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Thread: "Tornado" Shaped Cyclone

  1. #1
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    "Tornado" Shaped Cyclone

    I am thinking about building a cyclone DC for my shop with a different shape for the lower cone. I have noticed that tornadoes have a characteristic "tornado-ey" type shape. Not straight sided cones but pinched in on the sides. Almost a perfect cylinder near the ground that widens in a characteristic curve to a much wider cone at higher altitudes.



    Okay, I know I can build this with fiberglass using standard boatbuilding methods. But has this already been tried and found to be lacking?
    Last edited by John Messinger; 03-03-2009 at 3:53 PM.

  2. #2
    I'd suggest Googling Bill Pentz's name. He knows more about cyclones and dust collection than anyone I know.

    As to the shape, I doubt there's any real relationship between a tornado which exists in free space to a cyclone dust collection system which has the goal of moving dust to the center of the funnel. It would be real pretty though.
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  3. #3
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    The point of the cone is to increase friction on the materials to slow them down so they fall out of the air stream. I suspect that the regular cone shape that is almost universally used on cyclonic separators is best suited to that. It's also a lot easier to fabricate...
    --

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  4. #4
    Along the lines of what Jim said, I would think that the air would travel a much shorter distance within the cyclone, decreasing separation effectiveness...

  5. #5
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    John,

    If enough of us tell you "don't do it", are ya gonna do it anyway??

    My thoughts on this are the fact that in all air ducting, you want more or less GENTLE transitions. You don't want to do anything abruptly like doing step down from 6" to 4" as opposed to doing a taper.

    The gentle tapering of the cone allows the dust/chips to gently settle out. I don't know if the shape of a tornado (although not exactly sure what kind of shape you are thinking about...can you do a Sketch-Up of it?) would accomplish this. I'm thinking the physics of what is being done in these two environments are very different.
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  6. #6
    Quote Originally Posted by Chris Padilla View Post
    John,

    If enough of us tell you "don't do it", are ya gonna do it anyway??

    My thoughts on this are the fact that in all air ducting, you want more or less GENTLE transitions. You don't want to do anything abruptly like doing step down from 6" to 4" as opposed to doing a taper.

    The gentle tapering of the cone allows the dust/chips to gently settle out. I don't know if the shape of a tornado (although not exactly sure what kind of shape you are thinking about...can you do a Sketch-Up of it?) would accomplish this. I'm thinking the physics of what is being done in these two environments are very different.
    Definitely.
    Tornado cones have a very small,very powerful, suction vortice at the bottom of the cone (in some cases, multiple suction vortices). Assuming you reversed this, this would have the effect of slamming dust and chips down into a very small area with a lot of force, which is exactly what you don't want (since it may in fact, have enough force to maintain movement of the large particles, so that they make it back up the updraft side)
    You want a fairly wide cyclone, ideally one able to maintain movement of small dust but not large particles, so the large particles fall out.

  7. #7
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    Quote Originally Posted by Chris Padilla View Post
    John,

    If enough of us tell you "don't do it", are ya gonna do it anyway??
    HELL YAH! If yer all wrong I'll crow it from the mountain tops, of course if I'm wrong you'll never hear about it again.

    But seriously folks, here are my thoughts.
    1) There is a reason tornadoes are shaped as they are and the wind speeds so high at the vortex. So why not try it in the dust collection cone.

    2) The reason we use the cone is because it works better for separating the "fines" with lower energy costs than a filter. If we just use a box then the big stuff falls out anyway due to the force of gravity, but the fines stay suspended and simply follow the airstream up the exhaust. If we use a cylinder we would separate smaller particles much like a centrifuge is used to separate liquid suspensions.

    3) The cone is an improvement over a simple cylinder, because we get finer and finer particles as we proceed down the cone. But also, the finer particles probably take a whole lot longer to separate which I noticed when I had reason to use a centrifuge. Hence, the longer we force the fines to stay spinning in the smaller diameters, the more we separate them from the airflow.

    4) The tornado shape has a longer section of smaller diameter, and should be better at separating fines.
    Last edited by John Messinger; 03-03-2009 at 9:40 PM.

  8. Of course, having read all the above, I'm pretty sure an experiment is in order, don't underestimate the power of a wild idea

  9. #9
    I wonder ... could it increase the number of rotations you'd get ... bear with me - i suspend any and all physics and reality at this point as i'm just brainstorming ...

