Cyclone Design...why are there straightening vanes in the air outlet tube?

[Tom Lange]

I recently acquired a used Jet DC3 for a good price. One thing I don't understand is why there are crossed straightening vanes in the tubular guard or air outlet tube? I have some experience with industrial cyclones and this tube is where the smaller diameter vortex is that determines the separation efficiency for small particles e.g. 10 microns etc. But with our fans separate we never had anything INSIDE the tube.

I can see these vanes as useful for straightening the flow into the fan inlet...which is directly on top of the cyclone? Did the designers trade off fan performance for cyclone efficiency?

tom

[Wade Lippman]

You know what you get when you search on "Jet DC3"?
You might want to include a picture of what you are inquiring about.

[Jim Neeley]

Jet DC3? Penn State made a dust collector model DC3 that's a centrifugal fan shooting into a filter bag but there's no cyclone. Likewise, Google can't find it (and we all know Google knows *everything*! <g> )

Jet currently makes a 650, 100 and 1200 series for woodworking and a 500 series for metal, none of which are cyclones.

Could you have made a type? Also, pictures would be helpful.

Jim

[Michael W. Clark]

If I understand correctly, you have straightening vanes in the outlet tube? The only reason I could see for those is if the fan is rotating opposite the cyclone rotation.
Mike

[Tom Lange]

My Bad Jim... did make a typo.
... it is a Jet Dust Collection System Model JC-3... JC-3CF to be precise. Attached is an image of the vanes ... The image is looking at the top 1/2 of the cyclone from its bottom where the cone attaches. You can see the cross sheet metal and it goes about 1/2 way up the tube.

Tom

[Tom Lange]

I will get the hang of this yet... sorry here is the image of the vanes267356
Tom

[Tom Lange]

My bad... it was a Jet JC-3... here is an image of the straightening vanes in the outlet tube.267357
This would seem to try to straighten the flow out or break the vortex before going into the fan inlet on the top of the cyclone. But it also would seem to stop the inner vortex from spinning pretty far down in the cyclone hurting efficiency.

tom

[Michael W. Clark]

Based on the images I saw when I did a search, the fan and cyclone are spinning in the same direction, which is good. I'm with you, don't see the need for the vanes. They certainly don't help the efficiency and are something else to wear out.
Mike

[Wade Lippman]

Those are just below the impeller? I bet they are just to keep stuff out of the impeller; though nothing big should get that far.

[Phil Thien]

Based on the images I saw when I did a search, the fan and cyclone are spinning in the same direction, which is good. I'm with you, don't see the need for the vanes. They certainly don't help the efficiency and are something else to wear out.
Mike

They actually still improve airflow, even when the blower and cyclone spin in the same direction.

[Tom Lange]

Yes, they are just below the Impeller on the suction side.

I can see how they would both protect the fan from big stuff... Especially strings etc. I also could see how it would improve fan performance, and airflow, by stopping the inner vortex before going into the fan.

What I am wondering is how much it hurts efficiency on separating fine dust. Is that why it came with such a big cartridge filter...20" diameter and 5' tall, for a 3hp 1450 cfm 2 "wg?

Does anyone that have this model have trouble with too much 'large' dust carryover into the cartridge?

Seems like a nice unit. I cannot test it yet as my shop is still under renovation--moving from my basement to my garage. That is another thread for another day.

Tom

[Phil Thien]

What I am wondering is how much it hurts efficiency on separating fine dust.

Should have zero effect on separation.

[Michael W. Clark]

They actually still improve airflow, even when the blower and cyclone spin in the same direction.
Respectfully disagree.

[Michael W. Clark]

Should have zero effect on separation.
If it weakens the vortex, separation is negatively affected.

[Phil Thien]

Respectfully disagree.

"Swirl or Vorticity: Inlet swirl, or vorticity, is a frequent cause of reduction in fan performance. If the spin is imparted in the direction of wheel rotation, a situation corresponding to the use of inlet vanes arises: the fan volume, pressure, and power are lower than expected. if the air spin is counter to the wheel rotation, the volume and static pressure will be greater than expected and the brake horsepower will also be greater. In either case, spin always reduces efficiency. These conditions are readily overcome by installing vanes and a splitter at the fan inlet, as is graphically shown in Fig. 2." (Reference: http://www.krugerfan.com/brochure/publications/Tbn010.pdf)

"The spinning air exiting the cyclone affects the fan performance. In this case, the spin was in the direction of the wheel rotation, lowering the static pressure, flow rate, and horsepower. If the spin were opposite wheel rotation, static pressure and flow rate would increase with a dramatic increase in horsepower and reduction in fan efficiency." (Reference: http://www.banksengineering.com/Fan%20Troubleshooting%20ED100.pdf)

If you need more references they can be dug-up at my forum. Data is also available from Cincinnati Fan as well as others.

