Evaluation of ionic liquids as absorbents for absorption refrigeration systems using hydrofluoro-olefin refrigerant

Abstract

In this study, we evaluate the use of ILs as absorbents in a double effect absorption refrigeration system using HFO refrigerant. By examining the properties of various refrigerant/absorbent mixtures, we identify the most efficient refrigerant/absorbent pair for the aforementioned absorption refrigeration system. First, we identify a suitable HFO refrigerant for the system. Among the candidates in this study, R1336mzz(Z) and R1234ze(Z) can be used in the absorption refrigeration system because both have low flammability and high critical points. Then, we analyze the characteristics of ILs as absorbents in the absorption refrigeration system. Imidazolium ILs have relatively low viscosities of approximately 20 mPa s at temperatures exceeding 50 °C and high stability. Next, we analyze the characteristics of refrigerant/absorbent pairs. When R1336mzz(Z) and R1234ze(Z) are used as the refrigerant, [OMIM][BF4] have the highest solubilities in oprating conditions. The solubility value of R1234ze(Z) with [OMIM][BF4] is 0.256 at 289.89 kPa and 80 °C, while the solubility value of R1336mzz(Z) with [OMIM][BF4] is 0.154 at 128.02 kPa and 80 °C. Finally, we analyze the performance of the refrigeration system. When the R1234ze(Z)/[OMIM][BF4] is used in the absorption refrigeration system, the COP and cooling capacity of the system exhibit the values of 0.516 and 0.549 kW, respectively.