Home Brew Hydro:
A small hydroelectric project: Coanda Effect Water Intake (Rain Update)
Home Brew Hydro Saga
MK I: Early turbine and generator
MK II & III: New alternator and couplers
MK IV: shaft bearing and real world use
Coanda Effect water intake (New Rain Update!)
alt.energy.homepower discussion
The Screen
The Coanda Box in action
One of the more difficult things the home hydroelectric user faces is how to get the water in the pipe! I feel your pain, having grown up with gathering water from this very stream for house and drinking water since I was a little kid. Get up the hill and fix the water system my old man would say, glad he'd bred some offspring to do that wet cold job instead of him. But now the water requirements are much much higher.
The main issue I've faced is that this little ankle deep stream can range from being nearly a trickle in the hot part of the summer to a raging torrent in the winter. As you can see from the moss, moisture isn't an issue, but the trick is to make an intake that can withstand very high volumes of water filled with gravel, sticks and general debris and also have it work during the dry season without too much screwing around. This wasn't such a big deal when all I needed was 3/4th inch line to keep my home water reservoir full, but now we're talking serious water to run the homebrew hydro 24x7
My current intake does two out of three jobs pretty well. I used a fiber glass fish hatching box with a sewer drain screen inverted to keep out the leaves and other crap. Its great for low and mid level water. Right now, with the near drought we're having its been running just fine for a month or two. But the last big rain you can imagine 10x as much water in that same space just filled it with silt and washed the whole thing out.
Coanda Effect Wedge Wire Screen
I had been reading about the coanda effect for ages, especially as it relates to moving fluid through a screen:
Coanda effect is the phenomena in which a jet flow attaches itself to a nearby surface and remains attached even when the surface curves away from the initial jet direction. - thermofluids.co.uk - also see the wikipedia for more info
What does this mean to you and me? Well a screen with the right shaped wedge wire can 'pull' water through very small gaps at a much greater rate than would otherwise be expected, while keeping any debris larger than 1 mm out of your water -- and at the same time those larger debris are washed off the flat wires by force of water. The ultimate self cleaning intake. How cool is that?
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. This creates surface adhesion on the top surface of each wire which is the coanda affect. The surface adhesion directs water on each wire through the screen where water is diverted into a collection channel for further conveyance to a penstock or pumping station. -- coandaintakes.com
I've been lusting after such a screen for years, but with the price of stainless steel it was just too much to shell out. Till recently. I searched around for a source and came across Coanda Intakes and sent them an email asking if I could get a screen they might have lying around or whatnot for a good price:
Dear Zachary.
We can process a 2'x2' section on the back end of another order to eliminate
a set up fee. As for the slot, we would recommend a 1.0mm slot as this seems
to generally work best for most applications.
The cost will be $153.00 plus shipping costs.
Shipping: 7-10 days.
Thank you and we appreciate your interest.
Kind Regards,
Kevin Toler
Coanda Intakes, LLC
Tel: (304) 767-5055
Fax: (304) 763-3263
Fantastic -- Kevin set me up within a week or two with a nice 1 mm gap coanda effect stainless steel screen for less than $200 including shipping-- which only six months ago would probably have been $400. I guess that's one upside to the crap economy. He emailed later on with the news they were doing a 26" run so I got a 26" x 26" section for the price quoted above. Nice job & quick communication. I highly recommend Coanda Intakes for a quality product and great personal service. Made in America too.
Putting it together
There are two parts to the intake system. First the screen must be at a sharp enough angle that the leaves and other debris will slide off the screen and down stream, and second you must have a method for gathering the water into a pipe. I'm a big fan of food grade plastic olive barrels so I cut up one to sit beneath the screen and grab the water. I shored it up with a wood and internal aluminum frame to keep it stiff and to provide something substantial that the screen could mount on.
So I got that done and then figured out I didn't have a good spot to set the intake into the little stream where the water was dropping down enough to fit the thing in and let the water flow over the screen and into the olive barrel. What I needed was a waterfall, which there are several but they were in places where the canyon was so deep i'd be trying to send water uphill to get out. As you can imagine, gravity flow requires the intake to be the highest point in the system otherwise you are drawing with a siphon (which can work fine as long as there is plenty of water -- in low times it kills you). So I built a weir using some tin and fence posts. I lined it with UV resistant food safe plastic and i'm filling it in with gravel and rocks, with the hope it will silt in and basically raise the stream bed and provide enough drop for the magic of coanda to take place.
I know it looks kind of ugly with the plastic but once we get a really good rain i'll be able to trim that back since it should be full of rocks and silt. Just wanted to keep the water from finding a way around the weir long enough to fill itself in -- i've also been shoveling gravel and rocks into it. I don't think my angle is sharp enough so i'll probably cut another olive barrel that will fit better, but for testing it'll do for now. I need a big rain to hit and see if the weir holds up and how well it acts under extreme conditions. Till then I'll keep screwing with it.
Here's a longer shot of the area I'm working. Its a good hoof through some rough country to get here. Thus the tin weir rather than concrete and the olive barrel rather than something heavier. Its a hump to get anything up here.
Its hard to see here but the water just falls through those 1 mm gaps like you wouldn't believe. The debris are pushed away from the flow and now I'm just waiting for a big rain to see how she does in the big water.
Got a pretty good steady rain over the past few days. We're not at high water yet but this is about how it should be in a 'normal' winter:
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| Day 1: You can see the debris moves away from the flow pretty good. A few leaves get stuck. | Day 2: WOW. Look at all that crap that didn't go into the pipe. The force of water pushed it down and away from where the flow actually hits. Some things are stuck in it, mostly plant stems with leaves. The stems get stuck in between the 1 mm gaps and kind of hang on. | Day 3: Now we're cooking. This is the kind of flow that used to FUBAR my other intake. All the crap is washed off and so much water is flowing through the screen that its welling up out of the collector and flowing out the bottom. The small stuff stuck in there doesn't seem to occlude the water flow too much. |
So this looks like money well spent. I just need to get a few fittings to finish it off and shore it up a bit better. Check out the condition of my 'normal' intake today (day 3)
I have to admit to not securing the sewer drain screen like I would normally last time I was screwing around with it, but as you can imagine all kinds of crap is in that collection box -- sticks clogging up the line etc, and when the water REALLY gets high it can carry the whole thing on down the creek. Yup --the $200 for that new screen looks like it might have been worth it.
Big thanks to Coanda Intakes for the sweet deal. Hope I can make it work like it should.