5", Rectangular Inlet, Bellmouth Outlet with Air Straightener, Top Hat Separator

[retired2]

i would really talk to somebody at penn state and have them give you the real size of the bellmouth, they list em as 6" but they are more like 5.5

Just for comparison, my bell mouth came from a local spiral pipe manufacturer, and while it was a nominal 5" size, the actual size at the neck was 4-3/4".  It must be industry standard for them to be slightly undersized so they will fit into a starter pipe. 

If you think about it, you want the bell mouth to be the male end of the first joint, because that is the direction of flow.  If my bell mouth had been a full 5" in diameter, I would have had to crimp the end of the snap lock and insert it into the bell mouth.  That would not have been nearly as desirable, and might even have negated some of the benefit of the bell mouth. 

[jpgrenon]

One of the observations I noted from my ampere test was that the readings were lower with the separator removed than with the bellmouth installed.  I expected them to be higher.  I don't have an explanation for that, but it makes an argument that air rotation is not an issue.

I am not a science expert, but i believe that your amp readings show that the motor is facing more resistance when the seperator is in place, hence a higher amp reading. When you remove it you allow it to "relax".

Does this make any sense to you?

PS: i know this is an old post but i am very interested.

[retired2]

One of the observations I noted from my ampere test was that the readings were lower with the separator removed than with the bellmouth installed.  I expected them to be higher.  I don't have an explanation for that, but it makes an argument that air rotation is not an issue.

I am not a science expert, but i believe that your amp readings show that the motor is facing more resistance when the seperator is in place, hence a higher amp reading. When you remove it you allow it to "relax".

Does this make any sense to you?

PS: i know this is an old post but i am very interested.

CFM's and amp's move in unison.  As the blower moves more air, amps go up.  As it moves less air, amps go down.  So, you would expect any test condition with the separator removed to be giving higher amp readings because the system is moving more air.

My comment regarding the test data in question was specific to two test aberrations only.  The first was when the system was dead-headed, i.e. no inlet ports were open.  With the system dead-headed, I expected the readings to be the same with or without the separator.  The second condition that seemed contrary to expectations, was the test at my bandsaw with the bell mouth installed versus no separator.  In that case, the difference, while contrary to what was expected, was very small.

Now, one thing that might explain both these aberrations is that I discovered after lots of testing and after the referenced test data was posted and my comment made, that as the blower motor heats up amp readings start to drop a bit even for the same test conditions.  So, I should have performed all these tests after the motor had been running for some time to rule out differences due to thermal conditions in the motor.

Bottom line is I don't think you should make very much of these two isolated cases because given the circumstances they probably do not reflect a contradiction of what should be expected.

One last reflection on my comments.  At the time I thought these data excursions might suggest that air rotation does not affect performance.  As I later learned, and my subsequent testing showed, air rotation resulting from a close-coupled separator does indeed affect fan performance. And that is consistent with what industry experts also say on that subject.

[BernardNaish]

Hi Everyone, I have found a source of thin wall tube used as packaging. You will find it here:

http://www.cleartecpackaging.co.uk/clear-plastic-tubes.html

I think you may find that they have a presence in the U.S.A. as well. Unfortunately they say they are bulk suppliers and can only offer large quantitys. They do offer mini packs:

    34.6mmID x 200mm long – box quantity = 75 tubes  =  £40 that is about US$ 61.00

This is rather a lot of money but may be worth it particularly if several people can club together.

Keep innovating.

[alan m]

i dont think it is worth going to that expence. in a lot of the articals referenced in the clockwise/counter clockwise  thread , most of the testers used an x shaped straightener.
im planing on cutting 2  8" wide(8"pipe) strips of sheet metal leaving a few tabs to bolt it inside the pipe. i will cut half way up the midle of both strips so that they can slide inside each other.

[BernardNaish]

Alan. That sounds like a good plan. Please let us know how you get on with it.

I have a sample of these tubes now and they are perfect for the job but I cannot afford to spend that much. I would only need 11 for a 5" pipe. If I thought people would buy some off me at cost I might go for it.

I have a quick and dirty Thien lash up for the moment and of course it works but I want to make a top hat and I estimate that will cost me £100 in materials as I want to be able to experiment a bit so will need to duplicate some parts.

How do these cross straighteners work? What do they look like? Regards.

[BernardNaish]

Hi All, I have found this simple air straightener that requires very little pipe length to work:

http://www.vortab.com/pdfs/Principles%20of%20Operation.pdf

Keep spinning.

[retired2]

Hi All, I have found this simple air straightener that requires very little pipe length to work:

http://www.vortab.com/pdfs/Principles%20of%20Operation.pdf

Keep spinning.

One look at that website tells me my plastic tubes are very cost effective!

[BernardNaish]

Your tubes were very cost effective Retired2 and I managed to get a couple as free samples. Now I just need 9 more and I do not think their sales office will fall for it.  I made some straws today by removing both ends of baked bean cans and folding each to form two tubes of about the right diameter. It did not appear to make any difference  to the DC performance. I think this is probably because my system is far too turbulent with three right angle bends in the eight feet of 5" diameter steel tubes between my Thien and the DC fan. Also the tins are only 4" long.

To solve this I am going to get rid of the trolley and build a wooden frame, as you did Retired2, so that I can mount the fan directly to the DCs' rudimentary separator. This will get rid of a 2 foot long rectangular section duct that has a slow 90 degree bend and increase its height enough to have just one right angle bend and two feet of pipe. I think I will also be able to have a 15" length of straight pipe leading directly into the fan inlet. However I will install the straws as and when I can get hold of more suitable plastic tubes. I need to practise sweet talking sales staff.

I had hoped not to get so involved in researching but I find I cannot shake off thinking about and tinkering with Thiens. To have any hope of being able to get back to making furniture I think I will just have to make my top hat and do the work ASAP.

[Rudy81]

retired 2,

I wanted to thank you for all the work you did on your project and the time you took to make measurements etc.  I copied some of your excellent ideas and learned from your build.  I added a bellmouth and air straightener based on your data.  My build is larger than and although I have not fired it up yet, I am hoping it will work well.

[ORBlackFZ1]

When I have purchased Universal T-Track from Rockler and Aluminum Miter T-Bar from Peachtree, they have been shipped in plastic tubes.  I kept the tubes because I thought that they might be useful for something.  Now, I know what I can do with them.

[retired2]

When I have purchased Universal T-Track from Rockler and Aluminum Miter T-Bar from Peachtree, they have been shipped in plastic tubes.  I kept the tubes because I thought that they might be useful for something.  Now, I know what I can do with them.

That's exactly where mine came from, Rockler T-Track!  However, I think it was Phil who first suggested the best source, i.e. protective sleeves for fluorescent tubes from one of the big box stores.

[dabullseye]

nope it was me who said to check out the light tubes

[TX_Lenador]

The fluorescent tube covers work well. I came up with a combination of T12 and T8 sizes to create a snug fit in 6" duct. They are easy to cut and punch holes in to be able to fasten them together.

[ORBlackFZ1]

Question regarding the tubes....

I designed my Top Hat rotation in the same direction as my DC impeller rotates.  Do you think that I will need the tubes when I connect the Top Hat directly (with six (6) inches of flexible hose, of course) to the Top Hat?

Thanks,
Eric