Effect of air gap in novel fouling-free non-contact nanostructure solar still for potable water application from lake water

Abstract

Water scarcity is a major global challenge that requires the utmost attention. Solar desalination could be one of the possible solutions to this problem. Recently, interest has arisen in floating nanostructure that produces a significant desalination effect. However, due to the direct contact with contaminated water, the nanostructures undergo degradation/fouling over time. To overcome this fouling problem, in this work, we have designed and developed a novel non-contact nanostructure (NCNS) through chemical oxidation and coating that is physically and thermally decoupled from the water inside the solar still. The NCNS first absorbs the thermal radiation and then transfers its absorbed energy to water via infrared radiation, developing a contactless mode of heat transfer. Due to this non-contact mode of heat transfer, fouling is completely avoided. The absorptivity of the proposed NCNS front surface was 90%, while the emissivity of the back surface was 94%. Experiments were performed for six days without and with reflector by varying the air gap between the NCNS and Hussain Sagar Lake water to analyze the air gap's effect on NCNS solar still productivity enhancement. It was found that the 1 cm air gap was the most optimum among the different air gaps analyzed. Analytical modeling, fouling study, and in-depth water quality assessment were also performed, and the results were so promising that the freshwater obtained was safe for drinking and free from impurities, bacteria, and viruses. Therefore, such a solar still can be installed near the brackish lakes to get purified water so the local people can utilize it.