Turbine – Part II

I did a little bit of playing with numbers talking about the turbine in the Caddo Creek Dam thread. I’m going to expand on that here.
Casing Size
One of the things we have to keep in the back of our minds when doing virtual modeling is that at some point we may want to actually make the darn thing. That means finding a source and then use the dimensions of that source for the virtual bit.

Plastruct has a selection of Clear Butyrate Tubing in the sizes I might need.

In Part II of my Caddo Creek Dam thread I talk about “How about HP?“. There I ‘guess-ta-mated’ that the turbine casing is approximately three times the dia of the turbine wheel. If you used a 36-in turbine wheel then the casing would be about 9-ft in dia. From the center of the turbine shaft to the ground then would be around 4-1/2-feet. My original 12-feet of head then is reduced by that 4-1/2-feet to 7-1/2-feet of head. That would result in around 37-hp.

Reducing the turbine wheel to 24-inches would require a 6-ft dia casing .. 3-ft from the turbine shaft to the foor and leave us with a 9-ft head – and give us 22.24-hp.

Looking at it from another direction, I reduced the casing to 4-ft dia. That would give me a 16-in dia. turbine wheel. Putting info from the chart I calculated that with 9-ft of head and a 16-in dia wheel we can get about 24-hp. Not much but enough to power a small generator.

This was all based, by the way, on my imaginary Caddo Creek flowing 7,560 cu.ft of water a minute (see How Much Power?)

So. What does that mean then? That I need a casing 4-ft in dia. In O Scale that is 1-in dia tubing. Looking back at the tubing that Plastruct has available I see they have Catalog Code. BTB-32 – 1″ (25.4mm) OD, 15/16″ (23.8mm) ID. I will model the turbine on that then.

My best guess simply from scaling from photographs is that the casing length equals the casing dia.

So. 1″ OD (O Scale) would equal 4-foot full scale.

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