Numerical investigation on solar evaporation properties of nanofluids

Abstract. The optical absorption and heat transfer properties of fluid can be improved by suspending nanoparticles in a base fluid. Due to the strong photothermal effect around nanoparticles, water around the particles evaporates when exposed to light. Therefore, nanofluids can be used as the working fluid of solar evaporation devices. The evaporation heat transfer model of the Ag nanofluid is established. The temperature distribution and vapor concentration distribution around nanofluids are simulated at low concentrated solar power. Effects of the particle size and volume concentration on the evaporation performance are analyzed. When the volume concentration is small (fv  =  0.01  %  ), the effect of particle size on evaporation is obvious, and the evaporation increases with the increase of particle size. When the particle radius R increases from 5 to 40 nm, the evaporation amount increases 17.8% from 0.0286 to 0.0337 g. For the nanofluids with smaller particle sizes (R  <  20  nm), the evaporation tends to be stable with the increase of concentration, reaching about 0.0318 g. For the nanofluids with larger particle sizes (R  =  40  nm), the evaporation decreases significantly with the increased concentration. When the volume concentration increases from 0.01% to 0.1%, the evaporation decreases from 0.0337 to 0.0288 g. Therefore, the particle size and volume concentration should be considered comprehensively when choosing nanofluids as evaporation working fluids. When the volume concentration is >0.05  %  , the nanofluids with smaller particle sizes should be selected. We provide guidance for the utilization of nanofluids for solar evaporation.