Performance evaluation of absorption thermal energy storage/transmission using ionic liquid absorbents

Efficient thermal energy storage and transmission are considered as two of the most significant challenges for decarbonisation in thermal energy utilization. The liquid-gas absorption thermal energy storage/transmission system is promising approach to tackle these challenges, owing to the long-term stability, flexibility in heat/cooling output, and liquid medium. At present, the shortcomings of conventional absorption working fluids have triggered considerable interest in searching for novel working pairs, such as ionic liquids (ILs). However, it is still unknown whether ILs can work effectively in thermal energy transmission with long distance. In this study, the absorption thermal energy storage/transmission systems using IL absorbents are theoretically investigated. modeling frameworks for working pairs screening and performance evaluation are proposed. Results show that the IL-based working pairs present better or comparable performance than conventional working pairs (including H2O/Salts and NH3/Salts). Among the investigated IL-based working pairs, H2O/[EMIM][EtSO4] presents highest COP (around 0.62) and exergy efficiency (around 0.32), and is relatively close to H2O/LiBr. As for energy storage density, H2O/[EMIM][Ac] performs better than H2O/LiBr, presenting 137.4 kWh/m3 with a desorption temperature of 115 °C. The present work provides a straightforward screening of IL absorbents for thermal energy storage and transmission purposes. © 2022