Enhancement of Thermal Energy Storage in Solar Water Heating Systems Through Phase Change Materials

This study numerically investigates the integration of a paraffin-based phase change material (PCM) into a solar water heating system (SWHS) to enhance thermal energy storage and system efficiency. A flat-plate solar collector coupled with a PCM-assisted water storage tank was designed using SolidWorks and simulated in ANSYS Fluent employing a three-dimensional transient computational fluid dynamics (CFD) approach. The melting and solidification behavior of the PCM was modeled using the enthalpy–porosity technique, while conjugate heat transfer between the collector, working fluid, and PCM was fully resolved. Solar heat input was applied as a uniform heat flux boundary condition, and temperature-dependent thermophysical properties were considered to improve model accuracy. The system performance was evaluated under varying operating conditions, including mass flow rates ranging from 0.05 to 0.2 kg/s and solar irradiance levels between 600 and 1000 W/m2. The results demonstrate that higher solar irradiance combined with lower mass flow rates significantly enhances PCM melting dynamics and thermal energy storage capacity. Under optimal conditions (1000 W/m2 and 0.05 kg/s), the PCM achieved a melting fraction of 87%, while the overall thermal efficiency reached 65%. The numerical findings confirm that PCM integration effectively improves thermal performance, prolongs heat availability, and reduces reliance on conventional energy sources in solar water heating systems.