    Wider at the top, with a curved transition to the narrower portion below. Would this wider upper bit be more prone to resisting the fall of gravity such that it would let the air make another rotation or two up high? Rather - slow the falling of the heavy particles enough to get a few more rotations out of the same relative space.

    Take a cyclone with the standard 1:1.62 ratio (iirc, or whatever it is) - make a tornado shaped (bell shaped? horn shaped?) model of identical height and see if it wouldn't perform a bit better.

    I suspect adding rotations would increase the static pressure of the whole thing and therefore would require a bigger impeller/motor to drive it, though. But maybe it'd also have increased separation?
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  10. #10
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    Two problems

    John, you have three problems, two of which might be insurmountable.

    1) Tornadoes always form on the bottom of wall clouds which in turn form on the bottom of a thunderstorm.

    2) Tornadoes always travel from south-west to north-east as they are part of the thunderstorm. This might be mitigated by placing your collector in the south-west corner of the shop, and running your duct work toward the north-east corner.

    3) Tornadoes suck from the bottom up whereas a DC cyclone works from the top down.

    I built a Bill Pentz cyclone from a kit. It was one of those "fun" projects that I don't care to repeat. In spite of the work, I am quite happy with the results.
    Best Regards, Ken

  11. #11
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    I'm all for it.

  12. #12
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    John, I am suggesting that you not try to reinvent the wheel, and be disappointed at your results. I have a Clear Vue Mini cyclone, which I attach to my shop vac. They also make powered units, as does Oneida, and one or two others. The good thing about the clearvue, is that it is clear plastic. you can see inside. It is more than getting the right shape. Inside, there is a piece of plastic that starts the funnel effect to working. Got to their website, and look at their videos, and you will see what I mean. For $120 for the mini, then on up, I think you would be better off spending the money, rather than trying to do it yourself.

  13. #13
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    Quote Originally Posted by Tom Adger View Post
    John, I am suggesting that you not try to reinvent the wheel, and be disappointed at your results....
    Thank you for your sincere concern. However, I am a hobbyist with more money, and time than brains. And this seems like a neat idea to me so I'll probably move it ahead of the bookshelves my wife wants me to make.

    Quote Originally Posted by Tom Adger View Post
    I have a Clear Vue Mini cyclone, ... look at their videos....
    Thank you for the reference. The video is the cat's meow and appears to confirm, pretty much what I was thinking. The big stuff is going to come out anyway but it is the small stuff that needs to be thrown to the outside at very high speed in order to separate from the airstream.

  14. #14
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    Quote Originally Posted by Ken Garlock View Post
    John, you have three problems, two of which might be insurmountable.

    1) Tornadoes always form on the bottom of wall clouds which in turn form on the bottom of a thunderstorm.

    2) Tornadoes always travel from south-west to north-east as they are part of the thunderstorm. This might be mitigated by placing your collector in the south-west corner of the shop, and running your duct work toward the north-east corner.

    3) Tornadoes suck from the bottom up whereas a DC cyclone works from the top down.

    I built a Bill Pentz cyclone from a kit. It was one of those "fun" projects that I don't care to repeat. In spite of the work, I am quite happy with the results.
    At the present second I disagree with #3. I believe that BOTH have the lowest pressure at the top center. The vortex (bottom) of BOTH features high speed air moving horizontally in a circular manner feeding air to a low pressure center core that rises because the pressure is much lower at the center top. However I just poured myself a second Glen Livet.... Perhaps I should stay away from the table saw tonight...
    Last edited by John Messinger; 03-03-2009 at 7:59 PM.

  15. #15
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    Quote Originally Posted by John Messinger View Post
    ... But has this already been tried and found to be lacking?
    Well, nobody has yet answered that question in the affirmative, so I'm going to guess that no one present really knows with certainty whether it'd work worse, the same as, or better than the conventional shape. As one person mentioned, the conventional flat wrap conical shape is much easier to fabricate. And since that shape works, there's little incentive for a commercial enterprise to try something different when the "different" means "higher cost".

    Two ways of looking at the effort to try it. One has been mentioned, reinventing the wheel and possible disappointment with the result. But, what if the results aren't disappointing? I say go for it.

    Even if it's no better than the conventional shape, you'll have a cyclone for your shop. And, in the absolute worst case, it's performance turns out to be significantly worse than the conventional design, replacing the cone with a conventional shape will be simple and you'll have had the fun of trying something different. The reason I'm in this hobby is for the fun of building things, not for ownership of the finished product.
    Tom Veatch
    Wichita, KS
    USA

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