Mixed convection within trapezoidal-wavy enclosure filled with nano-encapsulated phase change material: Effect of magnetohydrodynamics and wall waviness

The present work investigates the mixed convection of nano-encapsulated phase change material (NEPCM) inside a trapezoidal-wavy cavity subjected to a magnetic field. The mixed convection results from the movement of the upper lid of the cavity and the temperature difference between the inclined cold side walls and the hot bottom wavy wall. The main goal of this study is to address the impact of wall waviness and the magnetic field on mixed convection on a disclosure filled with NEPCM. The governing equations representing the investigated case were solved by Galerkin finite element method (GFEM). The influences of lid velocity (Re = 1-1000), bottom wall undulation number (N = 1-4), and magnetic field strength (Hartmann number (Ha) = 0-100) on the thermal behavior and the flow patterns were examined and reported. The results revealed that the mean Nusselt number is directly proportional to the lid velocity (Re), whereas it is reverse proportional to the bottom wavy undulation number (N) and the magnetic field strength (Ha). The higher values of Re (e.g., Re = 1000) could lead to a 300% enhancement in local Nu values compared to those of lower Re values (e.g., Re = 1). At Re = 1000, increasing Ha from 0 to 100 and N from 1 to 4 reduced the mean Nusselt number by 53% and 30%, respectively. According to the findings of the present study, it is recommended that heat transfer augmentation should eliminate both the waviness of the bottom wall and the magnetic field since they hinder the free and mixed convection flow.