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Post by Deleted on Nov 5, 2014 0:05:24 GMT
It's good that people are starting to look at and question what has gone before. That's the only way that any progress in the development of our miniature steam locos etc. can be made. If only there was the time to do all the experiments needed!
John
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Post by Roger on Nov 5, 2014 8:35:52 GMT
The issues with coaxial are, incoming steam cooling outgoing steam, surface area exposed to flue gases vs steam volume passing through tube, turbulence of both flue gases and steam to maximise heat transfer and cleaning of flue and superheater surface. This is the reason I suggested some method of insulating the inner tube although I'm not sure about the method of doing that. Maybe a high temperature 'string' of insulation material wound round the whole length? |
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Post by sncf141r on Nov 5, 2014 17:21:13 GMT
As always, I'm out in left field;
1) DAG Brown, of Injector book fame, went through the "maths" in a Model Engineer article a while ago, and said that superheating was not required in miniature;
2) Of the last 10 or so full sized locomotives that I have worked on, about half were superheated.
3) My Tich has superheater flue completely blocked; still runs fine. My 2-8-2 had the superheaters removed by a previous owner; runs fine. A Sweet Pea in our club had superheater issues one festival weekend about 15 years ago and they were bypassed; runs just fine.
4) of the three (yes, sadly, three) locomotives currently being built in my workshop, 2 are designed saturated steam. One by a very well known builder - the prototype (Shay) was saturated, too.
Why all this argument about something that is not necessary? (said tongue in cheek, kind of)
JohnS.
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Post by Deleted on Nov 5, 2014 18:08:10 GMT
Could someone find out from IMLEC results what proportion of winning locomotives were superheated ??...........
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Post by Roger on Nov 5, 2014 18:12:01 GMT
I think a lot of this goes back to the comment someone made about however badly a locomotive is made, it still works. To some extent that is surely true of the subtlety of design. I don't doubt that these are 'not required' and that locomotives will work without it but that's not the question here.
Common sense tells us that the drier the steam, the less water you will use and the higher the efficiency will be. Throwing away water you've boiled but failed to expand to steam is clearly wasteful. The question is whether you get a higher degree of superheat from one type or another. It's all about subtlety, not whether the wheels go round or not.
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Post by Deleted on Nov 5, 2014 18:36:29 GMT
------- This is what WASTE looks like >>>>>>>>>>>>>>>>>>>>>>>>>>>>>  |
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Post by fostergp6nhp on Nov 5, 2014 18:38:38 GMT
From what I can find via Google the Houlet type has the normal arrangement of wet and dry headers. The wet steam passes down into the flue in a normal element size tube which is joined to a concentric tube length, the steam passes between the inner and outer tubes, flue gasses pass over and thro the concentric area. The steam then passes out of the concentric tube section into a normal tube and via a return bend back to the dry header with the dry side tube passing thro the inner tube of the concentric section.
This has got me thinking. How about 2 tubes in the flue passing into the outer of a concentric tube section which then passes out of the flue and is radiant in the fire box, the inner becomes the dry return. As its not concentric all the way there is no heat loss into the wet steam from the dry hot steam as almost all the flue length is of 2 separate tubes.
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Post by Roger on Nov 5, 2014 19:36:13 GMT
To borrow some information that Julian supplied on his Boxhill thread, it would appear that there is very little if any heat supplied to the steam in the flue itself, it's mostly in the radiant part that heat is transferred. If that's the case then the inside tube of a coaxial type needs to be insulated with some kind of string else the inner tube is going to significantly cool the steam from the radiant part. That makes sense to me and would account for some of the differences between the two types. I don't know how these conclusions were arrived at so I don't have any evidence to back this up. I've just asked these people if they can sell the fine cord that they use to make their insulated ropes from. That could be wound tightly round the inner tube. |
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jma1009
Elder Statesman
Posts: 5,918
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Post by jma1009 on Nov 5, 2014 20:20:41 GMT
if you jump to page 3 of the following link you will find some of jim ewins' thoughts on superheaters plus some of his criticism of the coaxial type. he also explains why some people think that with superheaters removed the loco appears to perform ok. www.maidstonemes.co.uk/media/DIR_17401/autumn85.pdfcheers, julian |
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Post by sncf141r on Nov 5, 2014 20:58:39 GMT
I think a lot of this goes back to the comment someone made about however badly a locomotive is made, it still works. To some extent that is surely true of the subtlety of design. I don't doubt that these are 'not required' and that locomotives will work without it but that's not the question here. Common sense tells us that the drier the steam, the less water you will use and the higher the efficiency will be. Throwing away water you've boiled but failed to expand to steam is clearly wasteful. The question is whether you get a higher degree of superheat from one type or another. It's all about subtlety, not whether the wheels go round or not. Roger - I'm not talking about a "badly made" locomotive; please don't misunderstand me. Why - if superheaters are so great, did the full size NOT use them for some locomotives? Why are locomotive appliances (over here - air compressors, sometimes steam driven water pumps, turbogenerators, and such) not superheated? Why would DAG Brown, who spent his career in the power industry (from what I understand) go out on a limb and go through the maths to show that superheaters are not "worth it" (my words) in our scales? Why is the amount of water used of interest to us? Why does it matter (other than for the fun of the competition) whether my Tich uses 4 teaspoons or 5 to do a lap of our track? (I've got 1/2 ton from Signal Fuels, and, believe me, that's a lot of years of running Tich!) Inquiring minds want to know.... (smile - I write this in fun, not in table pounding spill-the-beer anger) |
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Post by GWR 101 on Nov 5, 2014 20:58:46 GMT
Julian, Many thanks for posting that. Regards Paul
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Post by Deleted on Nov 5, 2014 20:59:35 GMT
Could someone find out from IMLEC results what proportion of winning locomotives were superheated ??........... I've long been of the opinion that the results from IMLEC are more down to the ability of the driver than the efficiency of the loco. A good driver can get good results even from a not so good loco. Pretty much like a good guitarist can make a crap guitar sound brilliant! John |
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Dave H
Involved Member
Posts: 91
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Post by Dave H on Nov 5, 2014 21:00:29 GMT
"DAG Brown, of Injector book fame, went through the "maths" in a Model Engineer article a while ago, and said that superheating was not required in miniature"
Well as "DAG" is usually a shortened form of, "Devils Advocate General" who was fooling who!
