Comparative CFD case study on forced convection: Analysis of constant <i>vs</i> variable air properties in channel flow

Abstract In this study, a steady-state forced convection heat transfer (HT) of air flow in a two-dimensional channel with a circular cross-section is numerically investigated. The analysis considers two heat sources at uniform temperatures along the lower surface of the mini-channel, with the upper surface remaining adiabatic to facilitate energy exchange. The heat sources are placed at distances L 1 = 3.5 m and L 2 = 1.5 m on the bottom surface. The finite element method is used to solve momentum-energy equations using Computational fluid dynamics (CFD) software, under constant and variable air properties. HT rates are computed for Reynolds numbers (Re ≤ 2,000) and Prandtl number (Pr = 0.713). The study evaluates the effects of Reynolds number, air thermo-physical properties, and thermal boundary conditions on hydrodynamic and thermal behavior. Results show that changes in the Nusselt number are significantly influenced by Re number, heat source configuration, and air properties. HT rate increases with Reynolds number, highlighting notable differences in centerline temperature, velocity, and conductive heat flux along the lower wall with variable air properties, with a maximum HT rate difference of 14% at T in = 20°C. Pressure also decreases with increasing Re number that shows good agreement between CFD results and empirical Shah equation.