Numerical Study of Phase Change Material Melting in a Square Enclosure under Constant Wall Heat Flux

Background: Phase change materials (PCMs) can store thermal energy through solid–liquid transitions, but their melting behaviour depends on material properties and heat-transfer conditions. Aims: The study aims to compare the transient melting response of paraffin wax, lauric acid and capric acid in a square enclosure under constant wall heat flux and to examine an idealized PCM building-envelope application. Study Design: Two-dimensional transient computational fluid dynamics using the enthalpy–porosity method. Place of Study: Department of Mechanical Engineering, College of Technology, G. B. Pant University of Agriculture and Technology, Pantnagar, Uttarakhand, India. Study dates: [1.7.2023 to 30.9.2024]. Methodology: A 20 mm × 20 mm PCM enclosure coupled to a 2 mm aluminium wall was heated at 1500 W/m², with the other external boundaries adiabatic. The reported calculations used 88,000 elements and a 0.1 s time step. Mass and applied energy are expressed per metre of out-of-plane depth. A separate capric acid building-envelope model was subjected to 200 W/m² for 1 h. Results: For the reported material-property set, the simulations predicted complete melting at approximately 50 min for capric acid, 80 min for paraffin wax and 120 min for lauric acid. The corresponding applied energies were 90, 144 and 216 kJ/m, respectively. These values describe energy supplied to the PCM–aluminium system, rather than PCM storage capacity. The idealized building model predicted an inner concrete-surface temperature of 305.48 K, a reduction of 9.52 K relative to the reference configuration. Conclusion: The reported simulations indicate an evolving contribution of buoyancy-driven flow during melting. The material ranking is conditional on the reported properties, particularly the paraffin viscosity. The building calculation illustrates surface-temperature buffering under the specified conditions but does not establish annual cooling-energy savings.