Bubble diameter in multiphase flow
 

Hi everybody,

I had posted a message about a week ago and have not got any response up to now. I really need an answer and your help.

Can anybody tell the significance of droplet diameter (a secondary phase parameter) that is defined in Define > Models > Multiphase > Algebraic Slip form.

I am trying to model a mixing chamber where pure air and pure water enter the chamber from two separate 1" diameter pipes and leave the chamber as a mixture.

I do not have the slightest idea of what the droplet diameter might be. Should I guess it, or is there anyway I can calculate it ?

Any comments will be highly appreciated.

Regards. Hbet

Re: Bubble diameter in multiphase flow
 

(1). What I would do is to find a similar tutorial sample first, then check it out to see whether the code can handle it or not. (2). You are assuming that everyone knows how to handle this complex multi-phase problem. (3). You will have to develop a model first and find out whether you can solve it or not.

Re: Bubble diameter in multiphase flow
 

At least review the Fluent Users' Guide to understand that bubble size shows up in the drag or interaction between the phases. The secondary phase diameter is one of the single most critical parameters in your multiphase calculations.

Review Perry's handbook of chemical engineering on two-phase flow. Identify your flow regime. This will tell you what multiphase model is most applicable to your application, e.g., small gas and lots of liquid means bubbly flow and you can use ASM or DPM, while relatively equal gas/liquid flows means large interfaces and VOF would be more applicable. You'll have to determine this.

Also check Clift, Weber and Grace, "Bubbles, Drops and Particles". An excellent text. You should find correlations to predict bubble size there...mostly atmospheric systems. If your system is under pressure, review literature on bubble columns, gas-lift reactors for correlations on maximum stable bubble size.

Re: Bubble diameter in multiphase flow
 

Hi!

I dont think ASM is appropriate unless the volume fraction of liquid is very small and the mass flow rate is also small.

If the volume fraction is greater than 5% then you will have to use Eulerian model.

Isa

Re: Bubble diameter in multiphase flow
 

Thanks a lot.

I will review the literature you mentioned. It seems that I am face to face with a difficult flow problem.

Regards,

Hbet

Re: Bubble diameter in multiphase flow
 

Do you mean that, ASM can not be used when the volume fraction of air is less than 95% (or in other words volume fraction of water is greater than 5%) ?

Hbet