Heat and mass transfer analysis and optimization of passive interfacial solar still

Abstract

Due to the fast thermal response and high solar energy efficiency, the passive interfacial solar still has become a reliable scheme for distributed water supply. In this paper, the thermodynamic performance of the interfacial solar still under different structures and operating conditions is studied experimentally, which provides an optimization direction for strengthening the distillation process. Firstly, based on the different Ra numbers, the calculation correlations for diffusion and convective mass transfer in the air interlayer were established to accurately predict the thermodynamic model of the interfacial distillation process. Then, the temperature distribution of the condenser and the growth process of condensate droplets were analyzed with the constant evaporation temperature. Simultaneously, the influence of different condensing structures and external variables on the heat transfer performance was compared. The results show that the interfacial still could obtain maximum evaporation heat under the vertical operation condition. When the evaporation temperature is 70 °C, the temperature difference between the wick evaporator and condenser can be increased by 49.5 %, after coupling a finned condenser with the aspect ratio of 7.2. In addition, a narrower interlayer spacing and a larger evaporation temperature could bring a higher equivalent heat transfer rate and evaporation efficiency. In a sunny weather, the interfacial solar still coupled with an extended condenser can reach a 4.81 kg/m2/day water yield and a 0.486 daily gained output ratio under 1 cm interlayer spacing.