PCM (Solidification & Melting): Storage Tank containing Phase Change Material

This project simulates the thermal performance of phase change materials (PCMs) within a storage tank using ANSYS Fluent, with solid–liquid phase change as the central theme. PCMs store and release thermal energy by melting and solidifying, and capturing that transition is the core of the study. Here the PCMs take the form of spheres arranged inside a vertical cylindrical storage tank. Hot water enters through an inlet pipe at the top of the tank at 0.1 m/s and 343 K, flows through the interior space around the spheres, and exits from the upper part of the tank. As the warm water transfers heat to the spheres, the PCM melts — and because this behaviour is governed by the phase change between solid and liquid states, the Solidification and Melting model is used for the simulation.

The process is inherently time-dependent, so a transient solver is used over a total simulation time of 100 s with a time-step size of 1 s. The study is carried out across several configurations to isolate the factors that govern melting: two PCM materials (paraffin and SAT-G), two sphere radii (4 cm and 5 cm) and two melting temperatures (333.15 K and 332 K). The aim is to investigate the fluid and thermal behaviour of the PCMs and to track how the liquid mass fraction evolves as a function of the spheres' physical size, the melting temperature and the material itself.

The geometry is three-dimensional and was created in Design Modeler, then meshed in ANSYS Meshing with an unstructured grid of 757,886 elements.

The heart of the methodology is the Solidification and Melting model, which is specifically formulated for the phase change process between solid and liquid states; it tracks the advancing melt front through the liquid fraction in each cell rather than meshing a moving interface explicitly. The two materials, paraffin and SAT-G, are defined in Fluent through their respective thermophysical properties so that each melts according to its own characteristics.

After solving, the simulation yields two- and three-dimensional contours of pressure, temperature, velocity and the liquid and solid mass fractions at the final instant of the process, together with a graph of the PCM liquid mass fraction over time. The results show that the longer the heating continues, the greater the fraction of PCM that melts; as the material absorbs heat and melts, the tank temperature rises, and the regions of higher temperature correspond to regions of lower pressure. As a study in solidification and melting modelling, the project demonstrates how the phase-change model can quantify the melting behaviour of PCMs in a thermal storage tank — revealing how material choice, sphere size and melting point together determine how quickly and completely the storage medium charges with heat.