Exfoliated graphene oxide-based nanofluids with enhanced thermal and optical properties for solar collectors in concentrating solar power

Abstract Nanofluids are considered a promising alternative to the classic fluids used in heat transfer processes. One interesting application of nanofluids is their use as heat transfer fluid in thermosolar plants, such as those using concentrating solar power (CSP) technology. In turn, graphene oxide is an interesting nanomaterial for preparing nanofluids for solar thermal applications due to its appealing properties, such as high thermal conductivity, easy exfoliation and high black coloration. Therefore, this study presents the preparation by means of a liquid phase exfoliation (LPE) process of nanofluids based on graphene oxide in a typical fluid used in CSP plants. The efficiency of the LPE process and the stability of the nanofluids were analysed using UV–Vis spectroscopy, particle size measurements and transmission electron microscopy. Thermal properties were also measured, improvements of up to 6.6% and 45.5% being found for isobaric specific heat and thermal conductivity, respectively. Finally, strong-colored nanofluids were obtained and their optical properties were therefore characterized. Due to the strong coloration of the nanofluids, they can be used for designing Direct Absorption Solar Collectors (DASC).