Numerical study of the critical heat flux in the nucleate boiling of hybrid nanofluids

Due to the growing need of industries to improve heat transfer methods, the nucleate boiling region is of special interest to researchers because fluid boiling makes it possible to achieve higher heat fluxes than processes that are based only on non-boiling convection heat transfer. In addition, the change of working fluid in boiling heat transfer systems from pure fluid to nanofluid improves the heat transfer characteristics and thus allows the transfer of higher heat flux at lower temperatures. At the critical heat flux point, where the heat flux is maximum, it is important to secure the boiling surface and protect it from overheating. The purpose of this study is to numerically simulate the pool boiling of a water-based hybrid nanofluid containing 30% multi-walled carbon nanotubes and 70% titanium oxide with a volumetric concentration of 0.5% on a polished copper circular surface and to investigate the heat transfer characteristics, especially the critical heat flux point. For this purpose, the boiling process of pure deionized water was first simulated by ANSYS-Fluent software and the results were compared with experimental data. According to the observed acceptable agreement, the mentioned water-based hybrid nanofluid, as boiling working fluid is numerically simulated by changing the density of nucleation sites and its heat transfer and heat flux characteristics are obtained. The results show that the critical heat flux for pure deionized water was occurred at 24.4 °C and is about 1.1 MW per square meter, while the critical heat flux for the hybrid nanofluid was occurred at 13 °C and is about 1 MW per square meter.