Entropy Generation and Heat Transfer in a Circular Cavity With Immiscible Fluids: Effects of Active Cylinder Position and Oscillating Magnetic Field

This study investigates entropy generation and heat transfer in a circular cavity containing immiscible air and TiO 2 –water nanofluid layers with a centrally positioned active cylinder under oscillating magnetic field influence. The governing equations were solved using the Galerkin weighted residual finite element method with a penalty formulation. The study examined the effects of Rayleigh number (10³ ≤ Ra ≤ 10⁶), Hartmann number (0 ≤ Ha ≤ 80), magnetic field wavelength (0.1 ≤ λ ≤ 0.9), nanoparticle volume fraction (0 ≤ ϕ ≤ 0.05), and active cylinder position (bottom, top, center, and right). Results indicate that cylinder position significantly impacts thermal performance, with the bottom configuration yielding up to 94.1% higher heat transfer rates than the top position. Increasing magnetic field strength progressively suppressed convective flows, reducing heat transfer by up to 16.9% while decreasing entropy generation by up to 82.3%. Nanoparticle addition enhanced heat transfer across all configurations by up to 23.8% as concentration increased from ϕ = 0.01 to 0.1, though at the cost of increased system irreversibility. The top position demonstrated remarkable thermal stability across varying Rayleigh numbers, making it suitable for applications requiring consistent performance. These findings provide valuable insights for optimizing thermal management systems involving immiscible fluids under electromagnetic influence, with applications in electronics cooling and energy systems.