J. Phil Thien's Projects

General Category => Thien Cyclone Separator Lid Discussion => Topic started by: guy48065 on February 11, 2013, 10:33:37 AM

Title: CW or CCW?
Post by: guy48065 on February 11, 2013, 10:33:37 AM
It's been stated that inlet angle & swarf flow direction doesn't matter.  I imagine that's true for a separator fed with hoses but what about when the baffle is mounted right on the fan housing?  Seems to me you would want the swirl to run the same direction as the impeller since it's so close it may be "coupled" to the air mass.

OR--is counter-rotation desirable in case it might reduce the amount of fines that get pulled in by the impeller?

Anybody ever play with this choice?
Title: Re: CW or CCW?
Post by: DarthVader on February 11, 2013, 11:06:18 AM
You want to keep the rotation going the same way when the impeller housing is directly on top of the baffle. switching directions is not advisable when the distance from the impeller inlet to the baffle outlet is minimal. the incoming air is still spiraling from the rotation of the impeller so reversing the direction of the baffle would cause turbulence upon entering the baffle...

my .02 at least
Title: Re: CW or CCW?
Post by: alan m on February 11, 2013, 11:21:14 AM
the golden rule with dust colection (and seperation) is reduce turbulance.

turbulance kills cfm  and allows bypass of seperaters.
in a top hat design the benifits are PROBABLY smaller that on a built in baffel design
i would definetly want the air spining the same way in a built in design.

retired2 (member here) i think did some reserh into air straighteners. he (?) found benifits in having one
Title: Re: CW or CCW?
Post by: retired2 on February 11, 2013, 12:45:22 PM

Below is a statement I've posted several times.  It comes from a Cincinnati Fan Engineering Manual regarding duct inlet spin.  As you can see, spin in either direct is undesirable, and it was very evident in my close-coupled top hat build.  When I added an air straightener, the air flow improved and noise level dropped due to the decrease in turbulence. 

Duct Inlet Spin

"A major cause of reduced fan performance is an inlet duct connection that produces a spin or pre-rotation of the air entering the fan inlet.  Inlet spin in the same direction of the fan wheel will reduce air volume and pressure ratings.  Inlet spin in the opposite direction of the fan rotation will substantially increase the motor horsepower requirements.  An ideal inlet condition is one which allows the air to enter the fan axially and evenly without spin in either direction."
Title: Re: CW or CCW?
Post by: guy48065 on February 11, 2013, 07:22:15 PM
Quote from: alan m on February 11, 2013, 11:21:14 AM
retired2 (member here) i think did some reserh into air straighteners. he (?) found benifits in having one
I'd like to read more about it but a search of "air straightener" turned up nothing.


Maybe I'm missing something...Why did Cincinnati Fan use an elbow on the intake of their 2-stage DCs, like everyone else?  Or were they referring to avoiding bends and elbows ahead of the inlet?
Title: Re: CW or CCW?
Post by: guy48065 on February 13, 2013, 10:53:51 AM
I'm also confused whether that quote is referring to the system inlet (where I thought spin was desirable) or fan inlet (and how would you control that?).
And in context is that quote about dust collectors where you are trying to separate material from air or ventilation
Title: Re: CW or CCW?
Post by: retired2 on February 13, 2013, 12:09:29 PM
Quote from: guy48065 on February 13, 2013, 10:53:51 AM
I'm also confused whether that quote is referring to the system inlet (where I thought spin was desirable) or fan inlet (and how would you control that?).
And in context is that quote about dust collectors where you are trying to separate material from air or ventilation?

I'll give you my opinion.  Cincinnati is talking about the negative effect of air entering the inlet of a centrifigal fan with a radial spin.  Spin in either direction effects the efficiency of the fan's impeller.  I do not think it matters what application you are talking about, dust or ventilation, there is still an adverse effect.  I would even go so far as to speculate that radial spin of a fluid would adversely effect the performance of a centrifigal pump.

When I was building and testing my Thien separator, I initially had it connected to my blower with about 6 ft of flex hose.  I did not take any FPM/CFM measurements in that configuration because I wanted to eliminate the flex hose since it causes 3X the line loss of smooth pipe.  However, when I close-coupled the separator to the inlet port of the DC (about 8"), the DC became much louder and when I put my hand on the housing, I could feel the increased turbulance.  That is when I added an air straightener in the hopes of getting rid of the objectionable noise level.  What I discovered after taking measurements with an anemometer, not only did the noise decrease, but the CFM's increased when the air straightener was added.

