Talk:Flash boiler

Quote from List of boiler types, by manufacturer: "monotube steam generator: A single tube, usually in a multi-layer spiral, that forms a once-through steam generator. The first of these was the Herreshoff steam generator of 1873". This seems to pre-date Serpollet's design of 1896. Does anyone have more information about Herreshoff? Biscuittin (talk) 12:28, 2 December 2012 (UTC)

See also Du Temple Monoplane of 1874. Biscuittin (talk) 12:32, 2 December 2012 (UTC)

Herreshoff was probably Nathanael Greene Herreshoff (1848 – 1938), who "Developed the first light steam engine and fast torpedo boats". Biscuittin (talk) 12:39, 2 December 2012 (UTC)

That's a reasonable description of a monotube steam generator. However this is an article on flash boilers instead.

Flash boilers have a somewhat unclear definition: some sources apply the term very widely, certainly overlapping with low water content steam generators. However as we have (or should have) a separate article on these, then we can best decide to take the narrower definition – even though this type of boiler was extremely rare in practice, with the monotube boiler being almost always preferred. Andy Dingley (talk) 12:58, 2 December 2012 (UTC)

I'd say that flash boiler and monotube boiler are the same. Please explain the difference. Biscuittin (talk) 13:22, 2 December 2012 (UTC)

We have an article Steam generator (boiler). I would say that both flash boiler and monotube boiler describe a boiler consisting only of tubes and having no drums. Biscuittin (talk) 13:28, 2 December 2012 (UTC)

Both uses tend to avoid "boiler", because that's what they're fundamentally trying to avoid.

Steam boilers, particularly firetubes but also watertubes, are filled with a mixture of water and steam. The steam causes problems – it disrupts circulation and it reduces heat transfer into it, being much less dense than the water. So it has long been recognised that a boiler works better with more water and less steam held within it. An important intermediate step was the submerged tube boiler, where the water tubes were held entirely full of water and the steam space is isolated above this.

The fundamental principle of any flash boiler, monotube boiler or steam generator is that they avoid steam content within them. Heat is transferred efficiently into liquid water, rather than into low-density steam. This is done by preventing boiling, either by stopping the water boiling through pressure, or by excluding the water and allowing the boiler temperature to rise (maybe to red heat), then pumping water onto it, where it "flashes" instantaneously into steam.

Monotube boilers use the first system. They may either boil gradually along their length (usually pumped circulation systems, such as the Velox) but where this boiling doesn't disrupt the circulation. Otherwise they can use the Benson supercritical system, where the pressure is sufficient to prevent boiling (within the heated volume) altogether. They key factor that both have in common is the use of some intermediate energy store between the combustion and the steam generation: either as superheated water, or as heated metalwork.

True flash boilers, with dry heated metalwork, are rare. Serpollet used them and they were used by model engineers in the 1950s for model racing hydroplanes, as described in Westbury's book. However apart from this, they're rare as hen's teeth. "Flash boiler" is far more widely applied to the monotube form, even though these don't involve any "flash" boiling, as Serpollet used.

Flash and monotube boilers are relatively recent, as they depend on materials technology and liquid fuels. Materials was a problem, as Serpollet's design for a lightweight boiler (by avoiding the water content) ended up just as heavy from the weight of constructional materials he needed for it to survive the heat stress. Later designs, after seamless drawn steel tubing became available, did mange to be lightweight. More important though is the need for a liquid fuel with a variable power burner. As there is no power reserve in a low water content boiler (there isn't – that's another common misapprehension), the burner power needs to track the power demand almost immediately (a similar situation to the naphtha engine).

A "boiler consisting only of tubes and having no drums" necessarily has to be a one-pass steam generator, because it has no volume to store evolved steam in. Yet it's misleading to see this as their defining factor. The point is the avoidance of boiling within the generator, so as to maintain efficient heat transfer into dense, unboiled water. Coincidentally that also equates to watertubes without drums, but an explanation of the boiler type has to describe it in the causal order. Andy Dingley (talk) 16:44, 2 December 2012 (UTC)

New article

To Andy Dingley: I have created Monotube steam generator. I expect you will say I've got it wrong so please correct it as necessary and add references. Biscuittin (talk) 17:32, 2 December 2012 (UTC)

Definition of flash boiler

Andy Dingley states above: "The fundamental principle of any flash boiler, monotube boiler or steam generator is that they avoid steam content within them. Heat is transferred efficiently into liquid water, rather than into low-density steam". This statement is clearly wrong. The Serpollet type contains very little liquid water, because it is instantly flashed into steam. The White type contains liquid water only in the upper coils, while the lower coils contain steam - see the patent.[1] Is there some expert committee in Wikipedia which can produce a definition of flash boiler? Biscuittin (talk) 15:39, 8 December 2012 (UTC)

"Avoid", not "exclude". Obviously boiling has to happen somewhere, but the point is that we restrict this to a controlled location and (most importantly) we don't allow it to disrupt controlled circulation. Yes, Serpollet is a true flash boiler (one of the few). Yes, the White (which is probably the first, but not the only one, of these long single-coiled-tube monotubes) has a flow of water from the inlet end and at some point this becomes steam. The point is that this boiling is controlled and constrained to a particular area of the boiler. Andy Dingley (talk) 17:16, 8 December 2012 (UTC)