[aliyah]

Hello guys,
I want to simulate cylindrical bubble column reactors. The btoom portion is air (primary phase) and top portion is air (secondary phase). Air is also introduced the bottom of the Photobioreactor as velocity inlet. Outlet is at the top as pressure outlet. In this connection, can i ask some experts on the following.

1. Which is most appropriate multiphase model? Eulerian or VOF?
2. I attempted to patch air at the top porion of the photobioreactor, however, i'm getting unacceptable results. The water velocity is increased and higher than air velocity. I suspect, this should not be the case since the air introduced at the bottom causes the water to move in any direction and it should be lower that the input air inlet velocity.

I am looking for someone working on this field where we can share our experiences together. Anyone interested, i would be happy to contact you.

Looking forward for any reply. Thanks

Aliyah

[CFDtoy]

Hello,
For your case, no need for VOF. You can use eulerian model and derive the distribution of phases pretty well. (Unless you want to track each and every bubble - I dont think that is the case!?)

From your info, you have air bubbled into a liquid chamber (is this the right set up?) or you have liquid entering from elsewhere? Where is the liquid inlet?

For eulerian fluid model, still use liquid as primary phase and gas as secondary and run your calculation and let us know how it goes.

This shouldnt be too hard to converge and get good results (based on what your deliverable is).

Cheers !

CFDtoy

Originally Posted by aliyah

Hello guys,
I want to simulate cylindrical bubble column reactors. The btoom portion is air (primary phase) and top portion is air (secondary phase). Air is also introduced the bottom of the Photobioreactor as velocity inlet. Outlet is at the top as pressure outlet. In this connection, can i ask some experts on the following.

1. Which is most appropriate multiphase model? Eulerian or VOF?
2. I attempted to patch air at the top porion of the photobioreactor, however, i'm getting unacceptable results. The water velocity is increased and higher than air velocity. I suspect, this should not be the case since the air introduced at the bottom causes the water to move in any direction and it should be lower that the input air inlet velocity.

I am looking for someone working on this field where we can share our experiences together. Anyone interested, i would be happy to contact you.

Looking forward for any reply. Thanks

Aliyah

[aliyah]

Thank you very much CFDtoy.
Yes, my model is a cylindrrical bubble column reactor where air is injected at the bottom like an orifice. I am not that concern about bubbles so I employed Eulerian as you suggested.
Unfortunately as evaluate the result, the turbulent kinetic energy is showing weird result as it only appears at the top most part of the reactor where I initially patch air (top 1/4 of the total volume of the reactor).
I am also conceren about injecting mass-less partcles. Is there a way I can monitor the location of the particles as calculation is on-going? I cannot figure out how so I just tried to save data every time step then i can determine the location of particles. This is very tedious to do since i am concern with the location of particle every minute and wish to run the calculation for a couple of hours. Any advise regardoing this matter is greatly appreciated.
Thanks,
Aliyah

[CFDtoy]

Hello,
looking at turb KE initially may not be worth it..initial discrepancies may be due to initialization (how you have initialized k,e everywhere when starting runs), or other numerical propagation..as time goes on, u, k, e etc will eventually smoothen. So, you shouldnt put too much emphasis on high values at the beginning..if you are really worried about it, consider modifying initial settings and re-run.

for monitoring, lagrangian type modeling is good. you can inject particles of small diameter and do stochastic modeling of the way they interact with the continuous fluid field.

Saving and other items, please look into the manual. It is very easy to - save data every Time step or at some specified iterations..

good luck

CFDtoy

Originally Posted by aliyah

Thank you very much CFDtoy.
Yes, my model is a cylindrrical bubble column reactor where air is injected at the bottom like an orifice. I am not that concern about bubbles so I employed Eulerian as you suggested.
Unfortunately as evaluate the result, the turbulent kinetic energy is showing weird result as it only appears at the top most part of the reactor where I initially patch air (top 1/4 of the total volume of the reactor).
I am also conceren about injecting mass-less partcles. Is there a way I can monitor the location of the particles as calculation is on-going? I cannot figure out how so I just tried to save data every time step then i can determine the location of particles. This is very tedious to do since i am concern with the location of particle every minute and wish to run the calculation for a couple of hours. Any advise regardoing this matter is greatly appreciated.
Thanks,
Aliyah

[faith]

hi guys.
I am simulating mixture of water and air in ansys cfd. I have a problem in boundary conditions. I have 2 outlets and 1 inlet. I need to set one of outlets as air outlet only (I mean only air exits from one of outlets) and the other one as mixture outlet. but went I want to define boundary conditions and set the air outlet the is no box to put percentage of air and water, only I can put percentage of mixture for any outlet. any one can help me?
thanks

[aliyah]

Thanks CFDtoy for your comments.

As you mentioned, saving data files every time step or number of iteration is simple. However, i want to monitor the location of the particles every second for a couple of hours. This is very tedious to do if i will save the data files every second. Too many data and numerous numbers.
I'm wondering if its possible to monitor the particles following the sole/monitors/surface or volume integrals where other properties such as temperature, velocity, ect. can be easily monitored.
Others suggests that this can be done by making a journal file for it. Unfortunately, i'm still new so i'm now studying about it.
Any advise you can share?
Thanks again.

[aliyah]

Hello Faith
I'm utilizing Fluent and not ANSYS however i guess both methiods are similar.
In Fluent, we can possibly set if the outlet is air or liquid via volume fraction where usually a value of 1 is for air and O for liquid.
Good luck to your simulation.

[zobekenobe]

Originally Posted by faith

hi guys.
I am simulating mixture of water and air in ansys cfd. I have a problem in boundary conditions. I have 2 outlets and 1 inlet. I need to set one of outlets as air outlet only (I mean only air exits from one of outlets) and the other one as mixture outlet. but went I want to define boundary conditions and set the air outlet the is no box to put percentage of air and water, only I can put percentage of mixture for any outlet. any one can help me?
thanks

I guess its late to reply to this message..but anyway for others coming to this thread ...

Specify the outlet from where only the gas is coming outlet using the 'Degassing Boundary Condition'

set the other as a Pressure Outlet Boundary Condition