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homebrew hydro update: coanda water intake - Page 9

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Posted by z on March 5, 2009, 1:36 am

With your posts in mind I watched my screen today when I was up there
attaching it to my water system (yeah I finally got the stupid 45 degree
fittings I was needing).  Seems to work like a charm btw!!!

I think the angle does exactly what you are talking about.  The water
falls at an angle and the screen is set at a similar angle, so when the
water strikes the screen it is more or less in line with the screen, but
just not horizontal

I was watching the water and the debris as it did its thing and the issue
I think you'd have with a horizontal setup are the small stones.  It is
pretty cool (I should have brought the camera damnit) -- the screen even
with the angle to it seems to produced a graded sort of stones that
larger than 1 mm.

Its hard to describe: the parts of the screen where most of the water is
striking is clear but for some plant matter.

In the area where less and less water are interacting with the screen you
see larger and larger particals building up.  There is some ratio of
gravity and slope of the screen (and friction I guess) that sorts very
small stones into a rough order of size (mass I suppose).  With the
screen flat I get the impression that those might build up since they'd
only have the force of water to move them down the screen and away.

Likesay i'm only observing -- i'm no rocket scientist :)

I'll try to get a pic next time.  

Now if only it would sort the gold out I'd buy you all a roller and we
could argue while drinking crystal !!

thanks again for all the help on this project


Posted by Bob F on March 5, 2009, 3:49 am
z wrote:

I don't think I suggested the screen should be flat. It should be sloped, and
the water flow onto to it should be sloped the same , to flow water over it
without changing direction. I guess it is obvious that debris will build up if
all the water goes down through the screen. When water flow increases more than
the screen and pentstock can carry away, I would expect the water flow to clean
off that debris as it leaves the far side of the screen. I suppose, it might
take some extra flow if significantly sized debris builds up. Your screen is big
enough that I would never expect this to restrict the water available to the
generator, although I could be wrong.

It would probably be nice if the pond source would settle out stones and sand
before thay can get to the screen. A clean trough from the pond to the screen,
picking up water not from the bottom of the pond should allow this.

You might check with the screen manufacturer to see if they suggest what water
flow angle the screen works best with. Those screens might be able to handle
fairly steep flows and still pass the water you need, but I don't really know. I
would expect that steep angles would lessen the debris collected, especially
things like rocks.

Having a smooth water flow onto the screen, would also lessen damaged from rocks
washing onto it. No impact.

Have fun!

Posted by z on March 6, 2009, 7:22 pm

Yeah I think the mental image I had of what you were describing must have
been off by some degree.  For some reason I had it in mind that the
screen would be flat in the flow, so I think we agree now that I've reset
my cortex :)

My intake is on that weir, so its not really a pond, just a break in the
stream to direct the flow onto the screen and make enough of a drop that
the collector can sit under the screen and have the water flow over it.  
The water behind the weir is about 1-1/2 feet so quite a bit of the
stones etc collect behind there.  Its just in the higher water situations
where the stones and stuff flow over.  Most of the time the screen is
just keeping floaters out.

Yeah.  Right now the size of the collector determins the angle and
placement of the screen.  I have another design in mind that would let me
arrange the screen closer to the flow and at various angles.  

But to be honest the sucker seems to be working and so i've got other
things to do.  What I'll probably have to do is maximize the water intake
this summer when the flow is much lower.  I'll need all that flow so
it'll be a good time to make it efficient.  Also it'll be nice and warm
-- perfect time to play around in water.  Now its kind of a cold job
dicking around up there while its raining and 40 degrees out :)

It is pretty fun -- cheers

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