Home Made Francis turbine

[scottylucas]

Hello,

Ive been doing alot of research on hydro power, and i have many many ideas, Initially I thought a Banki turbine would be the ideal turbine for my site, after i built one and really realized how the cross flow works, i don't think it's going to work properly and give me good efficiency. My new idea is a francis type turbine, I was thinking using a boat propeller for the turbine to turn a alternator or induction motor. I seen the kits on the internet like power pal, but it's just too expensive. Im just wondering if a boat propeller would serve the same purpose and do what i want and has anyone ever tried this before? My site has prob 10 meters of head or more but it's over a very long distance, but i have all the flow i want to an extent. Any comments or suggestions are greatly appreciated:) thanks

scott

[Flux]

If you have a long pipe run you will need some large and expensive pipe to use a propeller turbine. It will be somewhere between a Francis and a Kaplan but with none of the versatility of the true Kaplan. If you can match the specific speed then you may get an efficiency slightly above that of a Banki, but the chances of hitting everything right with a boat prop are not high.

Sounds like a perfect set up for a Turgo and well within reach of a Pelton. I think at that head an impulse turbine will work out far cheaper than a reaction turbine with its large diameter draught tube. The Banki will never reach the performance of a well designed reaction or even that of a Turgo or Pelton, but its simplicity and tolerance of crude construction will likely keep it ahead of your simple propeller turbine.

Flux

[scottsAI]

As Flux said, you can easily build a crude Banki and have it work. All other types require more precision in construction and implementation than a Banki.

Hard to beat using 3 sections of plastic pipe cut length wise in 4 to make a 12 blade Banki.

A plastic Banki can easily handle several hundred watts.

If much grit in the water, the plastic will fail faster.

Nice thing about a Banki, if more power is needed make it longer.

Make sure the pipe feeding the turbine is large enough without loosing pressure just before the nozzle.

Remember the job of the nozzle is to convert potential energy to kinetic energy. The nozzle area must be much smaller than the dia of pipe feeding it.

Have fun,

Scott.

[Ungrounded Lightning Rod]

I think boat propellers have the same problem when used as water turbines as aircraft propellers have when used as wind turbines:  The variable-thickness curvature that creates lift is on the wrong side of the blades.  So they're not as efficient as a purpose-built design with the right shape.

As Flux and Scott said, a Banki makes more sense.  Not only is it easier to build, it is to a large extent self-cleaning.  (Debris big enough to get stuck on the rotor openings when the water goes in on the first pass are washed off when it goes out on the second.)

[scottylucas]

What about if you used a impeller out of a torque converter, I mean, machine a pipe to go directly around the impeller and have an output shaft which drove a generator, the impeller in a torque converter is made to be driven by fluid i do believe. Ill take some photos of the banki turbine i have built and of the impeller on the torque converter i have an idea of using. if anyone has tried this before feel free to comment:)