Temperature Dependency of Thermophysical Properties in Convective Heat Transfer Enhancement in Nanofluids

The temperature dependency of the thermophysical properties of an alumina-water nanofluid and their effects on laminar forced-convective heat transfer enhancement in nanofluids have been investigated analytically in this study. Exact solutions have been obtained for hydrodynamically and thermally fully developed nanofluid flows in a tube subject to constant heat flux, with and without accounting for the temperature dependency of thermophysical properties. The solutions reveal that the anomalous heat transfer enhancement is possible, irrespective of the account of the temperature dependency of nanofluid thermophysical properties, such that the heat transfer rate exceeds the rate expected from the increase in the nanofluid thermal conductivity. A comparison between the solutions, with and without accounting for the temperature dependency of nanofluid thermophysical properties, indicates that the temperature dependency of thermophysical properties only reflects on the relative magnitude of the Nusselt number and its asymptotic value, and that it does not have any significant influence on the occurrence of anomalous heat transfer enhancement.