Measuring waterwheel efficiency

[rattis]

How did British engineer John Smeaton measure the efficiency of an overshot waterwheel?

I am doing an experiment with overshot waterwheels to find their efficiency, and found that John Smeaton measured their efficiency at about 65%. However I have no idea how he got this number, and I cannot think of an accurate way of calculating its efficiency.

My latest idea is to use a dynamometer to find the difference in forces, then multiply by the distance traveled (2prn (where n is number of revolutions in t seconds, and r is the radius of the axle)) Then divide it all by t; to get Power. This would be compared with a theoretical power output calculated from gravitational and kinetic energy going in.

Is this the correct way to go about this? Or not?

 

[FredGarvin]

That's a good question. I couldn't find anything in my research into it. However, I did find a link to a professor at Univ. of Minnesota. She has specifically called out Smeaton and his waterwheel work and she is researching exactly what you are asking about. A link to her page is here:

http://www.me.umn.edu/research/faculty/alexander.shtml

THE MEANINGS OF EFFICIENCY is the title of my current book manuscript, analyzing the process by which people transformed the concept of efficiency from a technical measurement in science and engineering into a popular social and cultural value...The first comes from the early industrial revolution, and considers the famous English engineer John Smeaton and his studies of waterwheel performance in the 1750s, for which he received national and international recognition. Although Smeaton did not use the word efficiency, his analysis of waterwheels and power greatly influenced the developing science of mechanical measurement.

Perhaps you could contact her and ask her directly. She has an e-mail link on her page.

From an engineering standpoint, it seems that you are following the basic premise of power out/power into get your efficiency. I think the hard part would be determining the actual power entering the wheel accurately, especially if you are using a natural source like a river.

Hope this helps a bit.

 

[rattis]

Thanks a lot.

Initially i am using a model and the water is flowing down a 'slide' coming from the tap. As the model is not very good the water sprays all over the place, so energy entering and leaving the system is hard to find