Performances of an absorption heat transformer cycle with water/deep eutectic solvents working fluids: Modelling and screening using a multiscale approach

Abstract

In this work, a tool was developed to evaluate the performances of working fluids composed of deep eutectic solvents as absorbents and water as refrigerant in a single-stage absorption heat transformer. The thermophysical properties required for the simulation were obtained using a multiscale approach involving the COSMO–SAC(+OH–ClBr) model for the vapour-liquid equilibria and group contribution models for the densities and heat capacities of the DESs. The predictive power of the model was assessed by comparing the results with the ones obtained with a conventional approach based on the non-random two-liquid model and empirical correlations derived from experimental data. The performances of the absorption heat transformer were evaluated using several criteria including the coefficient of performance, the circulation ratio and the heat input. The results are in agreement with the ones obtained with the classical approach. The performances of 32 deep eutectic solvents as well as the influence of the different temperatures of the process on the results are investigated. Results show that the best performances are obtained with deep eutectic solvents composed of ethylene glycol, glycerol, tetramethylammonium chloride, choline chloride and betaine, with coefficient of performance values comprised between 0.438 and 0.441, circulation ratio between 14.75 and 9.66 and heat input between 1982.11 and 2006.77 kJ.kg−1. In particular, the best performances were achieved with the pair water/{ethylene glycol:[tetramethylammonium][chloride]}, ratio [2:1]. Overall, the deep eutectic solvents with a higher ratio of hydrogen bond acceptor and lower molar masses showed better performances as absorbents in absorption heat transformers.