sgriggsFinally, as you point out thermic siphons and arch tubes were replaced with circulators for a net reduction in direct heating surface area on the J3a. The primary purpose of these firebox elements is to promote water circulation throughout the boiler, and especially over the firebox side- and crown sheets. I have not seen the circulator arrangement inside the 614's firebox, but I assume they are similar to those installed on Union Pacific's Big Boys and late Challengers. Those circulators (inverted "T"s), are designed to draw water from the firebox sides and expell it at the crown sheet. I assume this change was driven by maintenance needs (I have seen it written that UP avoided thermic siphons on its big power because siphons were found to be hard to maintain in service). I have never seen any data that suggests siphons and arch tubes had an efficiency advantage over circulators, so I'm skeptical that there is a significant difference in evaporative performance.
I am enjoying this technical analysis. (BTW, I do suggest retaining the spelling 'syphon' when referring to the Nicholson devices, as that's what they used...)
There were three fairly major problems with Nicholsons, and one potential one that I think was the most significant of all in emergency situations.
First, the things as constructed required a considerable amount of staybolting, and this had to be inspected, maintained, etc. like the regular firebox staybolting, except it was a pain to get to, to inspect, to clean, etc.
Second, the things put a nice quenching surface into the combustion plume, effectively black as night to any remaining chemical action there. I suspect this is one of the reasons some roads that tried chamber syphons -- ATSF on the 3460 class, as a notable example, perhaps? -- took 'em out rather quickly.
Third, the neck area and the general flow characteristics into the syphons from where the neck attached to the boiler structure was a pathetic thing. I don't really think the people who were promoting syphons really understood what circulation in the radiant section actually does, or even how the water there behaves (Porta described this stuff as being like 'boiling milk' even with reasonable boiler water treatment, for example). I am likewise unsure if they understood properly what the effect on circulation in the convection section was when flow through the syphons was at 'full cry'
The hidden 'ringer' was what happens when water over the crown gets intermittent for some reason. There was some claim that Nicholsons were 'safer' because they would pump water out over the crown and tend to quench it ... someone can probably find direct quotes or even the ads themselves; I think Richard Leonard has a couple of them on his site somewhere. It does not take much knowledge of Eisenhoffer and Leidenfrost, or of the behavior of boiler steels when repeatedly heated and quenched, to understand how ridiculous the idea was, or just what sorts of problems could develop if anyone actually came to test this "safety" idea. (As has been noted on this forum, C&O 1642 likely provided a demonstration of this...)
The arch tube circulators are a bit easier to fabricate, and of course are worlds easier to inspect and manage. To an extent they have the 'thermal barrier' protection (from the arch brick) that keeps them from being as much of a cause of radiant quench.
I agree with my father that it should be possible to use the technique Bulleid used on the Leader boiler fireboxes to make syphons. This specifically replaces the staybolting with full-pen-welded hollow tubes. I do not comment on anything else associated with this, like how the National Board ESC would react to it; just that it might be possible to remove the staybolting problems as an issue.
Somewhere my father has some drawings of his idea of piping air inside the syphons to oriented secondary-air jets. Not as much problem either with preheat or freezing at the nozzles ... and certainly less problem with induced turbulence trying to get effective mass flow of secondary air at appropriate preheat to the 'inside volume' of an American-size firebox. (I do not know whether this was a serious idea or not; it has a certain 'grandeur' to it. But it doesn't work nearly as well, if at all really, for arch-tube circulator setups...)
Meanwhile, I think there are some things going on in the front-end steam discussion that need to be addressed. Specifically, the idea that you are 'wasting' energy in the steam by blowing it out the stack. I understood Big Jim's comment to mean that any heat energy in the steam THAT WAS NOT USED TO INDUCE DRAFT was wasted ... not that it was a waste to use the steam for that purpose practically. Certainly that was a major point in what Giesl was saying.
There is an ongoing technical question about whether the residual energy in the combustion gas reheats the steam in the exhaust jet, particularly when turbulent mixing and subsequent entraining of the steam, 'momentum transfer', etc. are as good as they should be. My father and Jos Koopmans know much more about this than I do. The point of much of the 'modern' front-end improvements is to make the best possible use of exhaust for drafting, or to reduce the amount of steam needed for the 'right' draft (across a very wide and sometimes epically nonlinear range of flows!), and thereby allow diversion of more of the mass, or flow, or whatever, of the exhaust steam to 'recapture' in the Rankine cycle for any combination of its mass or heat content.
