Extended Corresponding States Research Articles

Critical lines for type-III aqueous mixtures by generalized corresponding-states models

An algorithm has been developed for calculating the gas-gas critical line of type-III binary fluid mixtures for extended corresponding-states (ECS) models. The algorithm searches for an extremum in pressure on the spinodal curve of an isothermal pressure-composition phase diagram of a binary mixture. The method has been applied to solutions of carbon dioxide and of nitrogen in water. starting at the water critical point. Two variants of ECS have been tested for their ability to represent reliablePVTx data in the nitrogen-water mixture. It is demonstrated that in the latter system both ECS variants produce an artifact in the gas-gas critical line in the range of 0–0.2 mole fraction of nitrogen.

A thermodynamic property formulation for air. II. Pressure and density estimation functions for the dew and bubble lines

As a companion to a new correlation for the thermodynamic properties of air in single-phase states, new values for the properties on the dew and bubble lines have been calculated. Phase equilibrium properties for air at low and moderate pressures were predicted from accurate equations of state for argon, nitrogen, and oxygen using extended corresponding-states (ECS) methods. For pressures near the critical pressure, property values were calculated using a modified Leung-Griffiths model for mixtures of argon, nitrogen, and oxygen. Available experimental data and newly predicted values have been used in developing new correlating functions for estimating density and pressure on the dew and bubble lines of air. Estimates of the accuracies of these correlations based upon comparisons of calculated properties to data from other sources are also included.

The prediction of high-density thermodynamic states using molecular shape factors

A new extended corresponding-states method for the prediction of high-density states for pure fluids is presented. The method incorporates the use of molecular shape factors. This approach requires accurate equations for the saturated-liquid density and the vapor pressure for the fluid in question. In addition, an equation of state for the vapor phase is also required. With this information, the molecular shape factors are calculated on the saturated-liquid line of the fluid being predicted, and they are assumed to be constant in the high-density, single-phase region along isotherms. This property prediction method is well suited for application to any fluid that has an equation of state valid in the vapor phase. Modern equations of state for nitrogen and oxygen were used to define properties of reference fluids in the development and testing of this new method. Experimental data for liquid ethylene were used to verify the accuracy of the new prediction method. Tests have shown that this approach predicts high-density data accurately to approximately six times the critical pressure and up to 85 % of the critical temperature. The results of these tests are presented and discussed.