4.7 Article

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

Journal

ENERGY
Volume 263, Issue -, Pages -

Publisher

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.energy.2022.125689

Keywords

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

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Absorption technologies using CO2/ionic liquid mixtures have great potential in utilizing renewable energy and waste heat. Through screening and optimization, the study identifies the optimal ILs and CO2/IL mixture for a transcritical CO2/IL absorption heat pump, leading to improved cycle performance.
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] approximate to[PF6]. [EMIM][C(CN)(3)] yields the highest heat transfer coefficient of 0.520 kW/(m(2).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 degrees C, the COP of CO2/[OMIM][Tf2N] reaches the highest 0.2614 with the optimum P-high 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.

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