Whatever we do with the ongoing discussion, let's not get mixed up with "thermodynamic improvements" related to saving exhaust steam that wouild make working locomotives less effective... in actual railroad practice...
Wizlish sgriggs Finally, as you point out thermic siphons and arch tubes were replaced with circulators for a net reduction in direct heating surface area on the J3a. The primary purpose of these firebox elements is to promote water circulation throughout the boiler, and especially over the firebox side- and crown sheets. I have not seen the circulator arrangement inside the 614's firebox, but I assume they are similar to those installed on Union Pacific's Big Boys and late Challengers. Those circulators (inverted "T"s), are designed to draw water from the firebox sides and expell it at the crown sheet. I assume this change was driven by maintenance needs (I have seen it written that UP avoided thermic siphons on its big power because siphons were found to be hard to maintain in service). I have never seen any data that suggests siphons and arch tubes had an efficiency advantage over circulators, so I'm skeptical that there is a significant difference in evaporative performance. I am enjoying this technical analysis. (BTW, I do suggest retaining the spelling 'syphon' when referring to the Nicholson devices, as that's what they used...) There were three fairly major problems with Nicholsons, and one potential one that I think was the most significant of all in emergency situations. First, the things as constructed required a considerable amount of staybolting, and this had to be inspected, maintained, etc. like the regular firebox staybolting, except it was a pain to get to, to inspect, to clean, etc.
sgriggs Finally, as you point out thermic siphons and arch tubes were replaced with circulators for a net reduction in direct heating surface area on the J3a. The primary purpose of these firebox elements is to promote water circulation throughout the boiler, and especially over the firebox side- and crown sheets. I have not seen the circulator arrangement inside the 614's firebox, but I assume they are similar to those installed on Union Pacific's Big Boys and late Challengers. Those circulators (inverted "T"s), are designed to draw water from the firebox sides and expell it at the crown sheet. I assume this change was driven by maintenance needs (I have seen it written that UP avoided thermic siphons on its big power because siphons were found to be hard to maintain in service). I have never seen any data that suggests siphons and arch tubes had an efficiency advantage over circulators, so I'm skeptical that there is a significant difference in evaporative performance.
Agreed. The construction of a thermic syphon, with the need to seal somewhat large penetrations in the crown sheet, accommodate the thermal expansion differentials, and their internal staybolted construction make them more difficult to maintain than arch tubes or security circulators.
Wizlish Second, the things put a nice quenching surface into the combustion plume, effectively black as night to any remaining chemical action there. I suspect this is one of the reasons some roads that tried chamber syphons -- ATSF on the 3460 class, as a notable example, perhaps? -- Third -- the general flow characteristics into the syphons from where the neck attached to the boiler structure was a pathetic thing. I don't really think the people who were promoting syphons really understood what circulation in the radiant section actually does, or even how the water there behaves (Porta described this stuff as being like 'boiling milk' even with reasonable boiler water treatment, for example). I am likewise unsure if they understood properly what the effect on circulation in the convection section was when flow through the syphons was at 'full cry' The hidden 'ringer' was what happens when water over the crown gets intermittent for some reason. There was some claim that Nicholsons were 'safer' because they would pump water out over the crown and tend to quench it ... someone can probably find direct quotes or even the ads themselves; I think Richard Leonard has a couple of them on his site somewhere. It does not take much knowledge of Eisenhoffer and Leidenfrost, or of the behavior of boiler steels when repeatedly heated and quenched, to understand how ridiculous the idea was, or just what sorts of problems could develop if anyone actually came to test this "safety" idea. (As has been noted on this forum, C&O 1642 likely provided a demonstration of this...)
Second, the things put a nice quenching surface into the combustion plume, effectively black as night to any remaining chemical action there. I suspect this is one of the reasons some roads that tried chamber syphons -- ATSF on the 3460 class, as a notable example, perhaps? --
Third -- the general flow characteristics into the syphons from where the neck attached to the boiler structure was a pathetic thing. I don't really think the people who were promoting syphons really understood what circulation in the radiant section actually does, or even how the water there behaves (Porta described this stuff as being like 'boiling milk' even with reasonable boiler water treatment, for example). I am likewise unsure if they understood properly what the effect on circulation in the convection section was when flow through the syphons was at 'full cry'
As with anything promoted to be a safety feature, there are limits to how effective they will be. If the crown sheet is completely uncovered, with the exception of the liquid/gas mixture bubbling out of the syphon to quench it, you will probably have film boiling (think droplets of water on a hot surface) with very little cooling of the sheet. Without proper handling of the situation by the crew, it's only a matter of time before a catastrophic failure occurs, syphons or not.
