FPROPS/Viscosity

Calculation of viscosity in FPROPS is currently in development. Ultimately, different publications provide different types of correlations (equations), so we implement a system that permits alternative correlations to be selected.

First correlation

Driven by the use-case of transport properties for supercritical carbon dioxide, the first required viscosity correlation follows this form

<math>\mu = \mu_0 \left(T \right) + \mu_r \left(\tau,\delta \right) + \mu_c \left(\tau, \delta \right)</math>

where dynamic viscosity <math>\mu</math> is the sum of an ideal (zero-pressure) component <math>\mu_0</math>, a residual component <math>\mu_r</math>, and optionally, a critical-region component <math>\mu_c</math>. Note that viscosity is said to increase to infinity in the vicinity of the critical point (which seems to suggest that it would make more sense to calculate in terms of something like an 'inviscidity' instead...?)