BN white graphene well-dispersed solar salt nanofluids with significant improved thermal properties for concentrated solar power plants

Abstract

Solar salt is the most commonly used medium for thermal storage and transfer in concentrated solar power (CSP) plants, and the utilization efficiency of solar energy is depended on the thermal properties of solar salt. In this work, atomic-layer-thick hexagonal boron nitride nanosheet (BNNSs, so called white graphene) were obtained and dispersed into solar salt uniformly to produce composites nanofluids. Attributed to the ultra-high thermal conductivity and a large specific surface area of BNNSs, which reduce the thermal resistance, and facilitate forming of more semi-solid boundary layer and nucleation sites, the as-prepared composites nanofluids show superior thermal properties. The properties enhancement mechanism and effects of the mass fraction of BNNSs on the thermal properties of nanofluids was investigated carefully. Compared with the pure solar salt, the solid-phase thermal conductivity, solid-phase and liquid-phase specific heat capacity was elevated by 76.79%, 29.8% and 12.82%, respectively. At the same time, the supercooling degree was significantly decreased from 12.2 °C to 4.7 °C. The enhanced thermal conductivity and specific heat capacity offer significant cost savings, and the reduced supercooling degree prevent phase separation and pipe blockage. Thus, the developed composites nanofluids can be used as a superior medium for CSP plants.