Questions

Zaktatir · October 18, 2011, 05:58

Hello Guys,

I am trying to model droplet entrainment by gas from water film and the deposition of this droplets too.

My question is how to model the drag between water droplet and water film. I am applying the three- fluid model approach and using CFX. I found only stuff dealing with droplet interaction time and turbulent effects which are difficult to implement in to this commercial code.

Reentrainment (deposition) plays too a very important role: at this moment Entrainment is well solved but because my droplet s becoming bigger they move under the water film.

thx Rebecca

ghorrocks · October 18, 2011, 07:16

Can you show an image of what you are trying to do? I do not understand yet.

Zaktatir · October 18, 2011, 08:53

I am trying to model the onset of droplet entrainment in stratified wavy counter current flow.

Droplet deposition on the water film should be taken in to account.

I am defining: Air (continuous), Water (continuous) Water-Droplets (disperse)...

If my droplets become bigger or if i have a big amount of them they fall down and go under the water film (Several trial to increase physically the Deposition rate don't lead to better modeling)

I am doubting, if its due to the euler-euler approach because Water-Film phase as well as droplet-phase have the same density...

Thx Rebecca

ghorrocks · October 18, 2011, 18:01

Quote:

My question is how to model the drag between water droplet and water film.

I do not understand this question. Why is there drag between the water droplet and the water film? I would have thought that if a water droplet touches a water film they would merge. So I do not see how drag is relevant.

Zaktatir · October 19, 2011, 03:21

In the Euler-Euler Approach i should define that drag coefficient between the phases even though the droplet merge to the water film. My problem again is i cannot model that merging (deposition ) phenomena very good. Still have droplets which tend to flow under the water film..

Jessica

ghorrocks · October 19, 2011, 07:47

Oh I see, the drops and the continuous bit are different phases.

Not sure how you would do this, it is a tricky model. Just a thought - can you use particle tracking rather than the dispersed eularian phase?

Zaktatir · October 19, 2011, 08:28

Droplets are produced in the domain and are not introduced from a nozzle or something.. that s particle tracking is not welcome.... i thought about defining a relative density of the droplets (assuming that they have a middle density) in order to keep that merging problem out (e.g defining an artificial buoyancy force between the water phase and the droplet phase).

Jessica

ghorrocks · October 19, 2011, 18:36

You can produce particles as needed here, you don't need nozzles or inlets.

But whether you do it by eularian or lagrangian approach you are going to have to do some development work to get it working. There is no simple approach to my knowledge.

juliom · October 20, 2011, 10:07

Wow I see it is a very complex simulation.
Are you using the Euler-Euler model (particle) model?
I think you might Use the MUSIG model, since you can work with different particles and diameter, and couple them via differente terms.!!

October 18, 2011, 05:58	Questions	#1
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	Hello Guys, I am trying to model droplet entrainment by gas from water film and the deposition of this droplets too. My question is how to model the drag between water droplet and water film. I am applying the three- fluid model approach and using CFX. I found only stuff dealing with droplet interaction time and turbulent effects which are difficult to implement in to this commercial code. Reentrainment (deposition) plays too a very important role: at this moment Entrainment is well solved but because my droplet s becoming bigger they move under the water film. thx Rebecca

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October 18, 2011, 07:16		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Can you show an image of what you are trying to do? I do not understand yet.

October 18, 2011, 08:53		#3
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	I am trying to model the onset of droplet entrainment in stratified wavy counter current flow. Droplet deposition on the water film should be taken in to account. I am defining: Air (continuous), Water (continuous) Water-Droplets (disperse)... If my droplets become bigger or if i have a big amount of them they fall down and go under the water film (Several trial to increase physically the Deposition rate don't lead to better modeling) I am doubting, if its due to the euler-euler approach because Water-Film phase as well as droplet-phase have the same density... Thx Rebecca

October 19, 2011, 03:21		#5
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	In the Euler-Euler Approach i should define that drag coefficient between the phases even though the droplet merge to the water film. My problem again is i cannot model that merging (deposition ) phenomena very good. Still have droplets which tend to flow under the water film.. Jessica

October 19, 2011, 07:47		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Oh I see, the drops and the continuous bit are different phases. Not sure how you would do this, it is a tricky model. Just a thought - can you use particle tracking rather than the dispersed eularian phase?

October 19, 2011, 08:28		#7
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	Droplets are produced in the domain and are not introduced from a nozzle or something.. that s particle tracking is not welcome.... i thought about defining a relative density of the droplets (assuming that they have a middle density) in order to keep that merging problem out (e.g defining an artificial buoyancy force between the water phase and the droplet phase). Jessica

October 19, 2011, 18:36		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	You can produce particles as needed here, you don't need nozzles or inlets. But whether you do it by eularian or lagrangian approach you are going to have to do some development work to get it working. There is no simple approach to my knowledge.

October 20, 2011, 10:07		#9
juliom Senior Member Julio Mendez Join Date: Apr 2009 Location: Fairburn, GA. USA Posts: 290 Rep Power: 18	Wow I see it is a very complex simulation. Are you using the Euler-Euler model (particle) model? I think you might Use the MUSIG model, since you can work with different particles and diameter, and couple them via differente terms.!!