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-   -   evaporation / vapor flux / groovyBC (http://www.cfd-online.com/Forums/openfoam/95058-evaporation-vapor-flux-groovybc.html)

oga_shin December 4, 2011 23:17

evaporation / vapor flux / groovyBC
 
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

gschaider December 5, 2011 05:57

Quote:

Originally Posted by oga_shin (Post 334617)
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

oga_shin December 11, 2011 01:53

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

gschaider December 11, 2011 07:14

Quote:

Originally Posted by oga_shin (Post 335421)
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

oga_shin December 13, 2011 04:43

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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