Simple Steam Turbine

Moderator: csonics

Post Reply
User avatar
csonics
Anne from Little Britan
Anne from Little Britan
Posts: 232
Joined: Tue Nov 17, 2009 11:17 pm
Boat Name: No Boat Yet
Location: Roseville, MN
Contact:

Simple Steam Turbine

Post by csonics » Wed Nov 18, 2009 4:21 pm

Posted on behalf of stevey_frac

stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Sat Sep 12, 2009 12:23 pm Post subject: Simple Steam Turbine
Just out of curiosity... Has anyone ever played with the idea of a steam turbine? It would be fairly low power perhaps 10HP, and require some next level CNC machining to get balanced discs, But at the same time, it would be more compact, and at high loads, probably comparable efficient to a non-compounding engine.

Plans are available from Reliable Steam Engines, and there is a concept patent found here:

http://www.green-trust.org/steamturbine ... urbine.htm

I'm curious. It would be a truly unique power train then!!
Back to top


87gn@tahoe
Full Ahead


Joined: 23 Feb 2009
Posts: 148
Location: South Lake Tahoe, CA
Posted: Sat Sep 12, 2009 10:10 pm Post subject:
I have given thought to a small turbine and a monotube boiler in a jet ski.. I think it'd be quite fun...

I wonder what the torque and HP output would be with the "Slotted Disk" turbine for a given size.. Somewhere in-between the "Tesla" and the conventional "Bladed" turbine?


Part of the draw of steam, for me anyway, is the joy of watching all of the moving parts.. "Kenetic Art" if you will.
_________________
Wesley Harcourt
-S.L. Wayward Belle (Mr. Grosjean was/is a genius.)
-S.L. George H. Sandin (Father's boat. Cut my teeth on that one.)
-'64 Buick Riviera
-'65 Buick Special WAGON
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Tue Sep 15, 2009 8:47 am Post subject:
I can certainly appreciate what you mean about kinetic art. A big part of the draw for me is being able to design and build the drivetrain myself. I would be a lot less enthousiastic about buying a cheap fully built steam boat, as opposed to going through and selecting the hull, building the engine, and putting together the boiler.

Ironically, the turbine is a lot easier to build. I don't have access to a machine shop, and I'd need to have all my castings sent out to have them machined. It's no small undertaking to build a decent sized steam engine from castings. I'd end up having to have a prebuilt engine sent. Probably the Twin M from tiny power. They are about $7000.

The other side of it is, I can get discs laser cut for about $200, assemble it, and have it welded for around another $100. With about $100 in other parts and odds and ends. I can put together a 15 hp turbine for around $500. And it would really scream! Peak RPM is 27000! And in reality, it'll take all the steam a 15hp boiler will put out. As you up operating pressure, you up power pretty much linearly. It's not as efficient at low RPM, but at full load it's comparable to a compound.

I'm going to do some more research, and maby build a small 2-3hp pilot plant. If it turns out... I'll put up a video or something.
Back to top


Maltelec
Site Admin


Joined: 23 Sep 2007
Posts: 156
Location: Cumbria, UK
Posted: Thu Sep 17, 2009 4:01 pm Post subject:
I have thought about a small turbine giving about 10HP. The issue is they only work well at their designed speed. Using hydraulics (hydrostatic pump - variable stroke idea) you would be able to run the turbine at its set speed and have fully variable prop speed to suit.

However its got a serious lack of nice shiny visibly moving parts for my taste.
_________________
I've got the vehicle , just need the boat.
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Thu Sep 17, 2009 4:33 pm Post subject:
I've been told there are used steam engines around. But I've yet to see a single one. I've been keeping my eye on Ebay and Kijiji, but so far, only model stuff. Tiny stuff.

As an aside though, and still not very pretty, Mike Brown solutions sells a 20 HP version fairly inexpensively.

