Abstract

Noble metal nanoparticles are introduced in solar applications to improve the photothermal efficiency of solar fluids used in direct solar absorption collectors. These metallic particles are interesting due to the effect of surface plasmon resonance (SPR), which usually occurs in the visible light spectrum, range weakly absorbed by most of the heat transfer fluids. When these nanoparticles are irradiated with the appropriate wavelength, the free charge carriers are perturbed and begin to oscillate with the same resonance as the irradiated energy. For this reason, particles able to interact with solar radiation can offer advantages in direct photothermal conversion processes, increasing the efficiency of solar collectors. In the present work, gold nanoparticles were introduced into water to be tested as a solar radiation absorber. Some studies confirm that with low concentrations of these nanoparticles in a base fluid, it is possible to increase the absorption capacity, obtaining a notable improvement in the efficiency of solar energy conversion to thermal energy. Three commercial nanofluids were tested, which contain gold nanoparticles with different sizes of 5, 20 and 50 nm. The particle size distribution was studied by measuring particles at different temperatures (25, 40, 60 and 85 °C) using the Dynamic Light Scattering (DLS) technique. The extinction coefficient of all samples was obtained by measurements with the help of a spectrophotometer. Finally, the temperature change achieved when lighting the samples with an artificial sunlight simulator was measured and photothermal conversion efficiencies were evaluated, with important increases when comparing the nanofluids with the base fluid. These results provide evidence of the improvement that occurs when nanoparticles are introduced into direct absorption solar collectors.