Thermodynamic Modeling of the Use of Alkane Mixtures as Working Fluids in Absorption Cycles

The main objective is to show the effect of the choice of the most adequate combination of activity-fugacity coefficient models on the vapor-liquid phase equilibrium (VLE) data quality and on the calculation of the enthalpies of the different vapor and liquid streams in a refrigeration absorption machine. Six alkane binary mixtures, i.e. propane or n-butane as refrigerants and n-heptane, n-octane, or n-decane as absorbents, were considered as working fluids for their proven positive characteristics. Two activity coefficient models, UNIFAC and NRTL, and two equations of state, virial and Peng-Robinson (PR), were tested. The obtained results showed that the UNIFAC-PR combination reproduced the VLE data reasonably well; hence, it should be recommended for this type of refrigeration systems operating with alkanes.