Calculating Temperature Gradient

pupo · April 29, 2016, 15:52

Good Night all!

I'm with a very minor, very noobish problem i can't solve/find a solution online:

how do i convert a a heat transfer coeficient at a wall ( q = 200 w/m² ) to an OpenFoam Fixed gradient boundary condition? ( gradient uniform ?????; )

I used to have this in a manual, that I foolishly borrowed a collegue, that explained this very clearly and now I'm stuck in this silly detail.

Thank you very much!

Best Regards,
Pupo

rapierrz · May 1, 2016, 02:02

Hi pedro,

For conjugate heat transfer if you want to apply heat flux to solid boundary you

can use gradT=q/Ksolid.

If you want to apply to boundary near fluid you can use gradT=q/Kfluid.

pupo · May 2, 2016, 05:37

Thnak you for the answer!

However, K changes with temperature on the fluid side... how do i account for that?

Best Regards

rapierrz · May 2, 2016, 07:12

For this condition you can use of groovyBc for example:

Wall
{
type groovyBC;
valueExpression "0";
variables "K1=0.6;K2=0.02;Keff=alpha1*K1+(1-alpha1)*K2";//alpha is volume fraction
gradientExpression "2000/Keff";
fractionExpression "0";
value uniform 293;

}

pupo · May 2, 2016, 11:53

Thank you, i had completely forgot about good old groovy :P

meanwhile i found this: http://openfoam.com/documentation/cp...ml/a00744.html

it seems to do what i want and to take into consideration the varying conductivity of the fluid.

Best Regards,

April 29, 2016, 15:52	Calculating Temperature Gradient	#1
pupo Member Pedro Join Date: Nov 2014 Posts: 50 Rep Power: 11	Good Night all! I'm with a very minor, very noobish problem i can't solve/find a solution online: how do i convert a a heat transfer coeficient at a wall ( q = 200 w/m² ) to an OpenFoam Fixed gradient boundary condition? ( gradient uniform ?????; ) I used to have this in a manual, that I foolishly borrowed a collegue, that explained this very clearly and now I'm stuck in this silly detail. Thank you very much! Best Regards, Pupo

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May 1, 2016, 02:02		#2
rapierrz Senior Member Hesam Join Date: Feb 2015 Posts: 139 Rep Power: 11	Hi pedro, For conjugate heat transfer if you want to apply heat flux to solid boundary you can use gradT=q/Ksolid. If you want to apply to boundary near fluid you can use gradT=q/Kfluid.

May 2, 2016, 05:37		#3
pupo Member Pedro Join Date: Nov 2014 Posts: 50 Rep Power: 11	Thnak you for the answer! However, K changes with temperature on the fluid side... how do i account for that? Best Regards

May 2, 2016, 07:12		#4
rapierrz Senior Member Hesam Join Date: Feb 2015 Posts: 139 Rep Power: 11	For this condition you can use of groovyBc for example: Wall { type groovyBC; valueExpression "0"; variables "K1=0.6;K2=0.02;Keff=alpha1K1+(1-alpha1)K2";//alpha is volume fraction gradientExpression "2000/Keff"; fractionExpression "0"; value uniform 293; }

May 2, 2016, 11:53		#5
pupo Member Pedro Join Date: Nov 2014 Posts: 50 Rep Power: 11	Thank you, i had completely forgot about good old groovy :P meanwhile i found this: http://openfoam.com/documentation/cp...ml/a00744.html it seems to do what i want and to take into consideration the varying conductivity of the fluid. Best Regards,