Steam turbine generator

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Dick_Morris
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Re: Steam turbine generator

Post by Dick_Morris »

I've been doing some design work to build a 1/8 scale generator. I ordered a couple of brushless out runner motors that will fit into the shell of a scale case. They are ball bearing and at less than $10 each I won't feel badly about testing them to destruction or dismantling and modifying them.

To get the complex shape of vanes I may try a 3D printed and investment cast wheel since I have the equipment to do it (and don't have access to CNC). The biggest problem I see is balance. However, it should be at least as good as a turbine wheel with the blades soldered to a disk.

That led me to the thought of having the impeller printed in metal by Shapeways. I'm too cheap to do it that way, but it may have potential. They give a plus or minus 5% accuracy, so some final machining or fitting the enclosure to the part may be required.
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dusty
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Re: Steam turbine generator

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RET wrote: Mon Sep 06, 2021 12:26 pm Hi Dusty,

"Have you run your turbine generator yet?"


Full disclosure; most of my knowledge about turbines comes from my work with gas turbine engines (aka, jet engines), I have never worked on steam turbines. That said, steam turbines and gas turbines are quite similar.

No, I have not run this turbine yet. I've spent the last few days attending to a few domestic chores and adjusting the placement of the two electric spark electrodes. Turns out that placing the spark directly in the fuel spay wont ignite the kerosene mist; instead, the spark needs to be placed on the edge of the spray where the fuel is beginning to mix with the turbulent air. I can't actually see the spray's border line so I needed to make multiple incremental adjustments to find the correct placement.
In a commercial steam turbine, I'm sure the design of the stator and rotor blades take into account the requirement for laminar flow wherever possible, because turbulent flow over the blades wastes energy.
Far worse than wasting energy, turbulent flow usually results in vibration of the blades which can cause anything from loud annoying humming or whistling noises to catastrophic failure of one or more blades breaking off.
The calculations and formulae required to achieve this are way beyond my simple knowledge and capabilities, I just know that in today's commercial units the calculations will be done to make the efficiency as high as possible. Curvature, shape and angle of attack will all vary as the blade radius changes, so blade design becomes very complex and all of this is only efficient at the design rpm., temperature and pressure for the turbine.
In the commercial world, turbine designers use CFD (Computational Fluid Dynamics) software to help determine blade shapes. It's true that turbine engines, like piston engines, have an small rpm range where they run at maximum efficiency, but also like piston engines, turbines will happily run at higher and lower rpm, just a little less efficiently.
in your pictures, the stator and rotors don't look right, the blades have to twist as the radius changes to keep the angle of attack the same. I also think the blades have to be closer together (more blades on the disk) and narrower at the root than at the outer end.
Early steam turbines were all built with un-twisted, straight blades,...they're not quite as efficient, but they do work. Take a look at fig. 67 on page 88 from https://archive.org/details/steamturbin ... ew=theater .
To get the maximum efficiency from a blade, it should be twisted from root to tip to compensate for higher apparent velocity at the tip compared to the root, ...however, when blades are very short, as they are in my very small turbine, the apparent velocity differences between root to tip are very small. My straight blades wont be as efficient as twisted blades, but I'm willing to sacrifice a little efficiency for the ease of blade manufacturing. In an ideal world, my blades would be more closely spaced, but as the diameter of the turbine gets smaller, so does the blade root area which must be kept large enough to withstand the high centrifugal forces on the blades at operational rpm.
You say a regular air compressor doesn't have the airflow required to spin the turbine up. What you might try is to only use two nozzles on opposite sides, that will give you higher pressure on the vanes and perhaps the rpm will be higher. Obviously, more nozzles will be required for more power, but if you just want to spin it up, fewer nozzles might work better.
Actually, I blocked off all but one nozzle for the compressed air test, but in retrospect, I don't believe I did a very good job of sealing off the unused nozzles. I need to force myself to take a break from the boiler design/fabrication and run the compressed air test again. There are days when I wish I had a twin,...then I usually snap back to reality and realize what a nightmare that would be :D
I'm sorry to "rain on your parade" a bit and I'm far from being an expert, I'm just trying to tell you what I see.

Hope this helps a bit.

