Thermodynamic performance analysis of a single-effect absorption refrigeration system operating with water and 1-ethyl-3-methylimidazolium-based ionic liquids mixtures

Abstract

Absorption refrigeration systems (ARS) are thermally-driven technologies used to generate cold utilities. When the working pair H2O/LiBr is used in ARS, severe crystallization and corrosion problems may arise. Aiming to avoid these issues, investigations concerning ionic liquids (ILs) to replace LiBr has been conducted. This paper presents a thermodynamic performance analysis for a single-effect ARS using water and two 1-ethyl-3-methylimidazolium-based ionic liquids as absorbents: 1-ethyl-3-methyl-imidazolium ethylsulfate ([EMIM][EtSO4]) and 1-ethyl-3-methyl-imidazolium tetrafluoroborate ([EMIM][BF4]), both not yet widely explored for this purpose. Simulations were performed using Engineering Equation Solver (EES) software. Results have shown that H2O/[EMIM][BF4] mixture is clearly unattractive. Particularly at lower temperatures in the absorber and condenser and higher temperatures in the evaporator, H2O/[EMIM][EtSO4] mixture presented COP and exergetic efficiency (ηex) profiles relatively close to those of the conventional H2O/LiBr. For an optimized case, COP and ηex were 8.2% and 19.2% greater for H2O/LiBr than for H2O/[EMIM][EtSO4] which has presented values of 0.764 and 0.114 respectively. For ηex this difference tended to decrease at higher temperatures in the generator, turning H2O/[EMIM][EtSO4] mixture competitive with H2O/LiBr at certain conditions, mainly in view of LiBr crystallization risk. The main contributions of this work regarding ARS studies is performing all the following studies simultaneously: sensitivity analysis, thermodynamic optimization and crystallization risk analysis also considering working pairs that still present some gaps in the literature.