Experimental Study of Evaporation of Nanofluid Droplets on Substrates under Solar Radiation

This work is devoted to the experimental study of evaporating droplets of titania-, silica-, and diamond-based nanofluids on a substrate under solar radiation. The influence of various factors, including the type of a material, concentration of nanocomponents, irradiation direction, droplet volume, and substrate material, on the droplet evaporation has been investigated. As a result, the critical concentrations of nanoparticles, at which the evaporation rate reaches a stable level, have been determined for droplets of the studied nanofluids. The regimes and stages of the droplet evaporation process have been analyzed for the cases of the subcritical and critical nanoparticle concentrations. The efficiency of droplet evaporation under solar radiation has been shown to strongly depend on radiation direction. The effects of droplet volume and substrate material on the evaporation rate have been studied. In addition to the evaporation efficiency, the morphology of the structures deposited from the droplets has been analyzed. It has been shown that these structures depend on the concentration and material of nanoparticles, as well as on the regime of droplet evaporation. The results of this study enable one to gain a deeper insight into the behavior of the droplets during evaporation under irradiation especially in the IR region and confirm the promise of application of nanofluids in the solar thermal energy systems.