Review of PCM charging in latent heat thermal energy storage systems with fins

Phase change materials (PCM) are considered promising tools for storing a high density of thermal energy in heat storage systems. The inherent low thermal conductivity of PCM can be remedied by using several thermal conductivity enhancers, especially fins. The effect of one or several thermal conductivity enhancers on the PCM melting was discussed in previous review articles. However, the impact of fin only on the PCM melting was rarely reported. The present article provides a comprehensive review of studies related to the thermal performance of PCM charging in finned annular heat exchangers as LHTES systems. The studies are classified according to the orientations of the LHTES systems (horizontal or vertical). This review includes a survey of several previous studies associated with the charging behaviour of PCM in horizontal and vertical annular thermal storage units equipped with fins. The effects of various factors on charging, such as geometrical factors of different fins, configuration, arrangement installation angle, pitch, number, thickness, and height, are reviewed. It was inferred that inserting the fin suppresses overheating in the top part of the thermal storage unit and improves the melting rate at the bottom part of the thermal storage. Therefore, the overall heat transfer rate is improved, and melting time is reduced. Also, the increasing the number, length, and thickness of fins indicated a pronounced enhancement in the melting process. At the same time, employing the non-uniform distribution of fins and/or using different fin dimensions (length and thickness) between the lower and upper parts of the storage unit improves the charging process. Decreasing the fin number and fin dimensions at the upper part and increasing them at the lower part result in an improvement of the thermal performance of the charging process. Also, decreasing the fin 's pitch and installation angle improves the melting rate. Furthermore, using the topologyoptimized structure for fins improves the thermal performance.