Thermophysical Properties of Dry and Humid Air by Molecular Simulation Including Dew Point Calculations with the Mollier Ensemble

Abstract

A pseudoensemble, the Mollier ensemble, is proposed for the dew point calculation of humid air systems. This approach combines features of the isobaric−isothermal (NpT) ensemble and the grand-canonical (μVT) ensemble. The molecular model for dry air is taken from previous work and compared to experimental data as well as to two recommended reference quality equations of state regarding vapor−liquid equilibria, thermal, and caloric properties. An excellent agreement is found for temperatures up to 1000 °C and pressures up to 200 MPa. For water, two different molecular models are considered, the popular TIP4P model from the literature and an optimized version that better describes the vapor pressure. Both water models are used in combination with the molecular dry air model to predict the compressed gas density as well as the dew point of humid air at 60 and 80 °C for elevated pressures up to 25 MPa. The results are in very good agreement with experimental data from the literature.