So, my experience suggests several things.  The Thien separator imparts a radial spin on the air exiting the outlet pipe.  That spin when close-coupled to a fan inlet will cause turbulence inside the fan that increases noise levels and decreases the performance of the fan.  Since my system is a counter flow arrangement, my comments only address that configuration.  However, I have no reason to dispute Cincinnati's comments that radial flow in either direction has a negative effect on on the fan's performance.

Title: Re: CW or CCW?
Post by: guy48065 on February 14, 2013, 07:55:04 AM
That seems counter-intuitive to me.  If the air entering the fan  spins in the same direction as the fan shouldn't there be less turbulence?  What is an air straightener?  If it's just a pipe then the air is de-coupled from the dirty air spinning around in the chamber, but is still spinning--inside the pipe--because it's coupled to the impeller.  Unless it's one of those bundles of plastic straws I've seen used to straighten a fan output.  In which case when used on the inlet I would think there would be some sort of shear effect going on where the "straightened" air hits the spinning impeller.  That can't be good for CFM or noise.

It's hard to wrap my mind around these effects.  I didn't have any fluid dynamics classes in college.

In any event many of these options aren't easily available to me.  My system is in a small closet and the pipes drop in from ceiling height straight down into the lid of my 2-stage DC.  Not much "wiggle room" there to change flow directions or greatly increase DC inlet height.

(http://home.comcast.net/~mburnette/Shopdustcoll.jpg)
Title: Re: CW or CCW?
Post by: retired2 on February 14, 2013, 12:14:50 PM
Quote from: guy48065 on February 14, 2013, 07:55:04 AM
That seems counter-intuitive to me.  If the air entering the fan  spins in the same direction as the fan shouldn't there be less turbulence?  What is an air straightener?  If it's just a pipe then the air is de-coupled from the dirty air spinning around in the chamber, but is still spinning--inside the pipe--because it's coupled to the impeller.  Unless it's one of those bundles of plastic straws I've seen used to straighten a fan output.  In which case when used on the inlet I would think there would be some sort of shear effect going on where the "straightened" air hits the spinning impeller.  That can't be good for CFM or noise.

It's hard to wrap my mind around these effects.  I didn't have any fluid dynamics classes in college.

In any event many of these options aren't easily available to me.  My system is in a small closet and the pipes drop in from ceiling height straight down into the lid of my 2-stage DC.  Not much "wiggle room" there to change flow directions or greatly increase DC inlet height.


You probably won't find air straighteners in a catalogue, or even at your local HVAC supply house.  You will probably have to come up with your own design.  My intent was to simply slip four straight vanes into my pipe and attach them somehow, i.e. rivets, weld, or maybe epoxy.  In the short term I've kept the "straws" that I used to test the concept simply because it works just fine.  My straws are about 1-1/4" in diameter.  To see photos, look for my build.  It has scrolled to about page 10 now. 

To answer your question about spin in the same direction as the impeller, I am guessing it reduces efficiency because it causes "cavitation".

Title: Re: CW or CCW?
Post by: guy48065 on February 14, 2013, 01:48:39 PM
Quote from: retired2 on February 14, 2013, 12:14:50 PMMy straws are about 1-1/4" in diameter.  To see photos, look for my build.  It has scrolled to about page 10 now.
To save anyone else the aggravation of searching back 18 months with no useful Search tools:
http://www.jpthien.com/smf/index.php?topic=563.0

OK so your Straightener is a bundle of "straws" similar to what I've seen the Mythbusters use in trying to get decent laminar flow from their cobbled wind tunnel.
Title: Re: CW or CCW?
Post by: retired2 on February 14, 2013, 02:23:43 PM
Quote from: guy48065 on February 14, 2013, 01:48:39 PM
Quote from: retired2 on February 14, 2013, 12:14:50 PMMy straws are about 1-1/4" in diameter.  To see photos, look for my build.  It has scrolled to about page 10 now.
To save anyone else the aggravation of searching back 18 months with no useful Search tools:
http://www.jpthien.com/smf/index.php?topic=563.0

OK so your Straightener is a bundle of "straws" similar to what I've seen the Mythbusters use in trying to get decent laminar flow from their cobbled wind tunnel.


