Effects of Nanoparticle Size on Properties of Nanofluid and Heat Transfer Enhancement in Spiral Exchanger Using Turbulators

Abstract

In energy systems that use nanofluids as heat transfer fluid, the physical properties of nanofluids are important parameters in the efficiency of various heat exchangers, including small-scale micro channels or large-scale heat exchangers. In the present work, a comprehensive study is conducted to evaluate the thermal performance of a spiral heat exchanger with ball-type turbulators using nanofluid Al<sub>2</sub>O<sub>3</sub>/water. To investigate the effect of particle dimensions on nanofluid properties, nanoparticles with sizes of 20 nm and 50 nm at a volume concentration of 2% were examined. Heat transfer rate in the heat exchanger, performance evaluation criteria, heat transfer coefficient value, pressure drop, friction factor, Reynolds-Nusselt numbers relationship and pump power for fluid circulation have been calculated. ANSYS Fluent software as a computational fluid dynamic method was utilized to analyze the spiral heat exchanger under different working conditions. It was observed that both thermal conductivity and viscosity values increased as the nanoparticle size decreased. Heat transfer coefficient analyses showed that nanofluids with 20 and 50 nm particles exhibited a maximum improvement of 30.59% and 21.53%, respectively, when compared to pure water at an inlet velocity of 0.1 m/s. Additionally, the heat exchanger with turbulator showed a maximum increase of 24.87% at an inlet velocity of 0.5 m/s compared to the heat exchanger without turbulator. Moreover, maximum heat transfer rate enhancement was found to be 14.07% when the exchanger was equipped with turbulators.