The selection of a suitable thermodynamic model for the prediction of enthalpy (H) and phase equilibrium (K) is fundamental to process modelling. Selection of an inappropriate model will result in convergence problems and erroneous results.

The selection process is driven by considering the following:

  • Process species and compositions.
  • Pressure and temperature ranges.
  • Phase systems involved.
  • Nature of the fluids.
  • Availability of data.

There are four categories of thermodynamic models:

  • Equations-of-State (E-o-S)
  • Activity coefficient (γ)
  • Empirical
  • Special system specific

Process Modelling Selection of Thermydynamic Methods (click to download) is not intended to be a rigorous analysis of the methods available and their selection but is offered as an aide memoire to the practicing engineer who is looking for rapid, realistic results from his process models. The study of complex systems invariably involves extensive research and expenditure of considerable manpower effort by specialists. There are extensive sources of data available from data banks run by DECHEMA, DIPPR and others. This paper presents practical selection methods and suggests techniques to test the validity of the thermodynamic model selected.