Experimental Study on the Effect of Nanoparticle Migration on the Convective Heat Transfer Coefficient of EG/Water-based Al2O3 Nanofluids

Abstract

In this paper, the effect of nanoparticle migration on the convective heat transfer characteristics of EG/water-based Al2O3 nanofluids flowing through a simple round tube with constant heat flux in a fully developed turbulent flow regime was investigated experimentally. Homogenous EG/water-based Al2O3 nanofluids were mass-produced using a modified two-step method with both a dispersion with a nanodisperser and centrifugal decanting. The suspension stability, particle size, thermal conductivity, and viscosity of the nanofluids were systematically measured. To observe the effect of nanoparticle migration, the convective heat transfer coefficient of the nanofluids was experimentally measured according to NBT values, which indicates the ratio of the Brownian diffusivity to thermophoretic diffusivity. The convective heat transfer coefficients of nanofluids increased by at least 12.4% and up to 22.7% depending on the NBT values at the fixed Reynolds number. Moreover, the convective heat transfer coefficient of the nanofluids decreased by 7.7% (low NBT value) or increased by approximately 13.2% (high NBT value) under constant pumping power. These results indicate that the convective heat transfer coefficients of EG/water-based Al2O3 nanofluids under each condition are strongly dependent on the NBT values.