Melting and solidification characteristics of cylindrical encapsulated phase change materials

Abstract

Thermal energy storage using encapsulated phase change materials (EPCM) has been attracting the attention of researchers in solar energy applications due to their high energy storage capabilities. However, the melting characteristics of EPCMs are affected by many parameters. In this study, experimental and CFD model were used to investigate the parameters influencing the melting and solidification characteristics of a cylindrical EPCM. The developed CFD model was validated with the experimental model's results and with experimental data from the literature. The CFD model is used to investigate the effect of changing the PCM type, heat transfer fluid (HTF) temperatures, HTF flowrates, number of fins and solidification temperatures. Lauric acid and paraffin wax at HTF temperature ranging from 55 to 73 °C and flowrates from 0.064 to 0.323 kg/s are compared. Then the number of fins from 4 to 12 were inserted inside the capsule and compared with the case without fins at the same amount of PCM. The solidification is simulated at HTF temperature from 20-35 °C. Results revealed that increasing the HTF flow rate by five times decreases the melting times of lauric acid and paraffin wax by 30% and 22%, respectively. The total energy stored in paraffin wax is much higher compared with that in lauric acid under the same HTF conditions. Furthermore, increasing the number of internal fins in the capsules to 12 enhances the melting time by 41% of paraffin wax at an HTF mass flow rate of 0.3238 kg/s and temperature of 73 °C. The presence of fins effectively enhances the solidification and melting time of lauric acid and paraffin wax.