Still a lot cheaper to make a turbine though. I don't know. I agree with you that the shiny slow moving parts would be more eye candy. And definately more quiet.
Back to top


Maltelec
Site Admin


Joined: 23 Sep 2007
Posts: 156
Location: Cumbria, UK
Posted: Thu Sep 17, 2009 5:59 pm Post subject:
Quote:
And definately more quiet.


Funny you should say that, I walked past a 200 HP steam turbine, and only realised it was running when I saw the rev counter! Amazingly quiet, only a faint hiss. I believe it used 180 psi.

The electric motor which did the same job (both ran large fans, they simply had extra steam to use) was deafening when it turned on.
_________________
I've got the vehicle , just need the boat.
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Fri Sep 18, 2009 7:27 am Post subject:
interesting... All the hobby turbines i've seen screamed like a banshee escaping hell... Perhaps it's because hobby turbines are poorly balanced or something?? I don't know...

odd to me that the electric motor would be defening as well. Perhaps the cooling fans for it were loud??
Back to top


87gn@tahoe
Full Ahead


Joined: 23 Feb 2009
Posts: 148
Location: South Lake Tahoe, CA
Posted: Fri Sep 18, 2009 9:49 pm Post subject:
Probably well insulated (many inches thick), as opposed to the electric motor, in which you want the heat to escape
_________________
Wesley Harcourt
-S.L. Wayward Belle (Mr. Grosjean was/is a genius.)
-S.L. George H. Sandin (Father's boat. Cut my teeth on that one.)
-'64 Buick Riviera
-'65 Buick Special WAGON
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Fri Sep 18, 2009 10:05 pm Post subject:
Good call...

I've looked more into it. I'm liking the tesla turbine.

I did some rudimentary steam usage calculations. a 20 HP tesla turbine running at 45% turbine efficiency would use 300 lbs of steam per hour for 120 PSI steam at 400 degrees. Reduce turbine efficiency to 15% and that obviously jumps up to 900 lbs. 35% to 45% has been demonstrated by small hobby turbines, and tesla's original 110 HP turbine built in the early 1900s was supposed to get closer to 60%. This is backed by the work of professor rice, who claims it's possible to get 95% turbine efficiency with the design, although this has never been achieved.

High speed bearings are going to be KEY.

More thoughts and musing to come. Stay tuned.

-Steve
Back to top


87gn@tahoe
Full Ahead


Joined: 23 Feb 2009
Posts: 148
Location: South Lake Tahoe, CA
Posted: Fri Sep 18, 2009 10:16 pm Post subject:
I think you will find that the tesla will have VERY low torque numbers... even at 100hp...

I think a traditional "bladed" turbine would be your best bet for use as propulsion.. It may be less "effecient" and harder to make, but it is the better design for the given purpose, in my opinion.
_________________
Wesley Harcourt
-S.L. Wayward Belle (Mr. Grosjean was/is a genius.)
-S.L. George H. Sandin (Father's boat. Cut my teeth on that one.)
-'64 Buick Riviera
-'65 Buick Special WAGON
Back to top


steamboatjack
Urchin


Joined: 01 Oct 2007
Posts: 39

Posted: Sat Sep 19, 2009 3:46 am Post subject:
There are a number of builders of Tesla machines in the UK, I am afaid I am one of the sceptics. not seen one yet which does any useful work. I would be very pleased to be proved wrong, but it seems to me that a pair of rose colored glasses are provided with the plans.

In this age of CNC machines surely a simple one or two stage (proper) turbine can be made easily? I guess the problems are three : A the limited speed range or power band and B the need to reduce the speed (I am guessing here but you would need at least 5000 RPM) and C a reverse feature.
I don't think A is a great problem on leasure craft but B/C would be. Conventional reduction gearing is the simplest but would be noisy, I like maltelec's idea of hydraulic transmission, electric would be a good option as there is now a good supply of electric boat parts.
regards Jack
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Sat Sep 19, 2009 6:39 am Post subject:
Indeed, Torque would be low. But at 30000 RPM your really not thinking about doing direct drive anyway. You would have to reduce it down to something reasonable.

