Understanding the effect of the condensation temperature on solar-driven reverse distillation for enhanced water production

Reverse distillation driven by solar energy decouples light-incoming and evaporation–condensation regions that are integrated together in conventional solar distillation, thereby providing diverse choices in materials and structures for enhancing vapor condensation. However, detailed experiments and discussion are scarce in exploring how condensation temperature influences the solar-to-water energy conversion efficiency in the reverse-distillation process and may thus constrict the further understanding and application in water production processes. A common impression is that a low temperature is good for vapor condensation and performance improvement but that may not be the case. An interesting conclusion from both experimental and theoretical exploration in this research is that the efficiency of the reverse-distillation device first increases and then decreases with the condensation temperature, indicating an optimal condensation temperature for obtaining the best water production performance. In indoor experiments with one-sun illumination, the reverse-distillation device with natural air cooling shows a distillate yield of 1.04 kg⋅m−2⋅h−1 and a solar-to-water energy conversion efficiency of 68.8 %, which is 9.4 % and 6.3 % more than that of a device with enhanced cooling by water flow and inhibited cooling by thermal insulation, respectively. In the outdoor experiments, the increase in efficiency using natural air cooling is 4.9 % and 7.1 % compared with the enhanced and inhibited cooling measures, respectively. The conclusion is further explained from the perspective of heat-and-mass transfer, which may provide meaningful guidance for designing a high-efficiency reverse-distillation system. In future water production, cooling measures should be cautiously considered according to the device structure and the actual working conditions to achieve better performance.