The compositions of vapor and liquid phases of a multicomponent system are functions of pressure and temperature. Therefore, the phase behavior of a fluid transported through a pipeline must be coupled to the pressure-temperature calculation algorithm. Both the Soave Redlich-Kwong and the Peng-Robinson EOS’s were considered.

A new procedure to calculate pressure and temperature profiles for multicomponent two-phase flow in pipelines was developed. This method, based on direct flash calculations at each pressure and temperature of interest, was compared to the method used by previous investigators based on interpolation of external arrays of physical properties.

The new procedure was found to be more accurate and easier to use than the one based on interpolation of external arrays. This was especially true when calculations were performed near the critical point.

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