Real Gas
 

In ansys-Fluent when i choose a correlation for real gas such as soave or Peng Robinson i have to select energy balance or not isnt neccesary?
Ill appreciate your help

Hi Lilo,

Whenever you choose a specific characteristic in Ansys Fluent (18.2 I work with and I am sure about) It Automatically turns on the energy method (or any other Method it needs) and will let you know that in the command section.
ie. When you choose ideal gas because it involves Temperature of the gas it turns it on.

Alternatively, you can read the manual; Theory section and user manual and will give you information on that.

Isothermal system
 

Thanks for reply me.

In this case,no matter whether an isothermal system?

Thans for reply me

No matter whether an isothermal system?

Yes becaeuse the ideal gas fluid for example is a function of temperature. Thats how it finds the density change. You can read more on the theory and user manual of ansys fluent.

No worries

If your system is isothermal, you can use the fixed values option in cell zone conditions to keep the temperature the same everywhere.

Just so you know, you can also specify the initial temperature field and disable the solution of the energy equation. To do this in the GUI go to solution controls and click Equations... This isn't the same as fixing the temperature constant but it demonstrates that there is a difference between specifying your EOS and solving the physics.