Did I say it wasn't a bundle of "straws"?  Regardless what you call it, it is an effective air straightener that has improved the performance of my DC.
Title: Re: CW or CCW?
Post by: alan m on February 14, 2013, 06:28:49 PM
retired2 s data (not independant or certified but still valid) shows a marked increase in cfm  with the straightener (and bell mouth)
for his 4.5" pipe he found a 47 cfm increase from using the air straightener on his bell mouth pipe. thats 12% increase.
there is also a noticable reduction in noise.
im not sure why its helping  but does it really matter. no but i would like to know so we might be able to optimise it better.

this bundle of straws seems to work.
did you find any info on the most effiecient ratio or no of pipes  to the area of the pipe . is there a study on this similar to the wonderfull  one you found on bell mouth fittings

im was thinking of putting a simple x across the duct going the full length of the duct.
Title: Re: CW or CCW?
Post by: retired2 on February 14, 2013, 06:53:46 PM
Quote from: alan m on February 14, 2013, 06:28:49 PM

this bundle of straws seems to work.
did you find any info on the most effiecient ratio or no of pipes  to the area of the pipe . is there a study on this similar to the wonderfull  one you found on bell mouth fittings

im was thinking of putting a simple x across the duct going the full length of the duct.

Alan,
I didn't spend much time looking, but I did not find much, if any, information online for air straighteners.  However, my gut tells me you will find very little difference in benefit between a bundle of tubes or several straight vanes positioned radially inside the pipe.  Length might be a different story.  I'm sure there is a point where the air straightener is too short to be of any benefit, and likewise a point beyond which adding additional length provides no additional benefit.
Title: Re: CW or CCW?
Post by: guy48065 on February 14, 2013, 07:52:13 PM
The thing that's nagging me about the straws is a hunch that in retired2's situation it's a band-aid that improves the undesirable counter-rotation of his tophat. 
"Cavitation" was mentioned.  If anything it seems to me that introducing an air mass to the spinning impeller in a straight line would cause shear--or cavitation.  I have no doubt this did improve performance and noise vs. presenting the impeller with an air mass spinning in the wrong direction.  Has anyone else tried this trick--on a separator that spins the air the same direction as the fan?
Title: Re: CW or CCW?
Post by: retired2 on February 14, 2013, 08:57:56 PM
Quote from: guy48065 on February 14, 2013, 07:52:13 PM
The thing that's nagging me about the straws is a hunch that in retired2's situation it's a band-aid that improves the undesirable counter-rotation of his tophat. 
"Cavitation" was mentioned.  If anything it seems to me that introducing an air mass to the spinning impeller in a straight line would cause shear--or cavitation.  I have no doubt this did improve performance and noise vs. presenting the impeller with an air mass spinning in the wrong direction.  Has anyone else tried this trick--on a separator that spins the air the same direction as the fan?

You can dismiss what I say, but to disregard what industry experts are saying makes no sense.  Here is another source for you.  It is a link to the US Department of Energy's sourcebook for industry titled "Improving Fan System Performance".  In it they say the same thing as Cincinnati Fan, i.e. pre-rotation in either direction has undesirable effects.  They discuss vanes and other methods to counter this undesirable rotation.

https://www1.eere.energy.gov/manufacturing/tech_deployment/pdfs/fan_sourcebook.pdf

I'm sure if you spend even a little time researching this subject, you will find more sources confirming these statements.
Title: Re: CW or CCW?
Post by: guy48065 on February 15, 2013, 09:33:21 AM
Dead link.
Title: Re: CW or CCW?
Post by: guy48065 on February 15, 2013, 09:37:38 AM
ahh...simple fix:
https://www1.eere.energy.gov/manufacturing/tech_deployment/pdfs/fan_sourcebook.pdf (https://www1.eere.energy.gov/manufacturing/tech_deployment/pdfs/fan_sourcebook.pdf)
Title: Re: CW or CCW?
Post by: guy48065 on February 15, 2013, 10:45:48 AM
Quote from: retired2 on February 14, 2013, 08:57:56 PM
You can dismiss what I say, but to disregard what industry experts are saying makes no sense. 
I am NOT dismissing what you have written (or quoted), I'm just trying to get a better understanding.  In your posts you have expressed concern that your counter-rotating top hat may be hurting performance.  As I have said the straightener may have helped you--but is it a universal improvement?
You incorporated this straightener in your counter-rotating top hat and wrote about it 1 1/2 years ago.  Surely someone has tried this on a normal-rotating system to see if it is an improvement?

