J. Phil Thien's Projects

Retired2,
You are correct, I am not being nearly as clear as I should be. Also important to note that the box store bends HAVE BEEN MODIFIED TO REACH THIS RESULT. I may not have made that clear enough either.
Also important to note that while the pic is of the short-radius bend THIS MAY NOT BE THE FINAL ASSEMBLY. This is during testing! That's why I haven't been posting pics yet...
Everyone in the shop was very surprised at the resultant airflow difference after what seemed like such a simple change. And we did test the short radius, long radius and the custom sweep to compare each. One thing that we have not finished testing yet is the effect of the short-radius vs long radius being so close to the blower. We want to know what differences (if any) there are on blower sheer compared to the distance the elbow is from the blower itself. It appears at this point that it is much more important to keep the air stream smooth coming into the bend initially; whether or not this solves that issue is still undetermined.

I would very much appreciate some feedback from you regarding real-world performance of your cyclone with the bellmouth installed. We did an initial flow test with one of the custom heat-blanket-formed bellmouths, and apparently the pipe had a crack in the inlet bend which failed. Since we didn't have another one made we decided to cut off the bellmouth such that the inlet was now more of a simple "flare" of approximately 45 degrees. When we tested it on the bench we found some minimal increase vena contracta as expected..... BUT.... BUT.... the cyclonic air action was much more circular and stayed closer to the perimeter of the cyclone.
This doesn't show up as any sort of volume/cfm/load change, but it could indicate a more (or maybe less!) efficient cyclonic separation, especially for fine light dust and the such.
So, putting all test numbers aside, did you happen to take notice of how the material moved around in your cyclone with and without the bellmouth? The design we are working with will allow quick-change of the inlet pipe, so we can real-world test different designs if there seems to be a benefit.
... after proofreading this post I have come to the realization that I need to get a life... :P

Ah Retired2,
I did not explain myself very well... :o
First let me explain what i mean when i say "modeling" vs "testing":

• When i say "modeling" we are running whatever part(s) through a computer simulation. This is awesome, but is not always able to take every odd thing that could change the outcome into account. For instance I continuously wonder what larger debris in the airstream will do.
  
• When I say "testing" (or sometimes "flow-testing") we are actually pushing air through the assembly, monitoring loss. Sometimes we also add colored smoke to the stream to see the effect. This airstream is typically generated from the flow bench and NOT from the cyclone blower, and sometimes changing the two changes the result. With the bench we can test CFM, Velocity, temperature change (friction)... we do not test amperage draw; Retired2 can attest to the fickle nature of what amp draw results tell us so we leave them out.

You are 100% correct that there is plenty of documentation in loss differences between tight and long radius bends; it is the reason we went to great lengths bending one in the first place. What we found when testing the two side-by-side after we modified the pre-made elbow was very surprising and interesting indeed.
As long as the airflow turbulence was minimal coming in to the elbows there was very little difference. Look, I'm certainly not a guru or all-knowing anything, I'm just reporting our test results.... even when they are sometimes not at ALL what we expect.
As for the elbow right at the blower- Right On! if you look at the image you will notice a short straight length of pipe; this pipe may or may not be long enough to prevent whatever turbulence the elbow introduces from fouling the blower. Haven't had the chance to test it yet, and that is why the blower is screwed to a chunk of 2x6 and not mounted on bushings yet. According to the modeling the stub that is on there should be fine if the airflow is good but when we introduce a small amount of turbulence then that stub needs to be a bit longer... or we need to address the turbulence with additional straighteners. Or something.

Keep in mind we are going at this a one big experiment; testing and challenging along the way. All this testing and fussing is why it is taking forever and a month of Sundays to get the job finished! like everyone else doing these things we're just looking for the best possible outcome for the application and restrictions at hand.
And hopefully shed some insight or helpful ideas along the way! ;D

Dusty,
Sorry for the delay in responding, work and all...  ;)
Read on for some interesting updates:
We spent two hours trying to bend a smooth radius offset 90 in a piece of 6" pipe... only to find out we could not get the bend tight enough to fit in the space we had! It was at that point one of the guys said this:

QuoteIt isn't necessarily how long the sweep is, only that it is a smooth radius.... right?

