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void fraction? volume fraction?

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Old   June 4, 2010, 07:18
Thumbs up void fraction? volume fraction?
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tacaro
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Two phase pipe flow is ofter featured with "void fraction" in the open literature.

How does it relate to "volume fraction" value obtained from post-processing function of Fluent?

Thanks
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Old   May 20, 2011, 03:35
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M. A.
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Hi friends,
I'm simulating a tube with water flow.
The tube encounters boiling near the wall.
I intend to calculate 'void fraction versus enthalpy' along the channel.
Can you help me how to calculate void fraction?

I'm in an emergency condition.
Waiting for your comments!!!

Thanks Everybody
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Old   May 21, 2011, 08:46
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David Stanbridge
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Tacaro, Void Fraction and Volume Fraction are the same
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Old   May 21, 2011, 12:16
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M. A.
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Hi swiftaircraft,
Yes you're right.
I've worked in single phase for more than 1 year.
But I'm beginner in multiphase flow.
Can you help me how to define multiphase in CFX-Pre?
Thanks
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Old   March 3, 2012, 17:29
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kahany
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depending on your multiphase modulus, you shoud find it under "phase". make sure that you present results for "phase-2"
I hope I helped.
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Old   March 12, 2012, 03:00
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M. A.
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Dear Talib,

Thanks for your reply.

Fortunately I could find how to use 2-phase flow in CFX.
But it didn't work well.

I asked a CFX worker and he told me that ANSYS CFX does not support 2-phase.
There are options in CFX-Pre to define the 2-phase, but the software doesn't understand it well.

For example, I'm defining a coolant tube located in a cube made of cu and an armour layer of Carbon on it. The heat flux deposits on the armour layer and then via condution, reaches to the coolant channel (The coolant is water).
By increasing the heat flux up to the 5 MW/m^2, we see phase change in the channel.
When the heat flux reaches 10 MW/m^2, and the coolant velocity is 1 m/s, the temperature is so hot that we have melting of the body. But CFX does not stop running and in CFX-Post I can see the outlet temperature of the coolant is more than 3000 K and obviously all the fluid changes to vapour. But the void fraction analysis yet shows that most of the coolant is yet fluid!!!

I couldn't find any solution for this matter yet.

I would be so thankful if any friend can help me in this issue!!!

Thanks all...
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Old   March 15, 2012, 12:32
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zainab p
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hello.i am actually working on a two phase model having a volume fraction of 0.5316.the problem is that the solution does not converge.can anyone help please?
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Old   March 15, 2012, 13:34
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kahany
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hi zeybi1604 , I would be happy to try and assist, but this is not enough information.
please elaborate on your problem (models, geometry, materials, etc.) and how exactly it is not converged. Where is the problem? Is it via mass conservation? maybe only via average void fraction, etc.
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Old   March 15, 2012, 14:17
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thank you for replying Mr Talib. i am doing a multiphase simulation using the mixture model inside a packed bed with the beads being solid inside the bed. the materials inserted are air(primary phase) and fines(secondary phase). the volume fraction for the fines is 0.5316. during the iteration process i get an error message "divergence in AMG solver x momentum". my aim is to find the fines accumulation inside the bed.take care
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