de Laval turbine

IIRC for rocket nozzles you need to know the amount of gas first and the atmospheric pressure where it will be used, and then you design the nozzle.

Dan

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Dan

The little booklet I referred to above walks you step-by-step through the nozzle and rotor design for a model turbine.

I build 1/16 scale models of locomotive steam turbo-generators, fully functional.

At that small size, 5/8" rotor dia. and .025" nozzle throat one can take some liberties with the nozzle geometry. The rotor blades are not that forgiving, even in small sizes. I use the Terry turbine blade design which gives 180 deg flow return... very effective. The small turbine described will light up 4 flashlight bulbs @ 2.5 volts @

1 amp @ 56,000 RPM, with 80 psig steam pressure. Increase the steam pressure and it will burn out the bulbs in a flash. A pressure regulator is necessary for unattended use on a steam locomotive.

Wolfgang

--You have *got* to post some photos! :-)

Agreed! That's been one of the big bugaboos to building a small steam launch - I wouldn't have any way to run the nav lights and the oil burner for the boiler. And while a double expansion auxiliary motor spinning a Car Alternator through a step-up gear would work...

But it sounds like your turbine is aiming for 10W output, and the small boat would need more like 1KW to 2KW output - unless you've got a lot of excess capacity available, it might have to scale up one notch.

-->--

I shall make an effort to post some pics over the next little while.

For electric power on a steam yacht I'd convert a 2 cylinder cast iron automotive air conditioning compressor into a steam engine -I did this for a friend- and run a good quality automotive alternator via a toothed belt, speeding up the drive by say 3:1. This would keep things quiet. Plans for this conversion were available in the popular do-it-yourself press in the late '70's or so.

As to powering a model racing boat... It has been done. There is - another- little book available, but not on-line as far as I know, entitled Experimental Flash Steam. It covers the topic of steam powered racing boats using flash or monotube boilers with piston steam engines mostly; one experimenter did build a turbine powered boat.

It is a fascinating book if you can find a copy, covering details such as feed, fuel, and oil pumps, and controls.

I think that a 1 to 2 KW small steam turbine is doable especially if you don't need electric output or if it doesn't have to look "scale". My little turbine's output is primarily limited by the scale alternator... you can only squeeze so many turns of a certain sized wire into the available space; whereas the power can always be increased by increasing the number of steam nozzles until you have reached full admission ie. a full 360 deg. nozzle ring. Nothing to stop one from fitting, at the design stage, 30, 40, or 60 steam nozzles.

The way I would approach it would be to design the steam nozzles as a full-admission nozzle ring and 3 or 4 pass terry turbine wheels as these are quite easy to make. With a small CNC mill even Laval (or was it Parson?) turbine wheels are not difficult to make.

Turbines are a fascinating subset of the live steam hobby and I would encourage those interested to have a go. But read up on it first as there is no sense in re-inventing the wheel.

Wolfgang

Ed, I'm not a steamer but have made quite a few de Laval nozzles in graphite, for small rocket motors. For motors under 1.5" diameter, the nozzles were (usually) formed using an ordinary 82 degree countersink for the entrance cone and a 29 degree cone-shaped carbide burr for the exit cone. They worked a treat.

Rules of thumb for rocket motors operating at about 600-1000 psi (may have nothing whatever to do with steam): diameter of exit is about 2x diameter of nozzle throat; throat length is as short as is practical but should not exceed 1/2 the throat diameter; rounding off the sharp edges of the throat will improve performance.

Hope this helps -- Terry "As a matter of fact, I *am* a rocket scientist... :-)

It's a great help, Terry. The hard part of this, for me at least, has always been to get *practical* information, and every bit helps.

Finally I'm accumulating some here. Now, all I need is time to put it to use.

-- Ed Huntress

Ed, I've uploaded a bunch of pages relative to turbines, 3 of which pages contain references to Model Engineer articles on building model turbines; they're at:

In ME No. 4320, 29 Feb.13 Mar 2008, is the second part of an article on a gauge 1 turbine loco pp.274-277. with some information on cutting the turbine blades.

HTH, Mike in BC

Hey, thanks, Mike. They look great.

Far be it from me to look a gift horse in the mouth, but for future reference, you might consider using the compressed TIFF format, rather than JPEG, when you want to reproduce a printed page. Because of the way the JPEG compression works, it makes the edges of letters (and any sharp edges) fuzzy, the fuzziness depending on how much you're compressing. TIFF doesn't do that, and you can save the space involved in reproducing color, if those settings are available to you. For an all-type page, or one with type and line drawings, you can use 2-bit compressed TIFF and usually you'll get a file that's both smaller than the equivalent JPEG, and much easier to read. It also prints much better.

However, in this case, I can read those pages perfectly well. I'm going to take a close look this weekend.

Thanks again.

-- Ed Huntress

Thank you for the advice, don't worry I shan't get in a tiff about it. :-)

Mike in BC

Ugh... Well, it's strictly in the interest of better computing for all. d8-)

-- Ed Huntress

Perhaps I should have put ("English humour") rather than a smiley face - I really do appreciate your telling me about the TIFF file compression. Or was your "Ugh" at the low level of my pun? Apologies offered. Mike

Yes.

I'll get over it.

Anyway, I'm looking forward to reading what you provided and learning more about these things. I saw a de Laval cream separator on my family's farm in New Hampshire over 50 years ago, and maybe I got fascinated by the name. But I'm impressed with the sophistication of de Laval's (and others') engineering on steam turbines in the late 19th century. They were really pushing the envelope.

-- Ed Huntress

Ed, further to our correspondence, I've uploaded a spreadsheet listing of Model Engineer references to to:

Now THAT should keep you busy for the weekend. Hope you have access to a library with old MEs.

Mike in BC P.S. Why don't the present publishers, who seem to have a predilection for digital whatevers, put out a complete issue on CD as National Geographic have done? Any one who'd go for this at say about $100 or so for the first hundred years email:

snipped-for-privacy@myhobbystore.com

Sirs, it would be of great help to those of us who constantly have to reference back copies of Model Engineer, but who don't have ready access to those back copies, if you would consider issuing a set of CDs similar in nature to those issued by the National Geographic magazine i.e. 100 years of back issues for a little over $100. I am quite sure that I am not the only person who would welcome such an offer. There would still be a demand for "hardcopy" back issues for those who prefer them, but a fully searchable CD would be of inestimable value to the rest of us. yours sincerely, Michael Gray

Mike, I don't think I responded to this old message, but thanks. There's half of my remaining lifetime of spare-time hobby study.

I'll work on that one for a while.

-- Ed Huntress