Numerical analysis of latent thermal energy storage system under double spirally coiled tube configuration with two separated paths

The current research attempts to illustrate results of a reliable 3-D numerical simulation to scrutinize the charging process of paraffin as the phase change material (PCM) in an innovative heat exchanger called double spirally coiled tube heat exchanger (DSCTHE) with two separated paths. The water as a heat-transfer fluid (HTF) streams through the double spiral tubes embedded throughout the latent thermal energy storage (LTES) system. The PCM melting characteristics under three different geometries are investigated. After validating the proposed numerical simulation model, the impacts of operational and geometrical factors including inlet temperature of HTF and radius of the inner spiral tube on the behavior of the LTES system in the course of the melting process are investigated in detail. In order to achieve better insight into practical aspects of the presented LTES system, the transient behavior of a PCM for all three considered cases under various working conditions is discussed. Moreover, the 3-D temperature and liquid fractions contours at various time frames are obtained. The findings reveal that a decrement in the radius of the inner spiral tube resulted in a lower capability to melt PCM at the commencement of the charging procedure but more efficiency at the final stages. Generally, the overall time essential for melting of 95 wt% PCM in the storage diminishes up to 126 % by reducing the radius of the inner spiral tube from 90 mm to 50 mm.