[Phil Thien]

If it weakens the vortex, separation is negatively affected.

It doesn't weaken the vortex, if anything it modifies the shape, intensifying it.

[Tom Lange]

We are getting to the guts of it.

Phil, i think you you are right and your references are helpful that the vanes are there to improve fan performance. That matches my own industrial experiences with large fans (300 HP), we always wanted a long straight inlet to the fan or straightening vanes. Since our fans were always separate from our cyclones (also big 10' diam and 30' tall) we did not have this problem that the compact design seems to create. Our outlet tubes (we called them tubular guards) were always free of any internal obstructions. That is why I was surprised when I got this thing taken apart for transport.

If the INNER vortex...not the outer one that runs along the large diam wall and cone... Is some how interfered with down near where the outer vortex inverts to the inner one-- then separation efficiency for the very small particles will be hurt. These particles are the ones where the forces from spinning in the outer vortex are not strong enough to get the particles through the air to contact the outer wall slowing them down. In my experience ... the smaller diameter inner vortex determines the separation efficiency...it spins faster...e.g. Tighter, and can push the particle into the outer vortex (folklore had it this happened down in the cone) and improve it chance to make it to the wall versus get carried up the air exit tube.

Doing a CFD calc ( something that itself is probably more costly than 3 brand new systems! ) would probably settle it, and may have to include the fan wheel which would be very complicated. I wonder if Jet or whoever designed it?.. ever did that? The rest of the cyclone's proportions seem well matched to the air ratings.

Good discussion though thanks for the input.
Tom

[Aleks Hunter]

WHen you say you always wanted a long straight inlet, How long do you mean, is there a rule of thumb for inlet diameter vs. length of straight run?

Thanks

[Tom Lange]

Aleks,
My memory was you need at least 4 inlet diameters after any disturbance like an elbow etc. So, if you have an 8" inlet, you would need at least 32" of a straight run before the fan inlet. If I had my old Fan Engineering manual ( it was small and black like a bible), I could look it up but I heard it was out of print and I don't have it anymore. With CFD so prevalent no one uses The old rules of Thumb any more...probably a good thing.

Tom

[Michael W. Clark]

Phil,
I don't disagree with your point about system effect on the fan. Like the reference states, inlet vane dampers or "cat's eye" dampers use this theory to reduce the fan flow and conserve HP. However, given the small size of the cyclone and fan (approximately 1/15th of the one in the TCF bulletin), any improvement in airflow due to the straightening vanes is going to minimal, if at all measurable. There are many other factors that are going to affect the flow in a much greater way. We generally do large cyclones as well. We are starting up one of our cyclone systems next month that has a quad arrangement (4 cyclones in parrallel), each cyclone is 50 feet tall and the system fan is 400HP. No turning vanes in the outlet pipes or flow straighteners, guaranteed performance of the cyclones. We used an inlet box on the fan inlet so the fan vendor would account for this system effect. Inlet boxes have a known system affect along with inlet elbows, outlet elbows, and inlet/outlet ductwork. If you have system effect factors on pre-spin air, I would like to see them as they may be useful. We have supplied some smaller cyclones in the past with vertical mount fans, no straightening vanes, and no performance issues. I would say that TCF probably supplied a large number of these fans and they design vertical mount fans for some of our scrubbers. Again, no straightening vanes in those either and they have cyclonic separators.

IMO, the straightening vanes were added for marketing. This is a retail, off-the-shelf cyclone system. They can test it without inlet duct or filters and rate it higher if there is any gain in volume. Thus giving them a marketing edge over their competitor. Since this is a light commercial / home-hobby unit, abrasion is not a consideration. An industrial cyclone on wood dust must be constructed to resist abrasion and is often constructed of abrasion resistant materials or uses linings in wear prone areas. The outlet pipe is one of the major wear areas. Anything you put inside that is required for performance, will be a problem later and could result in loss of product or non-compliance with environmental requirements. This, the added pressure drop, and expense is the primary reasons that straigheners are usually avoided if at all possible.

