Numerical Investigation of Using Nano-Encapsulated Phase Change Materials for Thermal Energy Storage

This study presents a numerical investigation of free convection-driven melting of nano-encapsulated phase change material (NEPCM) within a semi-bottle-neck-shaped porous enclosure. The cavity is differentially heated, with the left vertical wall kept hot, the right wall kept cold, and the remaining walls adiabatic. The enthalpy–porosity method is employed to model the melting process, while the Darcy–Brinkman model governs flow within the porous matrix. Parametric analyses are performed across a range of Rayleigh numbers (Ra = 10³–10⁵), fusion temperatures (θ f = 0.1–0.9), Stefan numbers (Ste = 0.1–0.9), nanoparticle volume fractions (ϕ = 0–0.05), Darcy numbers (Da = 10⁻ 4 –10⁻ 1 ), and Frank-Kamenetskii numbers (Fk = 0–1). Results reveal that increasing the nanoparticle volume fraction enhances thermal conductivity, leading to an improvement of up to 12.5% rise in the mean Nusselt number ( Nu a ). A rise in fusion temperature θ f from 0.1 to 0.9 leads to a 5.7% reduction in Nu a . Stefan number increases from 0.2 to 0.7, producing a 9% decline in Nu a , highlighting the latent heat damping effect. The Frank-Kamenetskii number, which characterizes internal heat generation due to exothermic reactions, significantly influences thermal transport: an increase in Fk from 0 to 1 decrease Nu a by approximately 7.7%, indicating thermal thickening and slower melting fronts. Additionally, the semi-bottle-neck geometry intensifies localized circulation, while the application of a magnetic field attenuates convection, offering a controllable method to regulate thermal performance. These insights are vital in developing NEPCM-based phase change thermal energy storage systems in porous environments.