CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

Two Dispersed Phases - Degassing Condition

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 19, 2022, 12:38
Default Two Dispersed Phases - Degassing Condition
  #1
New Member
 
Richard M
Join Date: Oct 2021
Posts: 12
Rep Power: 4
RichChemEng is on a distinguished road
Hello -

I have a water, oil and air in a stirred tank bioreactor system. The oil is defined by a homogeneous MUSIG model. The air is a dispersed, fixed-diameter particle.

I would like to simulate mixing, but unfortunately the degassing condition allows the oil to escape the top (unrealistic). When an open boundary condition is used, the system overflows.

Is there a way to modify the degassing BC to allow only the air to escape?

Thanks!
RichChemEng is offline   Reply With Quote

Old   April 19, 2022, 13:15
Default
  #2
Senior Member
 
Join Date: Jun 2009
Posts: 1,860
Rep Power: 33
Opaque will become famous soon enough
I am not very familiar with multiphase models; however, how many continuous phases do you have? You stated Air is dispersed with a fixed size, what about oil?

As far as I understand the degassing condition allows continuous phases to leave at an outlet, but not dispersed/polydispersed phases.

Also, MUSIG models only support one continuous phase, so which one have you set as continuous?
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
Opaque is online now   Reply With Quote

Old   April 19, 2022, 13:17
Default
  #3
New Member
 
Richard M
Join Date: Oct 2021
Posts: 12
Rep Power: 4
RichChemEng is on a distinguished road
There is 1 continuous phase - water.

Air is the dispersed phase (fixed diameter).

Oil is the polydispersed phase (homogeneous MUSIG).
RichChemEng is offline   Reply With Quote

Old   April 19, 2022, 15:49
Default
  #4
Senior Member
 
Join Date: Jun 2009
Posts: 1,860
Rep Power: 33
Opaque will become famous soon enough
Great!!

Have you tried setting oil as a dispersed phase, not polydispersed to see if it stays within the domain? It should since ALL dispersed phases should see a "wall at the outlet"

Perhaps the software is missing the "wall treatment" for the polydispersed phase at outlets?
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
Opaque is online now   Reply With Quote

Old   April 19, 2022, 15:50
Default
  #5
New Member
 
Richard M
Join Date: Oct 2021
Posts: 12
Rep Power: 4
RichChemEng is on a distinguished road
Thank you, but I need a population balance to describe the oil particle size and morphology.
RichChemEng is offline   Reply With Quote

Old   April 19, 2022, 16:05
Default
  #6
Senior Member
 
Join Date: Jun 2009
Posts: 1,860
Rep Power: 33
Opaque will become famous soon enough
I understand that, but you need to know what the software is doing with either option. Otherwise, you are stuck, correct?

Reading the configuration files of ANSYS CFX I could see the Degassing Condition assumes that Continuous and Solid Dispersed Phases see a "free slip wall" at an outlet, but other Dispersed/Polydispersed Phases see a true "outlet treatment".

Modifying the configuration files can get tricky very quickly to access hidden behavior.
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
Opaque is online now   Reply With Quote

Old   April 19, 2022, 16:09
Default
  #7
New Member
 
Richard M
Join Date: Oct 2021
Posts: 12
Rep Power: 4
RichChemEng is on a distinguished road
That is correct. The only other option would be to create some sort of expression as an "oil makeup." So when oil leaves the degassing outlet, you put back into the domain in a place that it would naturally occur due to splashing/fluid dynamics etc. Any thoughts?

I am not sure I am a capable enough user to modify the configuration file.
RichChemEng is offline   Reply With Quote

Old   April 19, 2022, 16:20
Default
  #8
Senior Member
 
Join Date: Jun 2009
Posts: 1,860
Rep Power: 33
Opaque will become famous soon enough
If you know how to search ("grep") files using the command line, you can find out where Degassing condition is defined

Go to your Ansys Inc installation directory, there should be an "etc" directory, and use the following command (assuming linux)

grep "Degassing Condition, OUTLET" ./*

you should find a file that contains the configuration for that Boundary Condition (BC
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
Opaque is online now   Reply With Quote

Old   April 19, 2022, 17:10
Default
  #9
New Member
 
Richard M
Join Date: Oct 2021
Posts: 12
Rep Power: 4
RichChemEng is on a distinguished road
Thank you. I will give it a try.

Thanks you
RichChemEng is offline   Reply With Quote

Old   April 19, 2022, 19:30
Default
  #10
New Member
 
Richard M
Join Date: Oct 2021
Posts: 12
Rep Power: 4
RichChemEng is on a distinguished road
How would I do this for a windows based system?

Thanks!
RichChemEng is offline   Reply With Quote

Old   April 20, 2022, 06:01
Default
  #11
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,830
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
The simplest way is to load the files in a text editor and use search to look for the target string. Even notepad has a search function which would work for this.
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote

Reply

Tags
bioreactor, cfx, degassing, dispersed phase, multiphase flow

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Question about different kinds of Boundaries and Boundary Conditions granzer Main CFD Forum 17 April 12, 2022 17:27
UDF for degassing boundary condition peaker007 Fluent UDF and Scheme Programming 5 November 23, 2015 12:55
Degassing BC for Three phases bubble column esq1 Fluent UDF and Scheme Programming 0 September 22, 2014 12:18
Two continuous phases and one dispersed phase modeling using CFX creddy_trddc CFX 1 August 13, 2013 22:23
CFX fails to calculate a diffuser pipe flow shenying0710 CFX 7 March 26, 2013 04:13


All times are GMT -4. The time now is 11:15.