Convective heat transfer and friction factor correlations of nanofluid in a tube and with inserts: A review

In the heat transfer area researches have been carried out over several years for the development of convective heat transfer enhancement techniques. The use of additives in the base fluid like water or ethylene glycol is one of the techniques applied to augment the heat transfer. Recently an innovative nanometer sized particles have been dispersed in the base fluid in heat transfer fluids. The fluids containing the solid nanometer size particle dispersion are called 'nanofluids'. The dispersed solid metallic or nonmetallic nanoparticles change the thermal properties like thermal conductivity, viscosity, specific heat, density, heat transfer and friction factor of the base fluid. Nanofluids are having high thermal conductivity and high heat transfer coefficient compared to single phase fluids. The enhancement in heat transfer coefficient with the effect of Brownian motion of the nanoparticles present in the base fluid. In this paper, a comprehensive literature on the correlations developed for heat transfer and friction factor for different kinds of nanofluids flowing in a plain tube under laminar to turbulent flow conditions have been compiled and reviewed. The review was also extended to the correlations developed for the estimation of heat transfer coefficient and friction factor of nanofluid in a plain tube with inserts under laminar to turbulent flow conditions. However, the conventional correlations for nanofluid heat transfer and friction factor are not suitable and hence various correlations have been developed for the estimation of Nusselt number and friction factor for both laminar and turbulent flow conditions inside a tube with inserts.