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The cycle performance of refrigeration cycles depends not only on their configuration, but also on thermodynamic properties of working pairs regularly composed of refrigerant and absorbent. The commonly used working pairs in absorption cycles are aqueous solutions of either lithium bromide water or ammonia water. However, corrosion, crystallization, high working pressure, and toxicity are their major disadvantages in industrial applications. Therefore, seeking more advantageous working pairs with good thermal stability, with minimum corrosion, and without crystallization has become the research focus in the past two decades. Ionic liquids (ILs) are room-temperature melting salts that can remain in the liquid state at near or below room temperature. ILs have attracted considerable attention due to their unique properties, such as negligible vapor pressure, nonflammability, thermal stability, good solubility, low melting points, and staying in the liquid state over a wide temperature range from room temperature to about 300°C. The previously mentioned highly favorable properties of ILs motivated us for carrying out the present research and reviewing the available ILs found in the literature as the working fluids of absorption cycles. Absorption cycles contain absorption heat pumps, absorption chillers, and absorption transformers.

The thermodynamic performance of the absorption chiller using (H 2 O + LiCl) as the working pair was simulated and compared with the absorption chiller using (H 2 O + LiBr). The effects of evaporation temperature on the performance coefficient, COP, generation temperature, concentration of strong solution, and flow rate ratio were also analyzed. At the same condensing and absorbing temperature, the simulating results indicated that the performance coefficient for (H 2 O + LiCl) is approximately equal to (H 2 O + LiBr) and the generation temperature was lower than that for (H 2 O + LiBr). On the other hand, the exergetic efficiency, ECOP, which is based on the second law of thermodynamics, for the absorption chiller using (H 2 O + LiCl), was more than the system using (H 2 O + LiBr) under the same operating conditions. The absorption chiller cycle was then optimized based on the coefficient of performance. The results show that the coefficient of performance of the absorption chiller, using (H 2 O + LiBr) at the optimum conditions, was around 1.5–2% higher than that of (H 2 O + LiCl).