Research on heat transfer performance of amphiphilic nanofluid solar gravity heat pipe

Modified graphene/deionized water (DW) based amphiphilic nanofluid (A-nanofluid) without surfactant was prepared through chemical method. The thermal performance of solar gravity heat pipe (SGHP) with A-nanofluid was investigated under different heating powers, incline angles and concentrations. It was found that A-nanofluid can reduce the start-up temperature of the SGHP compared with DW. Within the measured range of heating power, the thermal resistance of the SGHP filled with A-nanofluid is obviously lower than that with DW when the heating power is relatively small. However, the difference of thermal resistance of the SGHP filled with A-nanofluid and DW is almost negligible with the increase of heating power. The incline angle has great influence on the heat transfer capacity of the evaporation section when the incline angle is relatively small. When the heating power is 20 W and the nanofluid concentration (mass ratio) increases from 0.1% to 0.6%, the heat transfer coefficient of the evaporation section decreases by 54.7%; when the heating power is 40 W, the nanofluid concentration (mass ratio) increases from 0.1% to 0.6%, the heat transfer coefficient of the evaporation section decreases by 48.9%.