Well... RIGHT! So we took a conventional 90 degree elbow and examined the thickness of the plastic along the inner throat area; you know, where it makes the "sharp" bend. What we found was more than enough material to get in there with a port grinder (you could use a Dremel or sanding drum) and contour it into a smooth radius. Remember the bell-mouth discussion earlier in this thread? That outer 3/4" radius? Turns out that 3/4" radius was the magic number for the inside of the 90, and there was JUST enough material to get that in there (we blew a hole in the first elbow, be careful)! We flow-tested the connection in the attached image and it is almost EXACTLY the same as the model with a longer-radius 90. Lesson learned! As for the air straightener, you definitely want them regardless of whether your blower is close-coupled to your cyclone or not.. Straightening the airflow not only increases efficiency it also changes the characteristics of the airflow in the cyclone. In the modeling we noticed that straightening the airflow quickly in the outlet actually increased the velocity of the cyclonic air (the air going round-n-round in the separator). I haven't had time to finish the build yet (Yes, I promise to post pictures!) but the simulator indicates the best position is just above the separator outlet within the first 12"- 18' or so. We are working with 5 vertical vanes (don't have finish dimensions yet but the modeling indicates ~ 1-1/2" wide) that are 10" tall around the perimeter of the outlet pipe. As for cumulative efficiency, even without finished testing I can assure you it will be better. Have little or no resistance at the outlet prevents back pressure; back pressure will cause open-vane blowers like these to sheer and unload - basically the vanes "cut" through the air instead of "pushing" it... not good!

retired2,
Yes, I am proving your point... mostly! ;D
You are correct that this change will not necessarily be seen with an anemometer, but do not be fooled!
The increase in exit velocity will not change the system velocity (which is what you are measuring with the anemometer); what it WILL change is the efficiency of separation in the separator. By increasing the airflow at the bellmouth inlet we will decrease the airflow elsewhere in the separator:
The modeling showed that the increase in exit velocity slowed the vortex speed along the inner edge of the baffle by quite a bit. I can't say exactly how much the decrease is; The modeling software doesn't provide a speed at every point in the plane due to the complexity of the vortex, just a change of color of the flow line.
As for the financial monitor, well.... i married a bookkeeper! I don't think I could "misplace" $1.00 let alone $1,000! ;D

Sthutch,
Correct, this would be inverted inside the separator. As RobHannon mentioned there is no need for a bellmouth on the outlet of the blower.

QuoteHowever, as the outlet port in a top hat separator, my opinion is you would not find any measurable difference between an elliptical bellmouth and the bellmouths that are widely available commercially.  To put this in perspective, look at my test data comparing a straight ended pipe to the bellmouth I purchased from a spiral pipe manufacturer.  The difference is not huge by any means, and a straight pipe is the worst possible end condition for an entry port.

Retired2, your testing and work on these separators has been awesome; since I have access to airflow modeling and testing equipment I am only looking to help refine what you and others have already found... And yes any stock bellmouth would be better that the evil straight pipe! ;D
As for the reverse curve at the end of the bellmouth, we have found some very interesting points:

• When a straight-lipped bellmouth is used the lip produces a sheering effect on the cyclonic action causing more rotational vortexes above the lip. This leads to more individual vortexes (and more turbulence) in the air going into the exhaust stream.
• The reverse lip on the bellmouth is more efficient with the mouth only 1" below the top of the inlet pipe. At this height the air immediately above the bellmouth is nearly static, and the inrush into the bellmouth is very smooth.
• The velocity at the exit (the pipe end going to the blower) of the elliptical bellmouth compared to a straight bellmouth is nearly 3% greater!

