CFD Assessment of Convective Heat Transfer in a Rectangular Duct: A Nusselt Number Analysis

This study presents a numerical investigation of laminar convection heat transfer in a non-standard rectangular duct subjected to a uniform surface heat flux of 1250 W/m². Although mentioned in technical standards, this geometry remains underexplored in the literature, despite its relevance for compact thermal systems. Computational fluid dynamics (CFD) simulations were performed in ANSYS Fluent (2020 R2) using water as the working fluid at a constant Reynolds number (Re = 998). The aluminum duct (300 mm × 10 mm × 20 mm) includes a bottom wall thickness of 6 mm. Parametric variations of inlet temperature and flow velocity were introduced to evaluate their influence on the spatial evolution of local and average Nusselt numbers. The results identify the dominant transport mechanisms governing laminar convection in confined geometries and provide relevant information for the design of high-efficiency cooling systems and rectangular heat exchangers operating in confined space conditions.