Thermal design strategy for enhanced freshwater harvesting with interfacial evaporation

Abstract

• Propose a heat and mass transfer model for interfacial evaporation solar still. • Determine the influencing factors of interfacial evaporation solar still. • Strengthening the inside convective process is a key factor for improving efficiency. • The efficiency of an interfacial evaporation solar still can be 62.6 % under 1 sun. Solar driven interfacial evaporation is considered to be a low-carbon, environment-friendly technology for achieving efficient evaporation, but the solar still equipped with the interfacial evaporation structure is found to process low fresh water production rate and production efficiency. In this work, an optimization scheme for the interfacial evaporation structure of the solar still is proposed through the theoretical analysis of the heat and mass transfer process of the interfacial evaporation solar still. The theoretical results show that there are significant differences in the optimization design between the interfacial evaporation solar still and conventional solar stills. The fresh water production rate of interfacial evaporative solar still is less sensitive to the insulation performance of the solar still, while is greatly affected by the convective heat transfer process inside and outside the solar still. The solar still with interfacial evaporation structure can reduce the use of insulation materials to improve the illumination area and reduce the construction cost, without affecting the production efficiency of fresh water. Under the input energy intensity of 1 kW·m −2 , when the convective heat transfer process inside the solar still is strengthened, the theoretical fresh water production rate of the interfacial evaporation solar still can be increased by 28 %, and the efficiency can reach 73 %. However, different from the optimization results of the traditional solar still, the enhancement of convective heat transfer process outside the glass cover will lead to the decline of the efficiency of the solar still. The experimental results show that in a monoclinic interfacial evaporation solar still with an evaporation surface area of 60 cm * 60 cm, a high system performance can be achieved by attaching a thin layer of insulation material to the inner wall and using a 2 W fan for forced convection of internal air. Under the outdoor environment with the maximum light intensity of 1 kW·m −2 , the production efficiency of fresh water can be stabilized at 62.6 %. This work provides important guidelines for the design and optimization of solar still with interfacial evaporation structure.