Double-Diffusive flow and heat transfer of nano-encapsulated phase change materials in a circular cavity with partial porous region under magnetic influence

• Increasing nanoparticle volume fraction (ϕ) from 0 to 0.05 at Ra = 10⁵ enhances heat transfer by 128 % while reducing mass transfer by 10.3 %. • Magnetic field strength (Ha) increasing from 0 to 61 at Ra = 10⁵ reduces both Nu and Sh by approximately 55 % and 57 % respectively. • Mass transfer shows significant enhancement (389 % increase in Sh) as Lewis number increases from 0.1 to 10 at Ra = 10⁵. • Critical Darcy number identified at Da = 10⁻³; increasing Da from 10⁻⁵ to 10⁻¹ at Ra = 10⁵ improves Nu and Sh by 158 % and 218 % respectively. • Optimal fusion temperature (θ f = 0.6) identified for maximum heat transfer enhancement at Ra = 10⁵. A numerical investigation of double-diffusive natural convection and magnetohydrodynamics (MHD) in a circular cavity containing nano-encapsulated phase change materials (NEPCM) with a partial porous medium under magnetic field influence has been conducted. The governing equations were discretized using the Galerkin finite element method, and the resulting nonlinear system was solved through the Newton-Raphson iteration technique with PARDISO solver. The study examined the effects of key parameters including Rayleigh (Ra) number (10³-10⁵), Hartmann (Ha) number (0–61), Darcy (Da) number (10⁻⁵-10⁻¹), Lewis (Le) number (0.1–10), buoyancy ratio (2–6), nanoparticle volume fraction (0–0.05), and fusion temperature (0.1–0.9). Results show that increasing nanoparticle concentration from 0 to 0.05 enhances heat transfer (Nusselt number, Nu) by 128 % while reducing mass transfer (Sherwood number, Sh) by 10.3 % at Ra = 10⁵. The magnetic field demonstrates a significant suppressive effect, with Ha increasing from 0 to 61 reducing both Nu and Sh by approximately 55 % and 57 % respectively. An optimal fusion temperature of 0.6 was identified for heat transfer enhancement, while mass transfer showed minimal sensitivity to fusion temperature variations. The study reveals that proper selection of operating parameters, particularly Da and Le numbers, can improve system performance by up to 218 % in mass transfer and 158 % in heat transfer, providing valuable insights for the design of thermal energy storage systems incorporating NEPCM and porous media.