Experimental investigation of the heat and fluid flow of an Al2O3-water nanofluid in the laminar-turbulent transition region

Abstract

Nanofluids present enhanced thermal conductivity compared to their base fluid and then have become good candidates for heat transfer fluids. In this study, the convective heat transfer coefficient and the pressure drop are measured in a circular tube of inner diameter 4.4 mm and outer diameter 5 mm. The experiments were conducted from Reynolds number ReD of 500 up to 4500. After making sure that the results for water were in good agreement with the literature, five concentrations of a γ-Al2O3-water nanofluid were tested. The results show that the concentration has no impact on the critical Reynolds number corresponding to the laminar-turbulent transition for this nanofluid up to 5w%. Moreover, a slight enhancement of the convective heat transfer coefficient is noted in laminar flow with increasing mass concentration while no significant amelioration is observed in turbulent regime compared to water. On the other hand, the pressure drop strongly increases with concentration whatever the flow regime. As a result, the thermal performance (Convective heat transfer coefficient at constant pumping power) of this nanofluid is lower than pure water.