A) Based on torque / HP charts i've seen for real tesla turbines, at around 60% rated speed is where the torque peak is. This means your usable power band from around 40% of peak speed, to max speed. The Tesla should be able to do this without being hugely efficient, but as with all turbines, max efficiency comes at max speed.

B) The parsons (bladed) turbine isn't necessarily less efficient. But it's design and implementation is a LOT harder. You need to have many stages to get an efficient design, and each stage has to be matched to the ones before. Increasing steam volume has to matched with increased reaction area and lower pressure drops between stages. This is why it's much more difficult to have a parsons turbine efficient at lower speeds. They are more or less designed to run at some very efficient cruising speed.

C) The tesla turbine original patent included two nozzles. One for forward. One for reverse. A parsons turbine would have to have some sort of geared reverse which again adds to the complication.

Steamboat Jack: If you want to see a small tesla do some real work, check out this link

http://www.obilaser.com/AirPoweredTesla ... -Generator

They have a video of a run in which this turbine produces roughly 1/3 HP worth of electricity running of 50 PSI compressed air. Naturally, my design would use steam which yields more power, and I'd be running 120 PSI at least.

These turbines do work. 100 HP remains 100HP regardless of at what RPM it is produced at. 30k just requires different gearing then 200.

I'm not set on doing this, and it would be highly experimental. But I think it would be fun to at least try it. One thing that's going to be critical is making sure the prop isn't set so aggressively that the turbine can't spool up...
Back to top


fredrosse
Just Starting Out


Joined: 26 Sep 2007
Posts: 19
Location: Philadelphia, PA USA
Posted: Sun Oct 04, 2009 10:12 pm Post subject:
Sorry to jump into this thread so late. I am a mechanical engineer in the power industry, and have much experience with both reciprocating steam engines and steam turbines. I have built and operated a combined heat and power plant for my home, using both a steam turbine generator and a reciprocating engine - generator combination.

In very small powers (anything less than a few hundred horsepower) a reciprocating engine is the better choice, it will use much less steam than the turbine. At these low power levels, a practical steam turbine needs to turn at such a high RPM that its use for any mechanical drive application is just not feasible.

The proper design RPM for a 1 or 2 horsepower steam turbine is in the vicinity if several hundred thousand RPM, not practical for any application except possibly driving an equally fast gas compressor.

There have been small turbines built that run at lower RPM, most old steam locomotives had one, just behind the stack. They could light the headlight on the locomotive, and the boiler providing steam was so very large that the steam consumption of the little turbine was not a concern. These small low speed (3600 RPM) turbines had an efficiency of less than 1%, very poor.

The Tesla turbine was a novel concept, it worked, but its efficiency was not at all competitive with the steam turbines of that era, and it was abandoned for that reason. DIY enthusiasts are attracted to the Tesla machine, I think, because it looks so simple to build, and possibly because Tesla was such a wonderful innovator within the field of electricity. However, the Tesla turbine is not really a practical turbine, and beyond that, even the practical modern turbines do not reach into the realm of the power small powers we use in steam launch plants.
Back to top


DetroiTug
Warming the Engine


Joined: 19 Jul 2009
Posts: 73
Location: Outside Detroit
Posted: Mon Oct 05, 2009 10:16 am Post subject:
Fred,

Thanks for explaining my hunch.

Seems a small turbine would need an enormous amount of steam generation.

Ron

Last edited by DetroiTug on Wed Oct 07, 2009 11:00 am; edited 1 time in total
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Wed Oct 07, 2009 9:13 am Post subject:
fredrosse wrote:
Sorry to jump into this thread so late. I am a mechanical engineer in the power industry, and have much experience with both reciprocating steam engines and steam turbines. I have built and operated a combined heat and power plant for my home, using both a steam turbine generator and a reciprocating engine - generator combination.

