Mixed convection in buoyancy-assisting, vertical backward-facing step flows

Abstract

Mixed convective heat transfer results for laminar, buoyancy-assisting, two-dimensional flow in a vertical duct with a backward-facing step are reported. The present numerical study examines a wide range of inlet flow and wall temperature conditions to cover the domain from pure forced convective flow, where the buoyancy force effects are not present, to the inlet starved convective flow where the buoyancy force effects are significant and where the average inlet velocity is smaller than the corresponding natural convective value. The results compare very favorably with existing, but limited, experimental and numerical data. This study focuses on a backward-facing step geometry with an expansion ratio of 2, but the general observed behaviors are applicable to similar geometries with different expansion ratios. The buoyancy-induced flow decreases the reattachment length and pushes the recirculating region away from the heated wall. Velocity and temperature distributions along with Nusselt numbers and wall friction coefficients are presented for wide ranges of flow and temperature parameters.