Enhancement of buoyancy-driven flow in an annular system by using nano-encapsulated phase change material fluid

Abstract

This study examines natural convection heat transfer in a two-dimensional annular cavity, with the inner boundary stipulated by the orthogonal intersection of two ellipses. The geometric configuration is defined by the ratio of the radii of the heated inner surface to the cooled outer cylinder such as RR = a/r = 0.4. The enclosure is filled with a porous medium and exposed to a uniform magnetic field, while the working fluid comprises water combined with nano-encapsulated phase change material (NEPCM) particles. The governing equations that include buoyancy effects, magnetic forces, porous medium resistance and phase-change behaviour are resolved with the Galerkin weighted residual finite element method. The flow is presumed to be steady, laminar and incompressible. A comprehensive parametric study is conducted to investigate the impact of governing physical and geometrical factors, encompassing the Rayleigh number (103–106), Hartmann number (0–80), Darcy number (10–5–10–2), nano-encapsulated phase change material volume fraction (0–5%), and cavity inclination angle (0°–80°). The outcomes demonstrate the progression of the flow structure, thermal field, heat transfer rate and distribution of specific heat capacity ratio within the enclosure. The elevated Ra and Da amplify convective circulation, whereas the increased Ha inhibits fluid mobility. The incorporation of nano-encapsulated phase change material markedly enhances thermal storage and mitigates temperature differences. The findings underscore the promise of NEPCM-based fluids, in conjunction with tailored cavity geometries, particularly enhancing the cross-section angles of the heated obstacle for enhanced heat management and energy-efficient mechanical system applications.