Natural convection analysis of NEPCM suspension in a porous thermal energy storage unit with conducting wall under magnetic field effects

Energy efficiency in thermal systems critically depends on the design and performance of energy storage units, especially those capable of efficient thermal regulation. Among various thermal management strategies, latent heat thermal energy storage using Nanoencapsulated Phase Change Materials (NEPCMs) offers a promising solution due to its high energy density and ability to maintain a stable temperature during phase transitions. This study presents a comprehensive numerical investigation of natural convection heat transfer inside a circular porous thermal energy storage unit filled with a water-based NEPCM suspension. The configuration features two embedded active cylinders, one hot and one cold, thermally coupled via a conducting wall. The entire system is also subjected to a magnetic field, serving as an external control parameter for modulating the convective behavior of the flow. The governing equations are based on the Darcy-Brinkman-Forchheimer model under the Boussinesq approximation, incorporating the effects of flow resistance and non-Darcian behavior in porous media. These equations are nondimensionalized to generate the problem and numerically solved using the finite volume method. The primary aim of this work is to assess the influence of the thermally conducting wall on the enhancement and distribution of natural convection driven heat transfer within the NEPCM-filled medium. A detailed parametric study is conducted by varying the thermal conductivity ratio between the conducting wall and base fluid ( K* ), Rayleigh number ( Ra ), Hartmann number ( Ha ), Darcy number ( Da ), porosity ( ε ), Stefan number ( Ste ), and the dimensionless core melting temperature of the NEPCMs ( θ f ). Results show that thermal behavior in the system is largely governed by Ra, Da, Ha and thermal conduction through the solid wall, while the parameters such as Ste, ε , and θ f have a less pronounced influence. Interestingly, and somewhat unexpectedly, lower K * consistently yields better thermal performance across all scenarios.