# how can i model the ideal gas law in CFX?

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July 3, 2013, 10:05
how can i model the ideal gas law in CFX?
#1
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Join Date: May 2013
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Dear all,

I am trying to model the ideal gas law in CFX for the following model: The model consists of four walls with the same temperature and between the wall there is air (the ideal gas). The temperature of the walls is higher than the air temperature. We are using steady state computation. The gas is heated in the vicinity of the walls, therefore density and pressure vary. The density field, pressure field and temperature field have to match with the ideal gas law.

Up to now I get no proper results. Besides my setup, I also appended here the corresponding results I get in CFX. I suppose there are some errors in the boundry-conditions or I have an mistake in the setup. I would very much appreciate any advice regarding obvious mistakes or approaches to pinpoint the mistake.

Kind Regards
Attached Images
 Pressure Air.jpg (47.3 KB, 12 views) Pressure wall.jpg (48.0 KB, 7 views) Tempverteilung.jpg (55.4 KB, 11 views) wall geometrie.jpg (19.2 KB, 8 views) Velocity air.jpg (43.9 KB, 8 views)

 July 3, 2013, 17:01 #2 Senior Member   Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,171 Rep Power: 23 In steady state you would have no pressure or temperature variation, everything would be at the wall temperature. Seems you are trying to enclose the gas at one temperature then raise the temperature and watch the average pressure in the enclosure go up according to the ideal gas law?

July 4, 2013, 06:15
#3
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Join Date: May 2013
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that's right. Here are a few screen shots of my setups.
Thanks and regards
Attached Images
 Analysistyp.jpg (18.2 KB, 19 views) intialization.png (16.1 KB, 17 views) Solvercontrol.jpg (60.4 KB, 17 views) Wall.jpg (25.5 KB, 13 views)

 July 4, 2013, 07:20 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,729 Rep Power: 143 Please post your CCL. That is a much better way of describing your setup rather than screen images. You have not answered Erik's question. If you define all walls to have a defined temperature then the steady state result is the fluid is all at that temperature as well. You do not need a CFD simulation to tell you that. What are you trying to do with this model? What are you trying to learn?