Numerical and experimental investigations of hybrid nanofluids on pulsating heat pipe performance

This study investigates the thermal performance of a four-turns Pulsating Heat Pipe (PHP) using a weight concentration of 0.1 wt% Al2O3-CuO hybrid nanofluid, 0.1 wt% SiO2-CuO hybrid nanofluid and water both experimentally and numerically. The start-up pulsations, average evaporator temperatures, thermal resistance, two-phase flow, and non-linear temperature analysis were evaluated with respect to heating power and filling ratio of 10-100 W and 50-60%, respectively. Stability measurement and characterization of thermal conductivity and viscosity properties of hybrid nanofluids were determined. From the experimental results, the, thermal resistance SiO2-CuO hybrid nanofluid exhibited was the lowest, i.e. 57% lower than that of water, followed by the Al2O3-CuO hybrid nanofluid, i.e. 34% lower than that of water at the heat input and filling ratio of 80 W and 60%, respectively. Nevertheless, the thermal conductivity and viscosity of Al2O3-CuO hybrid nanofluid were higher than those of SiO2-CuO hybrid nanofluid. The increased viscosity found in Al2O3-CuO hybrid nanofluid would hinder the fluid transportation in PHP, thus augmenting the thermal resistance. Meanwhile, the hybrid nanofluids were able to achieve start-up pulsations earlier and they required lower heating power to reach start-up pulsations as compared to water. At low heating power (below 30 W), the differences in average evaporator temperatures for hybrid nanofluids and water were very small. However, at higher heating power (above 30 W), the differences were significant. The numerical results compared well with those earlier experimental work, thus indicating the reliability of the current numerical simulation. (C) 2019 Elsevier Ltd. All rights reserved.