Unusual boiler design

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DianneB
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Unusual boiler design

Post by DianneB » Fri Sep 28, 2018 6:38 am

A few years ago I started building a model of Trevithick's 1803 engine in 1" scale. I had some 4" copper pipe and 1/4" copper sheet so I used these for the boiler barrel and end plates.
Boiler 1.jpg
Needless to say, it passed hydrostatic tests easily but when tested for steam capacity, it was sadly lacking.

I recently redesigned the boiler adding Galloway tubes and doubling the number of flues, which calculates well on paper but while assembling the new boiler I realized how much heat goes into the heavy barrel and end plates! The weight will be helpful for traction but I am wondering if I may be loosing a lot of heat because of the heavy boiler shell? Logically it would be the same surface area as a lighter shell so there would/should be no additional loss though it will take longer to come to steam temperature than a lighter shell.

Trevithick's boiler had no lagging but I suppose I could add a thin lagging of some type to keep cold air off the copper plates?

Thoughts? Experiences?

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Fender
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Re: Unusual boiler design

Post by Fender » Fri Sep 28, 2018 7:08 am

The specific heat of copper is about 38% of water, meaning it only takes about one-third as many calories to raise the temperature of a pound of copper vs. a pound of water by the same amount. Obviously, since copper is such a good conductor of heat, some insulation would help. Perhaps wrapping the outside with aluminum foil would reduce heat loss?
Dan Watson

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gwrdriver
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Re: Unusual boiler design

Post by gwrdriver » Fri Sep 28, 2018 8:06 am

I would say you are not losing more heat on account of the plate thickness.
Heat loss depends upon the thermal conductivity of the material, its thickness, and exposed area, so heavier plates would actually help with heat retention as it would take longer for heat to migrate though the material than for a thinner plate. It would also take a lot more energy to bring heavier plates up to a given temperature than for thinner material, but that isn't "loss", that's just taking more time to get steam up.

I don't know that this is THE problem, which if changed or eliminated would solve the problem, but the end plates create a big heat sink and greatly increase the area exposed to air and therefore loss of heat. It would seem to me the solution would be to encase the boiler in an insulated cabinet.
GWRdriver
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NP317
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Re: Unusual boiler design

Post by NP317 » Fri Sep 28, 2018 9:30 am

Insulate.
~RN

Kimball McGinley
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Re: Unusual boiler design

Post by Kimball McGinley » Fri Sep 28, 2018 2:04 pm

Why do the plates extend out like that? Reminds me of fins on a radiator; can you trim them back closer to the barrel diameter?

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DianneB
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Re: Unusual boiler design

Post by DianneB » Sat Sep 29, 2018 7:31 am

Kimball McGinley wrote:
Fri Sep 28, 2018 2:04 pm
Why do the plates extend out like that? Reminds me of fins on a radiator; can you trim them back closer to the barrel diameter?
I could but then it wouldn't look like Trevithick's 1803 locomotive

John Hasler
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Re: Unusual boiler design

Post by John Hasler » Sat Sep 29, 2018 8:11 am

Fender wrote:
Fri Sep 28, 2018 7:08 am
The specific heat of copper is about 38% of water, meaning it only takes about one-third as many calories to raise the temperature of a pound of copper vs. a pound of water by the same amount. Obviously, since copper is such a good conductor of heat, some insulation would help. Perhaps wrapping the outside with aluminum foil would reduce heat loss?
Only with a layer of low-conductivity material under it.

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