Solar Heater of a Water Tank with PCM

Description

This project studies a solar water heater that uses encapsulated phase change material (PCM) for thermal storage, simulated in ANSYS Fluent. PCMs are attractive for this application because they absorb and release large amounts of latent heat while melting and freezing over a nearly constant temperature range, making them a self-regulating way to bank heat that arrives intermittently, exactly the pattern solar collection follows. The geometry is the annular gap between two coaxial tubes, with PCM filling that gap, built in Design Modeler and meshed in ANSYS Meshing with an unstructured grid of 5,803 cells. The inner wall, 0.0015 m thick, is held at a fixed 603.3 K to drive heat into the PCM, while the outer wall is set adiabatic so the PCM's thermal response can be studied in isolation from any outer heat loss.

Methodology

The energy equation is activated to resolve the temperature field, and the phase change itself is captured through Fluent's Solidification and Melting model, which tracks the PCM transitioning between solid and liquid as its temperature crosses the melting range. Because natural convection develops in the molten region and plays a strong role in how heat spreads through the material, the Boussinesq approximation is used to represent the buoyancy effects arising from temperature-dependent density changes. Setting up the phase-change physics requires specifying the PCM's solidus and liquidus temperatures along with its latent heat of melting. The study is structured to explore several variables: how the PCM's melting/freezing temperature affects performance, how the PCM volume affects storage behavior, and how the PCM-equipped tank compares against a tank with no PCM at all.

Analysis

Results are reported as contours of temperature, velocity, pressure, and liquid volume fraction. These fields track each other consistently through the simulation: as the PCM absorbs heat from the inner wall, its temperature rises and the liquid fraction increases correspondingly, and as it cools, the process reverses and the material re-solidifies. This direct correspondence between the temperature and liquid-fraction fields confirms the phase-change model is capturing the melting and freezing cycle correctly, providing a basis for evaluating how PCM properties and quantity affect the tank's thermal storage performance relative to a conventional, PCM-free design.