That last one is the real difference; as the air comes into the separator chamber it will slow down a bit which of course is the whole point... WHERE it slows down is what we would ideally like to control. If only we could get it to slow down right over the top of the slot in that awesome Thien baffle... separation nirvana! 8)
so more info:

• We know air behaves as a fluid in a closed vessel, so as it enters a larger chamber/pipe it will slow down.
• We cannot directly slow the air over the baffle slot mechanically as this would stop the cyclonic separation effect.
• Because (1) is true we know that if we DON'T allow the air to slow in one place then it will slow somewhere else.
• Because (2) is true maintaining velocity elsewhere helps move the slowing air closer to where we want it.

As for those adventurous souls looking to make a bellmouth out of PVC I say go for it! There has been all sorts of stuff done to heat the PVC (boiling water, boiling oil even!) DON'T. DO. THAT.
Like this:

• Go to your local dollar store and get a cheap stainless steel bowl. It needs to be ~10" on the top and anything less than 6" diameter on the bottom.
• Take that bowl and a $20 bill to your local commercial electrician. Flip him the $20 to wrap his heat blanket around your pipe and heat it up. Get it real hot...
• Put that bowl upside down on the floor, and push that really hot pipe down over it. Keep heating and pushing until the outer lip is ~14" diameter. This will take a while...
• The outer radius needs to be hand-formed. Use a heat gun to warm the outer lip and roll it back. I used a short slug of 1" metal stock as a guide (because I had it laying around)... This is surprisingly easier than it sounds.
• Lastly, trim the edge of the lip so it is even all the way around. I stood my pipe on the bench and set a pencil on a piece of 3/4" pine... and drew a line all the way around the perimeter. Cut it off with a cutoff wheel in a Dremel tool, sand the lip smooth and you're done. Total time was around 2 1/2 hours, cost (including bowl) was $23.90 plus the piece of pipe I already had for this project.

Not bad!
So as I get going on this separator project I will take pictures and post accordingly. Once I have the thing built we can do some real-world testing and see how all this math stuff works out (or not!). My woodworking skills really aren't much (cockeyed birdhouses mostly :o) and I look forward to learning....
Maybe Retired2 can help me build a router table! ;D

Good morning all!
Have a look at the attached picture; it is a profile schematic for a bellmouth intake design from Gordon P. Blair and W. Melvin Cahoon of Volvo-Penta Americas. These guys put huge amounts of effort into this research, and we've used this basic layout for all sorts of radius-ed intake inlets.
"De" is exhaust diameter, "Di" is inlet diameter, "L' is length and "Rc" is corner radius. Notice that "De" and "L" are equal; so optimally the length of the bellmouth from tip to concentric pipe is the same. "Di" is 2.13 times the exhaust diameter and is measured at the very end of the bellmouth before the end radius starts to turn back. The end radius "Rc" is .13 times the exhaust diameter. This end radius is important to smooth the inrush of air at "Di".
SO... if we are to use 6" pipe for our project, optimally the inlet bell would be 12 3/4" diameter and the end radius would be 3/4".
Now obviously these optimal dimensions will be constrained by other factors like available space etc. but hopefully this gives everyone some guidance!

