Effect Of Porous Baffles On Fluid Flow And Heat Transfer In A BackwardStep Channel: Numerical Predictions
Abstract
In this paper, numerical analysis is used to study coupled fluid flow and heat transfer in a backward-facing step channel with a porous baffle installed at its midpoint. This configuration is a canonical geometry for investigating passive heat-transfer enhancement in separated internal flows. Simulations are performed using COMSOL Multiphysics 6.0 and the finite element method to solve a four-field coupled system comprising the incompressible Navier–Stokes equations for laminar flow, the Darcy–Brinkman model for porous media, and the two-dimensional energy conservation equation for heat transfer. A comprehensive parametric study investigates the effects of Reynolds number (Re = 100–2000), Darcy number (Da = 0.001–0.1), and viscosity ratio (a = μporous/μwater = 3–7) on the velocity field, pressure distribution, and temperature profile at the channel outlet. The results show a linear increase in maximum outlet velocity with Reynolds number, consistent with the definition of Re and the fixed geometry. The laminar nature of the flow is confirmed through literature benchmarks and an unsteady sensitivity study. The maximum velocity is 0.167 m/s at Re = 2000, Da = 0.001, and a = 7; at the same Re and a, it decreases to 0.098 m/s when Da = 0.1. The inlet-to-outlet pressure drop (ΔP = Pin − Pout) increases nonlinearly with Re. At Da = 0.1 and a = 5, the pressure drop is approximately 0.49 Pa at Re = 2000, showing that form drag and flow separation depend strongly on permeability and geometry. The bulk outlet temperature decreases as Reynolds number increases because the higher mass flow rate distributes the fixed heat input over a greater mass of fluid. The total heat-transfer rate remains constant at 40.00 W/m, consistent with the fixed heat-flux boundary condition. At high Re, the maximum-temperature differences between Darcy numbers are approximately 0.15 K, close to the discretization uncertainty of 0.09 K. The findings show that smaller Darcy numbers and higher viscosity ratios enhance jetting and convective heat transfer, offering design guidance for porous-baffle heat-transfer devices such as compact heat exchangers and obstructed cooling channels. Thermal-hydraulic performance is evaluated using the average Nusselt number, pumping power, and performance evaluation criterion (PEC). The PEC ranges from 1.12 to 1.42, indicating that thermal enhancement exceeds the hydraulic penalty. The energy balance closes within 0.38% for all cases.