I haven't been following this closely but are radiant super heaters being considered? By radiant I mean the super heaters extend to the back of the firebox and presumably pick up a lot of heat. Worked for me in an Allen 10 wheeler.
Optimal number of boiler tubes.
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user 52078
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HMEEL,
You are on the right track with equal areas but actually equal hydraulic radius takes better account of the increased surface for fluid friction and the area. In practice, the slightly different tmperature gradient (and hence flue gas properties) makes a further tweek necessary.
Vietti,
As the OP was in relation to a vertical boiler, I did not consider radiant elements as they rather obstruct the firebox and coal firing. On a horizontal loco boiler, I would go with radiant elements.
Martin
You are on the right track with equal areas but actually equal hydraulic radius takes better account of the increased surface for fluid friction and the area. In practice, the slightly different tmperature gradient (and hence flue gas properties) makes a further tweek necessary.
Vietti,
As the OP was in relation to a vertical boiler, I did not consider radiant elements as they rather obstruct the firebox and coal firing. On a horizontal loco boiler, I would go with radiant elements.
Martin
Richard Hed
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I read that henry ford hired a mathemetician. He did not know if it would be worth hiring a mathematician but he did. The mathematician improved the engines and cars in general so much that he paid for the guys salary many times over.
My main focus on engines is the Coles/Ray which has lots of opportunity for simple improvements particujlarly where fluid (steam) enters the cylinder from the valve. The way it is designed creates "bounce", a very bad way to treat any fluid if one wants non-turbulent flow. That's also why I am complaining about the steam input bonnet being badly designed as tyhe steam flows in many different directions and each change of direction reduces efficiency.
BTW, when I was in high school (last week), my German teacher told us an anecdote about a German engineer and henry. Henry was having difficulty with his new generators for his cars. He could not solve the problem so he finally hired this German engineer to see if HE could fix ther problem. Well, the engineer, took the generator, spun it, listening intently with his ear to the generator and after a few hours oir so, put an X on the generator and said, "take out 16 windings right here". He charge henry $15000 for this, and in the depression era, this was MIGHTY sum, so henry wanted an accounting of what he was being charged for. So the German's account was thus: Chalk--$1, Labor--$1, Knowing where the mark went--$14998.
Needless to say, the $15000 was peanuts (boiled maybe) compared to what it solved.
Thanks for that insight (#162) Martin: I guess that with Gas firing, then radiant elements may help a little?
But I have a question:
If the Spear-end of the superheater heats the steam above the temperature of the Smoke-box end of the flue gases, especially if "radiant" elements, I assume the return run of steam then heats the flue gases... which in turn give some more heat to the run of steam coming in to the superheater... or whatever, so the smoke-box temperature is actually raised from the limiting temperature of the boiler water to the limiting temperature of the superheater steam.. at equilibrium?
As with the higher smoke box temperatures in the table post#26:
However it works, there is always a real limit that makes the steam temperature limited to the flue gas temperature without heat flow (I.E. Equilibrium) - I think? So I guess the speed of gas flows in the flue tubes and superheater tubes is such that we are not in equilibrium?
I also think "in reality" (rather than simple calculations that I do) the temperatures of gases change rapidly with expansion along the flues and steam pipes so the pressure drop that is causing the gases to flow in effect cools the gases (Gas laws). Which is why "boiler steam" (un-superheated) is always "wet" at the engine. - And why Turbines must use superheated steam and exhaust above the condensation temperature (pressure) to avoid water damage to turbine blades. - A major reason why turbines never worked in the limited space of locomotives?
Raygers, Do you have the engine you will power from the boiler? Be nice to see a photo.
K2
But I have a question:
If the Spear-end of the superheater heats the steam above the temperature of the Smoke-box end of the flue gases, especially if "radiant" elements, I assume the return run of steam then heats the flue gases... which in turn give some more heat to the run of steam coming in to the superheater... or whatever, so the smoke-box temperature is actually raised from the limiting temperature of the boiler water to the limiting temperature of the superheater steam.. at equilibrium?
