Augmented BACK equation of state for polar fluids and mixtures
Abstract
A five-parameter augmented BACK (ABACK) equation of state for polar fluids and mixtures is developed by using water as reference. The pressure of water is decoupled into nonpolar and polar pressures. The nonpolar pressure is calculated from the BACK equation based on the size and nonpolar energy of water molecules which were determined by Jorgensen and coworkers. The polar pressure is obtained upon subtracting the nonpolar pressure from the "total" pressure of water which is represented by the steam table equation of Keenan and coworkers. The polar pressure function thus obtained for water is generalized and augmented to the original BACK equation for the general description of polar fluids. Equation constants are determined from the vapor pressures and saturated liquid densities for 26 polar fluids. The sensitivity analysis and generalized correlations for these constants are also made. The equation is extended to mixtures by using quadratic mixing rules with two temperature-independent interaction constants. A substantial improvement in correlating the phase equilibrium data for water + paraffin mixtures at elevated temperatures and pressures is obtained. The new equation is also applied to correlate VLE data for other polar mixtures. With the binary interaction constants which were determined from equilibrium data, the predictions of densities, phase boundaries, isochores, Gibbs free energy changes of mixing, and enthalpies for a variety of polar mixtures are performed. The augmented BACK equation is then simplified, and the simplified equation is examined for its description of phase behavior and thermodynamic properties of mixtures containing polar components.
Degree
Ph.D.
Advisors
Chao, Purdue University.
Subject Area
Chemical engineering
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