Mike

[Michael W. Clark]

It doesn't weaken the vortex, if anything it modifies the shape, intensifying it.

Intensifying the vortex requires a higher velocity in the outlet pipe. A measurable efficiency gain requires a significant increase in velocity and therefore substantially more energy (pressure drop). If the flow increased by 10-15% as claimed in the TCF bulletin, you would not be able to measure the increased efficiency due to the slightly stronger vortex. The vanes in the outlet pipe only have the potential to disrupt the natural flow patterns of the vortex. If you had the 10-15% flow increase, you would see more efficiency attributed to the increased centrifugal force being applied in the body and cone of the cyclone, not due to a stronger vortex. This is simply not enough of a velocity increase in the outlet to have a significant, measurable effect.

I have run efficiency calcs that significantly increase the pressure drop of the cyclone through intensifying the vortex, only to yeild efficiency gains in the fractions of a percent. Of course this is cyclone and application dependant. The OP's cyclone is relatively small collecting wood dust which is considered coarse by most of the particulate dealt with in industry. The small cyclone on a small flow with coarse material is going to be very efficient. Most of the larger particles are easily collected. Since there are very few small particles, additional efficiency gains require considerably more effort. Pressure drop and centrifugal force play less of a role in fine particulate colletion. You need to allow more time in the cyclone for the fine particulate to move to the outside wall where it can be collected.

I think the biggest downfall of the home system setups is that there is no space below the cone for the dust to disengage from the vortex. The collection barrel is fine until the dust level gets too close to the bottn of the cone, then it is re-entrained and sent over to the filters. This is always happening on some level as the barrel fills, but becomes quite evident when the fills to the bottom of the cone and beyond. The finer the particulate, the more likely it will be re-entrained.

Mike

[Phil Thien]

I don't disagree with your point about system effect on the fan. Like the reference states, inlet vane dampers or "cat's eye" dampers use this theory to reduce the fan flow and conserve HP. However, given the small size of the cyclone and fan (approximately 1/15th of the one in the TCF bulletin), any improvement in airflow due to the straightening vanes is going to minimal, if at all measurable.

The improvements are proportional. That is, making the changes on a small (home hobbyist) system should yield the same percentage gain as on a larger industrial cyclone.

Yes, the #'s are smaller. But the home hobbyist is the guy that doesn't have any CFM to spare. Making a change to a cyclone that provides a 10 to 15% improvement in FPM may result in meaningful improvements, especially when it is already operating at the margins of what is acceptable for fine dust collection.

And it can allow the motor to work less hard, consuming less energy. And it costs nearly nothing to implement.

I don't agree w/ your assertion that it was added for marketing. As much as it pains me to say anything positive about Jet or WMH, LOL, it is a good design feature and I think they should be commended for it.

[David Kumm]

Michael. if a company ( I'm thinking Clearvue because of the ability to mold PTEG ) offered an add on vortex breaker for those with the ceiling room, could that improve efficiency with fines or would each unit need to be specifically designed for each cyclone. With sanders becoming more and more a home shop machine, dust in the cartridges is becoming more of a problem. Steel cyclones are expensive to modify for fine dust but a " plastic add on vortex breaker " should be affordable if it actually accomplishes something. Dave

[Phil Thien]

Intensifying the vortex requires a higher velocity in the outlet pipe. A measurable efficiency gain requires a significant increase in velocity and therefore substantially more energy (pressure drop). If the flow increased by 10-15% as claimed in the TCF bulletin, you would not be able to measure the increased efficiency due to the slightly stronger vortex. The vanes in the outlet pipe only have the potential to disrupt the natural flow patterns of the vortex. If you had the 10-15% flow increase, you would see more efficiency attributed to the increased centrifugal force being applied in the body and cone of the cyclone, not due to a stronger vortex. This is simply not enough of a velocity increase in the outlet to have a significant, measurable effect.

Respectfully disagree.

I want the vortex BELOW the tube, not IN the tube.

And I'm not saying the improvement in separation is going to be "significant." I'm saying these changes can and only will increase separation rates, they won't decrease them.

That is, adding straighteners doesn't make small improvements to airflow at the expense of separation. Straighteners yield small improvements in airflow, and if anything, improvements in separation as well.

[Phil Thien]

I forgot to mention, BTW, that straighteners also reduce noise.

