Excess enthalpy prediction for ionic liquids based absorption systems

Excess enthalpy is crucial in investigating absorption refrigeration and heat pump cycles. Apart from a direct measurement, it can be estimated from vapor-liquid equilibrium (VLE) data by using thermodynamic models. Models which can be used are equation-of-state (EOS) based model, activity-coefficient based methods, and generic Clausius-Clapeyron relation. This paper assesses the performance of different models in the excess enthalpy prediction of natural refrigerants/ILs pairs for absorption cycles. First, the fundamental theories on excess enthalpy prediction with different thermodynamic models are introduced. Then, the VLE data of two working pairs are fitted and used to estimate excess enthalpy by these models. The predicted results are compared with measured ones for the pair H2O/[emim][DMP]. The influence of fitted parameters on the excess enthalpy prediction is also discussed. The assessment reveals the predicted excess enthalpies have quite large deviations compared with the measured values. UNIFAC and Redlich-Kwong EOS models perform best with relatively smaller errors.