J. Phil Thien's Projects

The baffle is the cheese grater and it scrapes off the lower layer of air entrained with dust.
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Wouldn't the air stream along the side contain more dust due to centrifugal force than the air along the bottom of the air stream?

Has anyone considered a design where the wall follows a scroll pattern?  The drop slot would follow the outside of the path defined by the scroll and gradually narrow as it got further inside.  This would force the flow path to be longer and the inner area of the scroll would have a tight radius to increase the centrifugal force on the particles?

I was thinking more of short vertical slots a couple of inches tall by maybe 1/4 inch wide especially with a lip kind of like a cheese grater to "scrape off" the outer layer of air containing the majority of the particles.  I don't see why this would cause more swirl in the bucket than the long slot in the bottom except that it will add a little more air flowing into the bucket.

I've thought it would be interesting to make a double bucket where the inner bucket only received debris from the bottom slot and the outer bucket from the side slots.  One could quickly see the effectiveness of the side slots.

As to the sandpaper idea, I see your concerns.  However, from what I've been reading, getting the particles and the air containing them slowed down is part of the key to separation.  Compared to a cyclone, the Thien design has little flow length to slow the air stream.  So is it more important to slow the air stream or to maintain laminar flow (I wish someone knowledgeable would give us an idea if there is ANY laminar flow in the separator at all. My impression is that laminar flow is VERY difficult to get except with very low flow rates.)

I have seen some complicated testing methods proposed, starting with a board and then making many error prone measurements. Instead:

Start with a known quantity of something like bread flour, say one pound. Run it through the separator, then weigh it.  Better yet, take what is separated out and run it through again.  Keep repeating this until a significant portion, say at least 20% has been lost.

This way, you know how "fine" the material is that you are testing with.  It would also be easier to use a "standard" material for testing by  forum members. 

It might also be useful to have a "standard" design that could be used to evaluate modifications.  Then we would all be comparing apples to apples.

I'd like to elaborate (taken from another thread): :-\

Regarding thy physical process of separation, I would like to know more myself as that knowledge should lead to design improvements.
My take so far is:
Step one: Particles are moved to the outer diameter of the separator by centrifugal action as the air swirls around in the separator.  This air flow should be smooth (laminar) as turbulence will tend to re-mix the particles into the air stream.
Step two:  Once the particles have reached the outer wall, friction slows them down and they fall toward the outlet at the bottom of the separator (i.e. through the slot in the baffle in our case).

If the above is correct, I would think that a smooth outer wall would improve the cyclonic separation until the particles reach the wall.  From then on, a rough wall (course sandpaper, perhaps) would enhance the slowing down process.

I have also thought that slots placed in the lower outer wall would help remove the outer few mm of the air stream that contains the particles.  Obviously, the slotted portion of the separator would have to protrude into the collecting bucket.  This would not require the particles to "fall" out of the air stream which to me would seem to improve small particle separation - think of how dust "hangs" in the air and takes minutes to settle out compared to fractions of a second available to "fall" out in the separator.

Regarding thy physical process of separation, I would like to know more myself as that knowledge should lead to design improvements.
My take so far is:
Step one: Particles are moved to the outer diameter of the separator by centrifugal action as the air swirls around in the separator.  This air flow should be smooth (laminar) as turbulence will tend to re-mix the particles into the air stream.
Step two:  Once the particles have reached the outer wall, friction slows them down and they fall toward the outlet at the bottom of the separator (i.e. through the slot in the baffle in our case).

If the above is correct, I would think that a smooth outer wall would improve the cyclonic separation until the particles reach the wall.  From then on, a rough wall (course sandpaper, perhaps) would enhance the slowing down process.

I have also thought that slots placed in the lower outer wall would help remove the outer few mm of the air stream that contains the particles.  Obviously, the slotted portion of the separator would have to protrude into the collecting bucket.  This would not require the particles to "fall" out of the air stream which to me would seem to improve small particle separation - think of how dust "hangs" in the air and takes minutes to settle out compared to fractions of a second available to "fall" out in the separator.

I hope the above speculation is of interest and provokes some responses to correct and/or improve on the explanation and the improvement ideas.

If the point of the DC is to slow down the air so particles will drop out, wouldn't a rough inner surface be a good thing?  I am wondering if attaching a very course sandpaper to the lower half of the inner wall would be a good thing as it would slow the air just above the baffle slot.

Aside: has there been any though given to putting "deswirl" vanes below the baffle to minimize disturbing the already separated dust?

I'm Allen-in-Sheboygan (Wisconsing, that is).  I plan on making a DC soon for my woodworking basement shop.