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Warning: Independent variables were clipped during table generation

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Old   January 24, 2015, 13:12
Exclamation Warning: Independent variables were clipped during table generation
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Yousef
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I am running a double-pipe counter flow heat exchanger on CFX. The heat exchanger is suppose to run on Supercritical CO2, therefore I generated a Real Gas Properties (RGP) file using the generator tool for S-CO2, but whenever I run it on the solver, I keep getting this warning after each iteration in the solver:

****** Warning ****** |
| |
| Independent variables were clipped during table generation |
| at: END OF TIME STEP |
| 0 detailed warnings were printed because the maximum |
| number of warning messages was exceeded. |
| |
| The maximum number of detailed table clip warning messages can be |
| controlled with the following expert parameter: |
| |
| max table messages (default: 0) |
| |
| Please increase the number, if you need further details of the |
| locations and variables involved.


Though the solution does converge. I re-created the RGP file changing the pressure range to include the atmospheric pressure (Default reference pressure in CFX) and I noticed that the warning stops appearing! But I do not understand why does this happen since the atmospheric pressure is just a reference.

If anyone experienced similar issue please share

I am using ANSYS 15
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Old   January 26, 2015, 07:23
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Hello Simplyyy,

I got the same message once. I was simulating air with humidity and hence defined a user material.

The message, that variables were clipped during table generation, indicates that the range set by the user for generating the table for temperature and pressure is too small.
So it could be that at one point during your simulation you reach a pressure that lies outside the specified interval. By decreasing the lower bound of your table you can prevent that. Probably that is what you have done by setting it to atmospheric pressure.

Another advice: If you use user functions to model material properties (such as conductivity or heat capacity in terms of temperature) try to create enough sampling points since CFX only interpolates linear between them. You could incur a large error through this.

Hope this helps,

Simon
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