PCM Solar Collector

PCM Solar Collector CFD Simulation by ANSYS Fluent Tutorial

Description

This project simulates heat transfer within a PCM-based solar collector using ANSYS Fluent. The system centers on a U-shaped tube carrying water flow, surrounded by a cylindrical space filled with phase change material (PCM). This PCM region is itself enclosed by three concentric layers: an aluminum layer that absorbs incoming solar radiation, an air gap layer, and an outer glass layer.

The collector operates through a straightforward thermal pathway: sunlight passes through the glass layer, heating the enclosed air gap; this heat then transfers to the aluminum absorber layer, which in turn transfers heat inward to the PCM. During the day, as the absorber captures solar heat, the PCM absorbs part of this energy to drive its melting process. At night, as ambient conditions cool, the PCM releases its stored latent heat by solidifying, transferring that heat into the water flowing through the U-shaped tube — effectively storing daytime solar heat for use during colder nighttime hours.

Geometry & Mesh

The 2D geometry was designed in Design Modeler, consisting of two parallel pipes forming the U-shaped tube, surrounded by the cylindrical PCM layer. Around this, an incomplete cylindrical aluminum absorber layer was placed, followed by an incomplete cylindrical air gap layer, and finally an incomplete cylindrical glass layer as the outermost boundary.

The domain was meshed in ANSYS Meshing using a structured grid totaling 969,866 elements.

Methodology

The Solidification and Melting model was used to represent the PCM's phase-change behavior, with the material defined by a density of 910 kg/m³, specific heat capacity of 2100 J/kg·K, thermal conductivity of 0.5 W/m·K, and viscosity of 0.0273 kg/m·s. Its solidus temperature was set to 302 K, liquidus temperature to 310 K, and latent heat of fusion to 178,000 J/kg.

Radiative heat transfer and incoming solar radiation were captured using the Discrete Ordinates (DO) radiation model, which solves the radiative transfer equations across a discrete set of finite solid angles — well suited to this system's transparent glass layer, reflective surfaces, and wavelength-dependent transmission behavior. Solar ray tracing was activated to apply the solar load directly, requiring inputs such as the site's longitude and latitude, the date and time of the simulated radiation, solar direction, and both direct and diffuse radiation intensities. The laminar model and energy equation were enabled to solve the fluid flow and capture temperature variation throughout the domain.

Conclusion

Results include 2D and 3D contours of pressure, velocity, temperature, and the liquid mass fraction produced within the PCM. The results confirm that the PCM within the central cylindrical region undergoes a clear phase change, generating liquid within that zone as it absorbs solar heat. Comparing the U-shaped tube's inlet and outlet temperatures further confirms that heat is successfully transferred into the water flow — validating the collector's core function of capturing, storing, and later releasing solar thermal energy through the PCM's melting-solidification cycle.