Water wheel design

[SeanR]

Hi all,

I am in the process of designing a water wheel to harvest some energy from the exit of our lake. The head is 10 feet and flow will vary from 60 cubic feet minute to over 400 cubic feet minute. Because of the wide range in flow and relatively short head I have opted for an overshot water wheel.

I could probably get up to 30 to 40 feet head for a different type of turbine but that would mean at least 500 feet of penstock and as much of wire coming back to the house and so far my conclusion is I can't afford the pipe that could allow taking advantage of the flow during peak season.

My question is, does anybody have an empirical formula for the optimal bucket design. From the literature I have managed to find so far 20 degrees angle from the tangent of the wheel seems the best for a strait sided bucket in order to retain water as long as possible and also favour water entry while emptying rapidly before the return. But the optimal shape must be some kind of an ellipse in my mind and that is what I am looking for.

This is what I have drafted so far:

This link although in German has nice graphics:

http://www.opentheory.org/wasserrad/text.phtml

Suggestion on some books or literature on the net would also be great.

Thanks

Sean

[Nando]

SEAN:

The way you are proceeding, it seems that you are shooting your foot.

The 60 CFM = 28 liter/sec and 10 feet = 3.048 meters give you close to 516 watts

If you extend the pipe 500 feet and get 30 feet the power would be 516 * 4 = 2064 watts

If additional head is 40 feet, then 2580 watts minimum.

Then with the higher water levels you may obtain all the necessary needed power.

You may use sewer pipe, which is cheaper, for the project and then the design can be made to give 4 or 6 Kilowatts to fill all your needs, specially in winter.

The under short or over shot wheel should be calculated to the power yu can harvest and how to define the available torque.

The under shot fed with piping may produce better power than with the over shot.

A banki turbine would be much better with less mechanical work producing higher power, because for this low power, the turbine can be designed without multiplier gears or may be just one multiplying step.

Or do like a fellow did, started with low head and a short piping length and periodically he was able to get more pipe, so he installed and moved the turbine to the lower site until 4 years later he had all the power he could get from the site.

Nando

[steeolico]

Come ti ha consigliato il grande Nando anche io realizzerei una turbina Banki.

Ti invio il mio diario relativo alla turbina banki da me realizzata, ci sono anche le formule:

                   Translate Google

As the great Nando has advised to you also. I would realize one Banki turbine I send my per diem relative one to you to the turbine banki from realized me, are also the formulas:

http://www.fieldlines.com/story/2006/8/13/6320/26408

Steeolico

[Countryboy]

Hi SeanR,

  It all depends upon what you want to use the waterwheel for.  Do you want it for electricity generation, to pump water, power for a sawmill or grindstone?  Do you want torque or RPM?

It sounds like you might want it for electric generation.  If that's the case, you are wasting your time looking at an overshot wheel.  A 100% efficient overshot wheel will still be miserably poor at electric production - it spins too slow.

Try looking at a Mitchell/Banki turbine.  It will be substantially cheaper than building an overshot wheel, and much better suited for electric generation.

[SeanR]

Thanks for the replies.

I will try to give additional details on my project. The original plan was to produce electricity but also for the looks and maybe eventually to turn a stone.

I had thought of doing both a Water wheel and then eventually a modern turbine taking advantage of the total head leaving the wheel for fun.

The lake has about 1 million square feet and I could use about 8 inches for additional storage.

Nando you have got me re-thinking the project but the issue is to take advantage of the 60 cubic feet a minute (400 GPM) 4 inches will leave me with about 360 GPM at 0 effective head for 500 feet of pipe.

I will need about 5 4inch or Ideally a 8 inch penstock to do the job and 500 feet of 8inch is more than I can afford now but I will be looking in scrap yards for something.

Also with this I don't take advantage of higher flows in spring, but I must agree that more power year round is better than one short burst.

Steeolico,

I had seen your post last summer but had forgotten about it since; please let us know about final results. I am considering going that route a lot more now.

Countryboy,

I was hoping to use timing belts to multiply the RPM. I do believe that that is the most efficient low budget transmission I could achieve. I was also planning an axial alternator at about 500 RPM, 14 RPM with 2x 6 to 1 increase (14x36).

Dennis

Thanks for the reference, I spent I don't know how many hours on the net came across Spoom many times but never noticed the book store.

Thanks all I am now open to suggestions for a proper turbine.

PS I found a 3 HP induction motor at work today.

Sean

[RP]

Sean,

Could any of that penstock be replaced with an open ditch?  I'm assuming part of the 500' of pipe is simply to get past the slope of the levee wall.  I just wondered if you could go part way with no head in an open trough and then drop your penstock from that.

[Gog]

Hi Sean, though you seem to be leaning towards a turbine i thought I'd add a couple of things to keep in mind if building a water wheel from my playing with a 4 footer for a year or so.

Neighbors, That low frequency thump travels a long long way on a still night, tuning your water entry angle and entry point can reduce it a lot

Backwatering , If the water in your exit flume gets higher than bottom bucket height during high flow periods your output will be reduced to near zero

I'd also like to have vee belt somewhere in the driveline as it slips during high stress (flow) times rather than have the huge bang when a cog jumps a tooth.

Cheers

Keith

[SeanR]

Thanks for the suggestions.

I guess it will mostly be up to wich parts I can get my hands on first at low cost Pipe or steel.

But at one point I will end up with both if I can afford it.

The open ditch would be great but from the lake it goes strait to a 10 foot water fall.

I could not find any photos, will try and take a few shots this week-end

Sean

[zoocanoe]

Sean,

If you are looking for optimal bucket design for an overshot... you should look up the "fitz overshoot watersheel".  There is a series of 4 articles that explained how the curve is draw "Fitz wheels" by Robert L. Omland, they start in the July 1983 issue of OMN. You can get back issues on The SPOOM web page store.  {I really wish they would post a issue index}.  I have spent some time drawing a waterwheel I intend to build for a up and down saw mill some day.  I can post them if you like {and I figure out how to post imgs}.  

The waterwheel factory has purchased rights to the name and you can find good info at http://www.fitzwaterwheel.com/

zoocanoe