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

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 Duhring 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.