A review on the thermal conductivity and viscosity models of nanofluids Impact on convection coefficient calculations

Recent advances in technology have given the opportunity of developing structures of nanometer scale suitably dispersed in base fluids. The term nanofluids, introduced by Stephen U.S Choi, describes the liquid suspensions which contain these structures (nanoparticles, nanotubes, nanodroplets etc). Even though the branch of nanotechnology, where nanofluids can be categorized, is in its infancy the growth of research work in terms of engineering applications that has been done already indicates the interest of researchers in nanofluids. As mentioned above a lot of research work, both experimental and computational, has been done in the field of nanofluids. As far as heat transfer is concerned, all researchers reach the same conclusion: heat transfer is enhanced while using nanofluids as means of cooling or heating due to the improved, among others, thermal conductivity of nanofluids compared to the conductivity of the base fluid which in most cases is water. The purpose of this review is to present the research that has been done on heat transfer calculations as well as the basic properties of the nanofluids. For this reason the structure of the review is divided into two topics. In the first topic models of calculating the effective thermal conductivity and the effective dynamic viscosity of nanofluids are presented. The aforementioned models have derived from both theoretical and experimental analysis. The second section concentrates on summarizing the correlations which calculate the Nusselt number and thus the convection coefficient.