Heat transfer property of SiO2/water nanofluid flow inside solar collector vacuum tubes

Nanofluid is one of the innovative and promising heat-transfer fluids. In this work, SiO2/water nanofluid was prepared with two-step method by microfluidizer processor. The thermal conductivity and the transmissivity of SiO2/water nanofluid with mass fraction of 1%, 3% and 5% were tested in the experiment. The temperature variations and velocity distributions of working fluid including water and nanofluid were calculated via numerical simulation in order to discuss the heat transfer property of SiO2/water nanofluid flow inside the collector tube. According to the numerical model, water and SiO2/water nanofluid (5 wt.%) were chosen as the working fluids of solar-collector vacuum tubes in insolation experiment, respectively. The results showed that the heat-transfer property of SiO2/water nanofluid were higher than that of water and increased with the mass fraction. Meanwhile, the influences of the placing time of nanofluid on heat transfer property were also referred. The results indicated that longer nanofluid placing time, easier nanofluid agglomeration and this phenomenon led to its heat transfer character became weak. (C) 2017 Elsevier Ltd. All rights reserved.