[hellsblade.91]

Do we use real gas material in Fluent when we use high pressure for eg 18 to 24 bars ?

[LuckyTran]

It's up to you whether you like to or not.

[CFD-fellow]

It depends on the material and how much it deviates from Ideal gas model in comparison with thermodynamic tables. For example for air I will say no its not needed to use real gas model, but for steam the answer is yes in the mentioned pressure range.

[hellsblade.91]

Hi Behrooz,

Thanks for your reply. Could you make it clear and give an example when to use ideal and real gas in different situations/ boundary conditions?

[CFD-fellow]

Hi
It has no special time, it depends on accuracy. Real gas model gives more accurate results. For example imagine a steam nozzle with 21 bar pressure. If you use ideal gas model the mass flow rate passing through the nozzle will be around 10% lower than the value of mass flow rate predicted by real gas model which is so near to experimental value. But if you use 21 bar air nozzle the error will be so much lower (even lower than 0.5%) which shows that air also in high pressure values can act like an ideal gas. It's all about the density value.

[rewol]

Depends on the conditions of your case.

At high pressure values in mid-range temperatures, density deviation is relatively large from ideal values. Also at cryogenic temperatures (or near/below critical), ideal gas does not yield correct results for density either. Density deviation also affects thermodynamic properties of the fluid, since departure functions are all functions of density or molar volume in real gas case.

Note that FLUENT do not support transcritical states of the fluids in real gas models.

If your case is simulated in such conditions or in ranges that such conditions may occur, then real gas model would be logical.

Hope this helps.