Wizlish The arch tube circulators are a bit easier to fabricate, and of course are worlds easier to inspect and manage. To an extent they have the 'thermal barrier' protection (from the arch brick) that keeps them from being as much of a cause of radiant quench. I agree with my father that it should be possible to use the technique Bulleid used on the Leader boiler fireboxes to make syphons. This specifically replaces the staybolting with full-pen-welded hollow tubes. I do not comment on anything else associated with this, like how the National Board ESC would react to it; just that it might be possible to remove the staybolting problems as an issue. Somewhere my father has some drawings of his idea of piping air inside the syphons to oriented secondary-air jets. Not as much problem either with preheat or freezing at the nozzles ... and certainly less problem with induced turbulence trying to get effective mass flow of secondary air at appropriate preheat to the 'inside volume' of an American-size firebox. (I do not know whether this was a serious idea or not; it has a certain 'grandeur' to it. But it doesn't work nearly as well, if at all really, for arch-tube circulator setups...) Meanwhile, I think there are some things going on in the front-end steam discussion that need to be addressed. Specifically, the idea that you are 'wasting' energy in the steam by blowing it out the stack. I understood Big Jim's comment to mean that any heat energy in the steam THAT WAS NOT USED TO INDUCE DRAFT was wasted ... not that it was a waste to use the steam for that purpose practically. Certainly that was a major point in what Giesl was saying. There is an ongoing technical question about whether the residual energy in the combustion gas reheats the steam in the exhaust jet, particularly when turbulent mixing and subsequent entraining of the steam, 'momentum transfer', etc. are as good as they should be. My father and Jos Koopmans know much more about this than I do. The point of much of the 'modern' front-end improvements is to make the best possible use of exhaust for drafting, or to reduce the amount of steam needed for the 'right' draft (across a very wide and sometimes epically nonlinear range of flows!), and thereby allow diversion of more of the mass, or flow, or whatever, of the exhaust steam to 'recapture' in the Rankine cycle for any combination of its mass or heat content. Whatever we do with the ongoing discussion, let's not get mixed up with "thermodynamic improvements" related to saving exhaust steam that wouild make working locomotives less effective... in actual railroad practice...
While I agree that exhaust steam is put to an important use when it creates draft for the fire, from a strict thermodynamic efficiency standpoint the energy in the exhaust steam is wasted because it is not doing work at the drawbar.
sgriggsWhile I agree that exhaust steam is put to an important use when it creates draft for the fire, from a strict thermodynamic efficiency standpoint the energy in the exhaust steam is wasted because it is not doing work at the drawbar.
Now, if all of the energy could have been used in the cylinder, would there be anything left to exhaust?
I'd say it is the nature of the beast and no one ever figured out how to make it happen any other way, at least in a railroad reciprocating steam locomotive.
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BigJimI'd say it is the nature of the beast and no one ever figured out how to make it happen any other way, at least in a railroad reciprocating steam locomotive.
The real 'key' if you decide to go for the practical efficiency and 'automatic action' of a good steam-ejector front end is not to waste any of the available energy in the exhaust steam when you are producing practical draft with it.
That is why many of the fancy ejector and nozzle arrangements work 'better', and contrariwise why some of the "improvements" -- particularly most if not all of the wacky stuff done by the Union Pacific in the '30s right up to the pepperpot stacks on the FEF-4 design -- turn out to have problems that outweigh their 'advantages'. There's a limit to the number, type, and shape of vanes in a Kylchap arrangement, too;with four probably being too much already in a standard-gauge locomotive. if you have a copy of Sinclair's Development of the Locomotive Engine handy you can predict quite a bit of how and where you put the fancy eduction stuff for best effect.
Jos Koopmans has apparently figured out that a multiple-nozzle front end works like 'that number' of smaller chimneys, in scale, in parallel. (With some interesting things probably happening in the mutual area between the jets, but I think we need CFD rather than little models to figure out what that might be...) When you have good smooth mixing, and correct acceleration of the induced flow both in speed and in orientation of the gas flow as it mixes with the flow from the nozzles, there will be a 'sweet spot' or range of best entrainment and best mass ejection for any steam exhaust flow -- which may well be either too great or too small for what the fire at the other end, and the heat uptake along the way, calls for.
