Differential Pressures and Duct Design 101...

Not that I'm planning on designing any industrial dust collector ducts... but I am curious how the design work is done.
Any book suggestions on that? Is there a "ASHRAE Duct Design for Dummies" book around?
Here's the thing... I'm installing some instrumentation on several mid '80's design dust collectors for a steel mill. They have 'wet type' collectors made by an outfit out of Michigan named Schnieble, and they're in pretty good shape....
I'm putting pressure transmitters in various places and not liking the feedback I'm getting. The DP is not what it should be. I've talked to the engineers from Schnieble, and while they support these units they're no longer manufacturing them... modern technology triumphs again.
The manufacturer says all is (physically) as it should be... but then I got to looking at the original prints... circa 1980... and they show something called an 'evase' on the fan discharge. Now, I Googled this... and now have some understanding what it's supposed to do... but it isn't ON the units... I looked... twice. I still don't know how to pronounce it, though (=;.
Anyhow, the original fan design calls for 14.3" wc @ 48,000 CFM. I'm not measuring anywhere close to either number and I'm just curious as to why...
The customer will be happy if the DP is in range... but running 'out of design' has me curious... and curious minds WANT to know... )-.
Jake
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Jake wrote:

Jake, SMACNA sets the standards as far as duct Contruction (sizing, guage of material, stiffners, etc). ASHRAE sets the standard for quantifying how much air to be moved for varying applications, filtration etc.
So, to design duct system, you'll need SMACNA's Duct Construction Standards.
http://www.smacna.org/bookstore/index.cfm?fuseaction=search_results&topicID=4&cfidF71513&cftokenu048866
Do you know for a fact if your system ever achieved the design airlow & static?
Perhaps these guys can help you design & install the evase your system is calling for...
http://www.sdscorp.com.au/evase.html
as usual, if any of this is useful info, my paypal still works.
LOL j/k
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<snip>

Sounds like a major contributor to your discharge woe's. If it's not done close to correct, it'll turn in upon itself, (redirecting the energy)similar to a whirlpool in a white-water rapids. *(If someone has a more better analogy, please chime in.)
This seams to cover evase 101. http://www.aireng.com.au/Downloads/pdf/Diffuser%20&%20Outlet%20Perf.pdf

What you are getting now vs. what you will get, should you have the opportunity to remove the first discharge spool piece, should help determine your inlet design application worthiness since most all fan manufacturers will also show their fans discharge specs into free-air as well.
Also, a true RPM off the fan pulley (opposed to measuring and amp draw alone) narrows the variable of the fans true performance at any given time or after any alterations or adjustments.
And, for all other fan things; http://www1.eere.energy.gov/industry/bestpractices/pdfs/fan_sourcebook.pdf
-zero
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-zero posted for all of us...


--
Tekkie Don\'t bother to thank me, I do this as a public service.

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Ya...'zactly!...what he said...it ain't rocket surgery!.... :-)
--
Respectfully, Bob

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