Ionic liquid screening and performance optimization of transcritical carbon dioxide absorption heat pump enhanced by expander

Research output: Journal Publications and ReviewsRGC 21 - Publication in refereed journalpeer-review

10 Scopus Citations
View graph of relations



Original languageEnglish
Article number125689
Journal / PublicationEnergy
Issue numberPart A
Online published8 Oct 2022
Publication statusPublished - 15 Jan 2023


Absorption technologies show great potential in utilizing renewable energy and waste heat. In this study, novel CO2/ionic liquid (IL) mixtures are investigated to overcome the shortcomings of conventional working fluids. To screen the optimum ILs for a transcritical CO2/IL absorption heat pump (TsCO2-AHP), the absorption cycle models using 34 IL species are established to estimate the cycle performance. Within the selected candidates, [OMIM][Tf2N] yields the best cycle performance. For imidazolium-based ILs with different anions, the coefficient of performance (COP) is in the order of [Tf2N] > [C(CN)3] > [OTF] > [DCA] ≈ [PF6]. [EMIM][C(CN)3] yields the highest heat transfer coefficient of 0.520 kW/(m2·K) due to its better transport properties compared to other candidates. The high-side pressure optimization is conducted to maximize the COP. At the generator temperature of 138 °C, the COP of CO2/[OMIM][Tf2N] reaches the highest 0.2614 with the optimum Phigh of 10.289 MPa. By equipping an expander, the COP of the TsCO2-AHP is improved by 11.9% because of a larger cooling capacity and less electricity consumption. The main objectives are contributing novel potential working fluids, optimizing the cycle parameters, as well as selecting the best-performance CO2/IL mixture for improved development of absorption technologies.

Research Area(s)

  • Absorption heat pump, Carbon dioxide, Expander, Ionic liquid, Parameter optimization, Transcritical cycle