Secondary Flow and Entropy Generation of Laminar Mixed Convection in the Entrance Region of a Horizontal Square Duct

Abstract

The flow structure, heat transfer, and entropy generation characteristics in the entrance region of mixed convection under the effect of transverse buoyancy force are investigated numerically. Results are obtained for laminar flow of uniform inlet velocity and temperature through a square duct with uniform wall temperature. The buoyancy induced-secondary flow is observed in the entrance region where flow structure and heat transfer are significantly affected. The flow entrance region is extended by buoyancy, while the thermal entrance region is shortened. The developments of Nusselt number and local entropy generation are discussed in detail for Richardson numbers of 0 ≤ Ri ≤ 10, Reynolds number Re = 100 and Prandtl number Pr = 0.7. The total heat transfer rate and global entropy generation by friction increase with buoyancy, while global entropy generation by heat convection changes a little. The effect of Reynolds number on entropy generation is also discussed.