The new correlations for heat transfer in the cooling process of Al2O3 - Water nanofluids in pipe

Abstract

The aim of this experiment was to investigate convection heat transfer in the cooling processes of Al2O3-water nanofluid in concentrations of 0.15%, 0.25% and 0.5% by volume, respectively. The test section was a 1.25 m brass pipe with a 4.9 mm inner diameter and outer pipe of 38.5 mm diameter of a counter flow double-pipe heat exchanger. The temperatures at the nanofluid inlet in the inner pipe were a constant 40°C, and 23°C for the water at the inlet of the outer pipe. The results of this study indicated a more enhanced coefficient convective heat transfer of the cooling process than that of the heating process. The new equation of the Nusselt number obtained in the cooling process was Nunf=0.75Re0.846 Pr-2.28 φ0.03 at particle volume concentrations of 0.15%, 0.25% and 0.5%. The maximum ratio enhancement of the nanofluid heat transfer in the cooling process was 45.2% at a particle volume concentration of 0.25%, while for the heating process nanofluid heat transfer was same as that for distilled water.