Nanofluids as direct solar energy absorbers

Carbon nano horns with a mean dimension of 55 ± 15 nm, suspended in deionised water, is used as a black solar nanofluid and is stabilised by employing a new strategy called double stabilisation method to achieve long-term stability. Double stabilisation approach consists of adding a second surfactant that provides stability to the nanofluids even at high temperatures. The obtained solar nanofluids are exposed to an simulated sun condition to investigate the double stabilisation. Absorption spectra are measured by employing an integrating sphere in the range of 400-2000 nm. Averaging the data obtained for the different nanofluids, it is found that absorption values of nanofluid stabilised with sodium dodecyl sulphate alone are higher than those of nanofluid stabilised with sodium dodecyl sulphate and polyvinylpyrrolidone. However, for both nanofluids, it is found that the absorption spectra increase after being exposed to the artificial sun. These results demonstrate the enhanced performance of double stabilisation over single stabilisation and, also its effectiveness at high temperatures. Doubly stabilised samples is found to be better than singly stabilised suspension due to its high absorption combined with its high stability.