[pradeepramesh]

Hi ,

I am using laplacianfoam for a heat-block case. I have gone thru the discussion - "Mixed BC - heat transfer - laplacianFoam"
http://www.cfd-online.com/Forums/ope...acianfoam.html.

From the forum discussions - "externalWallHeatFluxTemperature" and "groovyBC" were pointed out.

I am interested to apply heat influx at the boundary wall.Please find the attached snapshot for more info.

How to apply "groovyBC" for defining heat influx at the boundary in a heat-block?

Thank you,
Pradeep

[gschaider]

Originally Posted by pradeepramesh

Hi ,

I am using laplacianfoam for a heat-block case. I have gone thru the discussion - "Mixed BC - heat transfer - laplacianFoam"
http://www.cfd-online.com/Forums/ope...acianfoam.html.

From the forum discussions - "externalWallHeatFluxTemperature" and "groovyBC" were pointed out.

I am interested to apply heat influx at the boundary wall.Please find the attached snapshot for more info.

How to apply "groovyBC" for defining heat influx at the boundary in a heat-block?

Thank you,
Pradeep

With "fractionExpression '0'" you're on the right track. What gradientExpression is supposed to to be depends on your physics (which heat-flux you want to prescribe). Rewrite it so that you get an expression "dT/dx = ....". Then you'll just have to take what is on the right hand side of that expression and write it down as a groovyBC-expression (Note: x in this case is not the x in the cartesian coordinates but normal to the wall)

[pradeepramesh]

Thank you very much Bernhard

[pradeepramesh]

Dear Bernhard,

For a case, flux is ------------>>>> q = -(k) * (dT/dx)

(dT/dx) = - q /k

We have :

"q" is the heat flux : q = 10 (W/m2),

"k" is the thermal Conductivity of the material : k = 200 (W/mK)

Outwall
{
        type                          groovyBC;
        value                         uniform 293;
        gradientExpression 	 “(-q)/k";
        fractionExpression 	 "0";
        variables 			 “q=10;k=200";
}

I would like request your feedback on the above mentioned BC.

Thank you!

[gschaider]

Originally Posted by pradeepramesh

Dear Bernhard,

For a case, flux is ------------>>>> q = -(k) * (dT/dx)

(dT/dx) = - q /k

We have :

"q" is the heat flux : q = 10 (W/m2),

"k" is the thermal Conductivity of the material : k = 200 (W/mK)

Outwall
{
        type                          groovyBC;
        value                         uniform 293;
        gradientExpression 	 “(-q)/k";
        fractionExpression 	 "0";
        variables 			 “q=10;k=200";
}

I would like request your feedback on the above mentioned BC.

Thank you!

That should work. Sign depends on your definition of the flux.

I usually limit myself to answers about the technical aspects of swak4Foam. Physics is your own responsibility

[pradeepramesh]

Thank you very much. It worked!

[costrom]

would it be possible to use a 'q' file that is the output from a different solver instead of defining one constant value for q on the boundary?

[gschaider]

Originally Posted by costrom

would it be possible to use a 'q' file that is the output from a different solver instead of defining one constant value for q on the boundary?

Currently no. Unless the data is a 1D-function q(s). Then you can use a lookup

I've explained it a number of times in different places: it is not THAT easy to do it in a general way (fileformats, different discretizations, error handling, parallel etc)

[costrom]

I apologize for asking a question that has been answered elsewhere, but...

I have a qMean file resulting from a dsmcFoam run, and I would like to use the heat fluxes from that as a boundary condition for a laplacianFoam runcase. is this currently possible in openFOAM 2.3.x without editing the *.h, *.c files?

[gschaider]

Originally Posted by costrom

I apologize for asking a question that has been answered elsewhere, but...

I have a qMean file resulting from a dsmcFoam run, and I would like to use the heat fluxes from that as a boundary condition for a laplacianFoam runcase. is this currently possible in openFOAM 2.3.x without editing the *.h, *.c files?

I'm not familiar with that solver. qMean is average in time or average in space as a function of time or space?

Depending on that timeVaryingMappedFixedValue might be able to help you

[calf.Z]

Originally Posted by gschaider

With "fractionExpression '0'" you're on the right track. What gradientExpression is supposed to to be depends on your physics (which heat-flux you want to prescribe). Rewrite it so that you get an expression "dT/dx = ....". Then you'll just have to take what is on the right hand side of that expression and write it down as a groovyBC-expression (Note: x in this case is not the x in the cartesian coordinates but normal to the wall)

Thank you for your hints. If my case doesn't consider the materials of the Wall, just having the internal mesh in fluid, how should I know about k and dT/dx? I want to give the constant heat flux on wall and I just know q. Thank you.

[gschaider]

Originally Posted by calf.Z

Thank you for your hints. If my case doesn't consider the materials of the Wall, just having the internal mesh in fluid, how should I know about k and dT/dx? I want to give the constant heat flux on wall and I just know q. Thank you.

There are boundary conditions that implement constant heat-flux in OpenFOAM. If your heat-flux has no spatial or temporal distribution then I'd recommend using these.
If you want to/have to use groovyBC the heat conductivity of the fluid is sufficient information to calculate the temperature gradient

[calf.Z]

Originally Posted by gschaider

There are boundary conditions that implement constant heat-flux in OpenFOAM. If your heat-flux has no spatial or temporal distribution then I'd recommend using these.
If you want to/have to use groovyBC the heat conductivity of the fluid is sufficient information to calculate the temperature gradient

Thank you for your reply.

I think I know the thermo conductivity of fluid in my case but I am using tabular method to get these thermopropertities. So kappa is changing with T and P and read from tabulated table.

And I am using externalWallHeatFluxTemperature BC to give the constant heat flux. But I am not sure if kappaMethod : fluidThermo is suitable for my case.

I use wallHeatFlux to check the heat flux after simulation. The result is far diffrernt from the setting one. But when I use #include wallHeatFlux to check heat flux during running, it give other heat flux values which are closer to the setting one in BC.
So I am confused about the different behaviors of the utility. I just use it in different moments and it gives me different values.

Any hint is highly appreciated.