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Heat Conduction / Cooling problem

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Old   May 7, 2017, 08:24
Default Heat Conduction / Cooling problem
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Antono
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Hi,

This is my very first post here. I am trying to perform 2D transient simulation of cooling down some object by stream of air.

Assumptions:
-Square object (Solid / Copper material - default properties) is inserted into the rectangle mesh (Fluid / Air material - default properties).
Picture 1. MESH of the problem

Models: Energy ON, Viscous (Laminar).

Interface: I created two interfaces during meshing. I have deleted the default interface connection and created my own in the solver. Coupled walls type.
Picture 2. Coupled wall interface window

BC
: Surrounding walls are adiabatic (insulated), velocity-inlet on left (293K, 1m/s), pressure-outlet on right.
The square has walls with convection thermal condition option selected (Heat transfer 10000, free stream 300, wall thickness 0.001 and cooper material type). Shadow wall is also Coupled wall type and cooper material.
Picture 3. BC on square wall

I patch the square initial temperature to be 350K or more, (air flowing is 293).


Results:
While i run my calculation for 0.05 time step / no. of iteration 1000 let's say. I got very strange results.
The air flowing by the square is heating up - that is correct. But the square reamains in the same temperature to matter how long air is flowing. I did simulations for 2 seconds and for 300 seconds. It looks like there is only heat transfer from the square to flowing air but no cooling of the square is vissible.
Picture 4. RESULTS

!!Please, can somebody help me how to perform such simulation to see that the block with patched initial temp. is cooling down?

Thanks,
Adam


Attached Images
File Type: png Picture_1 - mesh.png (20.3 KB, 22 views)
File Type: png Picture_2 - interface.png (75.9 KB, 26 views)
File Type: jpg Picture_3 - BC.jpg (126.5 KB, 26 views)
File Type: jpg Picture_4 - Results.jpg (97.9 KB, 25 views)
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Old   May 7, 2017, 16:02
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Lucky
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You should be using the coupled boundary condition on the wall and shadow-wall pair and not the convection boundary condition. Otherwise, you do not need to model the air.

Also I recommend you to check with an analytical result from the lumped heat capacitance model to estimate the timescale needed for the block to cool down.
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Old   May 8, 2017, 03:59
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Antono
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Thank you for the reply.

Please could you explain how I can set "coupled BC" in the thermal boundary conditions of the wall?

Of course the shadow-wall is set to coupled thermal boundary conditions but i can't see that option in the wall section - as shows the picture attached.
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Old   May 8, 2017, 07:59
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You are missing the shadow wall altogether for some surfaces.

At the fluid-solid boundary, you should have a wall shadow-wall pair (one goes to each zone). If you don't, then you missed something when you created the interfaces. Go back and fix it.
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cooling, heat conduction, heat transfer

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