Utilization of Pore Size Distributions to Predict Thermophysical Properties and Performance of Biporous Wick Evaporators

Abstract

A sintered copper porous medium is an extremely effective structure used to enhance the evaporative heat transfer properties of a heat pipe. It provides both capillary pressure to passively draw liquid in and increased surface area to more effectively heat the liquid. A biporous wick is particularly effective for this application as there are two distinct size distributions of pores; small pores to provide ample capillary pressure to drive flow through the wick and large pores to provide high permeability for escaping vapor. The modeling described in this work is based on the work of Kovalev who used a pore size distribution in order to determine the most probable liquid saturation at a given position. The model distinguishes phases by choosing a “cutoffâ€‌ pore size, where larger pores were assumed to be filled with vapor and smaller pores were assumed to be filled with liquid. For a given thickness and thermophysical properties of the liquid, this 1D model predicts the temperature difference across the wick for a given input power. The modeling proposed in this work yielded results that compare very well with experimental data collected on biporous evaporators by Semenic.