Optimization of system layout of thermal energy storage with multiple materials

Abstract

The objective of this research was twofold. The first objective was to investigate the performance of a latent heat storage system using multiple phase change materials (PCMs). Three phase change materials namely, Potassium Hydroxide (KOH), Potassium Nitrate (KNQ3), and Sodium Nitrate (NaNO3) were selected for this study. In this research, the performance of the thermal energy storage system (TESS) is analyzed by •evaluating key parameters such as liquid fraction and the amount of energy stored and retrieved during charging and discharging respectively. Two types of PCM layouts, uniform and cascaded, have been employed. The cascaded layout is of two types, slope down and slope up layout. Overall, the cascaded layout excelled in performance when compared to the uniform layout in terms of PCM melting and solidification time and in terms of energy stored and retrieved. The second objective was to investigate the performance of a combined sensible heat storage-latent heat storage (SHS-LHS) system with Aragonite as the sensible heat storage material and KOH as the latent heat storage material. The performance of the combined SHS-LHS is analyzed and compared with a sensible-only heat storage system by evaluating key parameters such as Heat Transfer Fluid (HTF) exit temperature, average temperature of the system and the amount of energy stored and retrieved. It was found that a combined SHS-LHS stabilizes the HTF exit temperature to around the temperature of the PCM during the discharge cycle which offsets the drawback of a sensible-only heat storage system. The amount of energy retrieved from the combined system is larger than the energy that is retrieved from a sensible-only heat storage system. All these findings point to the fact that using a combined SHS-LHS is highly advantageous as compared to a sensible-only heat storage system.