Investigating Flow and Heat Distribution of NE‐PCM in a Double Lid‐Driven MHD Octagonal Chamber

ABSTRACT Mixed heat transfer, commonly encountered in engineering applications, has led to a strong focus on maximizing heat transmission rates. This study explores heat transfer enhancement within a magnetohydrodynamic (MHD) double lid‐driven octagonal cavity. The cavity is filled with porous media and loaded with nano‐encapsulated phase change material (NE‐PCM), subjected to a uniform magnetic field. The Galerkin finite element method (GFEM) is employed to solve the governing equations. Key factors investigated include lid speed (Reynolds number, Re = 1–500), wall movement directions, magnetic field intensity (Hartmann number, Ha = 0–100), and cavity porosity (Darcy number, Da = 10 −5 –10 −2 ) and their effects on heat transmission rates. The numerical method was validated by comparing results with well‐documented data from the literature. The findings reveal that higher Re and Da values significantly enhance heat transfer rates, while higher Ha values reduce heat transfer rates. Specifically, at the highest Re, increasing Da from 10 −5 to 10 −2 enhanced the averaged Nusselt number ( Nu ) by 165%, while increasing Ha from 0 to 100 decreased it by 16%. Additionally, moving both walls in the same direction improved the average Nu by 350% compared to opposing wall movement. The study also found that increasing NE‐PCM concentration had a minimal impact on heat transfer efficiency, while reducing chamber permeability hindered suspension movement, thereby reducing heat transfer between the hot and cold surfaces.