Numerical study of a dual-PCM thermal energy storage unit with an optimized low-volume fin structure

Phase Change Materials (PCMs) are widely used as storage mediums in latent thermal energy storage systems and are useful to tackle the inconsistencies in energy supply and demand associated with renewable energy resources. However, weak thermal conductivity is the major disadvantage of PCMs, as they cause slow charging and discharging of thermal energy storage systems. The performance enhancement of a unique thermal energy storage unit design that consists of two PCMs and with optimized fins is demonstrated in the current study. Different arrangements of dual-PCMs are first examined by comparing the overall charging-discharging time. The proposed dual-PCM layout for a horizontal double-pipe energy storage unit, not demonstrated in existing work, reduces the total charging-discharging time by 13.6% compared with the conventional single-PCM case. Results from this study further show that applying nanoparticles is less effective than adding fins for the proposed dual-PCM design configuration. Adding nanoparticles to the dual-PCM design results in 2.2 times shorter charging-discharging time, while the proposed design with fins incorporated results in a remarkable 7.6-fold improvement in charging-discharging time. To further enhance the performance of the energy storage unit, response surface methodology (RSM) is used to predict the optimum fin angles, and results show that fins tilted at 51.1° and 42.6°, measured clockwise from the upper middle section and counter-clockwise from the lower middle section, respectively, reduced the total charging-discharging time by 7.5%. This article exemplifies a systematic approach to designing a high-performance LTES system that leverages the combined benefits of multiple PCMs and optimized fin design.