Enhancing thermal performance of phase change materials using conductive rods with length dependent melting dynamics

Phase change materials (PCMs) suffer from slow melting rates due to their low thermal conductivity, limiting their efficiency in thermal energy storage systems. This study numerically investigates the novel use of copper rods as conductive enhancers to accelerate PCM melting in a horizontally placed hemispherical cell. Using the ANSYS/FLUENT 16 with an enthalpy-porosity model, the impact of rod integration is examined to determine the optimal rod configuration for maximising heat transfer while minimising melting time. The results indicate that copper rods dramatically improved melting performance: a 20 mm rod can reduce total melting time by 70% (from 300 to 90 min), while 10 mm and 15 mm rods achieve reductions of 40% (to 180 min) and 50% (to 150 min), respectively. Clearly, the 20 mm rod enables 70% liquid fraction in 30 min, showing a melting speed four times faster than the no-rod case. Nonlinear scaling reveals diminishing returns beyond 15 mm, suggesting a cost-performance trade-off at this length. The 15 mm rod emerged as a practical balance between attaining 85% of maximum gain with a 50% reduction in melting time while utilising 25% less copper than 20 mm rod. Accordingly, this research provides critical insights for designing high-efficiency thermal storage systems, offering a roadmap to optimise conductive enhancements for real-world applications. By bridging the gap between material properties and system-level performance, the findings advance the deployment of PCMs in renewable energy and waste heat recovery systems.