Material properties (molar mass)

Shabi1992 · May 1, 2017, 07:07

Hello everyone,
I am trying to simulate the internal flow which the fluid is not exist in the material table in CFX. I don't know the molar mass and I can't calculate it as well. The flow is not very complex and there is no chemical reaction.
So now is it important to enter the molar mass value? Is it true that I run my project with molar mass = 1 ?
Best regards,
Shabi.

ghorrocks · May 1, 2017, 08:25

If your fluid is simple (for instance: incompressible and constant properties) then you don't need to molar mass and can use anything.

If you are not sure just do a sensitivity study and find out. Run a model with molar mass = 1 and another with it =1000. Compare the results and see if it makes a difference.

evcelica · May 1, 2017, 09:52

The program only uses molar mass in calculations that require it: Molar fractions of mixtures, ideal gas calculations, etc. It is ignored otherwise. But like Glenn says, it's always best to prove this to yourself with a sensitivity check.

Shabi1992 · May 2, 2017, 07:48

Quote:

Originally Posted by ghorrocks

If your fluid is simple (for instance: incompressible and constant properties) then you don't need to molar mass and can use anything.

If you are not sure just do a sensitivity study and find out. Run a model with molar mass = 1 and another with it =1000. Compare the results and see if it makes a difference.

Thank you very much.

Shabi1992 · May 2, 2017, 07:49

Quote:

Originally Posted by evcelica

The program only uses molar mass in calculations that require it: Molar fractions of mixtures, ideal gas calculations, etc. It is ignored otherwise. But like Glenn says, it's always best to prove this to yourself with a sensitivity check.

Thank you very much

May 1, 2017, 07:07	Material properties (molar mass)	#1
Shabi1992 New Member Join Date: Oct 2015 Posts: 28 Rep Power: 10	Hello everyone, I am trying to simulate the internal flow which the fluid is not exist in the material table in CFX. I don't know the molar mass and I can't calculate it as well. The flow is not very complex and there is no chemical reaction. So now is it important to enter the molar mass value? Is it true that I run my project with molar mass = 1 ? Best regards, Shabi.

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May 1, 2017, 08:25		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	If your fluid is simple (for instance: incompressible and constant properties) then you don't need to molar mass and can use anything. If you are not sure just do a sensitivity study and find out. Run a model with molar mass = 1 and another with it =1000. Compare the results and see if it makes a difference.

May 1, 2017, 09:52		#3
evcelica Senior Member Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,167 Rep Power: 23	The program only uses molar mass in calculations that require it: Molar fractions of mixtures, ideal gas calculations, etc. It is ignored otherwise. But like Glenn says, it's always best to prove this to yourself with a sensitivity check.