Effects of rib angle and rib orientation on flow and heat transfer in two-pass ribbed channels

The secondary flows generated by the rib and the U-shaped bend play a vital role in heat transfer enhancement in two-pass ribbed channels. This paper focuses on the combined effects of rib orientations (N-type and P-type) and rib angles (from 30º to 75º) on flow and heat transfer in two-pass ribbed channels. The 3D steady Reynolds-averaged Navier–Stokes equations coupled with SST k-ω model are solved by using commercial software ANSYS CFX. The CFD model has been validated by experimental data with a good agreement. In addition, the comprehensive evolution of secondary flows and its effect on heat transfer are analyzed in detail by using vortex core technology. The results indicate that the key factor for local heat transfer enhancement is to transport more secondary flows into downstream passage without weakening local secondary flow and energy dissipation of upstream secondary flow. Furthermore, the rib orientation in passage 2 should consider the influence of rib angle so that the local main flow secondary flow has the same rotational direction with the most powerful upstream secondary flow to reduce the energy loss and speed up the growth of local main flow secondary flow as much as possible.