As for the DOE link...well...
On page 13 "Airflow Control Devices":
Quote
Flow control devices
include inlet dampers on the box, inlet vanes at the
inlet to the fan, and outlet dampers at the outlet of
the fan. Inlet box dampers are usually parallel
blade dampers. Inlet vanes adjust fan output in two
principal ways: by creating a swirl in the airflow
that affects the way in which the air hits the fan
blades, or by throttling the air altogether, which
restricts the amount of air entering the fan. The
inlet vanes and dampers must be designed for
proper fan rotation and are to be installed in such
a way that these inlet vanes and dampers open in
the same direction as the fan rotation. The prerotation
or swirl of the air helps reduce the brake
horsepower of the fan. If the inlet dampers on the
inlet box are located too far away from the inlet of
the fan, the effect of pre-rotation may be lost or
reduced, and horsepower savings may be negligible.

They seem to be saying that the swirl at the centrifugal fan hub lessens the load on the motor.  They go on to state that a reverse rotation increases motor load as it "unwinds" the airstream.  Is it reasonable to assume that zero spin falls in the middle between helping and hurting the fan rotation?
Title: Re: CW or CCW?
Post by: alan m on February 15, 2013, 11:28:29 AM
thats seems to be contradicting each other
Title: Re: CW or CCW?
Post by: retired2 on February 15, 2013, 12:36:31 PM
Here is what the DOE document says on page 39 about rotation in the same direction as the blower.

"A pre-rotational swirl in the airflow rotates in the
same direction as a fan impeller.  This phenomenon
reduces the load on the fan and shifts its performance
curve down and to the left."

The last thing you want to do is move the fan performance curve down and to the left.  That is lowering SP and CFM's.  So the previous statement says exactly what Cincinnati Fan is saying in their Engineering Manual.  The article then goes on to say:

"If possible, the fan should be configured
so that there is enough distance from the closest
bend for the airflow to straighten out. Because space
constraints often do not allow ideal configuration,
an airflow straightener, such as turning vanes, also
shown in Figure 2-16, can improve fan performance."

Now, I don't know how it can be any clearer than that!  With regard to counter-rotation the article states:

"A counter-rotating swirl rotates in the opposite
direction of an impeller. This swirl creates an
additional load on the impeller. Although it tends
to shift a fan's performance curve upwards, a
counter-rotating swirl is an inefficient method of
increasing fan pressure."

Again, that agrees with Cincinnati Fan's comment that counter rotation increases the hp requirements substantially.  So, if you want to increase your SP and CFM's, go with a counter-rotation pre-spin - but you're motor might not last as long.

Frankly this whole discussion has become a little tedious, and I don't have any more time to waste on it.   I'm not sure why anyone would be so worried about an air straightener when their plumbing has 1xD bends and 90 degree tee's.  The line losses from these fittings far outweigh anything that an air-straightener can or cannot do for you.

Regards
Title: Re: CW or CCW?
Post by: guy48065 on February 17, 2013, 07:24:14 PM
The article snips do seem contradictory.  I've read the whole document and believe the section I quoted refers to the impeller inlet while the paragraph retired2 quoted is about the housing inlet.
Title: Re: CW or CCW?
Post by: Schreck on March 04, 2013, 05:42:23 PM
It was common in the HVAC field to use an assembly of inlet guide vanes to induce a pre-rotation in the air flow immediately prior to entering the fan inlet.  This pre-rotation in effect reduced the effectiveness of the fan's rotation, resulting in reduced discharge air volume and reduced fan power draw.  These inlet guide vanes are usually adjustable (i.e., their angle can be varied to vary the amount of pre-rotation and hence the volume of air delivered by the fan) and are modulated in order to maintain a static pressure setpoint at a location downstream in the supply air ductwork.  They may also be used as balancing devices, in which case they are adjusted shortly after installation to tweak the capacity of the fan, after which they operate at the same angle.  Below are a pair of images of inlet guide vanes mounted onto fan inlets.

(It is now standard practice to vary the fan output by varying the speed of the fan and motor through a variable frequency drive, but prior to VFD's, motors ran at constant speed and inlet guide vanes were used to control fan output.)

