After my last post on cyclones, I read some papers that
have raised questions in my mind about whether using
air ramps and neutral vanes in cyclones is a good idea. The
acutal quotes are below.
It seems like an inlet-vane or air ramp hurt the dust collection
efficiency quite a bit. Using either of these would mean that
the final filter needs to be cleaned about 3 times as often.
And presumably replaced 3 times as often.
Can anyone come up with a reason to use an air ramp in light of
this data?
Reference [1] has this to say about neutral vanes, which it calls
inlet vanes.
"Several modifications were made on the small-diameter cylcone in
attempts to improve its performance. ... The inlet-vane reduced the
pressure drop through the cyclone by about 60 percent. Unfortunately
it also reduced the cyclone collection efficiency. About three times
more material was emitted from the cyclone with the inlet vane than
from the unmodified cyclone."
Continuing on to air ramps, which it calls input helixes, [1] says:
"A cyclone with an inlet helix was tried next. ... This cyclone
with the inlet helix performed simalarly to the one having a flat
inlet vane. Both the pressure drop and efficiency were reduced
when the inlet helix was used. About two and one-half to three
times as much material was lost from the cyclone with the inlet
helix than from the unmodified cyclone."
Reference [2] is a preliminary report of a computer simulation
of a cyclone.
[2] says: "In the plan view of the cyclone streamlines air
makes one revolution in the barrel of the cyclone, then
makes an abrupt change in direction near the entrance (where
it collides with incoming air). This forces the dust-laden
air to make a tight turn inward and downward. The fact that
the air is leaving the dust behind at that point appears
to be more important to cyclone efficiency than the fact
that the dust is reintroduced into incoming air. This
alternate approach to understanding cyclone dynamics was
thought to possibly explain the results of an earlier
experiment attempting to prevent such reintroduction".
It then goes on to quote the material that I quoted
above.
[1] Baker and Stedronsky. July 1967. "Gin Trash
Collection Efficiency of Small-Diameter Cyclones", ARS 42-133;
USDA Argicultural Reseach Service
[2] "Dust Cyclone Modeling and Validation" a presentation
made by Funk and Hughs at the 2000 ASAE Annual International Meeting
ASAE Paper no. 004026
Bob S
Thanks Jim, I'm glad someone is finding these posts useful.
I did think of one reason for using either an air ramp or a neutral
vane for us hobby shops ... Many of us are frugal :-) and tend to skimp
on the size of the blower (because they are expensive) and/or the duct
work (hey, dollar is a dollar). There may not be enough pressure drop
(power) to drive an efficient cyclone and maintain significant air flow.
One alternative for reducing the pressure drop without screwing up
the air flow inside the barrel would be to use a larger diameter
cyclone. Within reasonable limits, that will reduce the pressure
drop consumed by the cyclone and won't have much effect on separation
efficiency; it might even improve it.
One paper, (Funk, Hughs & Holt. Engineering and Ginning: Entrance
Velocity Optimization for Modified Dust Cyclones. Journal of Cotton
Science 4:178-192 (2000) ) found that modified 1D3D cyclone got the
best separation performance with an input velocity of around 2,600 feet
per minute. That was also the lowest input velocity tested, though
looking at their graph, it looks like the best collection efficiency is
around 2,600 ft/min. The collecion efficiency peak is very broad.
The pressure drop was 4+ inches of water at 3,500 ft/ min but
only about 2.5 inches of water at 2,600 ft/min. That pressure
drop reduction is in the same league as an air ramp.
BTW, a modified 1D3D cyclone has an inlet that is D/2 x D/4, the vortex
finder has a diameter of D/2, the vortex finder is D/2 or a little longer
and the dust bin outlet has a diameter of D/3.
The drawback to using a bigger cyclone is that it is taller. Many of us
have limited height. Most of us can handle a footprint that is 2 or
three inches bigger but 3 inches wider will add at least a foot to the height.
Bob S
>
>Is that paper available online? I have read at least one Funk, et al,
>paper, but I don't remember the info you are citing here.
