Unexpected Heat Spread in Transient Heat Tranfer Analysis

[TakumiN]

Hi community!
This is my first post here.
I'm having a problem in my transient heat flow.

I made a 2D model that heats one surface of a concrete object.
It is supposed to be heated from left to right, but what I got was different from that.
The output obtained was a temperature distribution with alternating hot and cold areas along the mesh.
In addition, the cold area's temperature is lower than the initial condition 288K.
I expected a much smoother gradational heat spread.

I have my .sif file below, and the temperature distribution image.
I also attached an image that shows the heat flux inside the object, which shows that the magnitude of heat flux is spreading nicely, but when it comes to the X axis heat flux value, the positive and negative values are being reversed among the mesh.

I understand that some of the numerical values are kind of weird, but I just want to know what is causing this particular problem.
Any advice would be greatly appreciated.

Code: Select all

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

Simulation
  Max Output Level = 1
  Coordinate System = Cartesian
  Coordinate Mapping(3) = 1 2 3
  Simulation Type = Transient
  Steady State Max Iterations = 20
  Output Intervals = 2
  Timestep intervals = 600
  Timestep Sizes = 0.2
  Timestepping Method = BDF
  BDF Order = 2
  Solver Input File = case.sif
  Post File = case.vtu
End

Constants
  Gravity(4) = 0 -1 0 9.82
  Stefan Boltzmann = 5.670374419e-08
  Permittivity of Vacuum = 8.85418781e-12
  Permeability of Vacuum = 1.25663706e-6
  Boltzmann Constant = 1.380649e-23
  Unit Charge = 1.6021766e-19
End

Body 1
  Target Bodies(1) = 1
  Name = "Body 1"
  Equation = 1
  Material = 1
  Initial condition = 1
End

Body 2
  Target Bodies(1) = 2
  Name = "Body 2"
  Equation = 1
  Material = 2
  Initial condition = 1
End

Solver 1
  Equation = Heat Equation
  Procedure = "HeatSolve" "HeatSolver"
  Variable = Temperature
  Exec Solver = Always
  Stabilize = True
  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 = ILU0
  Linear System ILUT Tolerance = 1.0e-3
  Linear System Abort Not Converged = False
  Linear System Residual Output = 10
  Linear System Precondition Recompute = 1
End

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

Material 1
  Name = "Concrete Material"
  Heat Conductivity = 1.7
  Heat Capacity = 1000
  Emissivity = 0.9
  Reference Temperature = 288
  Density = 2500
  Heat expansion Coefficient = 0.00001
End

Initial Condition 1
  Name = "InitialTemperature"
  Temperature = 288
End

Boundary Condition 1
  Target Boundaries(1) = 1
  Name = "Air-Facing Interface"
  Heat Flux = 10000
End

Boundary Condition 2
  Target Boundaries(3) = 2 3 4
  Name = "Concrete-Facing Interface"
  External Temperature = 288
  Heat Transfer Coefficient = 1.7
End

[TakumiN]

I successfully resolved this problem!
I don't know why but raising the heat conductivity to about e6 times larger made the heat transfer smooth.
However, I'm not sure about none of the values I've set, so I would be happy to be taught which part of my solver settings are still weird.

TakumiN

[kevinarden]

In your sif you have body 2 assigned to material 2 but there is no material 2 definition. So I am not sure if you have 2 bodies?

[TakumiN]

Kevin

You're totally right.
This was the next model, and the second object was supposed to be the defect inside the concrete.
Sorry to make you confuse.
Material2 and Boundary Condition 3 was supposed to be added to this sif in the next model.

Thanks for your kindness.

[raback]

Hi,

If scaling conductivity with 1e6 saves your day you may have wrong units in your mesh. If it comes from CAD workflow the unit is often assumed to be "mm". Scaling the mesh with 1e-3 changes the unit to "m" and thereby solves the problem. Look for "Coordinate Scaling".

-Peter

[TakumiN]

Thank you Peter!
Adding "Coordinate Scaling = Real 1.0e-3" to the Simulation section worked perfectly with the original heat conductivity 1.7!
All my problems including the heat transfer problem was resolved, and I now understand the conditions I set much clearlier than before.

