Impact of the square rib on flow dynamics and thermal performance in the microchannel

A three-dimensional numerical investigation of flow and heat transfer has been carried out within a microchannel containing a square rib, focusing on flow separation, recirculation, and vortex shedding over the range of the Reynolds number (Re) from 12 to 1000. The study explores the impact of rib orientation, channel aspect ratios, and Re on the formation of recirculation bubbles, flow symmetry, and boundary layer behavior with a detailed impact of wall shear stress. At low Re, steady flow is observed with minimal recirculation behind the rib. As Re increases, flow separation occurs, leading to the formation of recirculation bubbles in the rib wake and along the sidewalls. Particularly for the rib with two sidewalls parallel to the vertical mid-plane of the channel and at Re = 85, flow separation initiates on the sidewalls of the rib but reattaches immediately. At 101 ≤ Re ≤ 400, the flow separation occurs on both sidewalls and the wake of the rib. A further increase in 400 < Re ≤ 900 leads to the merging of recirculation bubbles of the rib sidewalls and wake, with the recirculation bubbles center shifted to the saddle point. The wall shear stress highlights the flow separation near the sidewalls and wake of the rib. The critical Reynolds number (Rec) for flow transition is identified between 900 < Re ≤ 1000, where unsteady flow is characterized by the change of vortex shedding with time. Additionally, by applying heat flux to the bottom wall of the microchannel, the influence of varying Re on the average Nusselt number, friction factor, local heat transfer coefficient, wall shear stress, and vortex formations is analyzed.