>
>A transport velocity of 2600 fpm seems too low to prevent settling in the
>main trunk, even for horizontal runs. That probably explains why they
>didn't test at lower speeds.
>
>Jim
If you send an email to the right person at the ARS, that's the
USDA's Agricultural Research Service, they'll send you a copy. A
Google search on the title should turn up the right page to order
from. I don't remember where the right page is right now.
Searching for "cyclone" at
<http://www.ars.usda.gov/services/TekTran.htm> gives you abstracts and
summaries but it doesn't allow reading or requesting the papers. One
of the summaries turned up is
<http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=136360>
Dust Collection Efficiency of over-Sized Cotton Gin Cyclones that looks
interesting.
The 2,600 ft/min is the inlet velocity of the cyclone not the velocity
in the duct work. For example, going from a 6 inch round pipe ( 28 sq
inches) to a 4.5 x 9 inlet (40 sq inches, which is about right for
an 18 inch, modified 1D3D) will give about a 30% reduction in velocity.
As you've noted, dropping the velocity too fast or too far will
likely lead to choking. Reducing the velocity too fast will probably
cause unneeded pressure drop too.
Bob S
On Sat, 22 Nov 2003 21:08:08 GMT, Jim Wilson <[email protected]> wrote:
On Sun, 23 Nov 2003 06:35:57 GMT, Steve Knight <[email protected]> wrote:
>
>well I have been testing Bill Pentz's design and I know it works very well. I
>get about 2 to 3 weeks between cleaning the filter. I only loose a little
>airflow. but i make so much fine dust and that's what a cyclone misses. I get a
>couple of coups of very fine dust out. the stuff will float all over my shop
>when I clean the filter. more like smoke then dust.
> I have more airflow with his design then I did with my regular bag setup and
>a huge felt bag.
>
>--
>Knight-Toolworks & Custom Planes
>Custom made wooden planes at reasonable prices
>See http://www.knight-toolworks.com For prices and ordering instructions.
I'm glad to hear that you're happy with the cyclone.
BTW, your postings have convinced me that cannister filters are so much
better that it's not worth looking at fabric filters.
If the numbers from the paper I mentioned above are correct, then without the
air ramp and neutral vane you'd only have to clean the filter every
six to nine weeks instead of every two to three weeks. To me that would
be a worthwhile improvement!
OTOH, if your airflow dropped low enough you'd just not collect the
dust in the first place and you'd never have to clean the filter. :-)
How big a blower do you have? And how do you decide that your filter
needs cleaning? Did you build a manometer? Or do you just notice the
airflow is low?
Bob S
On Sun, 23 Nov 2003 15:54:08 GMT, Jim Wilson <[email protected]> wrote:
>Steve Knight wrote...
>> but i make so much fine dust and that's what a cyclone misses. I get a
>> couple of cups of very fine dust out. the stuff will float all over my shop
>> when I clean the filter. more like smoke then dust.
>
>Yeah, and that's the bad stuff. I wondered if this might be a problem and
>after some thought, came up with an idea.
>
>What if we mount the (cartridge) filter vertically, with a removable
>solid canister attached to the bottom end? The can would only need to
>handle a liter or two of dust at the most. Clean the filter periodically
>by spraying the outside with compressed air. The fine dust should fall
>into the can, which would be removed and emptied "after the dust settles"
>(G).
>
>IF this arrangement works, I do see a couple of drawbacks. A big one is
>that it takes more potentially otherwise usable shop space to mount the
>filter vertically, as opposed to horizontally near the ceiling. Plus,
>it requires access to all sides of the filter, which exacerbates the
>space problem. It also adds another 90-degree turn to the ducting. At
>first blush, the potential advantages would seem to outweigh the obvious
>drawbacks, at least to me.
>
>Anybody have any thoughts on this? Have you seen it before -- or even
>better -- have you tried it?
>
>Jim
So, are you're talking about a cross between canister filter and shaker
bags?
