A PCM-VOF hybrid framework for melting simulations with sharp solid-liquid interface tracking

Abstract

This study presents a novel numerical framework for simulating the melting process of Phase Change Materials (PCMs) by coupling an enthalpy formulation with a Volume-of-Fluid (VOF) interface-capturing approach (PCM-VOF). Unlike traditional enthalpy-based models, which often suffer from artificial interface diffusion, the proposed method explicitly resolves the solid-liquid interface through a conservative volume-fraction transport equation. Validation against four established benchmark cases demonstrates excellent agreement with experimental and numerical data, with deviations in average Nusselt number below 1%. Compared with the classical enthalpy method, the proposed PCM-VOF approach reduces interface thickness from approximately eight computational cells to nearly two cells in conduction-dominated regions, significantly suppressing numerical smearing. After validation, eight additional benchmark configurations were analyzed to evaluate the effects of fin arrangement and heated obstacle placement. The results demonstrate that conductive fins reduce total melting time by up to 95%, while locating the heated obstacle in the lower half of the enclosure increases the melting rate by approximately 2.28 times relative to upper placement. These findings provide quantitative design guidelines for optimizing latent heat thermal energy storage systems. The governing equations are discretized on a staggered grid system, with the convection terms in the momentum, energy, and volume fraction equations treated using the high-order accurate TVD flux-limiter scheme. The coupling between velocity and pressure is handled through the unsteady PISOR algorithm. The numerical results are presented in terms of solid-liquid volume-fraction distributions, temperature contours, streamline patterns, and temporal evolution of the melting rate.