Numerical Investigations on Heat and Mass Transport in Passive Solar Evaporators with Non-Uniform Surface Temperature

Passive solar desalination with no discharge promises great potential for sustainable desalination. Herein, we provide a comprehensive modelling scheme for the investigation of coupled heat and mass transport in passive desalination devices. Our modelling approach integrates mass, momentum, species, and energy transport models to study the coupled phenomena of wicking, solar-driven evaporation, and salt precipitation. Our numerical model can predict the impact of spatiotemporal variation in temperature, salt concentration, and wicking velocity on the evaporation flux and thermal efficiency of solar evaporators. The impact of the evaporator’s shape, solar flux, salt concentration, and light reflection by salt crystals has been studied on the evaporator’s performance. We observed a two-fold increase in evaporation flux when solar irradiance increases from 1000 W/m2 to 2500 W/m2. A reduction in the thermal efficiency of the evaporators is predicted at higher solar fluxes. The modelled evaporator can achieve an evaporation flux of over 0.5 kg/m2h under 1000 W/m2 for 3.5 wt.% saline water. The salt concentration along the z-position of the evaporator exhibited a double arch-shaped profile, which influences its evaporation performance. These findings provide vital guidelines for the design of high-throughput solar desalination systems.