Heat conduction simulation result is not consistent.

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Heat conduction simulation result is not consistent.

Postby Roy » 05 Dec 2017, 05:33

Hi there,
I'm trying to run two simple heat conduction problems, but the results are not consistent with the theoretical ones.

Case 01:
Geometry: 1 mm * 1 mm * 5 mm bar, built with AutoCAD.
format: iges
material: aluminum (generic), heat capacity = 237 (x) this is a typo
thermal conductivity = 237 (o)
type: steady state
heat load: 1 W (I suppose the unit is Watts) on a 1 mm*1 mm side area
boundary condition: temperature = 273 on the other 1 mm *1 mm side are.
Coordinate Scaling = 0.38


The result: After tuning the "Coordinate Scaling" to be 0.38, the temperature on the side where heat source is applied is 294, which is close to the hand-writing calculation.

However, when I tried to run the case with only the geometry changing to 1 mm * 1 mm * 2.5 mm, Elmer gave me the result of 278, which is supposed to be 283.

Could anyone help me with this?
Last edited by Roy on 05 Dec 2017, 18:56, edited 1 time in total.
Roy
 
Posts: 3
Joined: 05 Dec 2017, 04:34

Re: Heat conduction simulation result is not consistent.

Postby mzenker » 05 Dec 2017, 12:17

Hi,

a common problem in such cases is that the CAD model is using mm as length units, whereas Elmer assumes m. This can be fixed by writing

Code: Select all
Coordinate Scaling = 0.001


in the Simulation section (Free text field in ElmerGUI).
If that doesn't fix the problem, you could post your sif file so that someone can have a look at it.

HTH,

Matthias
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Re: Heat conduction simulation result is not consistent.

Postby Roy » 05 Dec 2017, 21:24

Hi mzenker, thanks for replying. The problem isn't fixed; the temperature is wrong (the temperature on the surface heat source is applied is 273. ). the sif file is shown below:

Header
CHECK KEYWORDS Warn
Mesh DB "." "."
Include Path ""
Results Directory ""
End

Simulation
Max Output Level = 5
Coordinate System = Cartesian
Coordinate Mapping(3) = 1 2 3
Simulation Type = Steady state
Steady State Max Iterations = 1
Output Intervals = 1
Timestepping Method = BDF
BDF Order = 1
Solver Input File = case.sif
Post File = case.ep
Coordinate Scaling = 0.001
End

Constants
Gravity(4) = 0 -1 0 9.82
Stefan Boltzmann = 5.67e-08
Permittivity of Vacuum = 8.8542e-12
Boltzmann Constant = 1.3807e-23
Unit Charge = 1.602e-19
End

Body 1
Target Bodies(1) = 1
Name = "Body Property 1"
Equation = 1
Material = 1
Body Force = 1
End

Solver 1
Equation = Heat Equation
Variable = Temperature
Procedure = "HeatSolve" "HeatSolver"
Exec Solver = Always
Stabilize = True
Bubbles = False
Lumped Mass Matrix = False
Optimize Bandwidth = True
Steady State Convergence Tolerance = 1.0e-5
Nonlinear System Convergence Tolerance = 1.0e-7
Nonlinear System Max Iterations = 20
Nonlinear System Newton After Iterations = 3
Nonlinear System Newton After Tolerance = 1.0e-3
Nonlinear System Relaxation Factor = 1
Linear System Solver = Iterative
Linear System Iterative Method = BiCGStab
Linear System Max Iterations = 500
Linear System Convergence Tolerance = 1.0e-10
BiCGstabl polynomial degree = 2
Linear System Preconditioning = ILU1
Linear System ILUT Tolerance = 1.0e-3
Linear System Abort Not Converged = False
Linear System Residual Output = 1
Linear System Precondition Recompute = 1
End

Equation 1
Name = "Equation 1"
Active Solvers(1) = 1
End

Material 1
Name = "Aluminium (generic)"
Heat expansion Coefficient = 23.1e-6
Heat Conductivity = 237.0
Sound speed = 5000.0
Heat Capacity = 897.0
Mesh Poisson ratio = 0.35
Density = 2700.0
Poisson ratio = 0.35
Youngs modulus = 70.0e9
End

Body Force 1
Name = "BodyForce 1"
Heat Source = 1
End

Boundary Condition 1
Target Boundaries(1) = 6
Name = "BoundaryCondition 1"
Temperature = 273
End





Does anyone know what the cause is? Is it due to the meshing or the process of importing CAD file?
Roy
 
Posts: 3
Joined: 05 Dec 2017, 04:34

Re: Heat conduction simulation result is not consistent.

Postby raback » 06 Dec 2017, 01:15

Hi

The unit of "heat source" in SI is "W/m^3".

If you want to apply a heat source on the face then use BC with "Heat Flux" the unit of which in SI is "W/m^2".

Thus if you know the total heating power you need to divide it with the volume or area, respectively.

-Peter
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Re: Heat conduction simulation result is not consistent.

Postby Roy » 06 Dec 2017, 05:51

Hi Peter,
Thanks for figuring out what I missed. It fixed the problem.


Matthias,
Thanks for the suggestion of having "Coordinate Scale" be 0.001, it really works. The reason why I didn't get the right results is that I misunderstood the units of Elmer.

Roy
Roy
 
Posts: 3
Joined: 05 Dec 2017, 04:34


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