In very small powers (anything less than a few hundred horsepower) a reciprocating engine is the better choice, it will use much less steam than the turbine. At these low power levels, a practical steam turbine needs to turn at such a high RPM that its use for any mechanical drive application is just not feasible.

The proper design RPM for a 1 or 2 horsepower steam turbine is in the vicinity if several hundred thousand RPM, not practical for any application except possibly driving an equally fast gas compressor.

There have been small turbines built that run at lower RPM, most old steam locomotives had one, just behind the stack. They could light the headlight on the locomotive, and the boiler providing steam was so very large that the steam consumption of the little turbine was not a concern. These small low speed (3600 RPM) turbines had an efficiency of less than 1%, very poor.

The Tesla turbine was a novel concept, it worked, but its efficiency was not at all competitive with the steam turbines of that era, and it was abandoned for that reason. DIY enthusiasts are attracted to the Tesla machine, I think, because it looks so simple to build, and possibly because Tesla was such a wonderful innovator within the field of electricity. However, the Tesla turbine is not really a practical turbine, and beyond that, even the practical modern turbines do not reach into the realm of the power small powers we use in steam launch plants.


The system efficiency for a small tesla turbine generating electricity running on compressed air built by hobbyist has been documented at around 30%. Hardly jaw dropping... But then.. small hobby reciprocating engines are generally around there or less anyways. I'll hunt for the link and post it if i can find it.

It is true that a 1 hp tesla turbine would probably be spinning at 200k RPM. But then, what i'm looking at is closer to 20hp, with a designed free wheeling speed of about 33k RPM and full load speed of around 18k RPM. Just like the parsons turbines on large naval vessels, this will be geared down to a few hundred RPM to drive the propeller.

For steam consumption, at full load, i'm anticipating about 600 lbs / hr of steam required.

I haven't built one yet. It might be a complete flop. The nozzles will be a pain to get right. But the flip side of it is... Why the negativity? It's not like no one has ever made them work? Tesla had a few running at several 100 HP. His big'un, with a 60" rotor stretched sure... But metallurgy has advanced a bit in the intervening 100 years... And here's the other, main advantage. His 110 HP turbine was roughly the size of a PC. Imagine what size a reciprocating steam engine running 100 PSI steam would have to be to produce that. Much more compact.

Anyways, i'm rambling...

barts
Lighting the Boiler


Joined: 02 May 2009
Posts: 32
Location: Menlo Park, CA
Posted: Wed Oct 07, 2009 10:13 am Post subject:
stevey_frac wrote:


The system efficiency for a small tesla turbine generating electricity running on compressed air built by hobbyist has been documented at around 30%. Hardly jaw dropping... But then.. small hobby reciprocating engines are generally around there or less anyways. I'll hunt for the link and post it if i can find it.

It is true that a 1 hp tesla turbine would probably be spinning at 200k RPM. But then, what i'm looking at is closer to 20hp, with a designed free wheeling speed of about 33k RPM and full load speed of around 18k RPM. Just like the parsons turbines on large naval vessels, this will be geared down to a few hundred RPM to drive the propeller.

For steam consumption, at full load, i'm anticipating about 600 lbs / hr of steam required.

I haven't built one yet. It might be a complete flop. The nozzles will be a pain to get right. But the flip side of it is... Why the negativity? It's not like no one has ever made them work? Tesla had a few running at several 100 HP. His big'un, with a 60" rotor stretched sure... But metallurgy has advanced a bit in the intervening 100 years... And here's the other, main advantage. His 110 HP turbine was roughly the size of a PC. Imagine what size a reciprocating steam engine running 100 PSI steam would have to be to produce that. Much more compact.

Anyways, i'm rambling...


