Numerical Study of the Effect of Non-Uniform Porosity on Hybrid Nanofluid Flow inside Porous Microchannel Affected by Magnetic Field
Abstract
: This study numerically investigated the flow of incompressible water-based hybrid nanofluid (Al 2 O 3 – Cu/water) in a two-dimensional horizontal microchannel with non-uniform porosity in the transverse direction. The medial region of the microchannel received a steady and uniform heat flux and was simultaneously exposed to a constant transverse magnetic field. While the remaining sections had an insulated wall without a magnetic effect. The results showed that the non-uniform porous layer suppressed the axial velocity, while the magnetic field further damped momentum by approximately 6–12% as Hartmann number increased from 0 to 40. Thermal response strongly correlated with flow inertia: the maximum dimensionless temperature increased from 0.03 at Reynolds number = 500 to 0.14 at Reynolds number = 10, confirming the dominance of conduction at low Reynolds number and convection at high Reynolds number. Increasing the hybrid nanoparticle concentration enhanced heat transfer; the local Nusselt number at the heated upper wall increased from Nu s ≈ 36 for the base fluid to Nu s ≈ 42–44 when using the Cu–Al 2 O 3 hybrid mixture with φ 1 = φ 2 = 0.04, representing a 15–20% improvement. Comparative analysis revealed that copper nanoparticles provide strong conductivity enhancement, whereas aluminum oxide improves thermal stability; they generate a synergistic effect absent in single-nanoparticle suspensions. The contour fields demonstrated a clear transition from diffusion-dominated transport (Re = 10) to convection-dominated flow (Re = 500), with isotherms tilting downstream and velocity lines becoming fully parallel at high flow rates. The numerical results show very good agreement with available analytical and numerical data for both velocity and temperature distributions. The small deviations observed confirm the accuracy and reliability of the present numerical model. Overall, the results demonstrate that combining non-uniform porosity with hybrid nanofluids under a magnetic field provides an effective approach for controlling the flow behavior and improving heat transfer performance in microchannel cooling systems. In addition, the close agreement between the present results and previously published studies confirms the accuracy and reliability of the numerical model.