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July 15, 1998, 23:55 
Twofluid models vs mixture models for bubbly flows

#1 
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Maybe you are a specialist in twophase problems and know which model, twofluid model and mixture model, is better for bubbly flows. It seems that many people use twofluid models, especially for engineering problems. But this kind of models has drawbacks, e.g., it needs two sets of governing equations, one for gas and the other for water, and thus is too complicated. On the other hand, mixture models seem to be less complicated, but I have not found some papers about their turbulence models. If you know something about this, please let me know. Thanks a lot.


July 16, 1998, 13:39 
Re: Twofluid models vs mixture models for bubbly flows

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It depends on what you are looking for with the model. Twofluid model can keep track of the movement and heat/mass transfer within each phase and also be able to calculate the velocity and heat/mass movement on the phase interface, the later of which is sometimes very important, or the focus of the study. The mixture model is simpler but does not give you the interface situation. Often, a seperate local formulations can be used (coupled with or based on the result from the mixture model) to get some limited prediction of the local parameters. Again, it all depends what you are looking for.


July 18, 1998, 20:49 
Re: Twofluid models vs mixture models for bubbly flows

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Yes, I agree with; a mixture model cannot describe interface phenomena in details. Actually the difficulty for a good understanding of a twophase flow araises from the phenomena. However, currently we are interested only in concentration of gas in water, and the mixture model seems to be nice. What I feel to be not sound for this choice is that no proper turbulence model is available.
Sir, do you know some work about the turbulence model? By the way, can you tell me some good references about the separate local formulations you mentioned? Thanks. 

July 19, 1998, 19:35 
Re: Twofluid models vs mixture models for bubbly flows

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I am not sure what you mean by mixture model. If it means the homogeneous mixture model (i.e. no slip, phases well mixed, etc.) I think that it does not make a lot of sense to look for a special twophase flow turbulence model. You can just use a singlephase model with apparant density, average velocity, etc. equivalent to that of twophase mixture.
Are you interested in average concentration or may be you want to know concentration profile. In the later case I would suggest using a twofluid model. You may want to check the following authors: Serizawa, Bataille, Lopez de Bertodano in any scientifc database (e.g. Compendex). If you screen through some issues of the International Jounal of Multiphase Flow you may find out interesting articles. Andrzej Matuszkiewicz 

July 20, 1998, 21:57 
Re: Twofluid models vs mixture models for bubbly flows

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Dear Andrzej,
What I mean by a mixture model is often refereed as to a pseudofluid model, which considers a bubbly flow as one pseudofluid by introducing a pseudodensity that varies between gas and water density extremes. One example of such model can be found in J. Fluid Mech., v240, p59, by Kubota etc. For such a model I cannot see the reason to simply apply onephase turbulence model. At least, in the well known kepsilon model, the constants are determined by some, althogth simple, experimental data. However, can we also find some experiment results for a mixture model? 

July 20, 1998, 22:10 
Development of a turbulence mo?del for pseudofluids

#6 
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As I mentioned in the last message, a main problem to apply a pseudofluid method for practical problems is to develop a proper turbulence model.
Any person has idea about such development? Thanks. 

December 8, 2009, 04:21 

#7 
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arif
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Hi, as you said, how can I do two liquid flow simulation and find concentration profile for mixture. Both liquid have inlet velocity. Thanks


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