As with the higher smoke box temperatures in the table post#26:
| EXIT TEMP FROM FIRETUBES |
| EXIT TEMP FROM SUPERHEATER FLUES |
| AVERAGE SMOKEBOX TEMPERATURE |
I also think "in reality" (rather than simple calculations that I do) the temperatures of gases change rapidly with expansion along the flues and steam pipes so the pressure drop that is causing the gases to flow in effect cools the gases (Gas laws). Which is why "boiler steam" (un-superheated) is always "wet" at the engine. - And why Turbines must use superheated steam and exhaust above the condensation temperature (pressure) to avoid water damage to turbine blades. - A major reason why turbines never worked in the limited space of locomotives?
Raygers, Do you have the engine you will power from the boiler? Be nice to see a photo.
K2
Here's my baby running on compressed air. This is the blub from the PM Research website
This is not a scaled-down model, but a full-size working steam engine. It is a replica of a rare old steam engine used for various small portable power applications a century ago. This engine was sold as a casting kit in 1895 by the Chas. A Strelinger Co. of Detroit, MI. The castings were made by their foundry, the Leland & Faulconer Mfg. Co., 480-500 Trombly Ave., Detroit, MI. It was rated then as 1/4 H.P. Think of it! A full-size working engine that you have built. A machinist's delight! The total height is 19 inches and the flywheel diameter is 6-7/8" inches.
Kit comes complete with 15 iron and bronze castings, all required hardware, gasket material, bar stock and complete working drawings. Machining and assembly required.
This is not a scaled-down model, but a full-size working steam engine. It is a replica of a rare old steam engine used for various small portable power applications a century ago. This engine was sold as a casting kit in 1895 by the Chas. A Strelinger Co. of Detroit, MI. The castings were made by their foundry, the Leland & Faulconer Mfg. Co., 480-500 Trombly Ave., Detroit, MI. It was rated then as 1/4 H.P. Think of it! A full-size working engine that you have built. A machinist's delight! The total height is 19 inches and the flywheel diameter is 6-7/8" inches.
Kit comes complete with 15 iron and bronze castings, all required hardware, gasket material, bar stock and complete working drawings. Machining and assembly required.
- Bore 1-1/2
- Stroke 2-1/2
- Double Acting
user 52078
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That's a lovely long stroke, long connecting rod engine. It reminds me of a really tall person walking along! Is it a piston valve?
I think the 6" boiler we have been discussing will be fine, provided you don't intend to generate 1/4HP on a continuous basis and the superheat option will help a lot in reducing steam consumption required by the engine.
Martin
I think the 6" boiler we have been discussing will be fine, provided you don't intend to generate 1/4HP on a continuous basis and the superheat option will help a lot in reducing steam consumption required by the engine.
Martin
Hi Martin,
Just read (again) the document from Post #10.
Brilliant!
I think I understood a bit more than before... (First reading was just a quick scan to appreciate what was being discussed.).
I am now curious to get my hands on "the programme" - so I can input existing boilers - and see how I can improve them? - by changing the external superheater in the smoke box, or whatever?
But I don't use coal. So would be interested if you had done a gas-fired option - perhaps "simple" flames (blue flames with not much radiant effect) versus Radiant element gas burners?
All I have done is Stephan's law for radiant as that energy that isn't in the simple "heat input" based on tables of BTUs versus jet size, gas, and pressure. - All assumed fully stoichiometric - all fuel burnt. Although in practice I get some CO on some boilers (that can set-off the CO alarm in my garage on the shelf above my running bench).
I now reckon I understand and agree your suggested solution for Raygers' boiler and agree the "usable steam" in the engine should be maximised. ("maximum effective volume of steam to the engine").
So Raygers, the option with the superheaters is a good one!
