What are these gas density options means?
 

In materal database settings,for example:real-gas-Soave-Redlich-Kwong， real-gas-peng-Robinson etc.

Regards!

Real Gas
 

These are model to model density of real gases. In reality, every gas is a real gas, i.e., their density is defined by some function of temperature and pressure. Ideal case is governed by Ideal-Gas law and most of the gases do follow this law at low enough pressure and high temperature. But there are certain phenomena that exist because gases are not ideal, such as, isenthalpic process that change the temperature of the gas during expansion in refrigerator evaporators.

Thank you very much,regards!