Cubic equation of state near critical point (~0.95 < Tr < 1)

[maistral]

Hi. I have read somewhere that cubic equations of state seem to have convergence issues when vapor pressure calculations are done near the critical point. Sadly, I have forgotten where I have have read it :(

I would like to ask some knowledgeable people regarding this, or can people point me I am the right direction about this topic?

 

[Astronuc]

Cubic equations (and even higher order polynomials) can be inadequate to describe properties near transitions such as the critical point.

See the NASA report, SURVEY OF HEAT TRANSFER TO NEAR-CRITICAL FLUIDS, November 1970
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19710003560.pdf

. . . experiments demonstrate that, near the critical point, large relaxation times are required for a thermally disturbed system to return to
equilibrium. One consequence of this is that the near-critical fluid under the dynamic conditions of heat transfer can be expected to experience some degree of thermodynamic nonequilibrium. This, in turn, will result in some uncertainty in applying an equation of state.

from bottom of page 5 of the report.

See also - J. V. Sengers, "Transport properties of fluids near critical points," International Journal of Thermophysics, May 1985, Volume 6, Issue 3, pp 203–232

On a similar matter, I have a particular interest in describing properties of structural alloys in the range of 0.9 - 1 T_m. One finds scarce information in the literature.