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Convective Heat Transfer - Buoyancy Flow Vectors Are Moving In Wrong Direction

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mrm01
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Convective Heat Transfer - Buoyancy Flow Vectors Are Moving In Wrong Direction

I've sent the model in to tech support but wanted to ask the question here too because it might help someone else.  Picture attached.

 

Situation:

 

  • Heat sink with total power of about 130 watts applied to a surface.
  • Ambient temp about 55C
  • No forced flow.  Cube shaped air volume with 0 psig on inlet and outlets to allow for buoyancy flow.
  • 50C temp applied at bottom of cube.
  • Using symmetry (half model)

Results:

  • The analysis gets very close to converging after 400 iterations but never stops.  Temperature deltas are extremely small so I stop analysis.
  • The flow vectors are correctly rising from the heat source but only locally near the surface of the heat sink.  About 10 to 20 in/sec.
  • Elsewhere in the air volume, the vectors are pointing in the opposite direction (towards gravity) and moving fast - 200 in/sec

I can't figure out what is causing the air to flow in the opposite direction.  It really is acting as though I have placed a velocity on the top of the volume

but I haven't.  Only zero pressure.  Has anyone else seen this in their models?  If so, how did you resolve it?

 

Mike

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Message 2 of 2
mrm01
in reply to: mrm01

Seems I had forgotten to set the air to "Variable" instead of "Fixed" though I swear I made that selection before running the analysis. Running correctly now.

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