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Old   December 4, 2011, 23:17
Smile evaporation / vapor flux / groovyBC
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shinya ogata
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Hi!

I want to calculate water evaporation with simpleFoam.
I have already added moisture field as X in simpleFoam solver.
And then, I am trying to make evaporation boundary using groovyBC.

I wrote a boundary condition of vapor flux referring to heat flux.

z_
{
type groovyBC;
value uniform 0;
gradientExpression "gradX";
fractionExpression "0";
variables
"alphac=5.8+3.9*mag(internalField(U));Xs=0.0167;al fadash=3.6*alphac/3600;capadash=1;rhodash=1.2;gradX=alfadash*(Xs-internalField(X))/(kappaEffX*capadash*rhodash);";

}

SimpleFoam has done without any error.
But amount of water evaporation is too little comparing to a experiment data.

Is the boundary condition which I wrote right ?

Shinya
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Old   December 5, 2011, 05:57
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Bernhard Gschaider
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Quote:
Originally Posted by oga_shin View Post
Hi!

I want to calculate water evaporation with simpleFoam.
I have already added moisture field as X in simpleFoam solver.
And then, I am trying to make evaporation boundary using groovyBC.

I wrote a boundary condition of vapor flux referring to heat flux.

z_
{
type groovyBC;
value uniform 0;
gradientExpression "gradX";
fractionExpression "0";
variables
"alphac=5.8+3.9*mag(internalField(U));Xs=0.0167;al fadash=3.6*alphac/3600;capadash=1;rhodash=1.2;gradX=alfadash*(Xs-internalField(X))/(kappaEffX*capadash*rhodash);";

}

SimpleFoam has done without any error.
But amount of water evaporation is too little comparing to a experiment data.

Is the boundary condition which I wrote right ?

Shinya
Don't know. Just two remarks:

a) never trust experimental data
b) if you use internalField like that I'd expect some kind of grid dependence. Try changing the resolution and see if that makes a difference
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Old   December 11, 2011, 01:53
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shinya ogata
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Hi gschaider !

Thank you for your advise!
I subdivided mesh and the amount of evaporation changed.
As you pointed, it could be mesh dependence.
I will try to find appropriate mesh.
Thank you again.

Shinya
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Old   December 11, 2011, 07:14
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Bernhard Gschaider
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Quote:
Originally Posted by oga_shin View Post
Hi gschaider !

Thank you for your advise!
I subdivided mesh and the amount of evaporation changed.
As you pointed, it could be mesh dependence.
I will try to find appropriate mesh.
Thank you again.

Shinya
Don't adapt the mesh to fit your results. Try to find a mesh-independent formulation. Something that might help you are these functions:
http://openfoamwiki.net/index.php/Co...g_to_need_are:

Good luck
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Old   December 13, 2011, 04:43
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shinya ogata
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Hi gschaider !

Your advise is right.
Even if I found appropriate mesh comparing with experiment,
I cannot use it with another model.
I will try to make mesh-independent formulation.

Thank you again.
Shinya
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