Accelerated charging of PCM in coil heat exchangers via central return tube and inlet positioning: A 3D analysis

This paper presents a 3D numerical analysis of the melting behaviour of a phase changing material (PCM) in a helix-shaped coil-tube heat exchanger, a critical component in latent heat storage (LHS) systems. The analysis explores the impact of the heat transfer fluid's flow route on the system's performance. Specifically, three unique designs of coiled-tube heat exchangers were assessed: a conventional central return tube with an inlet at the bottom, a central return tube with an inlet at the top, and a conventional coiled-tube. The key performance measures under investigation were the melting time of the PCM, average temperature, and average charge rate. Results revealed the central return tube configurations enhance initial melting rates and charging capacity compared to the conventional coil, with the top inlet design outperforming the bottom inlet by 16.5% in melting rate after 5000 s from the melting initiation. Meanwhile, the configuration with the central return tube at the top demonstrated incremental energy storage increases of 18.8%, 13.1% and 1.9% at operating time intervals of 1000, 5000 and 10,000, respectively, compared to the conventional system. These results underline the benefits of a central return tube with optimized inlet positioning in improving the melting effectiveness in LHS systems.