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

Difference of multicomponent and multiphase homogenous flows

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

Like Tree2Likes
  • 2 Post By ghorrocks

Reply
 
LinkBack Thread Tools Display Modes
Old   October 14, 2009, 10:35
Default Difference of multicomponent and multiphase homogenous flows
  #1
Member
 
Lukasz
Join Date: Mar 2009
Posts: 64
Rep Power: 8
Luk_Fiz is on a distinguished road
Hi all - I have partly theoretical partly practical question.
1) What is a difference between multicomponent and homogenous multiphase flows? Assume I have 2 fluids of different densities (fe. water and methanol), no mass nor energy transfer between. Looking through the CFX documentation I see that simulating it as multiphase homogenous flow it solves for volume fractions, after that calculates density (where? mean density?) and than solves momentum eqations.
If it is multicomponent than it solves for mass fractions, after that calculates mean density and momentum and so on in the end.

Am I right? Where is difference? Is in "multiphase version" density taken from material properties and than the momentum equations are solved with these densities without calculating mean value?
2) Assume these two luquids are in the long pipe with gravity. In case of simulating it as multiphase homogenous I see fast stratification. In case of simulation as multicomponent I see no stratification, OR VERY SLOW. Does it mean that in case of multicomponent treatment there is only signle "mean" (mass fraction-weighted) density and because of that it is non possible to stratify mixture?

Thanks for all answers because it makes me confused since quite long.

Luk
Luk_Fiz is offline   Reply With Quote

Old   October 14, 2009, 17:31
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,830
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Quote:
Am I right?
Yes, I think your explanation is about right.

Quote:
Where is difference?
The difference is the multi-component model assumes they mix into a single phase, which can be represented by a bulk density, viscosity etc. The components are mixed on a microscopic scale. Multi-phase homogeneous means you have multiple phases (eg gas and liquid) and they are separated on a resolvable scale.

Yes, a multiphase model (eg air and water) are likely to separate very quickly. I am pretty sure buoyancy also works with multi-component models - but keep in mind the separation occurs at a microscopic length scale so is likely to be slower than the multiphase approach.
ghorrocks is offline   Reply With Quote

Old   October 15, 2009, 03:53
Default
  #3
Member
 
Lukasz
Join Date: Mar 2009
Posts: 64
Rep Power: 8
Luk_Fiz is on a distinguished road
Thanks Glenn,
Now it seems for me that I understand this
Assume that mentioned flow in the pipe. It seems to be like this:
1) If we define it as multiphase homogenous mixture and we set volume fractions of inlet as 50%/50% than the gravity acts in the moment and stratifies mixture because 50% of volume (fractions) are occupied by ingridients of different densities. Thats why multiphase homogenous stratifies in the moment.
2) If we define it as multicomponent and we set mass fractions of inlet as 50%/50% than the fluid has equal (mass-weighted) properties and will not stratify or stratify very slowly in case of small inhomogeneities.

Thanks,
Luk
Luk_Fiz is offline   Reply With Quote

Old   October 15, 2009, 06:21
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,830
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Be careful comparing the separation rates. The density difference between air and water is around 1000, such as is commonly modelled in homogeneous multiphase models. Multicomponent mixtures are commonly used for mixtures of gases (eg O2+CO2+N2), and the density differences between these components is much smaller.

So the separation speed of a water/air mixture is much faster than a O2/N2/CO2 mixture simply because of the larger density difference.
ghorrocks is offline   Reply With Quote

Old   October 15, 2009, 08:04
Default
  #5
Member
 
Lukasz
Join Date: Mar 2009
Posts: 64
Rep Power: 8
Luk_Fiz is on a distinguished road
Yes, of course.

Thanks,
Luk
Luk_Fiz is offline   Reply With Quote

Old   September 30, 2012, 03:21
Default
  #6
New Member
 
prishor p k
Join Date: Jul 2012
Posts: 29
Rep Power: 5
prishor is on a distinguished road
hi all,
i am doing the simulation of gasification in Fluidized bed reactor. there are four components air, steam, biomass and sand..
my doubt is that can i consider this problem as 4 phase flow or consider as multi component 2 phase flow (gas-solid flow).??.
please help me.
thanks in advance,
prishor
prishor is offline   Reply With Quote

Old   October 1, 2012, 07:41
Default
  #7
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,830
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
How can this be a 4 phase model when there are only 3 phases (solid, liquid, gas)?

This should suggest the answer - the air and steam are both gases, so these are probably bets modelled as a gas phase multicomponent mixture. The two solids are modelled as two different solid phases.
ghorrocks is offline   Reply With Quote

Old   October 1, 2012, 11:37
Default
  #8
New Member
 
prishor p k
Join Date: Jul 2012
Posts: 29
Rep Power: 5
prishor is on a distinguished road
thanks Glenn.
you are saying the two solids can be treated as different phase even if they both are solids rite.??
how can i input both air and steam into FLUENT as components of gas phase.
prishor is offline   Reply With Quote

Old   October 1, 2012, 19:00
Default
  #9
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,830
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
If you are using Fluent then you are on the wrong forum. This is the CFX forum.
Danial Q and Mfaizan like this.
ghorrocks is offline   Reply With Quote

Old   April 2, 2013, 10:35
Post shock tube problem
  #10
New Member
 
srinath
Join Date: Apr 2013
Posts: 3
Rep Power: 4
srinath_cfx is on a distinguished road
Hi,

If I have a shock tube of Driver gas 'helium' and Driven gas 'air', is it multi-component flow. If this is the case will mixing take place at large time scales and contact surface disintegrate?

How to define a multi component gas?
srinath_cfx is offline   Reply With Quote

Old   April 2, 2013, 18:43
Default
  #11
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,830
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Have a look at the CXF tutorials on how to specify a multi-component gas.
ghorrocks is offline   Reply With Quote

Old   April 4, 2013, 05:29
Default
  #12
New Member
 
srinath
Join Date: Apr 2013
Posts: 3
Rep Power: 4
srinath_cfx is on a distinguished road
@ ghorrocks, Thanks
srinath_cfx is offline   Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
multiphase multicomponent physics ckleanth CFX 3 June 4, 2009 20:15
multiphase and multicomponent flow charles CFX 2 December 18, 2008 22:34
Multiphase multicomponent system David CFX 0 January 15, 2004 21:59
multiphase or multicomponent.... That's the probl july CD-adapco 1 March 7, 2002 03:27
Multiphase or Multicomponent Pandu Sattvika CFX 10 January 7, 2002 05:40


All times are GMT -4. The time now is 13:19.