Fluid Models

The models used in Multiflash to calculate phase equilibria and physical properties fall into several distinct groups.

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 Penneloux density (RKSA and PRA)
EOS 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 UNIFACor NRTL). Non-cubic EOS include LK, LKP and BWRS, which can produce improved prediction of thermal and volumetric properties,CSM (a series of high accuracy equations for reference fluids) and PC-SAFT primarily used to model polymer solutions.

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 halite 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 or Twu; for thermal Conductivity by Chung-Lee-Starling; for surface tension by McLeod-Sugden .


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.

For further information please contact:
Dr Beryl Edmonds, Infochem Computer Services Ltd, 13 Swan Court, 9 Tanner Street, London SE1 3LE, UK
Tel: +44 20 7357 0800 Fax: +44 20 7407 3927
Email: marketing@infochemuk.com
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This page was last revised in May 2006.