Thanks,
K2
Just read (again) the document from Post #10.
Brilliant!
I think I understood a bit more than before... (First reading was just a quick scan to appreciate what was being discussed.).
I am now curious to get my hands on "the programme" - so I can input existing boilers - and see how I can improve them? - by changing the external superheater in the smoke box, or whatever?
But I don't use coal. So would be interested if you had done a gas-fired option - perhaps "simple" flames (blue flames with not much radiant effect) versus Radiant element gas burners?
All I have done is Stephan's law for radiant as that energy that isn't in the simple "heat input" based on tables of BTUs versus jet size, gas, and pressure. - All assumed fully stoichiometric - all fuel burnt. Although in practice I get some CO on some boilers (that can set-off the CO alarm in my garage on the shelf above my running bench).
I now reckon I understand and agree your suggested solution for Raygers' boiler and agree the "usable steam" in the engine should be maximised. ("maximum effective volume of steam to the engine").
So Raygers, the option with the superheaters is a good one!
Thanks,
K2
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user 52078
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Steamchick,
Have sent you a p.m.
Martin
Have sent you a p.m.
Martin
Vietti, Considering your question about Radiant Superheaters... when in a vertical boiler such as we are studying:
I thought about this, as I play with Ceramic Gas Burners, which have good radiant heat output. On a vertical boiler, the "holes through the flues" become "Holes to let the radiant heat pass through" and escape, unless a superheater coil, or feed-water pre-heater coil, in the smoke-box captures the radiant heat. But a spear-ended superheater will naturally block the radiant heat from escaping, but just by the cross-sectional area of the spear-end. But every little helps for Model Boilers.
If designing for a radiant burner, it is better to have a horizontal boiler cylinder, with the radiant heater shining fully on the underside of the boiler, and have the exhaust gas flow to the end of the boiler and pass through horizontal flues to the smoke box. Ideally, the superheaters can be a single feed tube passing into the exhaust from the smoke box (location for the steam inlet manifold to superheaters), through the superheater flues, out and around the firebox end of the boiler, and pass beneath the boiler - perhaps along the side walls of the firebox? - to a manifold after exiting the firebox. I also like reflective linings on the inside walls of the firebox otherwise the radiant heat shining on those side walls is lost to heating the side-walls, not water.
Hope this helps a bit?
K2
I thought about this, as I play with Ceramic Gas Burners, which have good radiant heat output. On a vertical boiler, the "holes through the flues" become "Holes to let the radiant heat pass through" and escape, unless a superheater coil, or feed-water pre-heater coil, in the smoke-box captures the radiant heat. But a spear-ended superheater will naturally block the radiant heat from escaping, but just by the cross-sectional area of the spear-end. But every little helps for Model Boilers.
If designing for a radiant burner, it is better to have a horizontal boiler cylinder, with the radiant heater shining fully on the underside of the boiler, and have the exhaust gas flow to the end of the boiler and pass through horizontal flues to the smoke box. Ideally, the superheaters can be a single feed tube passing into the exhaust from the smoke box (location for the steam inlet manifold to superheaters), through the superheater flues, out and around the firebox end of the boiler, and pass beneath the boiler - perhaps along the side walls of the firebox? - to a manifold after exiting the firebox. I also like reflective linings on the inside walls of the firebox otherwise the radiant heat shining on those side walls is lost to heating the side-walls, not water.
Hope this helps a bit?
K2
user 52078
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Ah, but if you put a slow twist in the superheater elements you would block most of the radiant heat leakage, and improve the convective heat transfer and squeeze in a little more surface area................
Martin
Way out of my knowledge zone, perhaps already answered, but couldn't the super heater in a vertical boiler be a simple flat coil of tubing at the top of the fire box that conducts the steam going from the throttle to the cylinder? All radiant heat from the flame, no obstruction of the flues.
user 52078
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Well yes but......
