Double-effect/two-stage compression-assisted absorption thermal energy storage using LiNO3-ionic liquids/H2O working fluids

Abstract

A novel double-effect/two-stage compression-assisted absorption thermal energy storage system using LiNO3-[BMIM] (1-butyl-3-methylimidazolium) NO3/H2O for combined cooling and heating is proposed to enhance thermal performance under a larger concentration glide without crystallization. The thermodynamic calculation is conducted by Matlab based on the measured thermophysical properties, and its performance is compared with that of a system using other working fluids. The results show that this proposed system using LiNO3-ionic liquids/H2O with compressor assistance achieves a higher coefficient of performance and energy storage density at a larger concentration glide without crystallization. In comparison to LiBr/H2O, the generation temperature of this system using LiNO3-ionic liquids/H2O is reduced by over 50 K at a larger concentration f, which is beneficial for the utilization of solar energy. As the discharging temperature increases from 321.15 K to 333.15 K and f from 0.08 to 0.20, this novel system using LiNO3-[BMIM]NO3/H2O obtains the largest coefficient of performance of 1.36 and exergetic coefficient of performance of 0.46 at generation temperature below 354.2 K, compared to LiNO3/H2O and LiNO3-[DMIM][DMP]/H2O. Moreover, the maximum energy storage density based on LiNO3-[BMIM]NO3/H2O reaches 695.4 kJ/kg at a discharging temperature of 333.15 K and a f of 0.20. In comparison to the existing absorption thermal energy storage systems, the proposed system using LiNO3-[BMIM]NO3/H2O also shows outstanding performance in various aspects. This new system with the LiNO3-[BMIM]NO3/H2O alternative working fluid has a great potential for utilizing solar energy for combined cooling and heating.