Retired2 you are correct on both counts. Even if your blower and separator are 6-8' apart straighteners will have a positive effect especially if your separator is reverse-rotation. There is no need for a straightener after the blower...
One thing that works well as as a straightener is honeycomb plastic grid. Can be purchased in sheets and cut easily. two pieces 6-8" apart in the riser oriented so the grids are NOT aligned (45 degrees to one another) works really well. Have never flow-tested a straw style but my guess is the results would be similar.
Most of the dust collector mods I've seen have the blower mounted such that the separator outlet is straight into the blower and then there is an ell on the outlet into the filter media. This should be reversed, with the separator outlet having an ell at the top and the blower oriented so the outlet is pointing straight down into the filter. Again, avoid any restrictions possible on the "pushing" side of the system.
And Retired2 those standard close ells are beyond awful! It is really surprising that they are used in any system at all. Remember that air behaves as a fluid in a closed system; the vena contracta phenomena happens with liquid too, and those ells cause it big-time!
When we flow-tested the 4" close-couple 90 from the box stores we found airflow rates restricted so much that the effective size of the pipe was more like 2 3/4" :o
If you have a commercial electrician in your area they will have heat blankets for bending 4-6" schedule 40 PVC; that is the heavy wall pipe. Those blankets work great on S&D (non foam core) pipe. Throw the guy a few $$ (I think I paid them $60 to bend two 90's) and you will have nice long radius smooth wall turns.... and the woodbutchers shall rejoice! ;D

Sthutch,
I believe you are correct; the separator is being used as a handy way to mount the filter... however...
HOW-EV-ER.... this is introducing rotational airflow into the top of the filter, which then wants to be straightened out and then turned into the pleats of the filter. I'm not sure this is at all beneficial...  :o :o
Efficiency comes into play big time on the outlet side of things. Blowers (including exhaust fans for ventilation, which is what I am schooled in) are far better "pullers" than "pushers". much is being done to increase the efficiency on the "pulling" side while the "pushing" outlet side not so much.
4" pipe to a separator followed by 6" pipe separator to a blower with an 8" or 10" outlet with no bends... better to put an elbow at the top of the riser from the separator into the blower and have the blower exhaust in a straight line into the filter instead of the elbow on the outlet side.... of course space considerations come into play but you get the idea... I hope!  ;D
The potential exists to increase airflow while lowering motor load (amperage)... less turbulence in the exhaust stream = more efficient impeller load...  8)

I agree Retired2; no sense in having that ring on the filter. I see several shortcomings in the stock separator ring that could be brought up to snuff with the plazma cutter and a few minutes work with polishing disc. I have already created a bellmouth on a piece of 6" S&D pipe to use for the outlet... not nearly as difficult as it may seem, and the heated plastic actually WANTS to make a transitional radius instead of a fixed radius... which nearly negated the vena contracta. For those who want to test a belled piece of pipe look to see if you have a local speed shop that can flow-test high-horsepower engines....
I will try my best to post pics and tutorials in the style of Retired2... tough act to follow! ;)

Sorry for the confusion all,
attached is a better picture of what I am asking about; notice how the original separator ring is now on top of the filter. Seems to me this not needed and would actually be counterproductive.
As someone coming from the world of metal :o I am looking at the stock separator ring and wondering if the built-in inefficiencies could be worked out to make the metal ring a suitable candidate to replace the perpetually-problematic plexi/lexan products everyone struggles with.
All of this is a lesson in study and understanding before I start to build my separator and in no way is meant to diminish or slight all the absolutely awesome work done by others to date. Trying to get the best understanding possible! ;D

Retired2!
Have much of your posts and tests.... awesome!
Attached is a photo of somone's mod(not mine) using a dust deputy. Notice how the exhaust of the blower has an elbow going into the filter? I have seen this sort of mod where the original seperator ring is where that elbow is, and the top of the seperator is capped off with a piece of wood. If you look at the bottom of the filter there is a small dust bag to collect the knocked-down fines from the filter. It seems to me that a seperator ring at the top of the filter is needless and only serves to introduce more turbulence in the air going to the filter.
Thoughts?

Greetings all!
So I really wasnt sure how to word the subject.... but it kinda says it all :)
I am getting ready to build a pre-blower seperator and add a Wynn filter to an HF dust collector. Several builds I have seen remove the bag from the top of the HF cyclone, cap the top with plywood and then hang an open-bottom Wynn filter below with a collector bag or pail attached to the bottom of the filter. Question is, is that cyclone on top of the filter really neccessary? Any reason why the HF body shouldnt be used for the seperator and then just a simple box above the filter?