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-   -   CFX multiphase flow model (http://www.cfd-online.com/Forums/cfx/98073-cfx-multiphase-flow-model.html)

aximefu March 2, 2012 07:45

CFX multiphase flow model
 
In Fluent, There are two Multiphase Models:Euler-lagrange model and Euler-euler model. And Euler-euler model has three sub-model: VOF, mixture and euler, corresponding to specific different settings.

In CFX, there are free surface model, particle model, mixture model, Euler-lagrange and Eular-Eular model. Now I don't know if there is a similar sketch of Multiphase models in CFX? That is what is the relationship between several models above.

A thread about my question:
http://www.cfd-online.com/Forums/cfx/97226-vof-cfx.html

Do anyone have idea about this? Thanks!

juliom March 2, 2012 09:53

Hi dear friend.
VOF is one of the most demanding model of multiphase fluid flow.
If you want to make a similar choose of this model in CFX, I recommed you to use Free surface+ particle or mixture model. These are Euler-Euler models.
BUT firstly you might research more about your physics, in order to know which is the model that fit better for your problem.
Regards Julio M

aximefu March 3, 2012 06:17

Quote:

Originally Posted by juliom (Post 347314)
Hi dear friend.
VOF is one of the most demanding model of multiphase fluid flow.
If you want to make a similar choose of this model in CFX, I recommed you to use Free surface+ particle or mixture model. These are Euler-Euler models.
BUT firstly you might research more about your physics, in order to know which is the model that fit better for your problem.
Regards Julio M

I want to simulate the heat transfer and fluid flow in heat pipe, and I choose the free surface option in multiphase model. If water and vapor are set to be continuous phases, in Fluid Pair Models > Interphase Transfer the options I can choose are free surface and mixture. I use this two models to complete the computation, then the results don't seem to correct.
So was it ok to set both of water and water vapor to be continuous phases ?

juliom March 3, 2012 09:27

Please send me your cfx case to figure ir out.
You might make some calculus and deduction before selcting the correct model, if not you will be trying to find a nedle in the dark!!!

Ernesto10 August 20, 2013 13:47

Ayuda_CFX/FLUENT
 
Hola Julio, yo igual tengo problemas con la configuración de los modelos a utilizar, lo que quiero simular es una tubería que descarga vapor(a 7MPa) en una piscina de agua. Tendrás algún ejemplo de un problema similar. Saludos.

juliom August 20, 2013 13:53

Hola Ernesto.
Cada problema esparticular y requeire de diversos factores que se deben evaluar, como fracción volumetrica,distancia entre particulas entre otras cosas.
Tambien depende que tipo de vapor es, es vapor humedo o simplemente gotas de agua en una corriente de aire, como ves la morfologia es necesaria para escojer el mejor modelo.
En el caso que continue la discusión seria bueno que seguir en ingles para compartir la discusión con otros usuarios que quieran leer mas sobre el tópico.

Ernesto10 August 20, 2013 14:14

Ok, my problem is: i have 2 pipelines with steam (7 Mpa,540 °F, 100 kg/seg) this pipelines discharge in a pool water, i have used cfx and fluent but i have troubles with the models, in CFX:
this is that i have

-Multiphase model -free surface model standard

-Heat transfer -steam Saturation temperature
-water Thermal energy
-Turbulence -steam Zero equation
-water K-epsilon

-Interphase transfer Particle model
-Momentum transfer schiller Naumann
-Turbulence transfer none
-heat transfer Ranz Marshall

i'm sorry for my bad english

juliom August 20, 2013 14:25

Dear Ernesto,
Here I see several problems, first of all you ened to verify you volume fraction because it is possible that you may have been used a bad model.. You need to be very clear when a model can be used and when not.
On the other hand the boundaries conditions, are bot pipe discharing at the same pool?.
Which are you boundaries condition?
Are you interested on the phase changes?
First of all you need to have very clear the goal of your simulation.!!!
How good is your mesh?

mshf7 August 20, 2013 16:46

hi
 
would you mind helping me which modeling is more appropriat in analysing ship hull resistance?

juliom August 20, 2013 20:55

Are you trying to simulate a kind of waves?.
In case you want to run a FSI, i recommend you to ask the question to other member, because I do not have much experience on FSI.

ahmad786 September 17, 2013 14:27

Quote:

Originally Posted by juliom (Post 347314)
Hi dear friend.
VOF is one of the most demanding model of multiphase fluid flow.
If you want to make a similar choose of this model in CFX, I recommed you to use Free surface+ particle or mixture model. These are Euler-Euler models.
BUT firstly you might research more about your physics, in order to know which is the model that fit better for your problem.
Regards Julio M

juliom,
Hi Juliom.I am facing a hell of problems in simulating a flow in a steam turbine in CFX.The conditions for steam are:
1)-Dry saturated at inlet (P=5bar) of turbine with quality of "1"
Conditions of steam at the exit of turbine are :
2)-wet steam (P=1bar) with quality of "0.91"
Can u help me which model in CFX will be best in my case;
Secondly I am facing problems in assigning flow materials in CFX.
Currently I am using
"steam5vl" IAPWS -f97 libray as fluid material for my case.Is it right??
Should I use two materials steam gas and steam liquid from IAPWS library independently ??.Should I use homogeneous model or not?? Plz help me how should i assign flow materials for my case??

ahmad786 September 17, 2013 14:37

TWO phase flow
 
Hi all
I am facing a hell of problems in simulating a flow in a steam turbine.The conditions for steam are:
1)-Dry saturated at inlet (P=5bar) of turbine with quality of "1"
Conditions of steam at the exit of turbine are :
2)-wet steam (P=1bar) with quality of "0.91"
Can u help me which model in CFX will be best in my case;
Secondly I am facing problems in assigning flow materials in CFX.
Currently I am using
"steam5vl" IAPWS -f97 libray as fluid material for my case.Is it right??
Should I use two materials steam gas and steam liquid from IAPWS library independently ??.Should I use homogeneous model or not?? Plz help me how should i assign flow materials for my case??
Any one,plz reply.

ahmad786 September 21, 2013 16:41

Any One, to help .Please.

ghorrocks September 22, 2013 07:18

You are modelling a high pressure ratio multiphase flow, including wet steam conditions. This is a very complex model and I trust you have plenty of time available to develop and validate it. But it is far too complex to realistically expect to get any help on the forum. If you want help on it I would try either a ANSYS training course on multiphase flows or contact ANSYS support.

juliom September 22, 2013 09:49

Dear ahmad786
Sorry for my late answer I have been very busy these days.
First of all, this case is QUITE HARD, because it is not only multiphase flow. I mean, you have even mass transfer wich turns this case very hard.
AS you mentioned before, you have a quality of 1 and then at the outlet 0.91, as a result you have a mass transfer from one phase to the other. This is the difficult part here.
You need to develope a copde wich will be linked to the swolver to take this into consideration. I recommend to read more about it, i.e cooling tower which work under the same assumtion.
After you are able to handle this mass transfer the reaiming steps are easier. I agree with mr Glenn Horrocks, trying to get support from ANSYS.
My experience on multiphase fluid flow is more related to oil and gas where both phase are quite stable and the mass transfer rate is allmost negligible.


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