Thermal Properties and Solar Collection Characteristics of Oil-based Nanofluids with Low Graphene Concentration

In order to improve properties of the photothermal conversion of heat-transfer oil used for direct absorption solar collection, a small amount of graphene was added to the base oil. The dispersion stability, thermal conductivity, and kinetic viscosity of oil-based nanofluids with different mass fraction of graphene were experimentally measured and analyzed. The dispersion stability was obtained using microscope imaging system, thermal conductivity was measured by a KD2 Pro thermal conductivity analyser, and kinetic viscosity was determined by viscometer. In addition, the absorption characteristics of graphene/oil nanofluids with different kinds of nanoparticles were tested by spectrophotometer. Finally, the experiment of nanofluid-based direct absorption solar collector (NDASC) was carried out and analyzed. Results show that the thermal conductivity of nanofluids was improved significantly and the kinetic viscosity of nanofluids reduced compared with that of pure oil; the optical characteristics of Oil-based graphene nanofluids presented high absorption coefficient, high extinction coefficient, and low scattering coefficient; The addition of nanoparticles to pure heat transfer oil could obviously enhance heat collection efficiency, and graphene/oil nanofluids obtained highest heat collection efficiency compared with CuO/oil nanofluids and graphite/oil nanofluids, which verified its feasibility and superiority of oil-based graphene nanofluids applied to direct absorption solar collector (DASC). (C) 2017 The Authors. Published by Elsevier Ltd.