Effects of multiple obstructions on conjugate forced convection heat transfer in tubes

A numerical investigation has been carried out for conjugate forced convection heat transfer in tubes with multiple obstructions. The investigation included the ranges of Reynolds number Re, thermal conductivity ratio k(r), and the distance between two obstructions d of 50-600, 0.3-3.0, and 2.0-8.0, respectively. A fluid Prandtl number Pr of 7.56 is used. The obstructions create recirculation flow / back flow in the tube with increase and decrease of local heat transfer rates. Reversal in the direction of heat transfer occurs at certain locations of the tube due to the presence of the obstructions. At high values of Re and d, reversal in the direction of heat transfer occurs on the outer wall after the second obstruction. are overall heat transfer rate decreases with the decrease of k(r).