Enhancing thermal energy storage performance with expanded graphite composite: A comparative energy-exergy analysis

Organic phase change materials (PCM) hold promise for domestic thermal energy storage (TES) but face challenges due to their low heat transfer kinetics, limiting effective implementation in latent heat TES systems. In this study, a new commercial bio-derived organic PCM with a phase change temperature of 60 °C is investigated for domestic hot water applications. Our study investigates the efficacy of macro-encapsulation, expanded graphite (EG), and circular fins in enhancing the performance of organic PCM for TES. Through the thermal analysis, we demonstrate tangible improvements in heat transfer dynamics in a macro-encapsulated PCM/EG system. Macro encapsulation of the PCM/EG modules was an effective method to mitigate the segregation of molten PCM from EG and to augment the heat transfer performance of the PCM due to the extensive conductive network of the EG and circular fin combination. At 80 °C temperature and 4 l·min⁻¹ flow rate, the PCM/EG system demonstrated an average charging power of 125 W which is 257 % higher than the system without any enhancement. When the PCM/EG system is fully charged, it stored 164.6 % higher than that of the PCM heat exchanger even at the lowest inlet temperature and mass flow rate of heat transfer fluid at the same elapsed time. Besides, the average exergy efficiency of enhanced TES unit was 17 % higher than the unenhanced system. Overall, our study underscores the potential of microencapsulated PCM/EG systems as efficient solutions for domestic thermal energy storage, offering insights into optimizing performance and overcoming inherent PCM limitations.