Thermodynamic investigation of ternary ionic liquid working pairs and application in absorption heat transformers

To explore the application performance of ternary ionic liquid-based working pairs in absorption heat transformers, this study measured the saturated vapor pressure of H 2 O/LiBr+[EMIM][Ac], H 2 O/LiBr+[BMIM][I], and H 2 O/LiBr+[EPy][Br] solutions at temperature ranging from 25 to 200°C under different concentrations. The experimental data were correlated with an absorption heat exchanger model using the Non-Random Two-Liquid (NRTL) activity coefficient model and enthalpy calculation equations. Sensitivity analyses were conducted on condensation, evaporation/generation, and absorption temperature, with comparisons made to the conventional LiBr/H 2 O working pair. The results demonstrated that the traditional LiBr/H 2 O solution exhibited higher coefficients of performance (COP) and exergetic efficiency (ECOP) under varying condensation, evaporation, and absorption temperatures, but its applicable heat source temperature range was narrow, and it showed no advantage under high output temperature requirements. In contrast, the three ternary IL working pairs exhibited lower COP and ECOP values compared to LiBr/H 2 O, but H 2 O/LiBr+[BMIM][I] and H 2 O/LiBr+[EPy][Br] demonstrated broader applicable heat source and output temperature ranges. Among them, H 2 O/LiBr+[BMIM][I] exhibited the best performance, achieving superior system efficiency at heat source temperatures above 102°C, making it suitable for systems operating with unstable waste heat sources. Additionally, H 2 O/LiBr+[BMIM][I] achieved the highest optimal ECOP of 0.58 at an absorption temperature of 215°C, meeting high output temperature demands and offering significant temperature lift advantages. This study provides critical insights for the application of ternary ionic liquid working pairs in absorption heat transformers. Future research could incorporate system structure optimization and environmental-economic analysis to provide stronger scientific foundations for the application of ternary ionic liquid working pairs.