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homebrew hydro update: coanda water intake - Page 8

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Posted by vaughn on February 28, 2009, 3:18 pm
 


   Bummer.  You hardly ever hear of that happening any more.  When is comes
to cars, they don't make them like they used to, and that's a good thing!
Transmission shops are almost a thing of the past.

Vaughn





Posted by z on February 28, 2009, 5:08 pm
 


Yeah.  This was a 90 toyota 4x4 i got from my old man when he kicked
off.. it has A LOT of miles.  My mechanic buddy is working on it -- He
was saying if its just the main bearing (which it seems like it is) its
not that hard to change.  he's just trying to find the replacement parts
first.  Toyota used a number of transmissions during those years.

But I was on the way to buy those fittings when it went down .. my local
feed store didnt' have 2 inch fittings so its a 50 mile drive to get em.  
I'll get to town again soon enough and get those parts.

anyway enough bitching.. its an old toyota work horse that I don't
begrudge a little break down.

cheers

-zachary


Posted by Bob F on March 1, 2009, 2:38 am
 z wrote:

Would the debris clear better if you had a flat-bottomed channel feeding the
water onto the screen at the same angle as the screen, with no drop at the
screen? The water velocity would be higher.



Posted by z on March 3, 2009, 6:53 am
 

Could be.  Most of the coanda intake type setups i've seen have water
dropping down at an angle from a dam, or from a waterfall or some other
higher source

see the second pic at
http://www.canyonhydro.com/Resources/Guide/HydroGuide3.htm

or search wedge wire screen

I'm not saying I know the physics behind this 'coanda effect' but judging
from the way most applications are used and how the lit i've read over
the years goes the water must hit the wedge wires at an angle so to
'sheer' off layers of fluid, which follow the contour of the wire away
and down into the collection area:

http://www.coandaintakes.com/How_coandas_work.html
'The key to a coanda intake screen is the unique tilted wire design. By
tilting the profile wires upward into the stream flow, the leading edges
of each wire act as knives to slice off layers of water'

There are some practical matters which could create problems with a
direct flow setup.  In direct flow you its hard to manage the water -- my
current water intake is basically like you describe without the sexy
screen.

When dealing with variable water flow you've got to have an intake that
can take very high water and also work in very low water (summer)
conditions.

The flat screen would require some kind of damn or weir to manage the
flow.  Like the one I have now just sits flat in the stream but when the
big water hits, the water always digs down below the intake and
eventually the volume and pressure (and debris) builds to the point where
it dislodges and gets pushed down stream.  

The beauty of building the weir and letting the flow cascade onto the
screen at an angle keeps the force of that water pushing down on the
intake and doesn't allow it to push against it so you don't find it 200
yards down the stream after a big rain.  Also the weir provides a natural
break in flow so you don't get all that force hitting the intake
structure itself -- the dam takes that.

just my thoughts on why its a good idea to have the water all onto the
screen rather than at the same angle of the stream.  

But i've been known to be full of shit too so :)

cheers

-z

Posted by z on March 4, 2009, 5:32 am
 

This does sound like a good method.  I could probably build a channel and
attach it to the flow from the weir, but I have my doubts about it
withstanding some conditions.

Now some other stream it might never have a problem, but once in a while
we get like 12 inches in 10 hours -- its like a flash flood nearly.  That
little creek really rips down there and its got big limbs, small root
wads other big debris that if they get stuck against screen it puts a lot
of force on whatever mounts you have.

We haven't had one of those yet, but some winters they're pretty common.

Having the screen at an angle may let some of those roll off .. who
knows.





I appreciate it a lot -- lots of good advice here.  I got those nozzles
so i'll be testing them in the next few days.  They are interesting
design.




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