Particle shape effects on some of the transport properties of tungsten oxide nanofluids

Abstract

In this work, for the first time, particle shape effect on transport properties of nanofluids of tungsten oxide nanoparticles (NPs) in glycerol was investigated. For this purpose, WO3 NPs with different shapes using two methods of hydrothermal and microwave in the presence and absence of sodium chloride were prepared. The TEM images showed that the method of preparation and presence or absence of NaCl influence the morphology and shape of WO3 NPs. For mass fraction of 0.5, a maximum of 46.9% and minimum of 11.7% reduction in viscosity of glycerol were observed for the nanofluids having the maximum spherical and polygonal-shape NPs, respectively. The results showed that the viscosity of glycerol and the nanofluids decreases exponentially with increasing temperature. The effect of temperature on the viscosity of nanofluids with polygonal shape NPs was greater than those of other shapes. The thermal conductivity of glycerol and suspensions of WO3 NPs in glycerol was measured at different temperatures. The maximum and minimum enhancements in thermal conductivity were observed for the samples containing the greatest and lowest values of spherical and polygonal-shape NPs, respectively for all temperatures. A maximum of 6.7% enhancement in the thermal conductivity of glycerol at 40°C was observed when the NPs with a mass fraction of 0.5, prepared by hydrothermal method, was added. The thermal conductivity ratio of nanofluids increases with raising temperature linearly.