You made my day, thanks a lot!

[TakumiN]

This is my lateset sif file, and it is working well as in the attached screenshot file.
But here, I have one question, which might do something with the unit problem.

Is "Heat Transfer Coefficient = 0.005" in Boundary Condition 1 appropriate?
It is meant to be the boundary between concrete wall and the external air.

As I searched for a proper heat transfer coefficient, I found out that 5(W/m^2・K) may be good, so I set "Heat Transfer Coefficient = 5", but it didn't work. Although I was heating the wall, it went colder and colder than the initial temperature from the first time step.
So I changed it to 0.005, and it worked well. But I'm not sure why, since I recently added the mm to m scaling "Coordinate Scaling = Real 1.0e-3" and the unit problem must have resolved completely.
Additionally, I also want to know why then "Heat Transfer Coefficient = 1.7" is working well in Boundary Condition 2.

I would appreciate any advice. Thanks for your kindness.

Takumi

Code: Select all

Header
  CHECK KEYWORDS Warn
  Mesh DB "/home/takuminomura/Elmer2023/7_18/gmsh_W5_D3_P-25" "gmsh_W5_D3_P-25"
  Include Path ""
  Results Directory ""
End

Simulation
  Max Output Level = 1
  Coordinate System = Cartesian
  Coordinate Mapping(3) = 1 2 3
  Coordinate Scaling = Real 1.0e-3
  Simulation Type = Transient
  Steady State Max Iterations = 20
  Output Intervals = 1
  Timestep intervals = 200
  Timestep Sizes = 6
  Timestepping Method = BDF
  BDF Order = 2
  Solver Input File = case.sif
  Post File = case.vtu
End

Constants
  Gravity(4) = 0 -1 0 9.82
  Stefan Boltzmann = 5.670374419e-08
  Permittivity of Vacuum = 8.85418781e-12
  Permeability of Vacuum = 1.25663706e-6
  Boltzmann Constant = 1.380649e-23
  Unit Charge = 1.6021766e-19
End

Body 1
  Target Bodies(1) = 1
  Name = "Body 1"
  Equation = 1
  Material = 1
  Initial condition = 1
End

Body 2
  Target Bodies(1) = 2
  Name = "Body 2"
  Equation = 1
  Material = 2
  Initial condition = 1
End

Solver 1
  Equation = Heat Equation
  Procedure = "HeatSolve" "HeatSolver"
  Variable = Temperature
  Exec Solver = Always
  Stabilize = True
  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 = ILU0
  Linear System ILUT Tolerance = 1.0e-3
  Linear System Abort Not Converged = False
  Linear System Residual Output = 10
  Linear System Precondition Recompute = 1
End

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

Material 1
  Name = "Concrete Material"
  Heat Conductivity = 1.7
  Heat Capacity = 1000
  Emissivity = 0.9
  Reference Temperature = 288
  Density = 2500
  Heat expansion Coefficient = 0.00001
End

Material 2
  Name = "Air Material"
  Heat Conductivity = 0.02
  Density = 1.225
  Reference Temperature = 288
  Emissivity = 0.95
End

Initial Condition 1
  Name = "InitialTemperature"
  Temperature = 288
End

Boundary Condition 1
  Target Boundaries(1) = 1
  Name = "Air-Facing Interface"
  Heat Transfer Coefficient = 0.005
  Heat Flux = Variable Time
  Real
  0 1000
  600 1000
  601 0
  1200 0
  End
End

Boundary Condition 2
  Target Boundaries(3) = 2 3 4
  Name = "Concrete-Facing Interface"
  External Temperature = 288
  Heat Transfer Coefficient = 1.7
End

Boundary Condition 3
  Target Boundaries(4) = 5 6 7 8
  Name = "Void-Boundary"
  Heat Transfer Coefficient = 0.0000001
End

[Rich_B]

Hello,

If you could post your geometry file, with instructions on how to generate the mesh, then you will be more likely to get specific help with your case.

Thanks, Rich.

[raback]

Hi

If you do not specify "external temperature" then "heat transfer coefficient" will be applied with Text=0. Usually that is not the case.

-Peter