A phenomenological correction to an equation of state for the critical region

Authors

  • Grace F. Chou,

    1. Chemical Engineering Department, University of California and Materials and Chemical Sciences Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720
    Current affiliation:
    1. Air Products and Chemicals, Inc., 7201 Hamilton Blvd., Allentown, PA 18195
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  • John M. Prausnitz

    Corresponding author
    1. Chemical Engineering Department, University of California and Materials and Chemical Sciences Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720
    • Chemical Engineering Department, University of California and Materials and Chemical Sciences Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720
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Abstract

This work presents a phenomenological correction to improve a classical equation of state for representing phase equilibria and densities in the vapor-liquid critical region. This correction consists of two steps. The first step is a volume translation which locates the correct critical point; this volume translation also improves density predictions for pure fluids and mixtures. The second step provides a near-critical contribution to the residual Helmholtz energy which accounts for aomalous behavior near the critical point. For pure fluids, the near-critical contribution flattens the coexistence curve and pressure-density isotherms near the critical point. For mixtures, the near-critical contribution has only a small effect on the calculated coexistence curve; this effect is often masked by the choice of binary parameters in the classical equation which have a more profound effect on the calculated results.

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