Application to air, and to mixtures of nitrogen, oxygen and argon, of three-parameter corresponding states models based on reference equations of state

Abstract

In this work two three-parameter corresponding states models were applied to the prediction of thermodynamic properties of air and of mixtures of nitrogen, oxygen and argon. In one of the models the methodology was entirely analogous to that of a previously presented work for mixtures of major and minor components of natural gas systems but with argon and nitrogen as the reference fluids, with thermodynamic properties given by the corresponding reference equations of state. To improve even further the predictive capability of this kind of model, and to achieve accuracy levels that match those achieved with the current reference models for air and related systems, the second of the models incorporated three reference fluids, i.e. argon, oxygen and nitrogen. Thus, residual thermodynamic properties were obtained in this model by quadratic interpolation instead of linear interpolation as it is done in standard three-parameter corresponding states models with two reference fluids. By this novel device, the following percentage average absolute deviations were achieved: for binary mixtures, 0.167 in pρT data and 0.438 in bubble-point vapour pressures; for air, 0.079 in pρT data, 0.561 in isochoric heat capacities, 0.270 in speeds of sound, 0.197 and 0.315 in bubble- and dew-point saturation pressures, respectively, and 2.893 and 2.497 in bubble- and dew-point saturation densities, respectively. These results compared favourably with those obtained with three reference models currently available.