Fan output (in cfm) is highest when there is no pre-rotation of the air entering the fan inlet.   

Retired2's bundle of straws arrests an undesireable pre-rotation that is counter to that of the fan impeller. 
Air that is leaving the separator and entering the fan inlet spinning in the same direction as the fan impeller will reduce the net capacity (in cfm) of the fan. 

The discussion of elbows and turning vanes is something else altogether, pertaining to the duct design on the suction side of the fan. 
Title: Re: CW or CCW?
Post by: guy48065 on March 05, 2013, 08:22:51 AM
In a 2-stage DC where the fan sits on top of a chamber (drum, bag or Thien top hat) the air in the chamber should be spinning in the same direction as the fan rotation.  IMO any use of vanes or straws at the fan inlet causes frictional losses greater than any gain you might get from achieving a straight laminar flow.  The distance is too short.  Am I wrong in thinking this?

The issue is completely moot in a system where the separator is remote from the fan.
Title: Re: CW or CCW?
Post by: alan m on March 05, 2013, 09:46:38 AM
im no expert.
the only info i have to go one is retired2 s build adn the 2 articals posted about it.
all 3 claim that an air straightener improves cfm.
i dont know if you are wrong or not but you are right about there being a lot of extra friction added to the pipe due to the added surface area.


i dont think that it is moot if the fan and seperater are farther appart.
if there are gains to be gotton with them close coupled then in sure there are some gains still when they are farther apart.



schrek.


thats inrteresting
that seems to show that varying the rotation  can be used to fine tune the motor  speed and current draw.
Title: Re: CW or CCW?
Post by: Schreck on March 05, 2013, 08:23:41 PM
Quote from: guy48065 on March 05, 2013, 08:22:51 AM
In a 2-stage DC where the fan sits on top of a chamber (drum, bag or Thien top hat) the air in the chamber should be spinning in the same direction as the fan rotation.  IMO any use of vanes or straws at the fan inlet causes frictional losses greater than any gain you might get from achieving a straight laminar flow.  The distance is too short.  Am I wrong in thinking this?


In a 2 stage DC where the top hat is constructed to rotate air in the same direction as the DC fan that is mounted directly above it, the air in the chamber WILL be spinning in the same direction as the fan impeller, unless measures are taken to prevent this.  Should it be?  I suppose the question is, will the energy lost by stopping the pre-rotation in the short duct between the top hat and the inlet of the fan be more or less significant than the reduction in fan capacity that results from NOT stopping the pre-rotation of air at the fan inlet. 

It depends on the design of the device that stops the pre-rotation.  Less surface area is better, I would think.  Since we want to stop the rotation of air in a round duct, we only need to insert surfaces that are radial; concentric surfaces provide no benefit, but add surface area and therefore increase friction losses.  It may be enough to insert sheet metal in 2 planes into a short length of round duct.  Picture an X placed over an O.  A duct that is only 1 or 2 diameters in length with such an insert may be all you need. 

Measure DC motor amps with and without the straightener in place.  Higher amps will mean more CFM.  More CFM is good for a dust collection system, right?
Title: Re: CW or CCW?
Post by: retired2 on March 05, 2013, 11:32:38 PM
Quote from: Schreck on March 05, 2013, 08:23:41 PM
Measure DC motor amps with and without the straightener in place.  Higher amps will mean more CFM.  More CFM is good for a dust collection system, right?

Been there, done that......with an ampmeter and an anemometer.  Test results are posted in the thread describing my build, and an air straightener absolutely improves air flow in a close-coupled design!

Since my build imparts a counter-flow air rotation, the question has been raised whether or not an air straightener would provide similar results when the pre-rotation is in the same direction as the fan.  Well, if you accept what industry experts say about pre-rotation, i.e. CFM's are compromised more by a pre-rotation in the direction of the fan than by a counter-rotation, then it holds that an air straightener would benefit a pre-rotation in the direction of the fan more than one that is counter-flow.

My air straightener consists of multiple plastic tubes, simply for convenience of installation and testing.  This may not be the optimal design to minimize frictional losses, but in spite of that the test results show a very worthwhile improvement.  It is likely that a multi-vaned straightener would reduce frictional losses, but I think any further gains would be very small.  If I thought otherwise, I would have replaced the plastic tubes with crossed vanes long ago.