If you put the superheater in the firebox you will get really hot steam with a small coil because of the high temperatures. But if you reduce or cut the steam flow (sooner or later you will have to stop this thing) the temperature will go very high and that has the potential to wreck packings and seals in the engine and distort the superheater which will be near red hot coal or straight above a gas burner.
Conversely, if you put the superheater in the smokebox the overheating is largely avoided, but you need a large coil to get enough heat out of the relatively cool (by that point) combustion gases.
Superheaters in a large flue gives a good compromise performance that won't unduly overheat at low steam flow and doesn't need massive amounts of superheater surface. Not only that, this thread started with a desire to reduce the number of tubes in the boiler for simpler manufacture and putting a few large superheater flues in is a good way of achieving that.
Hope that shows the design issues here.
Martin
Hi Vietti, As far as I understand, Martin's mathematical analysis says you need far more superheater and hot gas than is possible in the smoke-box end of the boiler. Smoke box at (say) 250~300C whereas the smoke in the flue tubes starts at 700~900C and drops down to 250~300C... - That's cooking!
On boilers I have made/re-engineered, the "Top-of-the-boiler coils don't do so much to superheat the steam, compared to superheaters that go down to the fire-box, or through the firebox to exit from the firebox. (Some of those get the output steam pipe too hot for organic insulation! - It chars!).
I shall be doing some sums based on Martin's tuition to analyse what is going on instead of my "that's a bit hot" - to "That's Blummin HOT!"
I have run a twin compound engine and that really shows the difference of superheat. Without much superheat (Top-coil) it needs 20psi (boiler pressure) to run well while warming-up, dropping to 15psi (boiler pressure) when the second cylinder is hot enough to start working properly. But on Boilers with flue superheaters (as far as the firebox) of superheaters that go to the firebox and out, it runs happily at 8~10psi (boiler pressure) after warming-up. I use a ceramic gas burner in all these boilers so the steam is regulated by pressure = Burner power controlled by the gas tap, not by a boiler steam outlet regulator.
I.E. My experience backs-up Martin's theory.
Hope this helps?
K2
On boilers I have made/re-engineered, the "Top-of-the-boiler coils don't do so much to superheat the steam, compared to superheaters that go down to the fire-box, or through the firebox to exit from the firebox. (Some of those get the output steam pipe too hot for organic insulation! - It chars!).
I shall be doing some sums based on Martin's tuition to analyse what is going on instead of my "that's a bit hot" - to "That's Blummin HOT!"
I have run a twin compound engine and that really shows the difference of superheat. Without much superheat (Top-coil) it needs 20psi (boiler pressure) to run well while warming-up, dropping to 15psi (boiler pressure) when the second cylinder is hot enough to start working properly. But on Boilers with flue superheaters (as far as the firebox) of superheaters that go to the firebox and out, it runs happily at 8~10psi (boiler pressure) after warming-up. I use a ceramic gas burner in all these boilers so the steam is regulated by pressure = Burner power controlled by the gas tap, not by a boiler steam outlet regulator.
I.E. My experience backs-up Martin's theory.
Hope this helps?
K2
Hi Raygers, I have been doing some sums...
I have just put the cylinder and engine speed into my calculator and determined you need about a 0.57mm gas jet for Butane/Propane? - What fuel do you plan to use?
If a ceramic will cope with all the gas and air (6.7kW - which is well over what I think a 5 inch diameter burner can take), then this may be the ceramic for you? (or similar?).
https://gbr.grandado.com/products/g...EBuuJy2XH39sNhHHJxm6QW3GiZOOJ6C8aAmgDEALw_wcB
I can design the details for a burner air-intake (quite critical...) if you wish. But I may have to buy a ceramic and make the parts to prove the design before I let you know.... (Or sell you the burner?). OR I may need to make a stainless steel wire mesh burner to take the power....
I feel a project coming on here....
I'm just "messing about" right now, so no commitments...
K2.
