Fluid Models

Equations of State (EOS):

Mostly used in the oil and gas industry this group includes the cubic equations of state e.g. SRK and PR and their variants which include fitting to pure component vapour pressure and liquid density (RKSA and PRA). Equations of State based on RKSA with modifications to allow prediction of polar, particularly aqueous, phases - CPA (RKSA with an association term), RKSAINFO (RKSA with an NRTL style mixing rule) and PSRK (RKSA with a mixing rule based on variant of UNIFAC or NRTL). Non-cubic EOS include LK, LKP and BWRS, which can produce improved prediction of thermal and volumetric properties, CSMA (a series of high accuracy equations for reference fluids) and PC-SAFT primarily used to model polymer solutions.

Since version 4.0 the industry standard GERG-2004 model is included. It is particularly accurate for natural gas mixtures.

Activity Coefficient models:

These are typically used to describe highly non-ideal polar mixtures and include Ideal, Wilson, NRTL, UNIQUAC, UNIFAC, Regular Solution and Flory-Huggins.

Solid models:

Our software includes models for hydrates, waxes and asphaltenes plus a freezeout model for pure condensed solids such as ice, solid CO2 or halide scales.

Transport Property models:

The transport properties of fluids (viscosity, thermal conductivity and surface tension) can be modelled by mixing of the pure component properties or for; viscosity by Pedersen, Lorentz-Bray-Clark, SuperTRAPP method or Twu; for thermal conductivity by Chung-Lee-Starling or the SuperTRAPP method ; for surface tension by McLeod-Sugden or the Linear Gradient Theory (LGST).

For more information on models and flash calculations see our Models and Methods leaflet, our PC-SAFT leaflet, and the leaflet on Modelling Trace Elements - Mercury for mercury partitioning.