Experimental Study of Natural Convection Heat Transfer of TiO2/Ethylene Glycol Nanofluids

摘要

This work conducts heat transfer experiments with natural convection in a 80 x 80 x 180 mm vertical square enclosure (width x height x length) using variable volume fractions from 0.26% to 0.78% of TiO2/ethylene glycol (EG) nanofluids prepared using a two-step method. Measurement of the thermal transport properties of the nanofluids shows that thermal conductivity and viscosity both increase as the volume fraction of the nanofluid increases. Furthermore, the viscosity of the nanofluids decrease as temperature increases, but the change in viscosity at a fixed temperature is almost the same regardless of volume fraction. In contrast to pure EG, there is a shear thinning non-Newtonian behavior in the low shear rate region of gamma < 10 s(-1), although nanofluids are still treated as a Newtonian fluid for high shear rates of gamma > 10 s(-1). Nusselt numbers under different Rayleigh numbers are also obtained from experimental data, and for Rayleigh numbers between 10(7) <= Ra <= 10(8) the heat transfer of TiO2/EG nanofluids is worse than pure EG. The increased viscosity due to the addition of nanoparticles has a greater negative effect than the positive effect of the increased thermal conductivity.