IIRC, some of the Oneida units have the filter in that sort of arrangement.
Of course the Jet canister filters do essentially the same thing except they
use a flapper of some sort to scrape the dust off the inside of the filter.
I wouldn't worry too much about another 90 degree bend after the blower; it
can be a gentle bend in bigger pipe than used for the input duct. And it's
hard to do much better anyway. Whether it uses more space or less space
depends on the shop. For my cyclone, I've got the filters mounted vertically
above head height.
Bob S
On Mon, 24 Nov 2003 02:07:16 GMT, Steve Knight <[email protected]> wrote:
>I don't think mine has them. just the extended air inlet and the pipe going down
>the middle. the newer design.
>but remember I make far more fine dust then most people do. so for most they
>would go far longer between cleaning. mine does a fantastic job of separation.
>but when working tropicals like I do and like padouk I really make a lot of very
>fine dust.
>
That sounds like a neutral vane. That's where the inside of the air inlet
extends to the vortex finder (that's the pipe in the middle). A neutral vane
has about the same impact on the pressure drop and the separation efficiency
as an air ramp but it's a lot easier to fabricate. I didn't know that Bill
had changed his design. The last time I looked, his design used an air ramp
(a spiral ramp from the top of the inlet that goes around once and meets the
bottom of the inlet from the side).
>(G) it does not drop much but even a little bit will let some of the fine dust
>escape that I don't want out. it does not really need cleaned yet.
>
>>How big a blower do you have? And how do you decide that your filter
>>needs cleaning? Did you build a manometer? Or do you just notice the
>>airflow is low?
>
>right now I am using the one from my jet 2hp DC 12" I want to upgrade it to a
>14" My piping got a bit weird when I changed from the jet to the cyclone. Bill
>Pentz made mine and sent it to me.
> I know it need cleaning when I start smelling fine dust from cuts. I usually
>would get a 55 gallon can of fine dust and planer shavings between cleaning. no
>bulky shavings for me (G) all fine stuff.
>
>
>--
>Knight-Toolworks & Custom Planes
>Custom made wooden planes at reasonable prices
>See http://www.knight-toolworks.com For prices and ordering instructions.
It sounds like you might be right on the edge of not having enough air flow.
Those planes you make must be really sharp to make shavings that fine. :-)
Just smell it. That's how you know it needs cleaning. I like those simple
solutions. My dust capture isn't good enough for that; I really need an
overarm guard.
Bob S
On Sat, 22 Nov 2003 03:58:10 GMT, Jim Wilson <[email protected]> wrote:
>Bob Summers provided some more food for thought on cyclone DC's...
>
>Bob, just in case no one else responds...please don't be discouraged from
>posting on the topic.
>
>I, for one, have been carefully devouring all your posts on cyclones. It
>is my very next shop project, and the information from you (and Bill
>Pentz (!)) have been immensely helpful to me.
well I have been testing Bill Pentz's design and I know it works very well. I
get about 2 to 3 weeks between cleaning the filter. I only loose a little
airflow. but i make so much fine dust and that's what a cyclone misses. I get a
couple of coups of very fine dust out. the stuff will float all over my shop
when I clean the filter. more like smoke then dust.
I have more airflow with his design then I did with my regular bag setup and
a huge felt bag.
--
Knight-Toolworks & Custom Planes
Custom made wooden planes at reasonable prices
See http://www.knight-toolworks.com For prices and ordering instructions.
Bob Summers provided some more food for thought on cyclone DC's...
Bob, just in case no one else responds...please don't be discouraged from
posting on the topic.
I, for one, have been carefully devouring all your posts on cyclones. It
is my very next shop project, and the information from you (and Bill
Pentz (!)) have been immensely helpful to me.
If you don't stimulate a lot of discussion, it's only because so few
other folks have anything to add! (G)
Thanks,
Jim
Bob Summers wrote...