All this stuff I'm reporting, BTW, was first brought to MY attention by a gentleman that goes by the handle of retired2 at my forum. He is a retired engineer that found straighteners added to this Thien-based separator increased FPM (approx. 10%, up to 15% when used in conjunction with a bell mouth). The straighteners also reduced motor draw and system noise, as well. My own experimentation (and reading, of course) has confirmed this.

Separation rates are tricky to measure with the equipment I have. But they certainly haven't worsened.

[Michael W. Clark]

Michael. if a company ( I'm thinking Clearvue because of the ability to mold PTEG ) offered an add on vortex breaker for those with the ceiling room, could that improve efficiency with fines or would each unit need to be specifically designed for each cyclone. With sanders becoming more and more a home shop machine, dust in the cartridges is becoming more of a problem. Steel cyclones are expensive to modify for fine dust but a " plastic add on vortex breaker " should be affordable if it actually accomplishes something. Dave

Yes, but the issue is with ceiling height. If you blow the nominal 8' mark, your market is more limited. You can accomplish the same thing by not filling the bin to the bottom of the cone.

[Michael W. Clark]

The improvements are proportional. That is, making the changes on a small (home hobbyist) system should yield the same percentage gain as on a larger industrial cyclone.

Yes, the #'s are smaller. But the home hobbyist is the guy that doesn't have any CFM to spare. Making a change to a cyclone that provides a 10 to 15% improvement in FPM may result in meaningful improvements, especially when it is already operating at the margins of what is acceptable for fine dust collection.

And it can allow the motor to work less hard, consuming less energy. And it costs nearly nothing to implement.

I don't agree w/ your assertion that it was added for marketing. As much as it pains me to say anything positive about Jet or WMH, LOL, it is a good design feature and I think they should be commended for it.

The motor is working harder, reference your TCF example. The BHP went up. More air is being pulled at a higher pressure, and the fan is more efficient, but it is requireing more BHP/CFM. The increase in DP is more than the increase from flow, there is at least an addition 1" of SP required and one can only assume this is from the vanes. Even though the fan curve has shifted up due to a higher efficiency, they are at an operating point that is higher on the fan curve. The higher up the curve you move, the closer you get to an unstable operating point.

[David Kumm]

Yes, but the issue is with ceiling height. If you blow the nominal 8' mark, your market is more limited. You can accomplish the same thing by not filling the bin to the bottom of the cone.

So if you have a 2' length of flex from the cone to the drum, you are effectively creating your own vortex breaker and it doesn't really need to expand the diameter of the cone again? I run a long length of clear flex and the dust and air is spinning like crazy inside it. Dave

[Michael W. Clark]

Respectfully disagree.

I want the vortex BELOW the tube, not IN the tube.

And I'm not saying the improvement in separation is going to be "significant." I'm saying these changes can and only will increase separation rates, they won't decrease them.

That is, adding straighteners doesn't make small improvements to airflow at the expense of separation. Straighteners yield small improvements in airflow, and if anything, improvements in separation as well.

I am saying the increased efficiency due to a stronger vortex that results from a 10-15% flow increase will not be measurable. You are talking about efficiencies on the 1/10 of a % scale or less. There will be more efficiency improvement in the body of the cyclone due to the increased centrifugal force than from the increased vortex (notice this also has a pressure drop associated with it). If you are trying to collect fine material by applying brute force (pressure drop), you will be limited on the collection efficiency you can acheive.

[Michael W. Clark]

So if you have a 2' length of flex from the cone to the drum, you are effectively creating your own vortex breaker and it doesn't really need to expand the diameter of the cone again? I run a long length of clear flex and the dust and air is spinning like crazy inside it. Dave

It probably spins all the way to the drum, correct? The vortex extends much farther down than most people realize. The hose helps and it makes it much harder to pull the dust back up into the cyclone. A properly designed receiver is better and would require less headroom than a hose or pipe providing the same function.

[David Kumm]

It probably spins all the way to the drum, correct? The vortex extends much farther down than most people realize. The hose helps and it makes it much harder to pull the dust back up into the cyclone. A properly designed receiver is better and would require less headroom than a hose or pipe providing the same function.

So, would a properly design receiver be something a company could produce as an aftermarket add on that would make sense in conjuction with a drum or widebelt usage on a cyclone?

To PHil's example, what % of increase in cfm or fpm could be attributable to the addition of the bell mouth? My understanding was that a bellmouth inlet added significant enough flow that most units were tested with one for purposes of marketing claims. Dave

[Michael W. Clark]

So, would a properly design receiver be something a company could produce as an aftermarket add on that would make sense in conjuction with a drum or widebelt usage on a cyclone?

