Solar Heat Exchanger

Solar Heat Exchanger, ANSYS Fluent CFD Simulation Tutorial

Description

This project investigates a specialized solar heat exchanger design featuring a solar absorber plate, an air gap, and internal flow barriers that together capture solar thermal energy and transfer it to a working fluid. The system uses a dual-medium approach — an air gap positioned between the front plate and the absorber, paired with a water flow channel routed through strategic internal barriers to extend fluid residence time and improve heat transfer.

Heat moves through the system in stages: solar radiation is first absorbed at the absorber plate, warming the adjacent air gap through combined radiation and convection; heat then conducts through the absorber plate itself before transferring convectively into the water flowing through the extended channel formed by the internal barriers.

The domain was meshed in ANSYS Meshing using an unstructured grid totaling 304,200 elements, with increased resolution concentrated near the absorber plate and internal barriers to accurately capture the more complex local flow and thermal behavior in those regions.

Methodology

Radiation was modeled using the Discrete Ordinates (DO) model, chosen for its ability to handle scattering media, semi-transparent boundaries, specular surfaces, and wavelength-dependent transmission — all relevant to accurately capturing how solar energy moves through the air gap and interacts with the absorber surface. Solar ray tracing was used to apply the incoming solar load directly, with direct solar radiation set to 1150 W/m² and diffuse solar radiation to 80 W/m², striking the absorber plane at a perpendicular incidence angle.

Water entered the flow channel at 4 m/s and 30°C, with the outlet held at atmospheric pressure. The air gap was governed by natural convection combined with radiation heat transfer, while the absorber surface itself served as the primary thermal boundary receiving the solar load.

Conclusion

Results characterize the system's thermal and flow behavior in detail: temperature distribution throughout the exchanger reveals the primary heat transfer pathways, with the absorber's surface temperature profile and the water's progressive temperature rise along its extended flow path both clearly captured. Velocity and pressure results show how the internal barriers shape flow development, identify any recirculation zones that may enhance or hinder thermal mixing, and quantify the pressure drop introduced by the extended flow path.

Radiation-specific results further reveal how absorbed solar energy distributes across the absorber surface, the resulting thermal stratification within the air gap, and the relative contributions of direct versus diffuse solar radiation to overall system performance, alongside an assessment of thermal losses not ultimately transferred to the working fluid.

Together, these results demonstrate that combining strategic flow path extension with optimized solar absorption achieves effective thermal energy capture and transfer — providing practical guidance for barrier placement, flow rate selection, and overall design optimization in solar thermal heat exchanger applications.