I have just put the cylinder and engine speed into my calculator and determined you need about a 0.57mm gas jet for Butane/Propane? - What fuel do you plan to use?
If a ceramic will cope with all the gas and air (6.7kW - which is well over what I think a 5 inch diameter burner can take), then this may be the ceramic for you? (or similar?).
https://gbr.grandado.com/products/g...EBuuJy2XH39sNhHHJxm6QW3GiZOOJ6C8aAmgDEALw_wcB
I can design the details for a burner air-intake (quite critical...) if you wish. But I may have to buy a ceramic and make the parts to prove the design before I let you know.... (Or sell you the burner?). OR I may need to make a stainless steel wire mesh burner to take the power....
I feel a project coming on here....
I'm just "messing about" right now, so no commitments...
K2.
Thanks, Ken, for sure I am going to run at least one coal fire, probably more. I grew up in the steam train era, as probably you did also. Wallsend is just south of the Newcastle to Edinburgh line and remember seeing the trains flying along, smoke, fire steam, and great noise, every schoolboy fantasy. I'm hoping to put the boiler into a steam plant along with a water tank, condenser, and eventually a steam-powered water pump, it'll have to be hand-powered for now until I can get around to building one.
A ceramic heater will certainly be in my sights.
Hi Raygers, I know Wallsend, as Sunderland is just the other side of the Tyne tunnel and a few miles South. I grew up in Newport - Great Western line between London and Cardiff/Fishguard. (Like Wallsend, a big Roman fort - Caerleon). Used to go to local scrapyards as a lad, mid-1960s, and see the hundred or more locos awaiting the gas torch... Crawled inside rusty boilers, and climbed all over them. - The lot! - as Kids will.
We still drive over to Durham or Gateshead to watch any Tourist Preservation steam trains in summer. (Maybe 3 or 4 a year?). Or drive to N. York moors or somewhere to the preservation lines... Oh, the smell of coal and steam oil... I have to get my regular fix at Roker park (Sunderland) with the 5 in gauge locos there. - Or in my garage with gas powered boilers. (Misses the coal smoke smell though).
On Open days at the local club, there are always lots of comments from punters: "What's that smell?" (The coal smoke) and "OOOH! I remember that smell, Takes me back to childhood".
https://www.csmes.co.uk/index.htmlNostalgia ain't what it used to be...
K2
We still drive over to Durham or Gateshead to watch any Tourist Preservation steam trains in summer. (Maybe 3 or 4 a year?). Or drive to N. York moors or somewhere to the preservation lines... Oh, the smell of coal and steam oil... I have to get my regular fix at Roker park (Sunderland) with the 5 in gauge locos there. - Or in my garage with gas powered boilers. (Misses the coal smoke smell though).
On Open days at the local club, there are always lots of comments from punters: "What's that smell?" (The coal smoke) and "OOOH! I remember that smell, Takes me back to childhood".
https://www.csmes.co.uk/index.htmlNostalgia ain't what it used to be...
K2
BillHowcroft
Member
This is an interesting YouTube on researching the engineering of a steam locomotive:
Even more incredible is that the designers imagined all that in their heads in order to make their designs.... Design is not all about just joining A to B to C, etc. with shaped metal bits, but about understanding the motions that happen and realising what is needed to make those motions work and not break, wear, or destroy themselves.
Before computers, I plotted 10degree steps from a piston and crank motion through the whole of a set of linkages, including some obscure and "4-bar" linkages, to develop the required forces an motion at the end of the line. Based of the force required at each step of the motion of the final part, the linkages were attuned to give variable mechanical advantages from start to finish, as appropriate to the time I wanted certain distances to be covered by the final end of the linkage. All this driven by variable input forces at different stages of the motion, to give the right force at the far end that made things work. (A little bit like the task the valve gear designer did. Mine was at a single setting, Loco designers have variable settings! - Far more complex motion calculations!).