>
> One paper, (Funk, Hughs & Holt. Engineering and Ginning: Entrance
> Velocity Optimization for Modified Dust Cyclones. Journal of Cotton
> Science 4:178-192 (2000) ) found that modified 1D3D cyclone got the
> best separation performance with an input velocity of around 2,600 feet
> per minute. That was also the lowest input velocity tested, though
> looking at their graph, it looks like the best collection efficiency is
> around 2,600 ft/min. The collecion efficiency peak is very broad.
Is that paper available online? I have read at least one Funk, et al,
paper, but I don't remember the info you are citing here.
A transport velocity of 2600 fpm seems too low to prevent settling in the
main trunk, even for horizontal runs. That probably explains why they
didn't test at lower speeds.
Jim
Steve Knight wrote...
> but i make so much fine dust and that's what a cyclone misses. I get a
> couple of cups of very fine dust out. the stuff will float all over my shop
> when I clean the filter. more like smoke then dust.
Yeah, and that's the bad stuff. I wondered if this might be a problem and
after some thought, came up with an idea.
What if we mount the (cartridge) filter vertically, with a removable
solid canister attached to the bottom end? The can would only need to
handle a liter or two of dust at the most. Clean the filter periodically
by spraying the outside with compressed air. The fine dust should fall
into the can, which would be removed and emptied "after the dust settles"
(G).
IF this arrangement works, I do see a couple of drawbacks. A big one is
that it takes more potentially otherwise usable shop space to mount the
filter vertically, as opposed to horizontally near the ceiling. Plus,
it requires access to all sides of the filter, which exacerbates the
space problem. It also adds another 90-degree turn to the ducting. At
first blush, the potential advantages would seem to outweigh the obvious
drawbacks, at least to me.
Anybody have any thoughts on this? Have you seen it before -- or even
better -- have you tried it?
Jim
Larry C in Auburn, WA wrote...
> I can't tell if you're being serious or joking because many (most?) systems
> are just as you describe
No, not joking, just ignorant. Believe it or not, I haven't seen one
configured like that until your link. I feel a little sheepish, but also
encouraged -- at least the idea is confirmed. Thanks for the reference.
Cheers,
Jim
On Sun, 23 Nov 2003 15:54:08 GMT, Jim Wilson <[email protected]> wrote:
>What if we mount the (cartridge) filter vertically, with a removable
>solid canister attached to the bottom end? The can would only need to
>handle a liter or two of dust at the most. Clean the filter periodically
>by spraying the outside with compressed air. The fine dust should fall
>into the can, which would be removed and emptied "after the dust settles"
>(G).
this is about what I have I have a 8" lid on the bottom. I hit the filters with
my air house and dump the lid. I get one full lid and a couple of lesser. not
much escapes anymore but a little does. the way to stop it would be to blow then
wait a few minutes and dump it.
the best way is to put a hose or pipe on it run it outside turn on your system
and blow out the cartridges. one fellow has done this. but I don't have access
to the outside.
--
Knight-Toolworks & Custom Planes
Custom made wooden planes at reasonable prices
See http://www.knight-toolworks.com For prices and ordering instructions.
>BTW, your postings have convinced me that cannister filters are so much
>better that it's not worth looking at fabric filters.
they work so well two of the right ones will not restrict air flow at all. I can
take the endcap off of mine and little air comes out the end.
>If the numbers from the paper I mentioned above are correct, then without the
>air ramp and neutral vane you'd only have to clean the filter every
>six to nine weeks instead of every two to three weeks. To me that would
>be a worthwhile improvement!
I don't think mine has them. just the extended air inlet and the pipe going down
the middle. the newer design.
but remember I make far more fine dust then most people do. so for most they
would go far longer between cleaning. mine does a fantastic job of separation.
but when working tropicals like I do and like padouk I really make a lot of very
fine dust.
>OTOH, if your airflow dropped low enough you'd just not collect the
>dust in the first place and you'd never have to clean the filter. :-)
(G) it does not drop much but even a little bit will let some of the fine dust
escape that I don't want out. it does not really need cleaned yet.
