Effects of nanoparticles migration on heat transfer enhancement at film condensation of nanofluids over a vertical cylinder

The change in concentration and direction of nanoparticle migration can control the thermophysical properties of nanofluids. This dynamic is useful since it is able to improve the cooling performance by tuning the flow and heat transfer rate. In the current study, a theoretical investigation on the impact of nanoparticle migration on heat transfer enhancement of nanofluids condensate film over a vertical cylinder has been conducted. The Brownian motion and thermophoretic diffusivity have been considered by using the modified Buongiorno model which can take into account the effect of nanoparticle slip velocity. The results have been obtained for different parameters, including the Brownian motion to thermophoretic diffusivities N_BT, the saturation nanoparticle volume fraction ϕ_sat, and the normal temperature difference γ = (T_sat-T_w)/T_w. It is shown that nanoparticle migration has significant impact on the flow and thermal fields and considerably affects the heat transfer rate. Furthermore, heat transfer enhancement in film condensation is strongly depended on the thermophysical properties of nanoparticles such that alumina-water nanofluid exhibits higher cooling performance than titania-water.