Thermal behavior of aqueous iron oxide nano-fluid as a coolant on a flat disc heater under the pool boiling condition

Abstract

This paper experimentally focuses on the pool boiling heat transfer characteristics of gamma Fe₃O₄ aqueous nano-fluids on a flat disc heater. The nano-fluid used in this research was prepared using two-step method and was stabilized using nonylphenol ethoxylate nonionic surfactant, pH setting, and sonication process as well. Influence of different operating parameters such as heat flux (0-1546 kW/m²), mass concentration of nano-fluids (weight concentration 0.1-0.3%), bubble formation, critical heat flux (1170 kW/m² for water, 1230 kW/m² (wt%=0.1), 1320 kW/m² (wt%=0.2), 1450 kW/m² (wt%=0.3) and fouling on pool boiling heat transfer coefficient of nano-fluid as a thermal performance index were experimentally investigated and briefly discussed. Results demonstrated that the pool boiling heat transfer coefficient increases with increasing the mass concentration and the applied heat flux. In addition, the rate of bubble formation is significantly intensified at higher heat fluxes and subsequently, larger bubbles detach the surface due to the intensification of bubble coalescence. In terms of fouling formation, it can be stated that fouling of nano-fluids is a strong function of time and rate of deposition is increased over the extended time while the pool boiling heat transfer coefficient was not decreased over the time, as porous deposited layer on the surface are detached from the surface by bubble interactions. In terms of critical heat flux, capillary action of the deposited layer was found to be the main reason responsible for increasing the critical heat flux as liquid is stored inside the porous deposited layer, which enhances the surface toleration against the critical heat flux crisis.