particle extraction

dsmith · September 21, 2009, 23:05

Hi there,

I'm modelling a cylinder rotating and emitting dust particles tangentially at the bottom surface. I have this set up fine and it seems to be working well, when on it’s own. But now I need to add in an extraction system. Is it possible to model this as some sort of hose type object inside my flow domain? This is what I have been trying to do, but what do I set the boundary conditions as? It seems strange to have an inlet inside another inlet and doing this doesn’t work I have also tried using an opening at this inlet of the dust collection devise.

Also, the modelling of what’s causing the extraction of dust is not important as measurements of the velocity of air going through the collection the device have been measured.

Is the correct way to model this to add in some sort of momentum source at the face of the dust collection device?

I have attached a picture of my model (symmetry zx plane @ min y)

Cheers.

[IMG]file://///engcad4/dwh47$/My%20Documents/Research/With%20extraction/domain.png[/IMG]

ghorrocks · September 22, 2009, 08:10

Before you consider how to model it you should think carefully about exactly how the flow works, so you can define it properly.

It seems you have 3 factors you need to define:
1) The flow in the room
2) The flow in the extraction system
3) The dust generation

Assuming this thing operates in a normal ventilated room then the surrounding air flow is defined by the AC system or open windows or whatever makes the room air move. You should then incorporate these in your model to get the room air motion right.

For point 2 you need to consider how the extraction system works. Is it a pump with a filter? Then you should get the pump curve and filter characteristics. This will help you define the operating point of the extraction system. to implement this in your model it could be either a defined pressure or a defined flow rate, what ever matches the pump characteristics best. You could even put the pump curve in as a boundary condition if you are game. You mention you know the extraction velocity, so a specified velocity outlet sounds good.

For point 3 you have to define the size, amount, location and initial velocity of the particles. You suggest this is already known.

There should be no need in this model to use momentum sources. Simple boundaries should work fine.

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September 22, 2009, 08:10		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Before you consider how to model it you should think carefully about exactly how the flow works, so you can define it properly. It seems you have 3 factors you need to define: 1) The flow in the room 2) The flow in the extraction system 3) The dust generation Assuming this thing operates in a normal ventilated room then the surrounding air flow is defined by the AC system or open windows or whatever makes the room air move. You should then incorporate these in your model to get the room air motion right. For point 2 you need to consider how the extraction system works. Is it a pump with a filter? Then you should get the pump curve and filter characteristics. This will help you define the operating point of the extraction system. to implement this in your model it could be either a defined pressure or a defined flow rate, what ever matches the pump characteristics best. You could even put the pump curve in as a boundary condition if you are game. You mention you know the extraction velocity, so a specified velocity outlet sounds good. For point 3 you have to define the size, amount, location and initial velocity of the particles. You suggest this is already known. There should be no need in this model to use momentum sources. Simple boundaries should work fine.