Heat Transfer Optimization in Zigzag Trapezoidal TES Using Nanoencapsulated PCM Under MHD Effects

ABSTRACT In this study, we investigated the thermal performance of nanoencapsulated phase‐change material (NEPCM) under magnetohydrodynamic (MHD) mixed convection in a three‐dimensional lid‐driven trapezoidal chamber featuring a zigzag‐shaped lower wall. The approach of enthalpy–porosity was employed to model the phase changing progression, and the impacts of key parameters—including Reynolds number ( Re = 0–500), Hartmann number ( Ha = 0–100), zigzag number ( N = 0–4), NEPCM volume fraction ( ϕ = 0%–8%), and magnetic field inclination angle ( α = 0°–90°)—were examined. We found that increasing Re significantly increased the average Nusselt number, driven by stronger lid‐driven convection. In contrast, increasing Ha suppressed fluid motion via the Lorentz force, resulting in a reduction of up to 65% in heat transfer efficiency compared with the nonmagnetic case ( Ha = 0). Increasing the zigzag number from N = 0 to 4 reduced the average Nusselt number by approximately 23%, primarily due to flow obstruction and geometric resistance. Higher NEPCM volume fractions improved heat storage capacity and promoted more extensive melting by sustaining temperature gradients. Additionally, the inclination angle of the magnetic field had a notable influence. As θ increased from 0° to 90°, the magnetic field became more perpendicular to the main flow direction, which intensified the damping effects and further decreased both the heat transfer and entropy generation efficiencies. These findings demonstrate that the combined effects of magnetic field orientation, field strength, cavity geometry, and NEPCM concentration play a crucial role in optimizing thermal performance and phase‐change behavior in MHD‐driven thermal energy storage systems.