Melting and solidification in thermal storage: Influence of fin aspect ratio and positioning in a full charging and discharging cycle

Abstract

There are many advantages to using thermal storage with phase change materials (PCM). These systems present high energy storage density with potential for efficient thermal protection and thermal storage, with absorption or release of heat at a constant temperature and low volumetric variation. To increase heat transfer and optimize phase change processes, the application of fins is still the most widely used technique. Therefore, the present work aims to analyse the effect of fin aspect ratio and fin positioning in the melting and solidification process, as well as their cumulative effect under sequential conditions, in a rectangular cavity. The aspect ratios were varied in order to maintain the same amount of PCM mass, i.e., the same heat capacity. The analysis is done individually and sequentially, for thermal charging and discharging conditions. Validation with experimental data showed that the model is sufficiently accurate. Four fin aspect ratios and three positions were evaluated, totalling 24 configurations. Results indicate that: fins with a higher aspect ratio showed 16% higher melting rate compared to the lower aspect ratio, when in lower cavity positions; the higher aspect ratios showed 15% higher solidification rates than the lower ones; fins positioned in the lower cavity positions showed higher melting rates than for fins positioned in the upper cavity position: between 16% and 21%, depending on the aspect ratio; the solidification processes are independent of the fin positioning until approximately 90% solid PCM is reached; in average, the total solidification time takes 6.4 times longer than the melting time.