Laminar cooling of shear thinning fluids in horizontal and baffled tubes: Effect of perforation in baffles

The vortex generators are well known by their great efficiency to improve the hydrothermal characteristics of heat exchangers. The presence of baffles has proved its major role in the enhancement of heat transfer rates, but with a greater pressure drop. In this paper, circular perforations are introduced in the baffle embedded in a tube heat exchanger (THE) in order to reduce the pressure drop. The working fluid has a complex non-Newtonian behavior (shear thinning) modeled by the Ostwald's model. The influence of several geometrical and operating parameters on the flow fields and thermal characteristics of the heat exchanger are investigated. It concerns the presence of perforations in the baffle, the number of perforations (n(b) = 1, 2, 3 and 4), perforation diameter (d/D = 0.1, 0.26 and 0.4) and the Reynolds number (from 0.1 to 200). The predicted results revealed the advantage of perforated baffles in the reduction of pressure losses, also the thermal performance factor (TPF) at Re-g = 200 for the tube heat exchanger with d/D = 0.4 is found to be higher by about 13.6% and 6.5% than those at d/D = 0.1 and 0.26, respectively. An improvement in TPF by about 7% was obtained with n(b) = 4 compared to the baffle with only one perforation (n(b) = 1), at d/D = 0.1, Re-g = 200.