3” boiler project.

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ajoeiam

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Hi Doug,
snip
Personally, I avoid the complexity of the firebox of locomotive-style boilers. I don't need to do all that work for stationary boilers.
But a very efficient/powerful "stationary or marine" boilers is the 3 tube with multi-water-tube Yarrow type of boiler. I have a book with about 50 designs in it... the best I have read - by K.N. Harris. But there is another highly recommended that I have not bought yet... by Alex Wise.
Worth getting one or both to help you make the decision,
Regards,
K2
Hmmmmmm - - - - think I have an electronic copy of the Harris - - - but what is the one my Wise called - - please?
 

DJoksch

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I initially calculated the thicknesses from my reading and was concerned since this was my first boiler. I am fortunate finding this group as this the first to actually respond with technical comments. Í have much more information for the next build this Summer. I try to include an artistic balance so I can keep my projects in my home office after completion. The horizontal project will be 3” X 6” using another cutting from the material I used in this project for the shell. Thanks for the reading suggestions.
 

Steamchick

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Steamchick

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Hi Doug. As the copper sheet is thin (more than 3/16" is starting to get thick) I suggest you keep it for the "internal pressure" components only. You can get much more heat from an external burner than in a flue tube burner, as you would need for a marine boiler. So the trick is a large radiant shining onto the underside of the boiler, and some water-tubes, then the flue gases pass through the boiler flue tubes once or twice. The boiler with flue tubes is within your experience. The external water tubes beneath the boiler shell can be fitted into bronze bushes in the underside of the shell, all silver soldered together.
I'll see if I can find a design and post it?
Regards, K2
 

Steamchick

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Oh, just another idea... domed ends are much stronger than flat, as your copper is quite thin, and I am sure you can make domed ends by spinning? Spherical or elliptical.

K2
 

ajoeiam

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Steamchick

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Hi Doug,
I have been working to improve my understanding and calculations relating to the strength of boilers.
There seems to be a big gap in the papers I have researched that no-one has checked things like flue tubes in compression, yet the way they are situated in boilers means they must be calculated as a significant part of the boiler. (e.g. a compressive collapse of a tube would be likely to be catastrophic, as the end silver soldering would be expected to fail and the boiler eject its contents very rapidly!).
I have de-rated the "Permissible compressive stress" - following the ASME rules, plus converting the "ASME Permissible tensile stress" to "Permissible compressive stress" by the factor of:
Comp. stress = 45 (MPa) = 0.214
UTS at room temp. 210 (MPa)

So Here's my calculations on your flue tubes:
At 70psig:
σc = [(14.7 x 0.252 – 84.7 x 0.282) / (0.282 - 0.252 )] - [ 0.252 x 0.282 x (84.7 – 14.7) / { 0.252 ( 0.282 - 0.252 )}] :

σc = [(14.7 x 0.0625 – 84.7 x 0.0784) / (0.0159)] - [ 0.0625 x 0.0784 x (84.7 – 14.7) / { 0.0625 ( 0.0159)}] :

σc = [(0.9188 – 6.640) / (0.0159)] - [ 0.0625 x 0.0784 x (70) / { 0.0009937)}] :

σc = [(– 5.72) / (0.0159)] - [ 0.343 / 0.0009937] :

σc = [-360] - [ 345.2] = -705.2 psi:
This is less than the 767psi limit for copper at the temperature for NWP = 70psig.
I.E. The flue tubes are acceptable for NWP = 70psig.
This supercedes my post of #82, so if you need the correct calcs, please do not use post #82.

I understand you have rated your boiler at 50psig NWP., so it is OK.
Regards,
K2
 

DJoksch

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I updated my folder. Thanks! This has been a learning experience. I am sketching out a horizontal boiler around a remaining 12” length of the same material used as the shell for this project, but have not done the calculations yet. I’m deciding on either a fire tube or a Yarrow type. The revised tube calculation will help. Once I decide on the structure, I will post the design and the calculations. A 3-drum Yarrow design has some interesting issues at a small scale as well as how to pipe the water return to the lower drums. Need to study a bit more while I finish the layout board for the current boiler.
 
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