Inlet Screen Diffuser

[FishScreener]

I am designing a fish screening system for a gravity irrigation deiversion from a natural stream.

It is basically a wedge wire drum, 6-ft long, 18-in diameter, with 0.0675 wires and gaps. It is similar to a well screen, with a pvc diffuser inside of it with a bunch of 7/8-inch diameter holes to avoid hot spots.

My boss, (who is not an Engineer), is insistant that the holes need to be graduated in size going from small at the end by the discharge to large at the other end. This is based on having seen difussers designed for pump inlet screens where the differential head through the screen is measured in feet.

On the gravity diversions, I am designing for a head differential of 0.02 feet. I can't get enough flow difference due to the low head to see varying the size of the orifices in the diffuser.

Am I on the wrong track? Does anyone know of a web page or online reference, or even a book that explains the orifice sizing? So that I can show him my math is correct.

 

[BigInch]

I'd totally forget about orifice design and go right to fishscreen designing!

Can't really see the reason you're calculating orifice sizes for fish screens. There must be every kind of fish screen already designed. I Googled "fish screen design" and got 2 million pages of hits.

I'd start by looking at this one,

http://www.dfo-mpo.gc.ca/Library/223669.pdf

If you really do need info on orifice designing, Google it and you'll get 10 million hits on that one. In fact search eng-tips and you'll easily get over 100.

Maybe I'm just too lazy today to consider designing another wheel. Sorry.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[FishScreener]

Big Inch, you seem to miss the point and have trivialized the whole thing.

The screen sizing is easy, and so for that matter is the diffuser manifold design. But, I work with and for biologists, for whom the math is intimidating, and who want to rebuild whatever they saw in a catalog. Not understanding math, they are uncomfortable with equations I derive, particularly when it doesn't match the picture they have seen before.

Fish screen design is driven by biological criteria, such as swimming ability and size of the fish you are trying to protect. And, is thus species, site, and biologist dependant.

You alluded to the ease of finding information on intake screen and diffuser design online. So, what search string do you propose on what search engine? I did look before and was unsuccessful in finding any pertinent information.

 

[BigInch]

Right. OK.

"Does anyone know of a web page or online reference, or even a book that explains the orifice sizing?"

I often miss the point. Do these help?

theory & equations

http://www.omafra.gov.on.ca/english/engineer/facts/vfss_manual/vfssman34.htm#344

http://www.engineeringtoolbox.com/orifice-nozzle-venturi-d_590.html

equations

http://www.mycalculations.com/chem/jmm/chem14.html

http://www.knoxcounty.org/stormwater/pdfs/vol2/3-3-3 The Design of Extended Detention Outlets.pdf

online calculate orifice size

http://www.tasonline.co.za/toolbox/pipe/velorif.htm

http://www.mycalculations.com/chem/jmm/chem14.html

http://www.pumpuniversity.com:8080/...mula.jsp?id=6&name=Orifice+sizing+calculation

http://www.spiraxsarco.com/resources/calculators/orifice/flow-coefficient-to-orifice-diameter.asp

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain