Investigating the performance of novel green solvents in absorption refrigeration cycles: Energy and exergy analyses

Abstract

Energy shortage and environmental pollution are among the most serious challenges facing mankind. The utilization of efficient and green solvents has great urgency, if true action is to be taken to alleviate these issues. The Deep Eutectic Solvents (DESs) were recently introduced as sustainable solvents with special characteristics. These novel solvents have very low vapor pressures and can be “designed” for desired properties through the engineered selection of appropriate hydrogen-bond donors and acceptors. Research is necessary to investigate the feasibility of applying DESs in various industrial applications, including absorption refrigeration systems. Since the coefficient of performance (COP) and the exergetic coefficient of performance (ECOP) of an absorption refrigeration system depend highly on the properties of the absorbent and refrigerant, selecting a proper DES with particular attention to its physical properties, can dramatically affect its efficiency. In this study, three DESs were investigated as potential absorbents, consisting of Reline (1 Choline chloride + 2 urea), Ethaline (1 Choline chloride + 2 ethylene glycol) and Glyceline (1 Choline chloride + 2 glycerol), with ammonia as the refrigerant. A modified SRK-NRTL model was used to estimate the physical and thermodynamic properties of the DESs and their mixtures with ammonia. The COPs and ECOPs of the absorption refrigeration cycles were calculated within wide ranges of absorber and regenerator temperatures. The results were compared to literature systems, including ammonia/water and ammonia/ionic liquids cycles. The performances based on energy and exergy analyses showed that ammonia/DES working fluids have the potential to be used in such cycles.