Wrong solution?

[cfernandes]

I solved in Elmer a heat conduction problem with known results.

I simply used in one face a prescribed heat flux (150 w/m2) and a prescribed temperature(280 K). The result should be: Tmax = 288 K and T min=287.7 K.

But with Elmer I found Tmin=8.49 and Tmax=343.

What I missed about?

Sif file in appendix.

case.sif

(2.46 KiB) Downloaded 236 times

Thank you in advance.

EDIT: After try some more, I just found that the units of heat flux should be in kW/m2. So, with 0.15 instead of 150, I get the right solution. So, there is a problem with units of heat flux. According to the manuals it should be W/m2 which proved to be wrong. What I missed?

[dmitry]

Hi!
May be I'm wrong, but In the code Boundry Condition 5 seems overdetermined:

Code: Select all

Boundary Condition 5
  Target Boundaries(1) = 5
  Name = "BoundaryCondition 1"
  Heat Flux = 150
  External Temperature = 288
End

External Temperature do not play any role here. It sould be Heat Flux condition only

Code: Select all

Boundary Condition 5
  Target Boundaries(1) = 5
  Name = "BoundaryCondition 1"
  Heat Flux = 150
End

or like that (Newton condition):
Heat Flux = Heat Transfer Coefficient * (Temperature - External Temperature)

Code: Select all

Boundary Condition 5
  Target Boundaries(1) = 5
  Name = "BoundaryCondition 1"
  Heat Transfer Coefficient = 50
  External Temperature = 288
End

[mzenker]

Hi,

EDIT: After try some more, I just found that the units of heat flux should be in kW/m2. So, with 0.15 instead of 150, I get the right solution. So, there is a problem with units of heat flux. According to the manuals it should be W/m2 which proved to be wrong. What I missed?

could it be that your geometry is not in m? This could explain the factor of 1000 for your heat flux.
If your length units are mm, write

Coordinate Scaling = 0.001

into the simulation section (free text field in Model -> Setup in ElmerGUI), and the length units are scaled and you can set your heat flux in W/m2 as it should be.

HTH,

Matthias

[cfernandes]

Mzenker,

you are true.

I found that this was the solution.

Thank you.

Carlos Fernandes

[cfernandes]

Mzenker,

you are true.

I found that this was the solution.


Dmitry,

the sif is not actually accurate, but the main problem was the scalling of the model (mm instead of meter)

With the scaling and the right sif, everything works like a charm.

I used that simple example to figure the problem that I have in all my complex models.

Thank you all.

Carlos Fernandes

[dmitry]

Yes Mzenker is right, sometimes I foget about scale too