Identification of the phase of a fluid using partial derivatives of pressure, volume, and temperature without reference to saturation properties: Applications in phase equilibria calculations

The phase of a fluid (liquid, vapor) at a given state is normally identified by comparing the properties of the fluid at the given state with saturation properties. In this paper we present a thermodynamic method for determining the phase of a fluid from the partial derivatives of pressure, volume and temperature without reference to saturated properties. The method has immediate application in a variety of phase equilibria calculations, particularly for liquid–liquid or vapor–liquid–liquid equilibria calculations in process simulators.

Research highlights▶ It is important to identify the phase of split phases correctly in multiphase flash calculations. ▶ The paper shows relationship between phase and partial derivatives of p, v and T. ▶ The method has applications in process simulation, complex phase equilibria calculations.