental portion of the investigation, an analytical model was developed to predict the capillary evaporation limitation. When this model was used, the effects of variations in the geometric parameters of the microgrooves on the evaporation heat transfer were analyzed. The results indicated that when the half-angle of the trapezoidal grooves was fixed, the maximum evaporation heat transfer rate increased with increases in the depth and decreases in the width of the grooves. Predictions obtained from the analytical model were then compared with the results of the experimental investigation and indicated good agreement.