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-   -   Code behaves strangely when the geometry is changed (http://www.cfd-online.com/Forums/openfoam-solving/58105-code-behaves-strangely-when-geometry-changed.html)

nandiganavishal January 7, 2009 17:04

Hi All,, With reference to
 
Hi All,,

With reference to my previous message, I am solving an electro osmotic flow in a simple square channel. Here is a paper from that, but right now I am neglecting the velocity term.. I finished coding it but had some convergence issues because of the large values of the transport properties and hence I non dimensionalised them and now the code is
converging, my concentration values at inlet and outlet boundary conditions are same (=1). Hence the result should be 1 throughout right.. but stangely I am not getting 1.. instead I am getting some strange values... as mentioned in the earlier mesage, I would like to know whether I have coded them correctly or not..

Kindly do the needful...

Thanks

http://www.cfd-online.com/OpenFOAM_D...hment_icon.gif coupledFoam.tar.gz
http://www.cfd-online.com/OpenFOAM_D...hment_icon.gif controlDict

nandiganavishal January 7, 2009 17:26

Sorry I couldnt upload the pap
 
Sorry I couldnt upload the paper because of the file size limit... I am attaching the page where all the equations are given..

D1 = 1.96e-9 m2/s
D2 = 0.87e-9 m2/s
Z1 = 1
Z2 = -1
omega1 = D1/RT, R = 8.314J/molK, T = 297K
omega2 = D2/RT



nandiganavishal January 7, 2009 17:27

Sorry I couldnt upload the pap
 
Sorry I couldnt upload the paper because of the file size limit... I am attaching the page where all the equations are given..

D1 = 1.96e-9 m2/s
D2 = 0.87e-9 m2/s
Z1 = 1
Z2 = -1
omega1 = D1/RT, R = 8.314J/molK, T = 297K
omega2 = D2/RT

I have normalised all the equations and proceeded the coding and I am getting some strange results as mentioned previously.. Kindly give your valuable suggestions...

Thanks

Regards

Vishal




nandiganavishal January 7, 2009 17:37

Sorry I couldnt upload the pap
 
Sorry I couldnt upload the paper because of the file size limit...Here are the equations

dC1/dt = div(D1*gradC1)+ div(omega1*Z1*F*C1*grad(Phi))

dC2/dt = div(D2*gradC2)+ div(omega2*Z2*F*C2*grad(Phi))

div(grad(Phi)) = (-F*Z1*C1-F*Z2*C2)/e0*er

where,
Phi = electric field
F - faradays constant
e0 = permittivity of vacuum
er = permittivity of water = 80
D - diffusion coefficient
D1 = 1.96e-9 m2/s
D2 = 0.87e-9 m2/s
Z = valence number
Z1 = 1
Z2 = -1
omega1 = D1/RT, R = 8.314J/molK, T = 297K
omega2 = D2/RT

I have normalised all the equations and proceeded the coding and I am getting some strange results as mentioned previously.. Kindly give your valuable suggestions...

Thanks

Regards

Vishal

sachin January 8, 2009 04:17

hi Vishal, I am not very sure
 
hi Vishal,
I am not very sure but i am thinking this is because the grid size. I have strong doubts that the convergence also fails because of the big grid size, maybe there are issues with time step and Courant no also. Since your details never mentioned about these things. maybe that is missing.
This are just suggestions havent gone thru those long details.
regards
Sachin

nandiganavishal January 8, 2009 14:06

Thanks Sachin.. I had figured
 
Thanks Sachin.. I had figured out the problem and now the code is working fine... Thanks for the help.

nandiganavishal January 8, 2009 18:29

Hi, As mentioned earlier my
 
Hi,

As mentioned earlier my code is working properly and I get the desired results.

However, I have some queries. I have four variables C1,C2 and Phi and U. I obtain the values of these variables at each time step. Now I would like to calculate another parameter
T1 = -D1*grad(C1) - K1 * C1 * grad (Phi) + C1 * U
T2 = -D2*grad(C2) - K2 * C2 * grad (Phi) + C2 * U

Where D1,D2,K1,K2 are constants...

Then I would like to calculate I by integrating T1 and T2 over the cross section given by the formula

I = integral over S {(Z1*F*T1)+(Z2*F*T2)} dS

where S is the cross sectional area of the channel..

Kindly let me know how to proceed further..

Thanks

Regards

Vishal

nandiganavishal January 14, 2009 16:35

Regards Vishal
 
Regards

Vishal


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