Title: Re: CW or CCW?
Post by: phil (admin) on March 06, 2013, 06:36:40 AM
Quote from: retired2 on March 05, 2013, 11:32:38 PM
It is likely that a multi-vaned straightener would reduce frictional losses, but I think any further gains would be very small.

I agree, I bet any difference would be nearly impossible to even measure.
Title: Re: CW or CCW?
Post by: Schreck on March 06, 2013, 02:49:14 PM

[/quote]
Since my build imparts a counter-flow air rotation, .....

My air straightener consists of multiple plastic tubes,..... This may not be the optimal design to minimize frictional losses, but in spite of that the test results show a very worthwhile improvement.  It is likely that a multi-vaned straightener would reduce frictional losses, but I think any further gains would be very small.
[/quote]

Retired2, I agree with you.  Any further increase in your case would be minimal.  With a counter-rotation such as yours, any kind of straightener is very beneficial.  But you have a different situation than the one I was discussing.

The question I was addressing was guy48065's contention in reply#22 that close-coupled top hats and DC blowers SHOULD have a pre-rotation in the same direction as the impeller.  They will, but I don't think it is beneficial. 

I think pre-rotation in the same direction as the impeller reduces fan capacity, as you have stated repeatedly with supporting documents (thank you!). 
I also think that the insertion of a straightener in this situation would improve overall performance of the DC.  I think the additional friction is minor compared to the increase in fan capacity that would be gained by not having any pre-rotation. 

My suggestion to insert a straightener and measure the change in amps was directed at guy48065 or anyone with a close-coupled top hat and DC  that are oriented with the same rotation (I didn't think you were tuned in to this thread any longer!)

I'm liking the thought of a bell-shaped top hat outlet with radial straighteners, perhaps with the leading edges curved to ease the transition from swirling to straight airflows.....
Title: Re: CW or CCW?
Post by: alan m on March 06, 2013, 03:49:59 PM
Quote from: Schreck on March 06, 2013, 02:49:14 PM

I'm liking the thought of a bell-shaped top hat outlet with radial straighteners, perhaps with the leading edges curved to ease the transition from swirling to straight airflows.....

there could be something to be gained by thet.
it would be hard to acomplish for the average joe.
im thinking something like an air ramp(like what bill pentz has inside his cyclone) but only going maybe 1/4" of the way around.

i better get building my 8" before there are any more things added to the list
Title: Re: CW or CCW?
Post by: retired2 on March 06, 2013, 03:57:41 PM
Schreck,

I did understand the intent of your response.  I just wasn't sure if you had seen my test data which validates what has been stated by industry experts.  And I was merely pointing out that with what we know about counter-rotation that data can be used to infer what the results would be for the opposite rotation.

I stopped posting in this thread when it became clear guy48065 was more interested in arguing for argument's sake than he was in accepting the facts, regardless of the evidence or the source. 


Title: Re: CW or CCW?
Post by: Schreck on March 06, 2013, 07:59:37 PM
Well, I am very new to the forum, and I haven't read all of the threads.  But I did read your "5" rectangular inlet..." thread and found it very illuminating.  Measuring velocity pressure was a good move when you found the amp readings to be so close together.  I am curious about your test process: what did you use for an anemometer, was there a single reading taken in the center of the duct and was it fixed at the same location so it could not move in between tests?
Title: Re: CW or CCW?
Post by: retired2 on March 06, 2013, 08:22:45 PM
Quote from: Schreck on March 06, 2013, 07:59:37 PM
Well, I am very new to the forum, and I haven't read all of the threads.  But I did read your "5" rectangular inlet..." thread and found it very illuminating.  Measuring velocity pressure was a good move when you found the amp readings to be so close together.  I am curious about your test process: what did you use for an anemometer, was there a single reading taken in the center of the duct and was it fixed at the same location so it could not move in between tests?

I purchased a new Kestrel anemometer on ebay.  I forget the model number.  Kestrel is the same brand Phil uses, and I followed his practice for taking readings, i.e. take one reading at the edge of the pipe and one in the center, then average the results.

You have to be careful with these devices because very few can handle the velocities of small bore dust collection systems.  My readings were just inside the allowable range because I have a 5" system and I took my measurements some distance from the fan.   

If you are measuring velocities that you think exceed the limits of the anemometer, simply use a reducer, in this case an increaser, to up the pipe size where you will be taking your measurements.  Then just do the math to convert the fpm's for the larger pipe size to the smaller size.  And of course fpm can easily be converted to cfm for any given pipe size.

