Cascading laminar waterflow on glass.  I am building a "waterwall",
consisting of glass 2meters high and 3 meters long with water flowing
along the glass on both sides. I am having the water applied to the
glass thru a series of uniformly spaced holes in a pipe on either side
of the glass. The water does not uniformly "wet" the glass.  HOW DO I
GET LAMINAR FLOW ACROSS THE ENTIRE GLASS?  I have tried a variety of
pipe diameters and flow rates, but the first 1/3 of the length of the
pipe does not flow well.

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Request for Question Clarification by sublime1-ga on 04 Jan 2006 20:21 PST

The first third being the third closest to the water source?
My first thought would be to graduate the size of the holes
so that there's more flow in that third which is currently
diminished.

sublime1-ga

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Clarification of Question by chilidog-ga on 05 Jan 2006 19:40 PST

Clarification- 1)The "first third" is the section of the pipe nearest
the source. 2)According to basic fluid mechanics, the pressure (and
corresponding flow rate through the holes/jets) is higher nearest the
source. 3)I have increased the hole size in that area without success.
It resulted in more flow, but no better coverage. 4)Reducing the flow
thru the first holes by restricting the flow into the pipe(until the
flow out of the first holes is = or < to the flow rate of the good
performing section) does not improve the flow. 5)The glass has been
VERY thoroughly cleaned (with acetone). 6)I tried JetX which made the
water wetter, but that's not the problem. 7)I have incorporated a
smaller pipe inside the main pipe to carry some of the flow further
along the pipe. 8)I have not made a manifold to have the water enter
the pipe at multiple locations. 9) I am looking for a proven
application or knowledge of fluid mechanics that will eliminate
further empirical trial and error. Thanks.

You need to have constant flow across the glass as is flows. Either
vary the hole sizes as sublime said (smaller closer to the source) or
an easier way would be to have the source come from above and split
the sources with uniform holes.

It helps if the glass is pre-wet.  Just spray the glass with a little
wetting agent (go to the hardware store...teflon type of thing) or add
a little bit of soap to the water and it should help.  This will
reduce the friction for a more even slide.

To expand slightly on what Webravi said about wetting agents-- if
there is any grease or oil on the glass, the water will tend not to
flow there. The glass has to be clean, clean, clean. In addition to
water I would expect a small amount of ammonia and/or isopropyl
alcohol might help, a weakened version of... jeez, what's the blue
glass cleaning liquid they sell in stores...? That stuff, without the
blue.

Hey, a self-cleaning window!

This may be what webravi was getting at, but the problem sounds like
uneven pressure along the length of the pipe causing uneven flow. Try
running a parallel pipe with no holes, join the two ends and have the
source enter the solid pipe in the middle. That way the water enters
the pierced pipe from either end and pressure can equalize along the
pipe. Depending on the length required you may need to make additional
connections between the pipes.

I have a slightly different pipe configuration that should work
perfectly. Use a small tube from your pump feeding a larger pipe with
a quarter cut out down it's length. (I have a link to a really crappy
picture i made. It's looking at the pipe from the round end)

Normal pipe = O
My pipe =     G

(forget about the little horizantal line on the G)

if you then put a smaller tube (Red) feeding a larger tube with a slit
cut down it's lenght (Green) water (blue) will fill the pipe evenly
until it overflows on the glass(grey) side. The only downside is that
you have to have your pipe pretty close to the glass at the top. All
that would be required at this point is that the top pipe be close to
the glass.

http://nissaninfiniticlub.net/photopost/data/500/7014water.JPG