On the other hand, the usual towering plumes of smoke are a clear indication that some of the exhaust energy is being used very wastefully, and the high turbulence visible as it goes is even clearer. The flip side of this, of course, is that when the arrangements are made 'better', notably in terms of the Selkirk front end and arguably in the case of the PRR T1, you start needing some form of 'smoke deflector' PDQ to keep the exhaust ... including the nice white part of the condensing steam in cold weather ... away from the engine crew's view of the world. Then you have energy being 'wasted' in aerodynamics rather than steam thermodynamics... and that adds up, probably as 'measurably' as did the progressive engaging of individual car generators in the train acceleration curves in Kiefer's motive-power report.
It is easy to forget the importance of reduced back pressure at meaningful levels of mass flow in a 'regular' two-cylinder DA engine. There are approaches like the Holcroft-Anderson system that quite effectively recover much, perhaps most, of the latent heat in the exhaust steam ... at the cost of having to produce the draft on the fire by 'more complicated means' (this being the Achilles heel of the actual use of Holcroft-Anderson on the Southern Railway in the prewar years...)
The whole subject of condensing practice on locomotives, as opposed to ships, has been discussed repeatedly here (probably much more in the years before I started reading posts). There is little doubt that it didn't get done well for any reason that involved thermodynamic efficiency (rather than water conservation) and that at least one proposed operation (the ACE 3000) would very often have been an operational disaster in practice.
One of the great unsung opportunities lost in conventional steam history, though, is the work that was done on the condensing GE steam turbines while they were running in wartime service on NP. Apparently the guys working on them had figured out all the sources of difficulty and knew in detail what to do to build a better-working locomotive using that cycle (1200 psi admission, and very large plenum volume at the exhaust to keep the effective back pressure on the turbine low). If any of those guys' notes were preserved I would very much like to read them!
Wizlish One of the great unsung opportunities lost in conventional steam history, though, is the work that was done on the condensing GE steam turbines while they were running in wartime service on NP. Apparently the guys working on them had figured out all the sources of difficulty and knew in detail what to do to build a better-working locomotive using that cycle (1200 psi admission, and very large plenum volume at the exhaust to keep the effective back pressure on the turbine low). If any of those guys' notes were preserved I would very much like to read them!
Minor correction, the GE Turbomotives were originally built for the UP, who tried them for a bit and then turned them back to GE. GE then provded the units to GN for helper service, where they lasted about two years.
Efficiency was't up to expectations, especially with the units running on the LA&SL and the units needed a lot of maintennance. The record might have been a bit better had WW2 not prevented the R&D to get them working right. After the war, gas (combustion) turbines looked to be a lot more practical.
- Erik
erikem Wizlish One of the great unsung opportunities lost in conventional steam history, though, is the work that was done on the condensing GE steam turbines while they were running in wartime service on NP. Apparently the guys working on them had figured out all the sources of difficulty and knew in detail what to do to build a better-working locomotive using that cycle (1200 psi admission, and very large plenum volume at the exhaust to keep the effective back pressure on the turbine low). If any of those guys' notes were preserved I would very much like to read them! Minor correction, the GE Turbomotives were originally built for the UP, who tried them for a bit and then turned them back to GE. GE then provded the units to GN for helper service, where they lasted about two years. Efficiency was't up to expectations, especially with the units running on the LA&SL and the units needed a lot of maintennance. The record might have been a bit better had WW2 not prevented the R&D to get them working right. After the war, gas (combustion) turbines looked to be a lot more practical. - Erik
The specific point was that a great many of the problems that made the turbines unsuccessful on UP were apparently addressed during the time the locomotives were serving in the Northwest. I don't have the reference for this; it was given as an anecdote in a report about some other kind of power (I think in Strack's discussion of the gas turbines), but will see if I can find it.
The real problem was, I think, similar to that for Baldwin's Essl design of 'modular' diesel: it was just too expensive per usable horsepower, and too complex in comparison with what EMD was discovering it could provide.
I checked Turbines Westward by Thomas R. Lee - his book starts with the Turbomotives. He did write that the units did a year of reasonable service on the GN between Wenatchee and Spokane, with the units being retired in 1943 due to wheel rims thinning and the boiler on one of the units going bad.
Thermal efficiency was said to be twice that of conventional steam locomotives, but lower than the efficiency of diesel engines and to a lesser extent, gas turbines.
Lee did say that cost per horsepower was high with the Turbomotive.
weather could also have an effect on the test datea.
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