On about page seven of the thread for my build there are some photos of my test setup for anemometer readings.
Title: Re: CW or CCW?
Post by: guy48065 on March 06, 2013, 09:03:42 PM
Quote from: Schreck on March 06, 2013, 02:49:14 PM
My suggestion to insert a straightener and measure the change in amps was directed at guy48065 or anyone with a close-coupled top hat and DC  that are oriented with the same rotation (I didn't think you were tuned in to this thread any longer!)
Sorry--even though I have the test equipment necessary in the end any testing of my system will only be relevant to me unless I do a bunch of changes and test the relative merits.  I'm not motivated to do that any more than retired2 is motivated to try his straws on a normal-rotation separator (by building one).  What he is calling being argumentative was me imploring ANYONE ELSE to post their results with an air straightener.  Evidently nobody else believes in the idea enough to try it.
Title: Re: CW or CCW?
Post by: Schreck on March 07, 2013, 05:43:32 PM
Quote from: guy48065 on March 06, 2013, 09:03:42 PM
Evidently nobody else believes in the idea enough to try it.

Or maybe they are testing as we write and simply haven't posted yet!
Title: Re: CW or CCW?
Post by: alan m on March 07, 2013, 06:07:21 PM
i think the reason that it isnt on here more is that most people that build a seperater are happy with it the way they have it. they may mean to improve it but cant get around to doing it.
im like that. i built my 4" very crude seperater  really fast 
then built my 6" version quickly (slow to post it thow)
but am slow to get started on my 8" version. i cut the  some of the pieces but cant get the time to do it yet.
it is down to the fact that my 6" version is working well. i could leave it there its that good
most move on to other jobs and shop improvments that are a higher priority

i added an 8" flex hose between the 8" dc inlet and the 6" seperater
it was 6" before . i think there is more suctionbut its hard to tell. when thats a smooth pipe with the air straightener it should improve again
Title: Re: CW or CCW?
Post by: gunrackguy on March 10, 2013, 02:03:13 PM
retired2 I was following your build and noticed you have the same DC that I have with a CW rotation, and you separator has a CCW rotation and/or spin, so I guess that is the way to go or do you need to add strengtheners as this discussion implies. I am just about ready to build something similar to what you have and am undecided as to the direction of the separator. I like the idea of providing a new base for the entire unit. I have the pleated cartridge filter on mine.
Title: Re: CW or CCW?
Post by: alan m on March 10, 2013, 05:24:08 PM
if you put an air straightener inbetween it shouldnt matter which rotation the seperater is spining
build it what ever way works best for your shop
Title: Re: CW or CCW?
Post by: retired2 on March 10, 2013, 06:13:13 PM
Quote from: gunrackguy on March 10, 2013, 02:03:13 PM
retired2 I was following your build and noticed you have the same DC that I have with a CW rotation, and you separator has a CCW rotation and/or spin, so I guess that is the way to go or do you need to add strengtheners as this discussion implies. I am just about ready to build something similar to what you have and am undecided as to the direction of the separator. I like the idea of providing a new base for the entire unit. I have the pleated cartridge filter on mine.

I built a CCW separator because it was what gave me the best piping configuration, and also the best access to the separator and plastic waste bag.  As I eventually concluded, a close-coupled configuration should have an air straightener regardless of rotation.  If an air straightener is used, it makes no difference which rotation you choose, both should perform equally.  So, do what I did, use the rotation that suits you approach piping best, but be sure to use an air straightener.

Building a new base for the 50-760 has a lot of benefits.  As anyone who owns one knows, the support legs and brace seem to interfere with everything you want to do.  When I built my new base, I built it slightly larger than the Delta base, and the four legs do not sit in a rectangular configuration.  One leg is pushed back further to provide a clear straight run for the incoming main.
Title: Re: CW or CCW?
Post by: retired2 on March 10, 2013, 08:38:22 PM
Quote from: alan m on March 07, 2013, 06:07:21 PM
i added an 8" flex hose between the 8" dc inlet and the 6" seperater
it was 6" before . i think there is more suctionbut its hard to tell. when thats a smooth pipe with the air straightener it should improve again

Beware the placebo effect!
Title: Re: CW or CCW?
Post by: Schreck on March 10, 2013, 09:12:09 PM
Quote from: retired2 on March 10, 2013, 06:13:13 PM
  If an air straightener is used, it makes no difference which rotation you choose, both should perform equally.  So, do what I did, use the rotation that suits you approach piping best, but be sure to use an air straightener.

