Steam turbine generator

[RET]

Hi,

Remember what I said about the jet velocity being 4 to 6 times the blade tip speed even at 40,000 rpm? This means that you don't want to let the jet go "splat" against the blades as it would against a gear tooth or an impeller blade as you show in your picture, but for the greatest efficiency you want to turn the jet flow through more than 90 degrees. It takes a force to do the turning and this force is imparted to the individual turbine buckets when the flow is directed tangentially to the blade.

If you ,look carefully in the picture, you can see that each bucket pair has a "lid" on it to keep the flow where it should go. I did that by necking down the 1/8" end mill using a Quorn (a fancy miniature tool & cutter grinder from Model Engineer) and then hand sharpening the cutter under a microscope so I could see what I was doing.

These are two of the turbine wheels I made about 5 years ago.

The picture shows two of the sample wheels I made to see if I could. With the little CNC mill, it was easy. In that design, the idea is to have the expansion nozzle tangent to the centre of the wheel thickness. The wheel design splits the flow so half goes left & the other half goes right. The buckets will turn the flow through about 130 degrees. Each wheel is about 1 1/8" dia. by 3/16" thick.

I haven't tried it, but I think that if I put four nozzles around the wheel periphery, there would be enough torque to drive a locomotive with suitable reduction gearing.

Richard Trounce.

[daves1459]

I'm pretty sure your going to be disappointed with the reverse pump impeller concept. The impeller as shown in your picture is for a centrifugal pump. It works on the ratio of the radius of the I.D. or inlet to the vanes versus the radius of the O.D. or outlet of the vanes and the angle of the vanes. Vanes angled like in your picture are for high volume low pressure pumping. As the blades straighten out and become more radial their function changes to lower volume and higher pressure. In any case the pump impeller is not what your looking for.

You need what would usually be called a turbine. Turbine blades are curved and function by the air, steam, oil, or what ever fluid entering at an angle and following the curvature of the blade and exiting at a reversed angle so that the direction of the fluid is reversed and the momentum of the fluid is transferred to the turbine blade producing torque. The exchange of momentum of the fluid to the blade can be enhanced by giving the blade an air foil shape which will increase the fluid velocity and add some lift.

Don't be scared away by all this. Your rotary table can be used to create a reasonably good blade. Looking at you impeller picture imagine the blades are a "U" shape entering like the impeller blade but exiting at the same angle in the opposite direction. With the turbine on some sort of indexing device and the center eccentric to the rotary table so that the center of the "U" shape is on the center of the rotary table curved blades can be machined with a small diameter end mill. If the inside radius of the blade is larger than the outside radius a rudimentary airfoil will be created. Blades of this type can be machined either radially or axially using the same concept. Aim your steam jet at the inlet of the blade exactly as practical as the entrance angle of the blade inside radius. If you machine a slight diverging cone into your steam nozzle the exiting steam jet shape will have less turbulence and impart more momentum unto the blade.

[jscarmozza]

I'm winging it Builder, that's why I'm looking for advice from 'someone who knows'. RET and Daves1459, thanks for the heads up on the pump impeller route, I actually thought I was on to something with that approach...it was a wheel style I could build. OK, it's back to the drawing board, thanks for taking the time to reply with advice, I going to study your comments. John

[Builder01]

I don't know if it's possible, but, probably more first hand examination of working examples is in order. I would not try to invent something that I have never even seen a working example of. Take notes, then make one! This technique has always worked well for me. After you have made a successful example, then set out on your own.

David

[Wolfgang]

Hello turbine enthusiasts!

My personal philosophy is to "not reinvent the wheel" because life is too short to do that.

The turbine wheel and buckets I produced are a simplification of Stumpf, Curtis, and Terry turbine wheels.

Here is a text book from the turn of the last century that describes these very well.

http://icsarchive.org/asc/asc_steam_turbines_2_1917.pdf

Scroll down to page 13 and further for descriptions and illustrations.

I've looked for my CAD drawings of this device and found that I cannot open the .skd files any more with Autosketch. I need to work on this problem a bit. w

[Asteamhead]

Hello Wolfgang,
A photo may explain much better what I tried to explain above. Steam from the nozzle at the bottom of the case hits the teeth tangential before it leaves towards the exaust cavern at the left. This seems to work a bit like an ejector thus generating a slight (desired) vacuum arround the turbine wheel.

Best regards
asteamhead

[Fender]

I've heard of a scheme to build a "semi-dummy" turbogenerator. This uses a jet pf steam to spin some metal balls in the "generator" to make the traditional whine and steam exhaust, but doesn't produce any electricity. Does anyone have drawings of such an item?

[jscarmozza]

Daves1459, I'm going to give your wheel another try, I tried it once before but the gash style cutter that I made didn't have any relief and left a rough finish on the U, I also didn't get the spacing correct for them either. Thanks for the link Wolfgang, that's going to be an informative read, I'm not looking to reinvent the wheel either! I appreciate all of the information in all of the responses. Asteamhead, is my understanding correct, your turbine rides on the piston style ring seals and has no bearings? If that is correct, brass body with cast iron rings I would assume. I don't have any CNC machines, everything I do is manual, so I have to keep it simple. John

[Wolfgang]

Hello John,

The radial wheel you showed earlier will run but, it would require a large flow of low pressure air or steam. It is basically a low pressure device whether run as a compressor or turbine. No comment on its efficiency though.

For our models we are interested in high pressure (relatively) and low flow devices as these are small and use quite small amounts of steam.

You probably already know that any wheel with some kind of indentation can be made to run with an air blast; you have shown a gear wheel used as a turbine runner and I am certain that it will run. And who hasn't spun up a ball bearing with an air gun, just to see it race across a concrete floor with sparks flying.

Steamhead: Thanks for your reply; I now understand your statement. If I build some more T-G I will incorporate an expanding exhaust stack. From my hyperlink above there are also some ideas worth considering, w

Bliss. Wolfgang

BTW, all I have are manual machines. Surprising what can be achieved with patience, persistence, and ingenuity. w

[Wolfgang]

Hello Asteamhead,

Thanks for your reply; I now understand the principle you were describing.

Should I build more of these beasties I would incorporate an expanding exhaust pipe to enhance the venturi effect.

Kind regards, Wolfgang

[jscarmozza]

I made a new cutter today, on a 1" diameter wheel I can only cut the U to a depth of 0.070", is that deep enough? John

[Wolfgang]

Hi John,

My buckets were machined .080" deep at the bottom of the "U", with 12 buckets on the wheel.

Thus I think your depth of .070" will be fine. How many buckets does your wheel have? What diameter are you proposing for the nozzle throat?

Our discussion here has got the ol' brain cells moving and I am inclined to make a new wheel with .060" deep buckets and more thereof. In addition perhaps incorporate other changes discussed herein. w