Why no Porkies ?

[barts]

I would agree both boilers would report the same heat transfer rates due to the physics.... but apparently the simplicity of control afforded by just running the pump fast enough permits heat fluxes that are not practical (probably absent that perfect control) in small scale monotubes. This is based on measured practice in steam cars, not any theoretical analysis.

Note that the transition point of evaporation in a small monotube must be precisely controlled to achieve very high heat transfer rates, since the superheater needs to have lower heat fluxes than the evaporating section. Absent such precise control, if evaporation occurs too earlier the later portions of the evaporator segment may overheat. A flash-overfeed design is a good choice here since it permits a more open-loop form of control and assures adequate moisture in the evaporator.

Overheating the tubes is the thing to avoid in either boiler... in the Lamont, insuring that adequate moisture exists in tubes is critical. Since steam at our typical pressures takes up so much more volume than water, the speed of the mixture exiting the coil will be very high. This can cause significant back pressures and can lead to surging. Using a restriction in the entrance of the coil will help prevent such surging. Most Lamont boilers use centrifugal pumps; using one with plenty of extra head here seems wise to insure proper circulation. Our very small boilers don't need very big pumps; positive displacement pumps will also work here. A 3 hp engine might use 100 lbs steam/hr; a 2 gpm pump would provide almost 10x circulation over steam rate.

Anyone with an old high pressure hot water washer has a fine Lamont coil ready to go; all that is needed is a steam drum & pump.

- Bart

[Lopez Mike]

My lowly donkey boiler is looking better and better to me.
Mike

[87gn@tahoe]

Anybody try using fluid diodes on lamonts or even overly large economizers?

[SL Ethel]

A question to Bart or others on the list who may have experience with this:

Can you really use a reciprocating pump on a Lamont boiler? I have read many times that feed water (at atmospheric pressure) starts to get difficult to pump above 180 or so because it may flash to steam on the intake stroke. Would this not be a much greater problem on a lamont, where it would only take a very small decrease in pressure to flash part of the circulating water to steam?

Has anybody tried this? Do pressure washer pumps work, or is there some other sort of lower-speed pump that might work?

I have a hot water pressure washer at hand, and if this would actually work, I might even have a going boat this season - any guidance would be much appreciated.

Cheers,
Scott

[barts]

Here's a you tube video of a Lamont boiler made from a pressure washer coil and a procon pump from ebay...



To avoid problems w/ low NPSH, bring the coil discharge in at a tangent so that the water in the boiler rotates like mad... and setup the suction side so that the flow charges in - this will give you several feet of head.


- Bart

[SL Ethel]

Thanks for the explanation and video clip. Now I know what my new boiler needs to look like!

Cheers,
Scott