should I use real gas or ideal gas for the following simulation?

mario26 · January 15, 2022, 12:47

should I use real gas or ideal gas for the following simulation? Air flows in, it's an open system, and one wall is heated.

1) If I am to use a real model for the air, which model should I use? Redlich-Kwong ?

2) Where do I enter the outlet pressure at gauge pressure in the outlet area?

3) I have defined the following speed for named expressions: (Re*DynamicViscosity)/(Density*d)

does the calculator for DynamicViscosity and Density take the correct values at the input temperature of 298 K?

I hope you can help me.

Many Thanks

LuckyTran · January 16, 2022, 02:54

Should you use real gas or ideal gas? I can't answer philosophical questions for you. There are an infinitude of equations of states available (constant density for example) that may be appropriate.

1) If you're doing real gas because you want the most accurate equation of state available then I recommend to use the NIST REFPROP calculator.
2) In boundary conditions. Click on the outlet surface and edit. Set it to a pressure outlet if it isn't already.
3) Don't forget that properties are functions of temperature AND pressure. It should create a field which correctly uses the local temperatures & pressures. The function itself will calculate the correct quantity. If you're using a velocity inlet where you have control of velocity, temperature, and pressure, then you are good to go. But if you use one of the other inlets (where you specify stagnation properties), the behavior may be something different than what you expect.

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January 16, 2022, 02:54		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,673 Rep Power: 65	Should you use real gas or ideal gas? I can't answer philosophical questions for you. There are an infinitude of equations of states available (constant density for example) that may be appropriate. 1) If you're doing real gas because you want the most accurate equation of state available then I recommend to use the NIST REFPROP calculator. 2) In boundary conditions. Click on the outlet surface and edit. Set it to a pressure outlet if it isn't already. 3) Don't forget that properties are functions of temperature AND pressure. It should create a field which correctly uses the local temperatures & pressures. The function itself will calculate the correct quantity. If you're using a velocity inlet where you have control of velocity, temperature, and pressure, then you are good to go. But if you use one of the other inlets (where you specify stagnation properties), the behavior may be something different than what you expect.