I believe you're confusing mechanical efficiency w/ overall thermal efficiency. Tesla turbines do a much poorer job of getting the available energy out of 100 psi steam compared to reciprocating engines. I've never seen one in a boat, and I've seen hot air engines, Stirling engines, etc. put to that task. But one test is worth one thousand expert opinions, so I'm very curious as to what you find out. I do suggest you build one designed to produce 1 horse power and dyno it, comparing the steam consumption to that of a good small single. In practice, steam consumption at 125 psi sat., non-condensing is about 40 lbs/hp-hr for a slide valve engine, a Corliss or uniflow will manage about half that, with 5.5% to 11% overall thermal efficiency respectively. Note that if higher pressure or superheated steam is used, Corliss, compounds and uniflows do much better. A triple expansion or uniflow can reach 20% thermal efficiency at large power levels, better if very high pressure and temp. steam are used.

The size of most engines is largely irrelevant for marine applications; the boiler generally dwarfs the engine in terms of both volume and weight; thus utilizing 50% more steam to produce the same power as a very significant impact on the overall practicality of the application.

- Bart
_________________
-------------------
Bart Smaalders
S.L Otter
Menlo Park, CA
Back to top


DetroiTug
Warming the Engine


Joined: 19 Jul 2009
Posts: 73
Location: Outside Detroit
Posted: Wed Oct 07, 2009 11:11 am Post subject:
As one old steamer explained to me recently, the steam engine is really just a device to convert the boiler's power into actual work. Some engine's do it better than others. The actual "performance" of the system is determined by the efficiency of the boiler. Another way of looking at it...
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Wed Oct 07, 2009 3:50 pm Post subject:
Check out these documents. As an engineer in the field, perhaps you can tell me if i'm horribly mistaken?

http://www.frank.germano.com/images/itpeff1.jpg
http://www.frank.germano.com/images/itpeff2.jpg

I think the efficiencies claimed are basically turbine efficiencies, not overall thermodynamic efficiencies. Even still. A single stage bladed turbine would be comparable.

This isn't the example i was looking for, but it's still interesting.
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Wed Oct 07, 2009 4:07 pm Post subject:
Here is some more data on the Tesla turbine.


http://www.obilaser.com/AirPoweredTeslaTurbine.html

Check it out! He has an air powered turbine & generator that was able to operate at 38% efficiency. Note that this is NOT total cycle, and does not include losses in the compressor itself. It is based on the enthalpy of the compressed air going in, and the power out of the generator.
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Wed Oct 07, 2009 4:09 pm Post subject:
Here's an example of the generator running.

http://www.youtube.com/watch?v=hr3_UPvW-QY
Back to top


DetroiTug
Warming the Engine


Joined: 19 Jul 2009
Posts: 73
Location: Outside Detroit
Posted: Wed Oct 07, 2009 5:15 pm Post subject:
Take the power generated and compare it to the power it required to produce all that compressed air and there is the efficiency. I doubt it is 38%.

Don't take me wrong, I'm not arguing, this thread caused a bit of curiosity and some research around the web didn't turn up many people that agree with his findings.

As someone else said, best thing to do is build one and find out for sure.

Ron
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Wed Oct 07, 2009 5:57 pm Post subject:
DetroiTug wrote:
Take the power generated and compare it to the power it required to produce all that compressed air and there is the efficiency. I doubt it is 38%.

Don't take me wrong, I'm not arguing, this thread caused a bit of curiosity and some research around the web didn't turn up many people that agree with his findings.

As someone else said, best thing to do is build one and find out for sure.

Ron


Adding in the compressor adds many additional stages that don't exist in my application. The electric motor will be inefficient, the compressor itself will be inefficient. The compressed air is initially warm, and cools in the tank. That reduces efficiency.

The method he used, and the method that was stamped by an engineer, that claimed similar efficiency includes mostly the turbine itself.

