Numerical simulation of heat transfer to separation air flow in an annular pipe

Separation and reattachment of air flow through a sudden expansion in an annular passage are considered in this study. Backward facing steps play a vital role in the design of many heat related applications where heat transfer is concerned. In the present work, numerical simulation is performed using computer fluid dynamics package (Fluent) to study the effect of step flow in an annular passage. The results are compared with the preliminary experimental findings. In the study, the flowing fluid was considered heated uniformly from the beginning of the expansion. Constant heat flux approach was also considered for the heat transfer investigation. Annular pipe flow system having a step ratio of D/d = 1.8 was considered where d and D are representing the diameter of the pipe before and after expansion. Numerical simulation review shows that the reattachment point extends further with the increase of velocity for different occasions. Finally, the local Nusselt number (Nu) in separation flow increases with the increase of Reynolds number (Re).

► Numerical simulation is performed using CFD package (FLUENT).
► Enhanced Nu is obtained in backward facing steps.
► Nu and Re correlations show similar trend in concentric annular and step flows.