Experimental study of photothermal conversion using gold/water and MWCNT/water nanofluids.

This work experimentally investigated photothermal conversion behavior of Gold/water and MWCNT/water nanofluids at different volumetric concentrations (0.0001–0.004% and 0.0001–0.03%, respectively) in a direct absorption solar collector (DASC). The experiments were conducted for ~10 h outdoor on each test day, without interruptions. The results show that the tested nanofluids have excellent photothermal conversion capability even under very low concentrations. Specific absorption rate (SAR) presented an exponential decay with increasing volumetric concentration of nanoparticles in the sample while both the total energy stored by the fluid sample during the heating period and the stored energy ratio (SER) increased with the increase in nanoparticles concentration. The results indicate the existence of an “optimal” volumetric concentration, above which further nanoparticle addition becomes indifferent or infeasible. This optimal nanoparticle volumetric concentration was found to be 0.002% for the gold nanofluid and 0.001% for the MWCNT samples for the setup used in this work