[paul115]

Hello all,

I have the same problem like in this topic but I didn't find solution.
http://www.cfd-online.com/Forums/flu...r-mixture.html

I wanted to model mixing process of 2 fluids in a channel.
Have anyone idea how to resolve this problem ?
At the beginning I had been trying to declerate 2 fluids on 1 inlet . Next I made a baffle on inlet to channel to create 2 inlets and I want to put phase 1 water phase 2 oil and get a mixture at the end of channel. Any idea ?

I will be very grateful for all clues.

[paul115]

Anyone ? I really need it.

[CeesH]

Well, I assume you use some multiphase model. For each inlet, under the 'phase-2' tab, you can set under 'multiphase' the volume fraction of phase-2 (and for phase 1, it's 1-phase2 of course). Set them accordingly, that should solve your problem, right?

[paul115]

Yes. I'm using volume of fluid model. Yes I agree with volume fraction but when I set phase 1 on 1 inlet and phase 2 on 2 inlet I can't even declarate boundary condition. I can declarte them in mixture. Btw I have three options to set: mixture, phase 1 and phase 2. And when I set mixture on 1 inlet and phase 2 on 2nd then I can set volume fraction for 2nd inlet but what about 1 inlet ? I don't what mixture on it. I want phase 1. I don't understand algorithm how to anlyse this case.
I thought I'll be easy. I put phase 1st on 1 inlet phase 2 on 2nd inlet and mixture on output but It doesnt work.

[CeesH]

I have a bit of a hard time understanding what you mean. Could you provide an image of the mesh? I do assume that inlet 2 and inlet 1 are different boundaries?

Regarding the options: you have to set parameters for each phase and the mixture, even if pure phase-1 or phase-2 flows in. Wheter pure-1 or pure-2, or a bit of both flow in depends on the value you set for phase-2-multiphase

Best,
Cees

[paul115]

First of all, I am really grateful for your help.

So should I declarate inlet1 mixture and inlet2 phase 2 and set volume fraction 0,5 if I want to have for example 50% water and 50% oil ? And what about backflow volume fraction on outlet ? It also should be 0,5 ?

[CeesH]

Well, in essence, both inlets are always declared as a mixture. As soon as you use multiphase, every cell contains a mixture of all phases. Only in some cases the mixture contains 100% or 0% A. For computational purposes, it's still a mixture though.

Indeed you are right, if you want the inlet to be 50-50, set the volume fraction to 0.5. A volume fraction of 1 gives pure phase 2, of 0 gives pure phase 1.

backflow should be set at all outlets; in case there is a negative flowrate through part of the outlet (which can happen, for example if the operating pressure is higher than the pressure close to part of the outlet) then the outlet will turn into an inlet - and an inlet boundary needs a volume fraction.

This fraction should be determined based on what you know about the system. If you have only 1 outlet, the calculation is easy. If you have multiple outlets, make an educated guess: for example if one outlet should transport only oil, set the backflow to only oil.

[paul115]

Thank you very much. You really made me to understand a problem

[CeesH]

You're welcome!

[paul115]

Hello all,


I have question to density scale. I'm giving on 1 inlet fluid density 790 on the 2nd 889 and when I get results it looks like on the 1st inlet was 835 density instead of 790 and there isn't any sign of 790 density. Why ? I'm trying to mix 2 fluids and it looks like 2 separate objects in the pipe. There isn't any interaction between 2 fluids.
Maybe I should turn on an extra option or sth like that ?

Please help me. I will appreciate all clues.

P.S I marked on screen what I am wrtiting about

[paul115]

Anyone I really need to solve that problem but I don't have an idea

[Karu_p]

Paul could you able to solve the mixing problem. I have been working on the same thing for the last week. Anyway VOF is not correct for mixing purpose. DO reply me if you done it.

Thanks in advance