Renewable Energy: Solar Heater of Water Tank with PCM

Solar Water Heater with PCM Thermal Storage (Solidification & Melting) — ANSYS Fluent CFD Simulation

Phase change materials (PCMs) store and release large amounts of energy as they melt and freeze over a nearly constant temperature range — the latent heat of the phase change. That makes them a powerful, self-regulating way to store thermal energy, and they've become especially popular for solar applications, where heat is available intermittently and needs to be banked for later. This project uses ANSYS Fluent to study a solar water heater that uses encapsulated PCM in its storage tank, modeling how the material melts and solidifies as it charges and discharges heat — a modern approach to improving solar thermal storage.

The geometry, built in Design Modeler, is the annular chamber between two coaxial tubes, with the space between them filled with PCM. It's meshed in ANSYS Meshing with an unstructured grid of 5,803 cells. The PCM region's inner wall is held at a fixed temperature of 603.3 K with a thickness of 0.0015 m, driving heat into the material, while the outer wall is set adiabatic so the study isolates the PCM's thermal response.

The simulation activates the energy equation to resolve the temperature field, and the core physics is handled by Fluent's Solidification and Melting model, which tracks the PCM changing phase between solid and liquid as the temperature varies inside the storage region. The Boussinesq model is used to capture the buoyancy effects from density changes with temperature — the natural convection that develops in the molten PCM and strongly influences how heat spreads. Setting up the phase-change model requires defining the solidus and liquidus temperatures and the latent heat of melting for the material. The project is framed to investigate several factors: the effect of the PCM's melting/freezing temperature, the effect of the PCM volume, and a comparison against a tank with no PCM at all.

At the end of the solution, you generate contours of temperature, velocity, pressure, and liquid volume fraction. The results show full consistency between the temperature field and the liquid fraction: as the PCM heats up under the inner-wall boundary condition, it melts and the liquid fraction rises, and as it cools, the phase change reverses and the material solidifies. By the end of this project, you'll be able to set up a phase-change simulation using the Solidification and Melting model, apply the Boussinesq approximation for buoyancy-driven convection in a melting material, define the thermophysical parameters that govern phase change, and interpret coupled temperature and liquid-fraction results to evaluate a PCM-based thermal storage design.