Experimental absorption solubility and rate of hydrofluoroolefin refrigerant in ionic liquids for absorption chiller cycles

• Published in: Chemical engineering research & design Vol. 171; pp. 340 - 348
• Main Authors: Esaki, Takehiro, Kobayashi, Noriyuki
• Format: Journal Article
• Language: English
• Published: Rugby Elsevier B.V 01.07.2021; Elsevier Science Ltd
• Subjects: Absorbers; Absorption; Absorption chiller cycle; Absorption rate; Absorption solubility; Adsorption; Heat exchange; Heat exchanger tubes; Heat exchangers; Heat transfer; HFO-1234yf; Ionic liquid; Ionic liquids; Refrigerants; Refrigeration; Solubility; Temperature; Waste heat recovery; Waste utilization; HFO-1234yf; Absorption chiller cycle; Absorption rate; Absorption solubility; Ionic liquid
• ISSN: 0263-8762; 1744-3563
• DOI: 10.1016/j.cherd.2021.05.024

•Equilibrium solubility of HFO-1234yf in [BMIM][Tf2N] were measured and calculated using NRTL model.•The absorption cycle was evaluated a Dühring diagram and could operate with a heat source of under 80°C.•Absorption rate increased following the equilibrium solubility.•Outlet absorption solubility was 25–33% of the equilibrium solubility.•It will be necessary to investigate heat exchanger tubes to improve absorption performance. An absorption chiller cycle using HFO-1234yf (2,3,3,3-tetrafluoropropene) as an environmentally friendly refrigerant could allow for the efficient utilization of waste heat. In this study, we tested ionic liquids as absorbents for HFO-1234yf, and measured their experimental absorption equilibrium solubilities using a volumetric method. At 50°C, the solubility of HFO-1234yf in ionic liquids increased in the order: [BMIM][Tf2N]>[BMIM][BF4]>[EMIM][PF6]. We calculated the experimental solubility of the [BMIM][Tf2N] system using the non-random two-liquid (NRTL) model and evaluated its Dühring diagram. This confirmed that the absorption chiller cycle allowed heat exchange at 0°C with a generation temperature of 80°C. The absorption rate was measured via a volumetric method, and increased following the absorption equilibrium solubility when the experimental temperature and pressure conditions were changed. The absorption solubility obtained at the absorber outlet was equivalent to 25–33% of the absorption equilibrium solubility in the lab-scale falling-film absorber. To improve the absorption performance, it will be necessary to investigate heat exchanger tubes with higher wettabilities to reduce the thickness of the absorbent flowing on the heat exchanger surface.