Heat-transfer analysis of interfacial solar evaporation and effect of surface wettability on water condensation and collection

Abstract

The use of solar energy for interfacial water evaporation has become a promising roadmap with the global energy and fresh water crisis becoming serious concerns. A systematic study of thermal energy conversion efficiency in interfacial solar evaporation has great significance for improving evaporation efficiency. In this study, an interfacial solar water-evaporation device was proposed, and heat balance analysis were conducted to investigate dominant heat transfer modes for improving the evaporation rate. The results indicate that thermal conduction of the insulation layer accounts for 5% of the input solar energy, and an improvement in the evaporation rate should be focused on reducing the convective heat transfer and radiative loss of the photothermal-layer surface. In addition, a water-collection device was designed to investigate the effect of surface wettability on the water condensation and collection of steam generated by interfacial solar evaporation. It can be found that a hydrophilic wall surface is conducive to steam adhesion and the spread of condensed water droplets, water-film flow, and water discharge; this effectively improves the performance of water collection. The water-collection device which is comprised of hydrophilic side walls and a cover made of ultraclear glass coated with hydrophilic material, can obtain a water-evaporation rate of 8.32 kg·m−2 h−1, water-collection rate of 6.10 kg·m−2 h−1, and water-collection efficiency of 73.21% under ten-sun illumination. The performance of the water-collection device under outdoor conditions was studied and it can be concluded that the evaporation rate and water collection rate can be improved by increasing the irradiation flux on the photothermal layer of the interfacial solar evaporator, or by reducing the effect of outdoor airflow. This study can provide theoretical guidance for the design and performance improvement of solar-driven interfacial water evaporation and collection devices.