Particles in air flow

BachelorM7 · October 14, 2015, 02:17

Hello.

We are working on a bachelor about optimization of an ejector.
A quick overview of the structure:
There are two inlets and an outlet. In one of the inlets water flows, which is delivered by a pump. In the second inlet particles/powder will be sucked up from a bag. The water and the powder is mixed and leaving the ejector through the outlet.
The issues are: how do I add both powder and air at the other inlet?

Best regards
Anette
Student
Engineering College of Aarhus
Denmark

ghorrocks · October 14, 2015, 07:29

How are you modelling the powder? As lagrangian particles or as a eularian phase? And most importantly - why did you make that choice of multiphase model?

BachelorM7 · October 14, 2015, 07:34

I don't know how I am modelling the powder jet. That is one more question who needs to be answered.
We got the model as I described it from a company, which we are doing the simulation for. I don't know if that was an answer on your question about multiphase?

ghorrocks · October 14, 2015, 07:40

The boundary condition is implemented in very different ways between the two methods.

So it looks like you first better understand the difference between Eularian and Lagrangian particle models and select the one most suited to your application.

At first glance I would suspect that a powder is too fine with too many particles for a Lagrangian model, so a Eularian model would be more suitable. But you should look into that and confirm it.

BachelorM7 · October 14, 2015, 07:46

The powder is so fine, that it can't nearly be seen in a microscope, so the Eulerian model seems correct, but I will look furter into it.
But how can I set both powder AND air as material in one inlet?

ghorrocks · October 14, 2015, 07:53

So one inlet is pure water, and one inlet is powder and air? Is that right?

What does the air and water form? bubbles? drops? Fluid slugs? foam? stays separate with a clear interface?

BachelorM7 · October 14, 2015, 07:59

That is right!

We don't know what happen inside the ejector. We are just interested in to mix the powder and water. But when the powder is sucked out of the bag, air is also sucked with. Therefore, we need to add both powder and air to the inlet.

ghorrocks · October 14, 2015, 08:02

But again, the choice of multiphase model depends on the form the air/water fluid takes. I guess the air is fine bubbles and the volume fraction of the bubbles is quite small - is that correct?

BachelorM7 · October 14, 2015, 08:27

We also see that the volume fraction of air is quite small. But we don’t know the exact volume fraction of the air bubbles.

ghorrocks · October 14, 2015, 19:21

It is starting to look like a eularian multiphase model should work here. You will have water as the continuous phase with air as a eularian bubble phase and powder as a eularian particle phase.

Then the boundary conditions are set by setting the volume fractions of the components.

BachelorM7 · October 15, 2015, 02:53

It sounds interesting. How do we add continuous phase, eulerian bubble phase and eularian particle phase to the model in CFX?

ghorrocks · October 18, 2015, 19:43

Have a look at the CFX tutorial examples.

BachelorM7 · October 20, 2015, 03:58

Now we are using: air = "continuous fluid", water = "continuous fluid" and powder = "dispersed solid". How does that sound?
We have tried "particle transport solid", but we can't figure out how to use "volume fraction" in this model? If it is possible?

ghorrocks · October 20, 2015, 05:28

That sounds suitable if you have a distinct air/water interface which you intend to resolve. If the air is bubbles then air needs to be dispersed bubbles.

October 14, 2015, 02:17	Particles in air flow	#1
BachelorM7 New Member Join Date: Oct 2015 Posts: 11 Rep Power: 10	Hello. We are working on a bachelor about optimization of an ejector. A quick overview of the structure: There are two inlets and an outlet. In one of the inlets water flows, which is delivered by a pump. In the second inlet particles/powder will be sucked up from a bag. The water and the powder is mixed and leaving the ejector through the outlet. The issues are: how do I add both powder and air at the other inlet? Best regards Anette Student Engineering College of Aarhus Denmark

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October 14, 2015, 07:29		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	How are you modelling the powder? As lagrangian particles or as a eularian phase? And most importantly - why did you make that choice of multiphase model?

October 14, 2015, 07:34		#3
BachelorM7 New Member Join Date: Oct 2015 Posts: 11 Rep Power: 10	I don't know how I am modelling the powder jet. That is one more question who needs to be answered. We got the model as I described it from a company, which we are doing the simulation for. I don't know if that was an answer on your question about multiphase?

October 14, 2015, 07:40		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	The boundary condition is implemented in very different ways between the two methods. So it looks like you first better understand the difference between Eularian and Lagrangian particle models and select the one most suited to your application. At first glance I would suspect that a powder is too fine with too many particles for a Lagrangian model, so a Eularian model would be more suitable. But you should look into that and confirm it.

October 14, 2015, 07:46		#5
BachelorM7 New Member Join Date: Oct 2015 Posts: 11 Rep Power: 10	The powder is so fine, that it can't nearly be seen in a microscope, so the Eulerian model seems correct, but I will look furter into it. But how can I set both powder AND air as material in one inlet?

October 14, 2015, 07:53		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	So one inlet is pure water, and one inlet is powder and air? Is that right? What does the air and water form? bubbles? drops? Fluid slugs? foam? stays separate with a clear interface?

October 14, 2015, 07:59		#7
BachelorM7 New Member Join Date: Oct 2015 Posts: 11 Rep Power: 10	That is right! We don't know what happen inside the ejector. We are just interested in to mix the powder and water. But when the powder is sucked out of the bag, air is also sucked with. Therefore, we need to add both powder and air to the inlet.

October 14, 2015, 08:02		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	But again, the choice of multiphase model depends on the form the air/water fluid takes. I guess the air is fine bubbles and the volume fraction of the bubbles is quite small - is that correct?

October 14, 2015, 08:27		#9
BachelorM7 New Member Join Date: Oct 2015 Posts: 11 Rep Power: 10	We also see that the volume fraction of air is quite small. But we don’t know the exact volume fraction of the air bubbles.

October 14, 2015, 19:21		#10
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	It is starting to look like a eularian multiphase model should work here. You will have water as the continuous phase with air as a eularian bubble phase and powder as a eularian particle phase. Then the boundary conditions are set by setting the volume fractions of the components.

October 15, 2015, 02:53		#11
BachelorM7 New Member Join Date: Oct 2015 Posts: 11 Rep Power: 10	It sounds interesting. How do we add continuous phase, eulerian bubble phase and eularian particle phase to the model in CFX?

October 18, 2015, 19:43		#12
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Have a look at the CFX tutorial examples.

October 20, 2015, 03:58		#13
BachelorM7 New Member Join Date: Oct 2015 Posts: 11 Rep Power: 10	Now we are using: air = "continuous fluid", water = "continuous fluid" and powder = "dispersed solid". How does that sound? We have tried "particle transport solid", but we can't figure out how to use "volume fraction" in this model? If it is possible?

October 20, 2015, 05:28		#14
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	That sounds suitable if you have a distinct air/water interface which you intend to resolve. If the air is bubbles then air needs to be dispersed bubbles.