Numerical investigation of coupling approaches and dimpled structure on melting characteristics in PCM capsule packed-bed

In solar energy utilization, phase change material (PCM) spherical capsule packed-bed systems can effectively mitigate intermittency and fluctuation issues. However, convective heat transfer between the fluid and capsules significantly influences thermal storage, and the impact of different treatment methods on the phase-change process still requires in-depth investigation. This study employs numerical methods to analyze the effects of constant temperature, sequential coupling and bidirectional coupling approaches on the melting process. Results show that different treatment methods have a significant impact on the melting rate. The constant temperature method exhibits the fastest melting rate, while in sequential and bidirectional coupling methods, the melting rate accelerates with increasing inlet velocity due to enhanced convective heat transfer. The liquid fraction and flow pattern distribution vary depending on the method, with the bidirectional coupling method showing more uniform distribution of liquid PCM on the windward side compared to sequential coupling. Additionally, the dimpled structure accelerates the melting rate under all treatment methods, but the extent of enhancement differs: sequential coupling amplifies the enhancement effect compared to bidirectional coupling, while the constant temperature method weakens it. Finally, a correlation formula for the complete melting time is established, with an average error of 2.4 %.