Richard Trounce.
All comments on a new design are helpful and I always appreciate constructive criticism :D and if you believe I've made mistakes in anything I've stated so far, I expect you to point those out and lets discuss them. :D
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dusty
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Re: Steam turbine generator

Post by dusty »

Dick_Morris wrote: Mon Sep 06, 2021 8:18 pm I've been doing some design work to build a 1/8 scale generator. I ordered a couple of brushless out runner motors that will fit into the shell of a scale case. They are ball bearing and at less than $10 each I won't feel badly about testing them to destruction or dismantling and modifying them.
Brushless outrunner motors make great little alternators as demonstrated by the folks on "Tech Ingredients": https://www.youtube.com/watch?v=1yB49G756OI&t=387s
Skip ahead to the 13:00 minute mark to listen to his explanation on how to choose which size motor you want, or in your case, what to expect from the motors you've already purchased.
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Dick_Morris
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Re: Steam turbine generator

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From my Pyle-National generator file. There are several choices other than an MO-6. This one is circa 1895 to 1905.
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turbogenerator ca. 1904, Pyle-National type C.jpg
Early Pyle National.jpg
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Dick_Morris
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Re: Steam turbine generator

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Type E. Carl Ulrich sold 1/8 scale castings and plans for these about 40 years ago.
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Re: Steam turbine generator

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Type E2N.
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Re: Steam turbine generator

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Type K, circa 1918. It is covered by the same booklet as a K-2 and shares some of the same parts, including the armature. It looks like the K has a single ball bearing, the K-2 has two.
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Re: Steam turbine generator

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Type K-2. It is very similar to the K-240 and at one time Pyle-National offered a kit to upgrade a K-2 to a K-240. This is a from 1918 but Alaska railroad 557 was fitted with a K-240 in 1944. One difference is the number of polls in the armature. One of our K-240s has fewer segments. We were told by an expert on Pyle-National that it was from a K-2. After 250 watts was used by the headlamp there wasn't much left of the 500 available watts for the other lights. On 557 a second generator was fitted when a radio was installed.
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Dick_Morris
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Re: Steam turbine generator

Post by Dick_Morris »

Jerry Peters spent a couple of years rebuilding our three K-240s. All are now in top condition and ready for use.

Any guesses on what model I'd like to replicate in miniature?
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Dick_Morris
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Re: Steam turbine generator

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Skip ahead to the 13:00 minute mark to listen to his explanation on how to choose which size motor you want, or in your case, what to expect from the motors you've already purchased.
Dusty, thanks. I've only found a few Youtube videos on using the motors as generators. This is one of the most informative. I can't find a KV rating on the motors I purchased, but I should have a better idea in a week or so after I receive them. One video I found gave a web page for an kit to make your own out runner motor. I believe it came from the U.K. It would be interesting to see the instructions, but not worth the cost.

My first selection criteria was to find a permanent magnet brushless motor that would fit into the scale case. The ones I purchased were the only ones I found that would fit without altering the outside appearance. I initially ruled out the out runner style, but I discovered that the rotating outer case fits nicely in the scale case.

LEDs and the need for considerably less output make it much easier to design a working generator than when Francis Moseley sold his.

A correction on cost, my motors they were less than $5 each.
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Dick_Morris
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Re: Steam turbine generator

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The IBLS web page at has a section on generators at http://www.ibls.org/mediawiki/index.php ... _Generator. Included is a sketch of the Moseley pressure regulator. Also included is a full set of drawings for a 1" scale MO-6 by Doug Alkire along with a drawing of the full sized MO-6.
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Re: Steam turbine generator

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I mentioned above that there was an article on machining a 2-1/2" scale Pyle E-2 generator in the most recent LS&OR. The article was done by the editor, David Brush and a video showing the generator operating on air is at at https://www.youtube.com/watch?v=9aqlu8h ... RidgeShops.

In the comments he said he had also made a video of a 1-1/2" scale K-2 and it is at https://www.youtube.com/watch?v=pJxz5BY ... RidgeShops. He used the castings from New Zealand and a Tiger Motor 1306 -apparently no longer available. It appears to be higher quality and slightly smaller than the ones I ordered, but a lot more expensive. He used a 7806 regulator for his testing. Some more clues on what's worked for others!
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