# evaporation / vapor flux / groovyBC

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 December 4, 2011, 23:17 evaporation / vapor flux / groovyBC #1 New Member   shinya ogata Join Date: Sep 2010 Posts: 8 Rep Power: 6 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

December 5, 2011, 05:57
#2
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Bernhard Gschaider
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Quote:
 Originally Posted by oga_shin 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

 December 11, 2011, 01:53 #3 New Member   shinya ogata Join Date: Sep 2010 Posts: 8 Rep Power: 6 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

December 11, 2011, 07:14
#4
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Bernhard Gschaider
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Quote:
 Originally Posted by oga_shin 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

 December 13, 2011, 04:43 #5 New Member   shinya ogata Join Date: Sep 2010 Posts: 8 Rep Power: 6 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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