Using Solar Energy for Water Purification through Nanoparticles Assisted Evaporation: Theoretical and Experimental Investigations

Abstract

As per the estimates of the world health organization (WHO); by 2025, about half of the world's population shall inhabit water stressed areas. Water purification through usage of solar energy is a clean and lucrative option to ensure access to clean and safe drinking water. In most of the solar energy driven desalination systems, evaporation of water is one of the key processes. In this direction, we propose that addition of nanoparticles into the water (owing to their enhanced thermo-physical properties and optical tune-ability) could significantly enhance the evaporation rate and thus the pure water yield. In the present work, we have developed a detailed theoretically model to predict (and quantify) the evaporation rates when water/nanoparticles dispersion directly interact with solar irradiance. In order to clearly gauge the effects of adding nanoparticles, two systems have been studied (i.e. the one with and the other without nanoparticles dispersed in water) under similar operating conditions. Theoretical calculations show that addition of even trace amounts of nanoparticles (volume fraction = 0.0001) into water can significantly enhance (57-58% higher than the pure water case) the evaporation rates and the pure water yield. Furthermore, a detailed parametric study involving host of parameters influencing the evaporation rate reveals that nanoparticle volume fraction and solar irradiance are the most impacting parameters. The results of the developed theoretical model have been compared with the experimental results in the literature, the two have been found to be in good agreement except at high nanoparticle volume fractions. For completeness, proof-of-the -concept experiments simulating the theoretical model have also been carried out. Finally, experiments under the sun have been carried out to clean sewage water through evaporation via volumetric absorption process. The pH and total dissolved solids (TDS) measurements of the distillate collected though the aforementioned process revealed that indeed impure water (such as sewage water in the present work) could be effectively cleaned through nanoparticles assisted evaporation.