Efficiency of two working fluids constituted of a deep eutectic solvent and water in absorption heat transformer

The use of two working fluids constituted of deep eutectic solvents containing {choline chloride + glycerol} or {betaine + ethylene glycol} and water in an absorption heat pump was evaluated to produce upgraded heat. The liquid-vapor equilibria, heat capacity, and excess molar properties required for the simulation were measured. All experimental data were fitted using the nonrandom two-liquid (NRTL) model and empirical equations. The coefficient of performance calculated for both systems in different absorption heat transformers (AHT) operating conditions varies between 0.4 and 0.45. Simulations indicate that these working fluids and {ionic liquid + water} mixtures behave similarly. The coefficient of performance is of the same magnitude as those calculated with {ionic liquid + water} mixtures, but it remains below the conventional fluid {lithium bromide + water}. The simulated circulation rates for {betaine + ethylene glycol} and {choline chloride + glycerol} and water are comprised between 10.73 and 20.82, and 14.21 and 27.41, respectively. The calculated circulation ratio of {water + betaine + ethylene glycol} is lower than the value obtained with the most efficient {water + IL} or with {water + choline chloride + glycerol} but it is still two times higher than the one estimated for {water + LiBr}. Overall, the working fluid {water + betaine + ethylene glycol} appears to be more efficient than {water + choline chloride + glycerol} with better coefficients of performance. The deep eutectic solvents (DES)-based working fluids studied in this work allow one to work in a larger operating temperature range than {water + LiBr}. Furthermore, the waste heat sources of 353 K can obviously be enhanced to 450 K using {H2O + DES} as working fluids in AHT.