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use mixture model to simulate two-phase flow with phase change

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Old   September 7, 2016, 12:38
Default use mixture model to simulate two-phase flow with phase change
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hello, friends
I am trying to simulate a water flow along a 2*2 rod bundle inside a square channel with a constant heat flux at the rod surfaces. phase change will happen in the process. below is my setting:

mixture model and turn on the slip velocity and implicit body force.

energy: a cosine chop heat flux which is at the rod surface.

realizable k-epsilon model with standard wall functions.

i use UDF to model the mass and energy transfer between the water and vapor phase which works well. it works as several source terms.

in the operating conditions, pressure is 0, and give a specified density which is the density of vapor

the solution method is SIMPLEC, pressure is standard, momentum, k and energy is third muscle, volume fraction and epsilon is QUICK.

the factor for p is 0.3, for momentum is 0.5, for k is 0.5, for epsilon is 0.8, for energy is 0.98, the others are default.

result is: it can run for hundreds of steps, but always gain divergence after that.

so could you guys give some suggestions for the next step? or did I make any mistakes in the settings.
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File Type: jpg p.jpg (51.7 KB, 12 views)
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Old   September 7, 2016, 12:56
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Mixture model does not work with heat flux.
It should be setup with temp difference.
You must specify a temp diff between wall surface and cell temp.
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Old   September 7, 2016, 13:04
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Quote:
Originally Posted by shaonme View Post
Mixture model does not work with heat flux.
It should be setup with temp difference.
You must specify a temp diff between wall surface and cell temp.
thank you for your reply, here are more results about temperature. it has six spacer grids, so some temperature reach a little higher.
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Old   September 7, 2016, 13:06
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I only know the power of the rods, so it is hard to give a accurate temperature difference. heat flux is power/area
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Old   September 7, 2016, 14:13
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Have u found any phase change around the pipe (I mean at a distance from inlet)? If yes, then is it increasing?
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Old   September 7, 2016, 15:15
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Have u found any phase change around the pipe (I mean at a distance from inlet)? If yes, then is it increasing?
yes, phase change has happened, but not very good, I have some results but which is divergence. see pictures.
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