Effect of flow separation of TiO2 nanofluid on heat transfer in the annular space of two concentric cylinders

Abstract

In the wake of energy crises, the researchers are encouraged to explore new ways of enhancement in the thermal performance of heat exchanging equipment. In the current research, the SST k-? model and finite volume method were employed to augment heat transfer into the separation flow of TiO2 nanofluid in the annular space of two concentric cylinders. In the present investigation TiO2 nanoparticles of volume fractions, 0.5%-2% at Reynolds number range of 10000-40000, and contraction ratios from 1 to 2 were considered at constant heat flux boundary condition. Simulation results reveal that the highest enhancement in the heat transfer coefficient is corresponding to the annular pipe with a contraction ratio of 2 due to the generated re-circulation flow zone that begins after the separation point on the wall. Further, the surface heat transfer coefficient enhances with the increase of nanoparticles volume fraction and Reynolds number. The velocity distribution profile before and after the steps reveals that increasing the height of the step and Reynolds number, re-circulation regions also increases. Numerical results indicate that the highest pressure drop occurs at the Re = 40000 and contraction ratio of 2.