likely power calculation problems

[windyknight]

I have a fast flowing small stream nearby. Regulations prevent me from damming or diverting flow (hard to understand for you guys west of the atlantic!) but what doesnt seem covered is to use a bottom driven water wheel(by that i mean a paddle wheel dipped into flow) . There is a natural gulley a couple of feet wide running a foot deep and the speed of the water (pooh stick method) is 2yards per second.

A few scale drawings leads me to think optimum diameter of wheel is approx 4 ft if i aim for 6 inches of blade in the water, 8 blades gives one just entering water, 1 mid flow and one just leaving with each blade travelling approx. 2 ft in the water.

 Obviously with no load the wheel should rotate with perimeter at close to speed of water which I calculate will give a rotation speed of 15 rpm - ok so far?

Where i get stuck is deciding impact of putting some loading on wheel and what to aim for if say, I use blades 1 foot wide and 6 inches deep ( I dont want to obstruct flow too much or someone will surely complain -fish obstruction or some such!)

I understand the principal of head affecting power thru' a pelham or some such and my head tells me this wont work very well but my heart says different when i stand in the stream and feel the force of water on my boots.

I have built a wind genny using hugh piggot plans but to get any sort of voltage I would need a lot of gearing and associated power loss may nullify advantages.

Any ideas?

[hiker]

this may be of some help..............

     http://www.otherpower.com/scotthydro1.html

     http://www.otherpower.com/scotthydro2.html

[badmoonryzn]

Well, I'm in the west and we have the same problem here in Oregon. No dams no redirection, but have fun. Anyway I built a small undershot wheel like the one you are contemplating, and drove a car alternator without problem> the wheel was made out of wood and was 3 feet by 1 foot and it floated on a 4x4 mounted to a tree on the side of the river. I geared it up fifteen to one with an old electric scooter chain drive and wheel. It worked OK but I needed more speed. I figured it was going around 600 RPM or thereabouts, as I could not find my optical tach at the time. It was a one wire alternator and put out 13.2 at 12 amps. I need to find a better way to way to keep the RPMs up. Unfortunately after a month or so some debris came down the river and hit the float and ripped the thing off the tree. I did not see it happen, but I noticed the LED was not on in my shop so I went and looked to see why and it was gone. I found it downstream in a set of rapids right in the middle of the river. I needed a raft to go get it, so it sat out there for a couple of days. LOL By the time I got it the wheel had broke up land the floats were gone as soon as it was hit. I figure I need to make sure the unit is counter weighted and I need to use aluminium for the floats. If I make an arm that start in front of the wheel and floats about a foot the unit would ride up over debris. I'm sure that it was a log that hit it. The water was low and usually the river does not have big things floating down it during the summer especially near the bank. Live and learn I guess. I want to get the new otherpower/dan alternator out there to test it and them put in the 10k and use the otherpower alternator on the tower for wind. Nuts its snowing again. Oh well, I was very surprised how much power there is in the slow moving water. I need a way to calculate it. Good luck on yours.

Badmoon

[Nando]

You are not very clear with the description of the stream, a more detailed one is needed.

2. feet wide by 1 foot deep, make the wheel to have at least 10 inches under water and about 1.5 feet wide, then do not use blades, it would be a very poor wheel, build it like a Poncelet wheel, with full buckets 12 inch height size, and at least 1.5 buckets under water all the time, and since the depth is 10 inches the over all diameter should be 8 times for best torque, though, higher diameter will give better torque.
   
6. inches allowed to one side of the stream for the fish to pass without wheel interference, allows large size fish without any problems.
   
   

This bucket area and the water velocity will give you around 200 liter/sec that with the arm of the radius of the wheel will give you 200/.453 = 440 pounds and with an arm of about 3.3 feet for a total of 1450 foot-lbs at around 10 RPM.

Nando

[alancorey]

Hmmm, 150+ watts from a paddlewheel on an anchored float, now that's got me thinking of looking for good spots in the brook I've got.  Mine only has around 150 GPM or less most of the year though.

I wonder if the issue in windyknight's case isn't that he doesn't have head, but he's concerned about dams and diversions.  If it's flowing fast there must be some head somewhere.  I wonder if something like this might work:

Maybe this is what the post on 9/20/2006 was about, I don't know.  There aren't any permanent changes needed to the brook, or any damage risk other than erosion where you let the water out of your turbine.  You could actually set this up in the spring and take it back in in the fall if you weren't going to be using it.  Some hose or black plastic pipe run up the brook bed with the upper end bending down into a pool and weighted by rocks to hold it.  Very innocent-looking and easy to remove.  I've had one running for a few months now, although I'm still fiddling with getting enough voltage out of the hard drive motor I'm trying to use.  All I did though was to run the hose (plain old 5/8 garden hose in my case) and pour a few buckets of water into the upper end to get the sipon started, then stuck the end underwater and put the strainer on.  My strainer is a dish detergent bottle with holes drilled in it.

Don't bother with garden hose though, this is really just playing around.  After I'd done it I got a look at some tables showing friction losses.  I've got about 50 feet of head going through 400 feet of garden hose, with 2.5 GPM coming out.  I'll be lucky to get 6 watts out of it.  2 inch or 3 inch pipe would be worthwhile.

One nice thing about hydro turbines like Pelton wheels is that it's easy to get 1000 RPM or more out of them without any gearing.  Use a smaller wheel and it turns faster.  I was really hoping someone would jump in here saying that an axial flux genny could be useful at 15 RPM though.

  Alan