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Mixing Rules for van der Waals-Type Equations of State Based on Activity-Coefficient Models (1998)

Abovsky, V. ; Watanasiri, S.

Springer

International journal of thermophysics 19 (1998), S. 1429-1445

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ISSN: 1572-9567

Keywords: activity coefficient models ; equation of state ; excess functions ; mixing rules

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract A new approach for incorporation of the excess free energy from an activity coefficient model (ACM) into an equation of state (EOS) has been proposed. The approach is based on a concept that any ACM is valid at a low but finite value of compressibility factor. This condition allows us to analyze the “infinite pressure” approximation in a general way. It is shown that the “infinite pressure” approach neglects the contribution of the repulsive term of the EOS to the excess free energy of a mixture. This, in turn, introduces inconsistency which results in the difference in the calculated excess free energy of the EOS and the base ACM. The new approach defines parameter a of the EOS as an implicit function of compositions and temperature, thus requiring an iterative procedure using the “infinite pressure limit” as a starting point. The new approach can be modified to provide the correct composition dependence of a mixture second virial coefficient. Applicability of the new method has been tested for binary systems under vapor–liquid and liquid–liquid equilibrium conditions.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1021987603498

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Effective utilization of equations of state for thermodynamic properties in process simulation (1984)

Mathias, P. M. ; Boston, J. F. ; Watanasiri, S.

Hoboken, NJ : Wiley-Blackwell

AIChE Journal 30 (1984), S. 182-186

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ISSN: 0001-1541

Keywords: Chemistry ; Chemical Engineering

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology

Notes: Thermodynamic property computations using equations of state first require computation of the density root. Since higher level calculations such as single-stage flash, distillation and data regression are usually performed iteratively, properties are often demanded at conditions where the appropriate density root does not exist. A strategy of returning suitable pseudoproperties under such conditions is proposed. It has been successfully used in ASPEN (Advanced System for Process Engineering), a general process simulator developed at the Massachusetts Institute of Technology.

Additional Material: 7 Ill.