He is lucky that the original designs are available so really all he is doing is illustrating what went on in the Designers' brains. Very clever animations. But how clever to work it all out originally from a blank sheet of paper - Many decades ago?
Building it right is good, but designing it right is "Great".
Excellent "computer Modelling" though. I wonder how many hours to make that complete model? - Maybe less than making it in metal, etc?
K2
Before computers, I plotted 10degree steps from a piston and crank motion through the whole of a set of linkages, including some obscure and "4-bar" linkages, to develop the required forces an motion at the end of the line. Based of the force required at each step of the motion of the final part, the linkages were attuned to give variable mechanical advantages from start to finish, as appropriate to the time I wanted certain distances to be covered by the final end of the linkage. All this driven by variable input forces at different stages of the motion, to give the right force at the far end that made things work. (A little bit like the task the valve gear designer did. Mine was at a single setting, Loco designers have variable settings! - Far more complex motion calculations!).
He is lucky that the original designs are available so really all he is doing is illustrating what went on in the Designers' brains. Very clever animations. But how clever to work it all out originally from a blank sheet of paper - Many decades ago?
Building it right is good, but designing it right is "Great".
Excellent "computer Modelling" though. I wonder how many hours to make that complete model? - Maybe less than making it in metal, etc?
K2
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Also watched this.
The educational use of the animation. - Excellent!
Although I "teach" guys who know less than I about locos, I learned a few things about Big-Boy!
K2
The educational use of the animation. - Excellent!
Although I "teach" guys who know less than I about locos, I learned a few things about Big-Boy!
K2
Aside from this thread... but "testing lessons" for steam boilers. Yesterday I was at "the local club" and obtained the first certification for a modified "Stuart-Style" Scott boiler. The original maker had used thin end plates that had blown under pressure, so I had flattened the ends and fitted 6 stays - Then re-did the calculations of the design to show the NWP as 30psi - not the 60psi that it had been previously used at! Previously, the calculations would have had a Factor of Safety of about 1.3 without stays... - Now it has a FOS of >8 with stays. - As required for Federation Certification for the club and the Club's insurance. (And passed the examination - including calculations - and hydraulic test at 2 x NWP).
Next it must be built into the firebox and steam tested, but the Safety Pressure Relief valve was an old design, not acceptable to the examiner, so needs a modification.
Lesson learned:
Make it with the right THICKNESS of material, or de-rate it at "certification time".
Another guy had last year found his boiler design was only good for 30psi according to (later) calculations, but he needed 80 psi NWP for normal running... because of a manufacturing error made on some boiler plates, that had allowed a larger than desired space/distance between stays... That error, - before assembly - could have caused a catastrophic steam leak from a failed stay about 3 feet from his face, or other body parts, but the inspector identified the error and failed the boiler for 80psi NWP.
So take care to follow the design drawings for everything, especially stay spacings and plate thicknesses. "Too thick" is heavy and safe. But plates that are too thin, or stays too far apart, are actually dangerous if the boiler is not de-rated appropriately.
Cheers!
K2
Next it must be built into the firebox and steam tested, but the Safety Pressure Relief valve was an old design, not acceptable to the examiner, so needs a modification.
Lesson learned:
Make it with the right THICKNESS of material, or de-rate it at "certification time".
Another guy had last year found his boiler design was only good for 30psi according to (later) calculations, but he needed 80 psi NWP for normal running... because of a manufacturing error made on some boiler plates, that had allowed a larger than desired space/distance between stays... That error, - before assembly - could have caused a catastrophic steam leak from a failed stay about 3 feet from his face, or other body parts, but the inspector identified the error and failed the boiler for 80psi NWP.
So take care to follow the design drawings for everything, especially stay spacings and plate thicknesses. "Too thick" is heavy and safe. But plates that are too thin, or stays too far apart, are actually dangerous if the boiler is not de-rated appropriately.
Cheers!
K2
