# Eulerian twophase boundary condition for velocity inlet

**3**

Hello,

I have two boundary conditions. One velocity inlet with a continous phase a velocity boundary, which is pulsating. So it's something like a sinus-function. And a dispersed phase, where the velocity it's negative, so dispersed phase can go out of the inlet. Is a volume fraction=0 a good asumption or will it lead to only entering continous phase and mass flow of dispersed phase is zero. Should I then use an assumption for volfrac (something like volfrac=holdup of column). Or also a pulsating volfrac.

The outlet is a pressure outlet, where the backflow volfrac is one. The inlet is at the top of the column and the pressure outlet at the bottom.

So it's a countercurrent pulsating flow. It's for simulation of a liquid-liquid pulsed (and stirred) extraction column. The continous phase is the heavy phase and the dispersed phase is the light phase.

Gravity is considered in the model, so also the bouyancy, right?

Thank you

## Answers

327Forum CoordinatorHello,

It is not very clear about the boundary condition for the dispersed phase. Do you have a velocity-inlet condition for that as well?

Please embed a screenshot of the model with the boundaries highlighted.

Regards,

SD

24MemberNo, there is only one velocity inlet. The dispersed phase can flow from the pressure outlet, with the backflow.

Blue: velocity inlet volfrac=0 ?; velocity dispersed phase= 0.333e-3*1[kg s^-1]/(PI/4*((12*2e-3^2+6.6e-3^2-5.6e-3^2)*1[m^2])*881.5*1[kg m^-3]);

velocity continous phase: 0.333e-3*1[kg s^-1]/(PI/4*((12*2e-3^2+6.6e-3^2-5.6e-3^2)*1[m^2])*988.2*1[kg m^-3])-0.0654*sin(t*2*PI*1[s^-1])*1[m s^-1] ;(sinus function=pulsation)

Red: pressure outlet volfrac_backflow=1

The dispersed phase is the light phase. It is a countercurrent flow.

Here is another picture of the inlet with the sieve plate from another view

Thank you for your help

327Forum CoordinatorHello,

If volume fraction of the dispersed phase is set to 0 at the inlet, then only continuous phase will come in from the inlet.

The volfrac value should be based on experimental/test data for inlet loading of similar/same setup.

For example, if inlet loading is such that the dispersed phase occupies 0.2 fraction by volume, then volfrac should be set as 0.2.

Hope this helps.

Regards,

SD

24MemberYeah ok I understand. But the dispersed phase is going out (velocity is negative, I copied it wrong). And we have a pulsation here (see sinus function continous phase). So does it make sense, also to pulsate the volfraction? So when dispersed phase goes out, then volfrac=1 and for other timesteps, when continous phase goes in, then volfrac=0. So it is countercurrent flow. The dispersed phase is accumulating under the inlet

If I do it, like you said, then I have also to change the backflow volfrac of pressure outlet, right? The advantage of that might be that also a steady state solution is possible for initializing.

I appreciate your help

24MemberOr would it be possible to use another velocity inlet instead of pressure outlet. The velocities of the other inlet would be like in the inlet at the top, but multiplied by -1. It's important that countercurrent flow can occur.