Particle distribution in a suspension

BarDror · March 20, 2015, 11:54

Hi all!

I am trying to simulate the concentration of a suspension and the dispersion of its particles in a tube. I have read an experimental article about particle distribution in a tube. It says the concentration has its maximum at the center at the tube, and has its minimum at the walls. I would like to reproduce something like that. But I haven’t got any useful results yet.

My model is 2D (one element thick), and steady state, laminar. I use a multiphase fluid. It contains a fluid phase ’Continuous fluid’ and a solid particle phase, which is ’Particle transport solid’. The volume fraction is 0.5. I chose these settings based on a CFX tutorial: Chapter 11: Flow Through a Butterfly Valve.

There is Static pressure on the inlet, and average static pressure on the outlet. I set the wall’s perpendicular and parallel coeffs to 1, because it is an elastic collision.

Do you think that is OK? I doubt about the particle type. Should i try ’Dispersed solid’ option instead of this? Or something other?

I am observing the ’Average Volume Fraction’ variable at CFX-Post. I don’t really like that it is above 1. Is there something to do with that?

Thanks for your support!

ghorrocks · March 21, 2015, 03:53

You say the volume fraction is 0.5: VF of what? This is a very high voluem fraction for a lagrangian particle tracking model. This model is unlikely to be valid for this high VF.

Do you know what physical forces cause the particle concentration to increase at the centre of the tube?

BarDror · March 22, 2015, 06:32

Hi!
The particle volume fraction is 0.5 as well as the fluid volume fraction.

I haven’t find any specific name of the force. I read this: „particles which attemt to enter the tube along streamlines which pass very close to the wall are forced by the presence of the wall to leave their entering streamlines and to follow another located slightly nearer to the tube axis.” So I think that’s why the concentrarion increases at the center of the tube.

I also found something related with the Stokes drag, but I don’t really know how to set it. [Fig1 from: Mannan S. H., Ekere N. N., Ismail I. and Currie M. A., "Computer simulation of solder paste flow. Part I: Dense suspension theory", Journal of Electronics Manufacturing, 4 (1994) 141.]

ghorrocks · March 22, 2015, 17:21

I meant where in the simulation does the VF=0.5 occur

My point of VF=0.5 is too high for lagrangian particle tracking is fundamental. The only particle tracking model in CFX which is appropriate for VF levels this high is Eularian. Continue using Langrangian particle tracking at your own risk.

The force A is already implemented in CFX (of course). But note that it is only applicable at low VF, not high VF as you have (it does not account for the wakes of adjacent particles). All the other models you show are not implemented in CFX so you would have to implement them as a custom particle force model.

Have a look at the particle interaction forces included in CFX for the Eularian model. It already includes dense particle models, wall lubrication forces (which pushes particles off the walls) and some other models.

March 20, 2015, 11:54	Particle distribution in a suspension	#1
BarDror New Member Join Date: Aug 2014 Posts: 5 Rep Power: 11	Hi all! I am trying to simulate the concentration of a suspension and the dispersion of its particles in a tube. I have read an experimental article about particle distribution in a tube. It says the concentration has its maximum at the center at the tube, and has its minimum at the walls. I would like to reproduce something like that. But I haven’t got any useful results yet. My model is 2D (one element thick), and steady state, laminar. I use a multiphase fluid. It contains a fluid phase ’Continuous fluid’ and a solid particle phase, which is ’Particle transport solid’. The volume fraction is 0.5. I chose these settings based on a CFX tutorial: Chapter 11: Flow Through a Butterfly Valve. There is Static pressure on the inlet, and average static pressure on the outlet. I set the wall’s perpendicular and parallel coeffs to 1, because it is an elastic collision. Do you think that is OK? I doubt about the particle type. Should i try ’Dispersed solid’ option instead of this? Or something other? I am observing the ’Average Volume Fraction’ variable at CFX-Post. I don’t really like that it is above 1. Is there something to do with that? Thanks for your support!

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March 21, 2015, 03:53		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	You say the volume fraction is 0.5: VF of what? This is a very high voluem fraction for a lagrangian particle tracking model. This model is unlikely to be valid for this high VF. Do you know what physical forces cause the particle concentration to increase at the centre of the tube?

March 22, 2015, 17:21		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	I meant where in the simulation does the VF=0.5 occur My point of VF=0.5 is too high for lagrangian particle tracking is fundamental. The only particle tracking model in CFX which is appropriate for VF levels this high is Eularian. Continue using Langrangian particle tracking at your own risk. The force A is already implemented in CFX (of course). But note that it is only applicable at low VF, not high VF as you have (it does not account for the wakes of adjacent particles). All the other models you show are not implemented in CFX so you would have to implement them as a custom particle force model. Have a look at the particle interaction forces included in CFX for the Eularian model. It already includes dense particle models, wall lubrication forces (which pushes particles off the walls) and some other models.