Real gas modelling
 

Hello, I am trying to run a simulation with real gas model from NIST using ch4a as working fluid. When I try to initialisate or run the simulation its not converging in Fluent,
in my simulation, inlet temp 110K, 0.02 kg/s ch4, pressure outlet 53 bar. just ıwant to see the phase change, ı try to understand the supercritical fluid, firstly ı tried to fit the curves at MATLAB, but there were wrongs with interpolations. ı reserach the rgp table from nist to CFX, ı couldnt, how do we deal with?

I would like to reproduce your problem. Could you please create and upload a small example that demonstrates this? For example, pressure-driven flow in a straight cylindrical pipe.

I'm guessing you mean methane (CH4) not ch4a.
There will not be a phase change at this high of a pressure, as it is above the 46 bar critical pressure. In normal terminology your fluid would be a subcooled liquid since for supercritical you have to have both the pressure and temperature above critical. But in RGP tables and CFX it is a supercritical fluid (vapor) since either pressure or temperature is above the critical point. So your simulation should start with vapor, not liquid. You will have difficulty transitioning between this vapor and liquid if you are not crossing the saturation curve. Tell us more about exactly what you are doing and where you think this phase change will occur.