If for instance, you had a boiler that operated at 50% efficiency, which is quite possible, and run a turbine that had 38% efficiency, you would expect your cycle efficiency to be 19%. Now there will be losses in the lines, especially if they aren't insulated. And you will have losses in your condenser. Either way, 10% would not be unreasonable thermodynamic cycle efficiency.

At present, the plan is to build one and test it. If it performs as advertised, it goes in the boat. If not... I can always put in a regular marine reciprocating steam engine. Probably the Mike Brown 20 hp.
Back to top


barts
Lighting the Boiler


Joined: 02 May 2009
Posts: 32
Location: Menlo Park, CA
Posted: Thu Oct 08, 2009 12:30 am Post subject:
The diagram factor is the traditional indicator of mechanical efficiency in reciprocating engines; it varies from ~60 % on single cylinder slide valve engines, to upwards of 90% for large jacketed poppet or rocking valve engines.

Note that this does not represent the overall thermodynamic efficiency!

For most small steam installations, the efficiencies are very poor due to practical difficulties in expanding the steam sufficiently.

For a steam plant running at 120 psig and condensing to 70F, the max. possible
thermodynamic efficiency w/ a ideal working fluid would be

1 - RejectT/AddT, where RejectT and AddT are the absolute temperatures
at which heat is reject and added to the system... in parochial units:

1 - (460 + 70)/(460+350) = 34%

Of course, this would require a very large perfectly insulating triple expansion engine, since the volume of steam expands so much (260 fold!) ; most singles, for example, exhaust after perhaps expanding the steam to three times it's original volume, exhausting at 275F and 30 psig pressure, which yields:

1 - (460 + 275)/(460+350) = 9.2% max. possible efficiency - which explains the
5% numbers for real efficiency numbers for singles....

To improve steam engine efficiency, you want to do two things:

1) expand the steam more:
Use a compound, triple or Uniflow engine design; design the engine to be
large enough to run linked up and still provide sufficient power. Use poppet
or other quick acting valves to realize short cut-off w/ minimal pressure drop.

2) minimize condensation during expansion:

Lag the cylinders, use reheat between expansion stages, superheat the steam,
jacket the engine w/ boiler exhaust, etc.

Most of us don't need to worry about this; our small power plants consume little fuel even running inefficiently; our worry is usually to get sufficient power to keep up w/ the larger boats during the steamboat rallies.

- Bart
_________________
-------------------
Bart Smaalders
S.L Otter
Menlo Park, CA
Back to top


fredrosse
Just Starting Out


Joined: 26 Sep 2007
Posts: 19
Location: Philadelphia, PA USA
Posted: Sun Oct 11, 2009 4:23 am Post subject:
Didn't mean to be negative, just stating the technical facts.

I would expect the Tesla turbine to use at least twice as much steam as an impulse or reaction type turbine. That was the result of real tests conducted by Westinghouse for Tesla about a century ago.

Be careful when efficiency numbers are quoted by those who do not have legitimate testing apparatus, and often have a strong propensity to report exaggerated efficiency.
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Tue Oct 13, 2009 10:14 am Post subject:
I've done a bunch more research into this, and this is what I have discovered.

Yes it is easy to make a tesla turbine. It can be done with a set of CD's. However, in order to make an efficient turbine, one that is able to operate at high efficiencies, and produce lots of useful power there are a number of technical requirements.

It ends up being a pretty long list.

The discs shouldn't be flat, but tapered. This allows for the changing thickness of the boundary layer of the steam at different temperatures and pressures.

The outlet size has to be matched to the inlet size. Most hobyists tend to have in outlet to small for real useful power generation. Large outlets translates to higher disc stresses.

You still need to run superheated steam. Wet steam is still going to cause issues in the housing. The discs might not wear, but a hole in the housing... Not all that useful.

Everything more or less would have to be stainless to be able to take the heat, and not rust. Any rust would ruin the surface of the blade, and cause problems.


For the time being, it's looking like I'll be switching back to a compound. Small turbines are possible. But not practical.

-Steve
Post Reply