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Non-physical Temperature raising in pipe

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Old   April 30, 2014, 16:38
Default Non-physical Temperature raising in pipe
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Luiz Eduardo
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Hi,

I am simulating a two-phase bubbly flow case (liquid-gas) inside a long and straight (small diameter) pipe with the following:

1) 2D axisymmetric
2) bubble diameter constant equal 0,5mm
3) Gravity (pipe at the vertical)
4) Eulerian model implicit
5) Energy is on
6) k-ep realizable with standard wall function
7) Boundary conditions: mass-flow-inlet, pressure-outlet and wall thermal condition of convection, with a small U global, i.e. the pipe is well isolated and there is a good temperature difference between the inside and outside.
8) Operating pressure around 10^7

The gas phase (secondary) is ideal gas or Peng-Robinson real gas and liquid phase has a constant density.

Fluent send a warning telling that for compressible ideal or real gas models with buoyancy, it is recommended that the operating density value should be zero. What is happening is that when I do this, I have a temperature raise along the pipe which is not expected. When I use the operating density with a mixture density (high enough) this doen't happen.

Any ideas? Thank you in advance!

Best regards,

Duda
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