Thermal performance analysis of thermocline combined sensible-latent heat storage system using cascaded-layered PCM designs for medium temperature applications

One tank type thermocline thermal energy storage (TES) concept is considered as a possible cost optimized solution for the medium temperature industrial applications, e.g., chemical processing, beverages industry etc. However, one of the drawbacks of this TES configuration is higher thermocline degradation at the end of discharging cycles and overall decrease in performance. In current work a new type of combined sensible-latent heat configuration is introduced to counter these issues. The concept of the proposed thermal storage configuration is to use structured sensible heat cheap material with the space between them occupied by encapsulated phase change material (PCM) capsules, forming cascaded layered packed bed along the tank height and the heat transfer fluid flows between them. A comprehensive unsteady numerical model is formulated based on two-phase Schumann model equations to evaluate performance of the each proposed prototypes. The numerical simulations are performed to investigate the effect of combined sensible rod structure and multi-layered PCMs designs on thermocline temperature profiles, exergy outputs, total thermal energy storage, efficiency in the use of total storage capacity, utilization ratio and the proportion of PCM effectively changing phase. The comparative analysis is performed for four different configurations, i.e., single layered sensible rod with PCM (SLSPCM) arrangement and the three cascaded layered sensible rod with PCM (CLSPCM) arrangements. The overall results show that the TES with a volume fraction arrangement of (40%-20%–40%) is performance wise the best configuration followed by (25%-50%–25%) and (10%-80%–10%), respectively. And SLSPCM is the lowest in the row. The analysis presented in the current study shows that the use of multistage PCMs having suitable combination of layer thickness and fusion temperature together with the inclusion of cheaper structured filler material, offer an efficient and cost effective TES alternative.