Various numerical approaches have been adopted to solve the single-stage isothermal flash problem. These approaches result in two classes of methods. The first includes equation-solving methods that try to solve a nonlinear equation system; the second is based on a minimization of the total Gibbs free energy. Most of these methods may fail to find a solution or may lead to erroneous solutions near critical conditions when an equation of state is applied to both the vapor and liquid phases.
M. N. Ammar and H. RenonCentre Reacteurs & Processus Ecole Nationale Superieure des Mines de New methods for solving the problem are proposed. Combining the Paris simplicity in structure of the conventional successive-substitution method and the efficiency of some unconstrained minimization algorithms, they all ensure convergence to local minima of the Gibbs free energy. The new methods are compared from the standpoints of computer storage and calculational effort requirements. The performance of these methods is tested on four multicomponent systems taken from literature, and a comparison is made with other published methods.
The measurement of ionic self-diffusion coefficients of the lanthanide ions (III) in asymmetrical electrolytes (3:1) solutions of in hydro-organic water - dioxan mixtures (at a low dielectric constant) gives evidence of the progressive association of ion pairs.
The study of different physical - chemical properties in all the domains of composition shows the existence of three regions with distinct behaviours.
The application of association theory to such an asymmetrical electrolyte (3:1) with a polyvalent cation enables us to delimit the validity of the Bjerrum and Fuoss theories.
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