Graphite/diamond ethylene glycol-nanofluids for solar energy applications

The rapid development of thermodynamic solar systems requires increasingly efficient absorption materials. This work reports on the investigation of light-intensity dependent optical properties of graphite/nanodiamond suspensions in ethylene glycol, in the perspective to evaluate their potential for direct absorption solar collectors and solar vapor generation. The study was carried out two sample types, differing in the ash content (0.3% and 5.9% wt in the powder), and at three concentrations each (0.0025%, 0.0050%, 0.0100% wt in the fluid). A high sunlight extinction was found, with full absorption in 15 mm and 30 mm path lengths for the 0.0100% and 0.0050% wt concentrations, respectively. This makes investigated nanofluids appealing as volumetric direct solar absorbers in solar collectors. Moreover, by characterizing optical properties at high incident intensities, we proved the creation of vapor bubbles in the base fluid via optical limiting effects active at least from ultraviolet to near infrared wavelengths. This result propose graphite/nanodiamond-based suspensions for sunlight-induced vapor generation application as well.