Numerical study of the influence of rib orientation on heat transfer enhancement in two-pass ribbed rectangular channel

Strong secondary flow generated by ribbed channel and U-shaped bend is the key for forced convection performance and energy dissipation in U-shaped cooling passage. This investigation studies the coupling of nine different rib orientation and the 180-degree bend on overall friction loss and forced convection in the U-shaped passage by ANSYS CFX commercial CFD package when Re = 30000. The comprehensive evolution of secondary flow is visualized by vortex core method and colored by turbulence kinetic energy. The qualitative results show that the Nu ratio and overall pressure loss in the downstream passage (Passage 2) is highly affected by the upstream geometry. The N-type rib orientation in Passage 1 delivers more disturbance energy into Passage 2 where P-type rib orientation can reduce the momentum loss of the upstream secondary flows and pressure loss. Based on the understanding of interaction of secondary flow near the bend, modified bend geometry is proposed with 9% thermal performance gain over the existent optimized rib orientation. This investigation suggests vortex core method is a promising visualization tool for the flow control and optimization in U-shaped cooling channel with angled ribs