Steam turbine generator

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dusty
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Re: Steam turbine generator

Post by dusty »

Steamer Al wrote: Tue Sep 14, 2021 2:33 pm Also interesting to note that some of the compressor blades in modern high bypass turbofan engines on airliners are investment cast. Although I'm sure its an alloy we could only dream of getting ahold of!

https://www.foundrymag.com/molds-cores/ ... ine-blades
The blades discussed in the linked article are used in the HOT section of the engine, not the compressor. And it's not so much the alloy their made of (typically close to a standard INCONEL) that makes them so strong and heat resistant, but more the internal design and manufacturing process. As the linked article describes, after the blades are cast, they're placed into a vacuum chamber where they're induction heated to near melting, then allowed to cool very slowly which allows the metal blade to form into a single crystal, which is far more heat resistant then a standard casting. Also notice the many small holes in the blade being held; modern hot section turbine blades are cooled by routing a small amount of high pressure air from the compressor into internal air channels cast inside the blades, thereby cooing the blades both internally and also externally as the cooling air blows through those many holes and forms a thin laminar air flow over the blades external surfaces. High pressure turbine blades in a typical gas turbine engine are subjected to combustion gases at 1500 C (2732 F), temperatures which fortunately steam turbines never reach.

I think it's safe to say that we hobbyists can safely use standard casting methods and standard alloys for our steam turbines. :D
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Steamer Al
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Re: Steam turbine generator

Post by Steamer Al »

Wow thanks for the fascinating explination!! Not much comparison to hobby work as mentioned but interesting none the less.
rrnut-2
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Re: Steam turbine generator

Post by rrnut-2 »

" As the linked article describes, after the blades are cast, they're placed into a vacuum chamber where they're induction heated to near melting"

They are also cast in a vacuum, both the turbo wheels and the jet engine parts. They are also heat treated in vacuum heat treating ovens and are not induction heated at this foundry. The alloys that are used, we could not afford to use in the hobby.

Jim Bronson
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Dick_Morris
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Re: Steam turbine generator

Post by Dick_Morris »

I'm making some progress. I did some test prints to check for fit and appearance. There are still lumps and bumps to add as well as finishing the turbine cover and turbine end bearing cover. After I get the parts to fit and look right I will print them in castable resin and cast them in silicon bronze.

These little motors are sure tiny!

These are both out runner motors, meaning the stationary coils are on the inside and the outer case contains the magnets and spins with the shaft. Out runners are larger diameter and shorter and will fit into the case where the the in runners of approximately the same power would be too long.

I bought two variations. The larger one has the output shaft and mounting flange on the same end. The smaller has them on opposite ends. They both fit, although I'll need to put in a trough to hold the wires on the bigger one to prevent interference. On the other one the wires are on the back side.

I made up a bridge rectifier to convert the three phase AC output into pulsating DC. a good sign was that when just spinning the shaft quickly with my fingers and only the volt meter for a load I was able to momentarily get half a volt. Next I'll do some testing to see how much they will put out by driving them in my mill, which has a VFD so it can be set for a specific, repeatable speed, and I will use an infrared tach to set the rpm accurately. I will drive a resistive load and use a multimeter to check current and voltage.
Attachments
in hand.jpg
in-hand 2.jpg
3.jpg
Last edited by Dick_Morris on Sun Sep 19, 2021 6:26 am, edited 2 times in total.
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Dick_Morris
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Re: Steam turbine generator

Post by Dick_Morris »

I remembered I had a number of reprinted International Textbook Company/International Correspondence School lessons in my collection of tech data and found the lesson on "Headlights." About half of the content is on turbine generators and there is a good explanation of the Pyle-National K-240.

Before I found this I was puzzling over how the steam was used in the K-240 as it has two wheels with a space between them. Now it makes sense. The third file helps to explain how it works but it appears that instead of reversing buckets covering the entire periphery of the wheels that there is only a short section of about six or eight reversing buckets.
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k240-1.jpg
k240-2.jpg
K240-3.jpg
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Dick_Morris
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Re: Steam turbine generator

Post by Dick_Morris »

I acquired several small motors so I could test them for possible use as the generator end of a steam turbo-generator. Three that I bought were marketed specifically for drones and one was probably surplus and designed for a consumer product.

My goal was to see what voltage and amperage could be expected at a speed that a small turbine might turn.

All motors are “outrunner” style. The outside shell with magnets rotates around stationary coils. (This style is better suited for stuffing into a miniature turbo-generator because they are shorter than the inrunner style, which has a stationary shell.) All have two ball bearings. They are all brushless and require a three phase controller to supply the power when used as a motor. When used as a generator three phase power is generated, which can be converted to pulsating DC with a bridge rectifier. Their cost ranged from $5 to $15.

The motors are rated by the diameter and length of the stator and the kv rating is the speed in rpm for each volt supplied when they are operated as a motor. (Since they are actually three phase AC motors, there must be some industry standard that equates voltage applied to the controller to the output frequency to the motor.)