>How big a blower do you have? And how do you decide that your filter
>needs cleaning? Did you build a manometer? Or do you just notice the
>airflow is low?
right now I am using the one from my jet 2hp DC 12" I want to upgrade it to a
14" My piping got a bit weird when I changed from the jet to the cyclone. Bill
Pentz made mine and sent it to me.
I know it need cleaning when I start smelling fine dust from cuts. I usually
would get a 55 gallon can of fine dust and planer shavings between cleaning. no
bulky shavings for me (G) all fine stuff.
--
Knight-Toolworks & Custom Planes
Custom made wooden planes at reasonable prices
See http://www.knight-toolworks.com For prices and ordering instructions.
>That sounds like a neutral vane. That's where the inside of the air inlet
>extends to the vortex finder (that's the pipe in the middle). A neutral vane
>has about the same impact on the pressure drop and the separation efficiency
>as an air ramp but it's a lot easier to fabricate. I didn't know that Bill
>had changed his design. The last time I looked, his design used an air ramp
>(a spiral ramp from the top of the inlet that goes around once and meets the
>bottom of the inlet from the side).
Ok I was not sure what it is called. you have it right. it is a pretty effient
design. I get very good airflow.
>
>It sounds like you might be right on the edge of not having enough air flow.
I have great flow using the blower I have. my pipe is a bit weird as I had it
centered in the middle of my tools but then it got moved back into the corner
and the pipe is a bit weird now. it just costs too much to change it. it will be
cheeper and easier to put a 14" blower on the cyclone.
but I bet I have better airflow then most. it's just that I make finer dust
then most.
>
>Those planes you make must be really sharp to make shavings that fine. :-)
>
>Just smell it. That's how you know it needs cleaning. I like those simple
>solutions. My dust capture isn't good enough for that; I really need an
>overarm guard.
the real challenge is to get the dust caught in the first place. most of my
tools needed mods. my delta 14" bandsaw has a 4" hole in the door. my jet 6x48"
and disc sander had two 4" hoses on it on on each tool. I had to seal the
original ports as they were worthless.
my yet 6x89 edge sander has a 6" hose and a 4" hose on the end. my tablesaw
has a 4" hose on bottom and a modified overarm guard with a 4" hose. everything
has 6" as close to the tool as possible.
--
Knight-Toolworks & Custom Planes
Custom made wooden planes at reasonable prices
See http://www.knight-toolworks.com For prices and ordering instructions.
I can't tell if you're being serious or joking because many (most?) systems
are just as you describe such as:
http://www.pennstateind.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=PSI&Product_Code=TEMP142CX&Category_Code=CYTEMP14
--
Larry C in Auburn, WA
"Jim Wilson" <[email protected]> wrote in message
news:[email protected]...
> Steve Knight wrote...
> > but i make so much fine dust and that's what a cyclone misses. I get a
> > couple of cups of very fine dust out. the stuff will float all over my
shop
> > when I clean the filter. more like smoke then dust.
>
> Yeah, and that's the bad stuff. I wondered if this might be a problem and
> after some thought, came up with an idea.
>
> What if we mount the (cartridge) filter vertically, with a removable
> solid canister attached to the bottom end? The can would only need to
> handle a liter or two of dust at the most. Clean the filter periodically
> by spraying the outside with compressed air. The fine dust should fall
> into the can, which would be removed and emptied "after the dust settles"
> (G).
>
> IF this arrangement works, I do see a couple of drawbacks. A big one is
> that it takes more potentially otherwise usable shop space to mount the
> filter vertically, as opposed to horizontally near the ceiling. Plus,
> it requires access to all sides of the filter, which exacerbates the
> space problem. It also adds another 90-degree turn to the ducting. At
> first blush, the potential advantages would seem to outweigh the obvious
> drawbacks, at least to me.
>
> Anybody have any thoughts on this? Have you seen it before -- or even
> better -- have you tried it?
>
> Jim