steam turbine and generator

Small turbines ‘Oi-vay’!. You would get more power out of a small oscillating steam engine that out of a small turbine. I have heard a lot of reasons for the low efficiency of these little brutes. But I am still not convinced.

In the mid to late ‘80 I had a lot of correspondence with the late Prof Chaddock on this subject. A few years ago I tried to get help with a letter to the editor Model Engineer.

The problems you will have are

A.   The bearings - they tend to ‘fry’ I tried all sorts even old battery electrodes!

B.   The gearing - most wheels seem to need the attention of a good dentist after a few minutes.

C.   Balance - Prof Chaddock wrote to me and said that he had to get the centre of rotation within 0.000002” the centre of mass. He did this with two razor edges some ‘bluetak’ and a small scraper.

D.   Low power output - it is abysmal I used to test run mine using a magnet and a coil connected to an old oscilloscope. I could hear the speed fall off when I connected them together.

E.   The turbine wheels I tried: DeLavals, Stumphs, and once as an absolute masochist a three stage Curtis   Stumpf wheels are the easiest to make with a little cone shaped end mill.  DeLavals you can make in two stages. Stage 1 gash your wheel. Stage 2 make a small hollow thin walled saw edged cutter to cut the ‘inner’ side of the blades.  I did not worry about the outer side of the blade. Sometimes I just gashed the wheel, shaping them made little difference. 

F.    Test them on a stout bunker. I used to disintegrate 75 to 85% of them.

G.   Have 50 times more steam available than you think you will need. Then treble that amount. Small Turbines are GREEDY. At low speeds they drink it and at high speeds they consume it as if it was going out of fashion!

I spent about 6 years on the project and got nowhere!

Finally remember that the speed of sound (in air) increases by about 0.6 M/S per degree C. So be careful when folk talk about steam flow being supersonic it often is not.

Paul - it may have been genetics or just stupidity – think the latter. From memory the Swiss gentleman uses a DeLaval type rotor. My DeLavals were slab cut turbines rotors were gut with a slitting saw set to give a 60° (or there about) angle of attack. I also tried by drilling and reamed a series of holes near the rim of the rotor at about 70°. It worked, and is how I built the Curtis.

There is something you could try as you are talking about 2” (50 mm) diam rotor. Make your rotor from non-magnetic stainless and insert a rare earth magnet and a pickup coil in the case. Keep your bearings well outside the hot area. The coil(s) can be rectified to give DC. You might just get enough power to run a bright LED.

Any way good luck and remember at the sizes we are working, I was assured by some aerodynamicists, that our blades are below their Radar so aerodynamic shapes were not all that important. 

Dick Parsons