These particular models were selected because the O.D. would fit within the approximately 1” diameter of the inside of the generator case. On all but the Namiki the output is on the opposite end from the mount. Because of that the Namiki may take some creativity to get the wires past the rotating shell. I got the Emax in two kv ratings because I wanted to see how the output of two similar motors with different kv ratings would compare when used as generators.

My test fixture was built around a an ancient Dremal rotary tool, a couple of multi-meters to check voltage and current, a three phase bridge rectifier, a couple of 10 ohm, 10 watt resisters, and a rat's nest of test leads. After vibration caused it to drop on the floor and break the brackets for the Dremal, a C clamp was added.
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test fixture.jpg
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Dick_Morris
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Re: Steam turbine generator

Post by Dick_Morris »

I haven't found performance information when using these motors as generators anywhere, so I'm sharing it in case anyone else wants to go down the rabbit hole. This is what I measured. I'm also attaching the specs for the motors I used. These should be considered as representative of the possible choices, not a recommendation. It appears that motors sized 1406 and smaller will fit with plenty of room to spare for 1/8 scale, although I can't say whether there is a limitation on the size that the 1-1/8" turbine will turn. Since others have got outputs with hand wound motors over 6 volts and 1 amp, these should be practical unless the starting torque is too high.
Attachments
Hobbyking specs modified.jpg
ecomax specs.jpg
Namiki specs.jpg
Performance.jpg
Namika and VSpec
Namika and VSpec
Last edited by Dick_Morris on Tue Oct 12, 2021 4:48 am, edited 2 times in total.
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Dick_Morris
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Re: Steam turbine generator

Post by Dick_Morris »

While checking motor performance I've also been doing the 3D modeling of some of the parts and doing some test prints.

Modeling the 1.125" diameter rear door wasn't too hard, but the lettering and Pyle-National emblem consumed several full days of learning curve.

Now that the test stand has done it's job for testing motor performance, I'll remove the Dremal and replace it with a nozzle and guide passage so I can try out different turbine wheel configurations on air to drive one of the motors.

Several builders have successfully used a paddle type wheel, and they are a lot easier to make if one doesn't have a CNC mill. I'll give that style a try for comparison purposes. (The flange left of the vanes on the paddle wheel was for printing purposes and will be removed.) A design with curved vanes fed from the side at a 30 degree angle should be a lot more effective and efficient. Since printing different designs in plastic is relatively easy, I will do some testing before committing them to metal. The current plan is for a 1.125" by .25" wheel.

There was some concern expressed earlier about the safety of using a bronze casting for the turbine wheel, and that concern probably extends to using 3D printed plastic for testing. When I had my Dremal apart to replace a crunchy bearing, I noted that the fan was a 2" diameter piece of injection molded plastic and it turns at 30,000 rpm. That makes me more confident that I can do the air testing with a printed turbine, but will arrange some sort of scatter shield just in case.
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20211011_230904.jpg
rkcarguy
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Re: Steam turbine generator

Post by rkcarguy »

Great info posted with the updates!
Looks like they have really good power output potential.
I think the key is going to be in limiting the pressure to the wheel so the motor isn't over-revved. I feel like at the full boiler PSI it's going to want to spin much faster than 30,000rpm.
You may have to go larger amperage on the diodes, and/or epoxy them into/onto a heat sink.
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Dick_Morris
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Re: Steam turbine generator

Post by Dick_Morris »

I think one of these should meet my power needs. I'm guessing that .5 to .75 amps at about 5-6 volts will be plenty. I have some LED bubs and need to check their power requirements.

I plan on a pressure regulator. I'm also thinking of electronically adding a load in case of over voltage to protect the generator from destroying itself due to overspeed. I only have rough thoughts on how to do it and I'll cross that bridge when I need to. Voltage to the bulbs will be run through a voltage regulator and probably have a capacitor to filter the pulsating DC. At this frequency, it shouldn't take much of a capacitor.

I also have some 4 amp diodes, but they are considerable larger. I may be able to fit the small ones into the case but I'm doubtful that the larger ones will fit. I think the 1amp diodes may be OK. Each pair in the bridge only passes one phase or 1/3 of the total current.

I worked as an electronic technician for about 15 years, but that was 30 years ago so I'm having to relearn some of the fundamentals and what products are available today.
John Hasler
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Re: Steam turbine generator

Post by John Hasler »

> I also have some 4 amp diodes, but they are considerable larger.
> I may be able to fit the small ones into the case but I'm doubtful that the larger ones will fit.

Look at surface mount components. Example:
https://www.digikey.com/en/products/det ... TP/2642031
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PRR5406
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Re: Steam turbine generator

Post by PRR5406 »

THis is fascinating, Dick! I am most anxious to hear how your experiments deliver.
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