Experimental investigation of ionic liquids as substitute for lithium bromide in water absorption chillers

Ionic liquids (ILs) have been proposed as alternative absorbents for absorption chillers, e.g. to cope with crystallization. Since there is a huge amount of different ILs available, it seems to be convenient to choose a suitable IL for an absorption chiller not by experimental trials but rather by theoretical modeling. However, the model's results must be validated with experimental data to evaluate their prediction quality. In the paper at hand the performance of three different ILs ([Choline][OAc], [emim][Cl], [mmim] [EtCO2]) and lithium bromide is compared experimentally in a fully operable absorption chiller with water as the refrigerant. The cooling capacity, the coefficient of performance, the specific circulation ratio of the chiller and the heat transfer capability of the absorber are determined. When using LiBr, the highest cooling capacity is achieved, and the highest heat transfer coefficients and presumably the least mass transfer resistance are present. The experimental data show that equilibrium state simulations will lead to completely erroneous results. Neither LiBr nor the ILs come close to their equilibrium state and differences amongst the investigated absorbents are huge. It furthermore seems almost impossible to choose suitable ILs for absorption chillers by investigating isolated physical properties. (C) 2020 Elsevier Ltd. All rights reserved.