Simulation on pool boiling heat transfer considering the integrated effect of engineered microchannels and mixed wettability

Abstract

Comparing with the abundant experimental investigations on the pool boiling heat transfer, this study aims to explore the integrated effect of engineered microchannels and the mixed wettability on the enhancement in pool boiling heat transfer in a wide range of geometric and physical conditions. A two-dimensional transient volume of fluid (VOF) model was adopted to simulate the bubble behavior and thermal performance on different surfaces including the hydrophilic plain, hydrophilic microchannel, hydrophilic microchannel with hydrophobic top, and hydrophilic microchannel with hydrophobic bottom, respectively. The vapor volume fraction, velocity vector field, temperature of solid/liquid interface, and average heat transfer coefficients (HTCs) on different geometric surfaces were obtained based on the numerical model. It was found that hydrophobic areas are necessary to be added in the hydrophilic channels to facilitate the bubble nucleation and detachment due to the merit of the mixed wettability. However, it is crucial to optimize the width and location of the hydrophobic areas and the height of the hydrophilic microchannel for the prevention of early formation of vapor blanket and promotion of liquid replenishment. With the hydrophobic area on the top of the microchannel, the maximum solid/liquid interface temperature was 392.8 K, which decreased by 0.91 % comparing with that on the hydrophilic microchannel. While with a hydrophobic bottom (W1 = 2 and 4 μm), the max average HTCs were 508.2 kW/(m2K) and 503.5 kW/(m2K), which were 16.4 % and 11.4 % higher than that in hydrophilic microchannel (W1 = 2 and 4 μm), respectively. The simulation results indicate that the microchannel with optimized mixing of the wettability can efficiently promote the bubble to move upward and liquid to rewet along with the hydrophilic wall, forming the separation of vapor-liquid pathways to further enhance pool boiling heat transfer.