Nanofluids-based and porous media-based solar evaporation: A comparative study

Water vaporization through direct volumetric solar collectors has recently attracted a significant attention of the scientific research community. Many studies suggested plasmonic nanoparticles, such as gold nanoparticles, to produce solar clean water effectively. However, there is a lack of studies comparing the feasibility of using gold nanoparticles for solar applications with other cheap materials at the same operating conditions. In this study, well-controlled experiments were performed to clarify the mechanism of the solar evaporation process using gold nanofluids and micro-sized porous medium. The results show that gold nanofluids are not feasible for solar evaporation applications especially solar still technologies. This infeasibility is mainly due to the high cost and the low absorbance of gold nanofluids comparing to the porous medium. High nanofluid concentration is needed to trap the solar energy in a thin layer at the liquid-gaseous interface. Using carbon-based, micro-sized thin porous medium produces solar water vapour at higher rates than that produced by gold nanofluids. Also, increasing the solar intensity enhances the evaporation rates, but unavoidably reduces the efficiency due to the increase in the heat losses related to the accompanied high temperatures.