Solar photothermal conversion characteristics of hybrid nanofluids: An experimental and numerical study

In this work, the Fe₃O₄, Cu and Au with different concentrations and the hybrid nanofluids were prepared and characterized to enhance the solar photothermal conversion performance based on the direct absorption concept. An extensive experimental study was carried out with different sample nanofluids under a solar simulator. The experiment was first conducted with Au nanofluid in three cases to investigate the effect of different test conditions, and the test condition where the simulated sunlight was absorbed by the sample nanofluid only once with minimum heat loss to the surroundings was determined for later research. Based on the experimental results, below conclusions have been reached: 1)the solar energy absorption performance of nanofluids with plasmonic nanomaterials, i.e., Au or Cu, is much better than that of nanofluids with non-plasmonic nanomaterials, i.e., Fe₃O₄ and DI water, due to the effect of localized surface plasmon resonance; 2)the larger the concentration, the higher the solar energy absorption efficiency, but the increasing rate of the absorption efficiency slows down gradually with the increase of the concentration; 3)a numerical method to predict photothermal conversion efficiency of nanofluid under solar radiation has been proposed; 4)the novel idea of employing hybrid nanofluid to enhance the solar absorption performance has been experimentally and numerical validated, which can enhance the solar photothermal conversion when mixing two nanofluids with different absorption peaks, and there is an optimal mixing volume fraction for hybrid nanofluid.