Water Delivery Channel Design in Solar Evaporator for Efficient and Durable Water Evaporation with Salt Rejection

Recently, solar evaporators composed of photothermal materials and their carriers have been designed and produced to enhance the solar evaporation rates based on interfacial solar heating. However, maintaining the high evaporation rate while preventing salt accumulation remains a challenge. In this paper, a water transport channel was designed to move the brine outside the solar evaporator to the expandable polyethylene (EPE) foam around the evaporator, thereby preventing salt accumulation in the evaporator. The concentration of the treated seawater was not increased during continuous evaporation and therefore avoiding the treatment of the high-concentration brine. The salt-rejecting solar evaporator was composed of a top layer of photothermal materials for high solar absorption, a thermal barrier layer of EPE foam for floatation and heat insulation, and a rationally designed water transport channel of air-laid paper (ALP) for fast seawater delivery to the top layer and outside the evaporator. The water evaporation rate of the simulated seawater by the salt-rejecting evaporator under 1 kW·m–2 solar irradiance was significantly enhanced to 1.46 kg·m–2·h–1 (accompanied by a photothermal conversion efficiency of 91.7%), which was 3.74 times higher than evaporation rate of the simulated seawater alone. The salt-rejecting evaporator also displayed excellent stability and durability as the evaporation rate was unchanged after 16 cycles of use. Finally, the potential application of the salt-rejecting evaporator was demonstrated in a practical setting by packing 25 evaporators in an EPE foam plate.