Electric field combined nanofluid to enhance photothermal efficiency of the direct absorption solar collector

Compared with conventional surface absorption collectors, nanofluid-based direct absorption solar collectors (DASC) have superior optical absorption performance and photothermal conversion efficiency. However, problems such as nanoparticles deposition and large temperature difference inside the collector still limit the development of DASC systems. To solve these problems, this paper firstly proposed to apply the electric field to manipulate the motion of nanoparticles to make the upper and lower nanofluids to exchange heat in the DASC system. The Al2O3-thermal oil nanofluids with the concentration of 0.01-0.3% are prepared, and the trans-mittance of the nanofluids and photothermal conversion as well as mechanism are performed and analyzed. The results show that the electric field can reduce the temperature difference inside the collector and improve the photothermal conversion efficiency of the DASC system. The temperature rise and photothermal conversion efficiency of 0.2 vol% Al2O3 nanofluid at voltage of 10 kV are 62.11 degrees C and 87.85%, which are 19.24% and 14.17% larger than those without electric field respectively. Under the action of electric field, the resuspension of deposited nanoparticles and heat transfer between upper and lower nanoparticles work together to improve the photothermal conversion efficiency of DASC system.