A critical review on convective heat transfer correlations of nanofluids

Nanofluids are engineered colloids made of a base fluid and nanoparticles, which become potential candidate for next generation heat transfer medium. Nanofluids have higher thermal conductivity and single-phase heat transfer coefficients than their base fluids. The heat transfer coefficient increases appear to go beyond the mere thermal conductivity effect, and cannot be predicted by traditional pure fluid correlations. This review summarizes the correlations development for fluid flow and heat transfer characteristics of nanofluids in forced and free convection flows. The review shows that most of the investigations recommended conventional friction factor correlation of base fluid for pressure drop prediction of the nanofluids for both laminar and turbulent flows in minichannel as well as in microchannel. However, the conventional correlation is not suitable for heat transfer coefficient of nanofluid and hence various correlations have been suggested for the Nusselt number for both laminar and turbulent flow. However, the large deviation of predicted values for proposed correlations has been observed may be due to strong influence of particle properties and nanofluid composition on flow and heat transfer characteristics, lack of common understanding on basic mechanism of nanofluid flow and insufficient experimental data on nanofluid heat transfer. Hence, a general framework for heat transfer correlation needs to be developed.