Watch yourself, dude... You get to dinking around with pressure vessels, especially the fairly "high octane" ones like a boiler a foot and a half across will be if done right, and you're sailing into potentially dangererous waters - Definitely physically, possibly legally in some places. Take all the precautions. An exploding boiler is *NO* kind of fun, and live steam carries one helluva nasty bite, with a surprisingly low head needed for it to be serious bad news.
Sounds to me like you're getting ready to try to power up that Tesla turbine you made in full "old-school, just like Nick dunnit" mode? If so, fergawdsake don't freewheel it with live steam! At least, not without wrapping a couple layers of blankets or similar around the housing as burst-shielding for when those CDs decide to go all to pieces from the amount of CF.
If you know where you can get a stack of old hard drives for ultra-cheap or free, I think I'd be looking *REAL* hard at grabbing a bunch of those, and disassembling them for the platters... Of course, add "blast shielding" if you end up with metallic discs.
As for your specs for a boiler...
I've got an idea bouncing around, but I need another detail from you first...
Exactly what is the planned heat source? Propane/LP-Gas-ring? Electric? Wood fire? Fuel-oil furnace gun? 30 acres of mirrors focused on the top of a 20 foot tower? :) Other?
What would folks say to the concept of drilling/tapping an appropriately-sized hole in the side of a (properly prepared... Safety first, boys and girls! Let's not be blowing ourselves up!) small propane tank in order to mount the water-injection system on it? Ain't those just about 18 inches in diameter?
Seems to me that if you had the right kind of burner/heat source, a propane tank would work nicely - A chamber already rated for pressure (though I'd have to look it up to see exactly HOW MUCH pressure...) with a convenient fitting designed for dealing with pressure...
Am I crazy, or does that sound like a reasonable concept?
Don't forget a blow-off/overpressure valve of some sort, and a gauge... Couple more holes to be drilled/tapped.
Oh, yeah... Almost forgot! It needs some bells and whistles... Well, a whistle, anyway... See if you can brew up a steam whistle to hang on it
- It's sorta traditional, doncha know! :)
Another idea that just hit me... Mom had, passed down from grandma, this jumbo canning kettle. Seems to me it was pretty close to 18 inches across the bottom - might have even been more. The one mom had had a stamp in the bottom of it. If memory serves, it read "Max Working Pressure 60 PSI", and the blowout plug was stamped/engraved 45. Mom never took it much above 18 pounds (according to the gauge built into the lid) when using it for canning.
That'd be a pretty good head of steam for a CD/HD-platter size unit, I'd think...
Go for the coil of tubing,The smaller diameter keeps the stresses in the system lower than for a larger diameter vessel. Pump the water continuously through the coil,into a small separator vessel then back through the coil. Take your steam supply off the top of the separator. Make sure you have a safety valve on the separator. If you plan on using it to drive a CD based Tesla turbine, forget it. The heat will soften the CD's and the whole thing will come unstuck with great vigour!
Pick up a couple of old Audel's books, the one for powerplant engineer is good and covers a heap of detail on steam. As with anything, if you go into it with awareness of what can be done, and how, it'll work better and you'll have more fun.
Not that this is an answer to your question, but it is with great sadness that I learned (a couple of weeks ago) that South Carolina is preparing legislation that will require inspection and licensing of steam boilers. Who wouldda thought that it hadn't been done decades ago! Reminds me of when, about 10 years ago, SC decided to outlaw open alcoholic beverage containers in motor vehicles. After 25 years here, I'm still finding out just how "quaint" this state is...
Well, if I ever get a steam engine (I'm serious about wanting one), I'll have to make sure the boiler won't kill me, lest I violate the law.
The inspection and licensing of boiler is one of the bits of government meddling I agree with. Even a small boiler explosion would leave most of the Bagdad firecrackers for dead in terms of energy released. A small boiler exploded in a laundry in Tasmania about 30 years ago and killed about a dozen people. It was a new boiler that had been sealed up for hydrostatic testing. The commissioning engineer got sick and another was sent to replace him. He didn't know that the safety's had gags on them and that the burner control line was blanked off, They believe that it blew at about 5 or 6 times its rated pressure. Ripped the boiler plate about 2 feet from the back end. Didn't go on a weld. They are pretty fussy about oiler here in Aus now.
Sorry, forgot the separator question. It's a small vessel that the ends of the coil are connected to. The heat boils the water in the coil, the steam rises to the separator, the steam is taken from the top of the separator and the water continues to circulate through the coil. If you are serious about building this, you'd better do some more research. Its a little more complicated that the usual tea kettle. Designs have evolved since the 1700"so best practice these days is pretty sophisticated. During the industrial revolution in England there was an average of one steam explosion per day until the invention of the dead weight safety valve!
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