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May 22, 2010, 11:33 
Additional Variable BC

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May 22, 2010, 12:42 

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Jordi
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It looks like a diffusion, is that your system? You do not provide very much info on your problem, but if it's like a heat convection, where C is temperature, then you can fix both temperature (C) and transfer coeff. (H) at the same surface, can't you?


May 23, 2010, 18:49 

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Glenn Horrocks
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Can do this with a gradient boundary with a CEL expression. Should be easy.


May 24, 2010, 15:19 

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Thank you so much Glenn
Your advices have always helped me and other students. But would you please explain it more for me? or refer me to a tutorial or example? I don't know how to interpret a gradient boundary. Thanks again Last edited by Eli; May 24, 2010 at 15:47. 

May 24, 2010, 15:26 

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Quote:
C is a scaler variable and shows kind of concentration in the simulation, I just don't know how to define the Left hand of equation. 

May 24, 2010, 18:42 

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Glenn Horrocks
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Recast the equation as dC/dx=H/K(CC0) then you have the gradient of the scalar at the boundary is a simple function. Set the function to a CEL expression and it is done.
Set this for the additional variable boundary condition at the walls. 

January 13, 2011, 09:57 

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Lance
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Quote:
V*CD*dC/dn = k*C, where V, D and k are constants and C is my additional variable. The problem is how to calculate the dC/dn as it is the gradient in the normal direction from the wall. Any suggestions? 

January 13, 2011, 17:53 

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Glenn Horrocks
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Will the CEL variables normal, with extensions like _Coordinate_Direction help you? See the CFX reference guide, "Quantitative CEL functions in CFX"


January 14, 2011, 05:56 

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Lance
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And can I define AV.Gradient X (...etc) in PRE as well? And btw, how do I define the boundary condition at the wall? The units resolve to [kg/(s m^2)]. Transfer coefficient+additional variable or Flux in? Last edited by Lance; January 14, 2011 at 12:16. 

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