Computational simulation of heat transfer to separation fluid flow in an annular passage

The separation and the reattachment of water flow through a sudden expansion in an annular passage have been considered in this paper. In the present work, numerical simulation is performed using the computational fluid dynamics package (FLUENT) to study the effect of step flow in an annular passage. In the study, the flowing fluid was considered heated uniformly from the beginning of the expansion, and the constant heat flux approach was also considered for the heat transfer investigation. The annular pipe flow system having step ratio of D/d = 1.8 was considered, where d and D are representing the diameter of the pipe before and after expansion. The increase of flow reduces the surface temperature along the pipe to a minimum point, then gradually increases up to the maximum and hold for the rest of the pipe. The minimum surface temperature is obtained at flow reattachment point. The position of the minimum temperature point is dependent on the flow velocity over sudden expansion. In general, the local Nusselt number (Nu) increases with the increase of Reynolds number.