A CFD modeling and investigation of a packed bed of high temperature phase change materials (PCMs) with different layer configurations

In recent years, one of the most important issues is optimization of thermal energy-storing technologies. Using phase change materials (PCMs) with specific phase change temperatures allows us to store latent heat as thermal energy. This is one of the most efficient ways to store thermal energy. The objective of this paper is to investigate the discharge performance of a packed bed filled with multi layers of high temperature encapsulated PCMs through a CFD modeling via Comsol multi-physics software. Results of simulation are compared to results of the experimental researches of the literature and there is good agreement between them. The influence of each layer's height and porosity along with different configurations of the PCMs according to their phase change temperatures (ascending and descending in flow direction) are analyzed. It is observed that increasing the inlet velocity of heat transfer fluid (HTF) and increasing the porosity of layers of PCM in the packed bed have similar outcomes and makes the packed bed deplete more rapidly. Some new configurations are suggested and optimized regarding Delta (tutl), which is defined as the ratio between duration of receiving energy with desired temperature to total discharge time of the packed bed, during the discharge process. Results indicate that by setting the layer heights of the PCMs in a descending order and also having the porosity of each layer to decrease in the flow direction, results with 29.2% better performance can be obtained. Optimization of Delta(tutl) can be a defining factor in designing of packed beds and also a concentrating solar power (CSP) plant.