Diameter of barrel for lid type baffle separator?

[tvman44]

Would a larger diameter barrel give better separation of fines (flour) in a Thien separator with the baffle attached to the lid (not a top hat)?  Thinking about building another and debating if it would be worth the extra space to use a 50 gal barrel instead of a 30 gal barrel, because space is limited in my small shop.

[giovanotti]

Per my experience, not.
Point of separation is particle centripetal speed, crashing against the wall, reducing the speed and falling down to the container. Lighter is the particle, smaller must be diameter, generally more tough (unefficient) is separation.
This is written out of my experience, dealing with fine wood pellet ash.
I cannot back it up with any calculation.
Just idea: Dyson uses bunch of small cyclones in one device. They have very small diameter.

[tvman44]

Thanks for the reply.  If I look at it one way it seems larger diameter may be better, but from the other way of thinking larger may not be as good????

[phil (admin)]

The smaller the diameter, the greater the velocity, the better the separation, albeit at a cost (resistance).

Resistance is proportional to the speed (of the air) squared.

It is a bit of a balancing act, hitting the desired separation rate while not giving up so much CFM that a lot of the dust isn't being captured at the source.

[tvman44]

Thank you Phil, I think I will use a 30 gal barrel.  I have another separator I made awhile back using a 30 gal barrel and it works real good so I probably should not mess with success. :)