To PHil's example, what % of increase in cfm or fpm could be attributable to the addition of the bell mouth? My understanding was that a bellmouth inlet added significant enough flow that most units were tested with one for purposes of marketing claims. Dave

David, Yes, the reciever could be added later provided headroom exists. You would want to keep it installed all the time. No harm in having it on planer, shaper, jointer applications either.

A bellmouth hood entry loss factor is about 0.04VP. A plain end duct hood entry loss factor is about 0.93VP. A duct with a 4000 FPM (VP=1"wg) velocity and having a plain opening (round duct end) will have a hood entry loss of about 1.93"wg (1" of loss is added as an acceleration factor to get the air from 0 FPM up to the duct velocity). The same duct with a bell mouth will have a loss of about 1.04"wg. If the duct is connected to a flat plate (table saw cabinet), you have an entry loss factor of 0.5 or hood static pressrue of 1.5"wg assuming 4000 FPM duct velocity. The bell mouth absolutely affects system losses and therefore fan operating point. Even though you have reduced the losses, you are pulling more CFM and usually more BHP or amp draw.

[Phil Thien]

The motor is working harder, reference your TCF example. The BHP went up. More air is being pulled at a higher pressure, and the fan is more efficient, but it is requireing more BHP/CFM. The increase in DP is more than the increase from flow, there is at least an addition 1" of SP required and one can only assume this is from the vanes. Even though the fan curve has shifted up due to a higher efficiency, they are at an operating point that is higher on the fan curve. The higher up the curve you move, the closer you get to an unstable operating point.

I did not say "always," I said "can." In the case of retired2 (at my site), he found adding straighteners reduced motor draw while also increasing airflow:


"What I've since discovered is that it isn't an aberation at all, but rather it is part of a consistent pattern that shows the addition of an air straightener allows the fan to move more air with fewer amperes. If you go back to my test data and compare the numbers for a given test without the air straightener to the same test with the air straightener, you will see that in every case the fan is moving more air with fewer amps when the air straightener is installed. So, if your DC is marginally powered for your system, as mine is, milking every last ounce of performance out of the fan is important." Reference: My forum, which I cannot link here. PM me if you need links.

[Phil Thien]

I am saying the increased efficiency due to a stronger vortex that results from a 10-15% flow increase will not be measurable. You are talking about efficiencies on the 1/10 of a % scale or less. There will be more efficiency improvement in the body of the cyclone due to the increased centrifugal force than from the increased vortex (notice this also has a pressure drop associated with it). If you are trying to collect fine material by applying brute force (pressure drop), you will be limited on the collection efficiency you can acheive.

I never said the improvement would be dramatic. I merely said separation would be increased, not decreased.

Small increases are still increases.

More is better.

[David Kumm]

I'm interested in knowing what a properly designed receiver would look like. How could it be built? Dave

[Michael W. Clark]

The dimensions are relatively simple but I cant give them out for proprietary reasons. Ive been told they are on the internet, maybe even on our site somewhere.
Mike

[Tom Lange]

It is an interesting catch 22. You work really hard to move as much air away from your woodworking device ... to carry away not just the chips and shreds but the fine dust as well...only to have that dust escape the cyclone. Provided the cartridge filter works (as I said it seemed pretty big... rated for 2 microns and is 10 " diameter and 5' tall) that is a trade off well worth making. However, if that bag below the cartridge becomes filled up with more than a gallon of fines per hour of shop use ... I don't know if I like the trade off. When I picked up the unit there were too many 'larger particles' in that bag for my taste. Does anyone else out there have any experience ? Especially with sanding... 100 to 150 grit? Cutting out the vanes is strongly on my mind, but with everything painted that is something I won't be able to weld back easily if the unit does not function. I am just building my shop and upgrading from a 1HP Penn State DC (4" through a trash can ... essentially a chip collector) that was in my basement shop.

[Wade Lippman]

When I picked up the unit there were too many 'larger particles' in that bag for my taste. Does anyone else out there have any experience ?

For the 10th time, if you are getting a gallon of fines per hour and any large particles, you have a serious problem.
Almost certainly a leak, but if you have absolutely ruled that out, I suppose it might be worth a try to cut the vanes out. I doubt they are the problem, but they probably don't help much.

