Efficient medium temperature thermal energy storage (TES) can help to eliminate the imbalance between energy demand and supply. In this study the issue of thermal ratcheting in TES system is avoided by using structured sensible heat storage material. Another technical issue of temperature drops at the end of discharging cycles occurring in only sensible material filled TES is overcome to some extent by using phase change material (PCM) between sensible rod structure (SRS) providing stable fluid outlet temperature. A comprehensive transient numerical model is formulated by solving separate equations for heat transfer fluid and storage materials using energy balance method coupled with enthalpy technique to study the influence of phase change temperature in the PCM. The numerical model predicts thermal stratification behaviour and thermocline formation along the symmetry-axis. A detailed parametric analysis of the combined sensible-latent heat thermal energy storage is performed to investigate the effect of porosity variation, inlet velocity and feature size of sensible heat storage material on total energy utilization, effective discharging efficiency and effective discharging time using thermocline characterization. The results indicate that discharging efficiency of hybrid TES tank can be increased by using lower velocity of fluid at inlet, by decreasing porosity or by using reduced SRS feature size. The study offers suggestions for optimized design and governing parameters of a new type of combined sensible-latent heat TES configuration, while avoiding thermal ratcheting with stable fluid outlet temperature for an application specific process. |
