Thin film evaporation in microchannel membrane for solar vapor generation

Thin film evaporation is investigated in microchannel membranes for solar vapor generation. Microchannel membranes provide a novel way to stimulate thin film evaporation for capillary pumping and efficient vapor generation in compact devices. On the top of the membrane, there is a thin layer that absorbs wide-range solar spectrum and converts solar energy to heat. The heat is conducted through the channels' walls into the liquid menisci that ultimately generates vapor. Due to capillarity, liquid is continuously replenished from the bottom side of the membrane into the menisci at the top. High heat transfer rates occur in the thin film region due to the small thermal resistance across the film where liquid thickness is less than a micron. The augmented Young-Laplace equation and the kinetic theory for mass transport are used to model the evaporating thin film in microchannel membranes. The effect of vapor pressure, channels spacing, and slip length on the interfacial evaporative mass flux is included. The influence of variable wall temperature profile is discussed. A new model is developed to account for the effect of rough sidewalls. The proposed work aims to offer a basis for designing thin film evaporation devices for power generation and thermal desalination systems.