(365c) The Expanded Fluid Concept for Transport Property Correlations

The Expanded Fluid concept is straightforward: as a fluid expands, the distance between the molecules in the fluid increases and the properties which are related mainly to intermolecular forces change in a systematic manner that can be correlated. In other words, properties such as viscosity can be correlated to density. This simple principle is at the heart of many viscosity correlations such as the corresponding states viscosity model. The corresponding states approach, which uses the critical point as a reference, begins to fail for viscous fluids that are near their glass transition at ambient conditions such as heavy oils. The Expanded Fluid model, first proposed by Yarranton and Satyro (2009), uses a fitted compressed state density (the density at which the viscosity tends to infinity) as a reference point. The model is structured as a departure from an independently determined gas viscosity so that the complete fluid phase region is mapped; the critical point viscosity is predicted from the change in density.

In this contribution, the Expanded Fluid model is briefly reviewed including its pure component form and its application to mixtures and characterized crude oils. The Expanded Fluid principle is then applied to thermal conductivity to develop a new model based on the same compressed state densities used in the Expanded Fluid viscosity model. Similar mixing rules are developed and a similar extension to characterized oils. Finally, the relationship between diffusivity and viscosity is demonstrated to illustrate how the three transport properties, viscosity, thermal conductivity, and diffusivity, all relate to fluid expansion.

Reference: Yarranton, H.W., Satyro, M.A., Ind. Eng. Chem. Res., 48(7), 2009, 3640-3648.