Volumetric solar heating of nanofluids for direct vapor generation

Traditional solar-thermal receivers suffer from high surface temperatures, which increase heat losses to the surroundings. To improve performance, volumetric receivers based on nanopartides suspended in liquid (nanofluids) have been studied as an approach to reduce surface losses by localizing high temperatures to the interior of the receiver. Here, we report measured vapor generation efficiencies of 69% at solar concentrations of 10 sun using graphitized carbon black, carbon black, and graphene suspended in water, representing a significant improvement in both transient and steady-state performance over previously reported results. To elucidate the vapor generation mechanism and validate our experimental results, we develop numerical and analytical heat transfer models that suggest that nanofluid heating and vapor generation occur due to classical global heating of the suspension fluid. This work demonstrates high nanofluid-assisted vapor generation efficiencies with potential applications in power generation, distillation, and sterilization. (C) 2015 Elsevier Ltd. All rights reserved.