[Tom Lange]

One of the things we did with our cyclones to prevent re-entrainment ... something we used to have a lot of issues with build-up in the 'throat' was to put something we used to call a 'Chinese hat'. Not the most politically correct in todays world... but it was almost exactly the angle of the cone. Is this what people call a 'vortex breaker' today'? I know those cyclones are still in use today after 30 plus years. The cone 'reflected' the inner vortex back up the tube keeping the area at the throat discharge 'quiet' from turbulence and allowed material that slid down the wall and dropped below that hat to be separated. We used those is really short cyclones where we could not put in the really tall ones. It worked surprisingly well. I have not seen that in any hobby cyclones? Come to think of it... if there is still a vortex in the collection drum because of a really short discharge pipe before the drum... you could add it to the lid of a 55 gal drum or fiber drum. Tom

[Tom Lange]

I have a question on % efficiency you guys are talking about. Are you guys talking mass % of the total stream or a particle count efficiency? In other words, # of 10 micron particles separated divided by the # of 10 micron particles in the incoming air stream. Is that what you guys are saying will only improve by 1/10 of a %? Or are you talking lbs. of dust separated (all particle sizes) divided by the total lbs. of dust in the incoming air stream? I completely agree that if you have only fractions of a % change on a particle basis, then the 'more airflow' from 'straightening vanes' is a MUCH better tradeoff. On the other hand...on the lbs of dust basis... I just don't know it is the single digit micron dust that we are really trying to get out. Without straightening vanes...I know that increased pressure drop will occur across the cyclone as a square of the inlet airflow anyway and the separation efficiency should also go up for the really small particles because the inner vortex will be spinning faster. I would expect the pressure drop through the cyclone with straighten vanes to be higher, at the same airflow, then without them? Is that wrong? Or is it that the vanes 'stop the vortex' at the same airflow and reduce the pressure drop. Tom

[Tom Lange]

I would want the vortex below the tube as well... but it seems hard to imagine that you could have no vortex and then 1 inch later have a fully developed one. I am worried that it kills the inner vortex all the way to bottom. We used to see material contact the inside of the outlet tube so I know it was a wall that contacted dust and slowed particles down ... if they had enough gravity to work their way down that tube wall and back into the bigger diameter you could still capture them. If you just fed in fines from a sander and nothing else you could get a sense of that. Maybe wood dust is so light sp. gr. that it changes this thinking. We used to believe that the other larger particles help the efficiency which is why efficiency experiments are probably hard to do. Koch and Licht published a good paper on efficiency curves, where they used pretty good methods IMO, in the late '70's, but that reveals how long it has been since I have been in this game. tom

[Michael W. Clark]

Hi Tom
I've heard of the china hats you mention but Im not familiar with their application. What I was referring to is another chamber below the cone to allow the dust to disengage and the clean gas to turn and go back up the center of the cyclone.

The efficiency I was referring to is % weight. The small cyclone is inherently very efficient on the coarse dust, 20-30 micron. The smaller single digit micron dust takes a lot of energy or a larger cyclone to see a noticable efficiency improvement.

My thinking is in line with yours on the inner vortex formation. If you eliminate it in the outlet tube, there would likely be an effect below the outlet tube.

I think Wade is likely correct on the leaking. While I don't think the vanes help, I don't think they would disrupt the efficiency as much as you are experiencing. Also make sure there are no interior ledges when you put the body back together. It should be lined up properly.

[Phil Thien]

I would want the vortex below the tube as well... but it seems hard to imagine that you could have no vortex and then 1 inch later have a fully developed one. I am worried that it kills the inner vortex all the way to bottom. We used to see material contact the inside of the outlet tube so I know it was a wall that contacted dust and slowed particles down ... if they had enough gravity to work their way down that tube wall and back into the bigger diameter you could still capture them.

My experience has been that once something is entrained in the air mass in the finder, it is nothing getting out.

BTW, how were you seeing stuff contact the inner walls of the vortex finder? Were you working with separators made from transparent material?


If you just fed in fines from a sander and nothing else you could get a sense of that. Maybe wood dust is so light sp. gr. that it changes this thinking. We used to believe that the other larger particles help the efficiency which is why efficiency experiments are probably hard to do. Koch and Licht published a good paper on efficiency curves, where they used pretty good methods IMO, in the late '70's, but that reveals how long it has been since I have been in this game. tom

[Tom Lange]

It left smear marks ... We were working with a material that was not a liquid, but when it contacted a surface at high speed it would leave part of itself behind. We called it 'make up' but it would accumulate to a certain thickness and the abraid away.
tom