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thermotools / thermopack

Thermopack is a thermodynamic model library for fluid properties and PVT calculations
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Critical parameters for Lennard-Jones fluid #46

Closed vegardjervell closed 1 year ago

vegardjervell commented 1 year ago

I noticed that the critical point in the fluid file for the Lennard-Jones fluid is inconsistent with the default parameter set for saftvrmie, and that the default parameter set for saftvrmie gives a critical point below 50 K (the default minimum temperature for the numerical solvers. Additionally, the critical point solver fails for pure LJF, even though tmin is set below the critical point, unless the "correct" values are supplied as initial guesses .

Of course, we can use any parameters to represent the LJF, but I think it would be nice to use default parameters that ensure the default behaviour is that the phase envelope is at temperatures above tmin. If we use e.g. eps_div_k=100, we can do ourselves a favour by having a simple link between reduced temperature and real temperature.

morteham commented 1 year ago

The lower limit when solving for the crtical point was too high due to the faulty critical paramaters. Modefied paramaters and added option to ovverride volume limit in solver.