Dust Collection Question

[Jim Dunn]

Can retangular ducting be used for dust collection. Have any of you engineers done the air flow caculations on this type of pipe profile. I'd like to use 3x8" or something similar so as to keep it as close to the wall as possible. That will give it a low profile. Believe me when I say I can use the extra 3" of space.

[Michael Gabbay]

Jim -

I'm no engineer (and I did not sleep at a Holiday Inn Express last night :D ) but I would think that the corners would collect dust. Additionally, the rectangular shape may not be the most efficient chamber for air flow.

My 2 cents...

Mike

[Tom Hintz]

I have actually seen test data on this stuff at a NASCAR team when I did that sillyness. The square shape is far less efficient than round. It has something to do with the boundary layers of air flow..(I saw it, didn't understand the high-tech stuff). Air piles up in the corners and drags on the rest where in a round tube the air is more constant over the entire area.
They were experimenting with radiator and brake duct openings and how they transitioned to round, and if they HAD to transition to round. They all use round as close to the duct as possible so square ain't getting it.
How does this impact the air volume and velocity generated by a DC? I dunno.

[Bill Lewis]

What they said, round is more efficient.

That being said, A DC system using rectangular (HVAC) ducting would also tend to suck in the flat walls of the ducting. Possibly to collapse.

[Jim Dunn]

Thanks all. Never gave a thought to the ducting collapsing :( Was a good idea for about 15 seconds though.

[Bob Johnson2]

I saw in one of the DC do it yourself books where the author built a vertical manifold out of wood (It looked roughly 6"x6"x3'). He didn't make mention of having any problems. Had round 4" drops coming off of that.

[Steven Wilson]

You would have more resistance to flow (higher SP) and would need to have the duct made out of a heavier guage for the same frontal area as round pipe.

[Jim Dunn]

Steve, are you suggesting that it would need to be at least 4"x?. If that is the case then I'll just stay with the 6" SDR35 pipe. I had wanted to reduce the dimension from the wall to the outside of the pipe to something less than 4". This would have allowed me to place items closer to the wall.

[Steven Wilson]

No, I'm saying that the resistance will be higher on rectangular duct than circular duct for a given cross-sectional area. Further, the rectangular duct will not be as structurally sound as the round duct for a given guage of sheet metal. Since I don't use rectangular ducting I don't know what the increase in resistance would be. If you have the right measurement equipment you can figure it out.

[Chris Barnett]

Think about an oval duct, either transition to/from oval or use all oval [with the thin side toward your equipment :) ]....a little higher resistance but not as high a potential to collect the nasties. Call an HVAC company (or two , three until you get cooperation] and ask if they can sell you the oval duct...then start asking a few more questions like...how much air do you need, how big a fan or blower, and on, and on and on. If you get ahold of a nice guy, he can help you solve this one, and you could result with a pretty nice setup.

[Randy Moore]

Jim,

If you have had any sheet metal work done where you work at your waste water plant get them on the phone or talk to someone in person. Explain what you are trying to do. They should be able to figure loads, the lenght of the ducts and everything associated with the system and tell you sizes of duct, the fan and answer any questions you might have.
Randy