Science Buddies: "Ask an Expert"

Hey so I'm doing an experiment on hydroelectric generators. The two I'm testing are the oscilating water column (OWC) and the tapered channel (TAPCHAN). I have research and everything, but I need help getting small scale generators to test it on. I'm thinking of making my own, but I can't find some of the materials, especially a small scale Kaplan turbine for the TAPCHAN and another small scale Wells turbine for the OWC. If any of you answer-ers out there know where I could get small generators on scale to eachother, or the parts to make and test them, I would reaaaally appreciate it a lot. Thank you!


PS my email is [removed]

PPS I'm also wondering how I would test the total electrical energy produced by the generators over a period of time. Would I use something like an ammeter or something?

Hello Sciencefair98,

Both the Kaplan and Wells turbines use custom fabricated parts and are generally manufactured for a specific installation. A quick web search I did turned up no turbines small enough for an experiment.

You can find some project ideas at these links.

https://www.sciencebuddies.org/science- ... p021.shtml
https://www.sciencebuddies.org/science- ... p037.shtml
https://www.sciencebuddies.org/science- ... p028.shtml

More discussion is found by searching https://www.sciencebuddies.org/science- ... l?From=Tab for "water turbines."

Building a Kaplan turbine would be a very difficult task requiring several machine tools. The Wells turbine is simpler, but it requires aerodynamically shaped blades. Another type of turbine that always turns the same direction is used in small vertical-axis windmills. Search the web for "vertical axis windmill."

If you want to get into fabricating your own substitute for a Wells turbine, why not adapt the idea behind vertical axis windmills to a reversible-flow water situation? I don't think you will get an efficiency as high as a Wells turbine, but it would make an interesting project to see how well you could do.

Think carefully about the amount of work in building and testing such a turbine, especially if you have a firm deadline. Also, be sure such a project would conform to the rules if you are doing this for a school project.

Small electric motors that also function as generators could be hooked up to any turbine you build. The power generated by your generator and turbine at any instant is represented by the product of the voltage and current being supplied to whatever load you use. The total energy produced over some period of time is the power times the length of time. For example, if your setup generates 12 volts and one ampere, you are generating 12 watts of power. If it runs for two hours, you have generated 24 watt-hours of energy.

Let us know how your project goes, and ask more questions if you wish.

Good luck, WW

Oh ok

If I used normal propellers for the OWC and TAPCHAN and added air valve flaps for the OWC, would I still get relatively the same results? Or should I use a normal propeller for the TAPCHAN and make a vertical axis windmill for my OWC? I'm kinda confused now that I can't use those special turbines...

Sciencefair98,

The Kaplan turbine differs from other propeller type turbines because its blades can be tilted as the rate of water flow changes. Fixed propellers can be used to make a turbine, but then it isn't a "Kaplan" turbine. See http://en.wikipedia.org/wiki/Kaplan_turbine.

I'm assuming this is your first turbine project. I think you may be underestimating the challenge of building even a simple turbine. I suggest you choose one type and work on it first. A fixed propeller would be easiest. After you finish and test a simple turbine, you can move on to more sophisticated ones. Professional design and construction projects are done this way, especially when working on something for the first time.

Building and testing a simple turbine requires you to confront several problems that you should solve, and if you solve them well, you have a very good project. Please look at the suggested projects I linked to in the last note. Two of them don't ask you to permanently mount the propeller and one of them uses an air fan that is already mounted in an appropriate housing so all you have to do is attach it to a tube. This fan has very carefully designed bearing to allow it to rotate without losing much energy to friction. How would you design and make the bearings for a custom turbine? How would you protect them from the water?

But in spite of several simplifications, those projects are considered complicated enough for a beginner. I like your aiming high, but don't aim too high on your first try.
Do a web search for "homemade water turbine" to see examples of simple designs. Also do a search for "Pelton turbine." It's popular for amateur construction for several reasons, and you'll find many examples of it on the web.

Let me know what you decide to do, and good luck. WW

Ok

So I'm just going for a basic understanding on the TAPCHAN, so I'll just use a normal propeller or fan. But what exactly should I do for the OWC turbine? I don't really want to use a one way propeller and air flaps. I'm going for a turbine that spins the same direction no matter what the airflow. Should I try and make that multi directional vertical windmill thing you suggested for the OWC? Plus, I just looked at the OWC experiment you suggested to look at. How does the one-way fan work when air is being drawn out? I didn't see any air valve/flaps.

PS thanks for responding so fast

Actually, never mind the last post. I think I will use a one way computer fan for the OWC. But I don't know where to get a small regular turbine for the TAPCHAN. If you know where I can get one, please respond soon. I need to have the TAPCHAN turbine so I know how big to get the computer fan (to have them on the same scale).
Thank you!

Sciencefair98,

I don't know of any waterproof generator you could use underwater. Unless the generator and propeller assembly has seals to keep the water out of the generator, it probably won't work long before it is damaged by the water.

You could use a belt to transfer the propeller motion to the generator or you could put a right angle in the piping so the propeller shaft would go out through the wall of the pipe at the right angle. Even if you extend the propeller shaft outside the water, you probably will need a pulley or gear system to make the generator spin faster than the propeller. You could use the propeller from a computer fan as your underwater propeller. Most small motors intended for model cars, planes, etc. will also function as generators.

Any design you come up with will not be nearly perfect. Optimizing just the propeller alone for the flow rate and pressure you will have is complicated and uses math beyond what I suspect you know right now. It will be nice if you just get it to work reasonably well and you understand the principles. By aiming for a more complex design than what is shown in the Science Buddies project ideas, you have chosen a complicated project.

The Wells turbine works when the fluid is flowing either direction because the blades are symmetrical: the propeller spins the same direction for either direction of fluid flow.