Here is an interesting paper that seems to confirm this.  Look at test case #4 on page 9.  The diagram indicates the rotation in the cyclone outlet is opposite that of the cyclone.  With straighteners, it does not matter.
http://www.banksengineering.com/Fan%20Troubleshooting%20ED100.pdf (http://www.banksengineering.com/Fan%20Troubleshooting%20ED100.pdf)

Title: Re: CW or CCW?
Post by: alan m on March 11, 2013, 04:56:42 AM
Quote from: retired2 on March 10, 2013, 08:38:22 PM
Quote from: alan m on March 07, 2013, 06:07:21 PM
i added an 8" flex hose between the 8" dc inlet and the 6" seperater
it was 6" before . i think there is more suctionbut its hard to tell. when thats a smooth pipe with the air straightener it should improve again

Beware the placebo effect!

iv noticed that since i changed the hose there is less noise . i had to tape a piece of timber to the 6" hose to stop it osilating from the suction. the 8"cant move like that because it is a lot more ridgit. and there is no obstruction there.

there does feel to be an increase in air flow at the end of the duct run but it is only small .
i also havnt tested it  so it could be a placebo effect
Title: Re: CW or CCW?
Post by: retired2 on March 11, 2013, 01:56:31 PM
Quote from: Schreck on March 10, 2013, 09:12:09 PM
Quote from: retired2 on March 10, 2013, 06:13:13 PM
  If an air straightener is used, it makes no difference which rotation you choose, both should perform equally.  So, do what I did, use the rotation that suits you approach piping best, but be sure to use an air straightener.

Here is an interesting paper that seems to confirm this.  Look at test case #4 on page 9.  The diagram indicates the rotation in the cyclone outlet is opposite that of the cyclone.  With straighteners, it does not matter.
http://www.banksengineering.com/Fan%20Troubleshooting%20ED100.pdf (http://www.banksengineering.com/Fan%20Troubleshooting%20ED100.pdf)

Or look at Case Study #2 on page 7 - it also confirms that an air straightener will improve performance of a system where there is pre-rotation, regardless of direction.   

Good find Schreck, another really good resource.  Too bad the ductwork and fittings suppliers like Oneida Air Systems don't sell air straighteners for the common sizes of round duct.  I've got a small sheet metal break, so I will fabricate my own once it becomes a priority.  In the meantime, the plastic tubes are working just fine.   
Title: Re: CW or CCW?
Post by: Schreck on March 30, 2013, 09:53:38 AM
Here is another paper that includes fan curves showing the impact on airflow, static pressure and HP on systems with pre-rotation in different directions.  See figure 2c.  The fan curves confirm what retired2 found when he installed straighteners to correct his counter pre-rotation. HP and therefore motor amps fell, airflow did not change drastically, but fan efficiency was greatly increased.  So a decrease in amps does not always mean less airflow, it could mean higher efficiency.

http://www.krugerfan.com/brochure/publications/Tbn010.pdf (http://www.krugerfan.com/brochure/publications/Tbn010.pdf)
Title: Re: CW or CCW?
Post by: retired2 on March 30, 2013, 01:35:42 PM
Quote from: Schreck on March 30, 2013, 09:53:38 AM
Here is another paper that includes fan curves showing the impact on airflow, static pressure and HP on systems with pre-rotation in different directions.  See figure 2c.  The fan curves confirm what retired2 found when he installed straighteners to correct his counter pre-rotation. HP and therefore motor amps fell, airflow did not change drastically, but fan efficiency was greatly increased.  So a decrease in amps does not always mean less airflow, it could mean higher efficiency.

http://www.krugerfan.com/brochure/publications/Tbn010.pdf (http://www.krugerfan.com/brochure/publications/Tbn010.pdf)

Another good find Schreck.  It is probably worth repeating that installing an air straightener where pre-rotation exists can result in a lower amp reading while still producing more air flow.  Those two statements seem contradictory, and anyone who has read the thread on my build will see that initially I thought the air straightener was decreasing fan performance because I was looking at amp readings, which were going down.  Only when I took anemometer readings did I realize the air straightener was giving me the best of both worlds, i.e. more air and less power.