Nice article by the way Julian.
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Post by Roger on Nov 5, 2014 21:21:26 GMT
I think a lot of this goes back to the comment someone made about however badly a locomotive is made, it still works. To some extent that is surely true of the subtlety of design. I don't doubt that these are 'not required' and that locomotives will work without it but that's not the question here. Common sense tells us that the drier the steam, the less water you will use and the higher the efficiency will be. Throwing away water you've boiled but failed to expand to steam is clearly wasteful. The question is whether you get a higher degree of superheat from one type or another. It's all about subtlety, not whether the wheels go round or not. Roger - I'm not talking about a "badly made" locomotive; please don't misunderstand me. Why - if superheaters are so great, did the full size NOT use them for some locomotives? Why are locomotive appliances (over here - air compressors, sometimes steam driven water pumps, turbogenerators, and such) not superheated? Why would DAG Brown, who spent his career in the power industry (from what I understand) go out on a limb and go through the maths to show that superheaters are not "worth it" (my words) in our scales? Why is the amount of water used of interest to us? Why does it matter (other than for the fun of the competition) whether my Tich uses 4 teaspoons or 5 to do a lap of our track? (I've got 1/2 ton from Signal Fuels, and, believe me, that's a lot of years of running Tich!) Inquiring minds want to know.... (smile - I write this in fun, not in table pounding spill-the-beer anger) I do take this in the spirit it's intended, I'm just engaged with the subject of the conversation, that's all. So, point by point.... I did indicate that it was poor design and not poor build quality, I probably should have made that clearer. Ancillary equipment doesn't use enough steam to be worth superheating, the savings are not worth the bother. I know nothing about DAG Brown, but I don't defer to anyone's experience or qualifications, I'm only interested in facts. I don't know what tests or analyses he performed so I can't comment. Most people don't have an unbiased view and he may well have been looking to prove a case. Who knows. Without data it's impossible to comment. The amount of water or coal consumed is of interest to some of us because it's satisfying to get the best performance from a locomotive. You could argue that you only need a few flues, or that it's unimportant if valves or seals leak, or if the valve timing is imprecise, who cares? It's about subtlety and making the most of the energy in the fire. You don't have to care about it, but personally I find it interesting and hope that it will lead to a more eager and powerful locomotive than one that didn't have superheaters. It's easy to make a locomotive that works adequately, but quite another that works at its best. It costs next to nothing to add them so why wouldn't you when you get improved performance? Presumably some shunting locomotives didn't bother with superheaters because efficiency was of little importance to them. They were always near a water and coal supply. Equally well, using less coal or water would clearly save money on an express train. |
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Post by Roger on Nov 5, 2014 21:42:37 GMT
if you jump to page 3 of the following link you will find some of jim ewins' thoughts on superheaters plus some of his criticism of the coaxial type. he also explains why some people think that with superheaters removed the loco appears to perform ok. www.maidstonemes.co.uk/media/DIR_17401/autumn85.pdfcheers, julian That's a very interesting piece although it doesn't really provide any evidence of the inferiority of the concentric type, just opinion. I'm sure he has more to say on the subject but it's not very revealing what's said there. I'm perfectly happy to accept that they may not be as efficient, but he seems to concede that there are large differences in performance for different designs of concentric superheaters. I don't think they've had enough critical examination with a view to their improvement to dismiss them just yet. Fitting the way they're done on Julian's STEPNEY is so elegant that it pretty much negates any argument about the ease of construction. Whether that's the case for ease of manufacture when there are more elements to be connected in a header is open to question. |
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steam4ian
Elder Statesman
One good turn deserves another
Posts: 2,069
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Post by steam4ian on Nov 5, 2014 22:09:12 GMT
------- This is what WASTE looks like >>>>>>>>>>>>>>>>>>>>>>>>>>>>> I notice that Hagley has fallen for the "Media trick". Whenever the Media report on pollution they show pictures of steam clouds from cooling towers. The "real" polution comes from the boiler stack behind the towers. If we want to settle the superheater argument we need somebody to build two small boilered Tiches; one with superheat the other saturated with care to make the surface area of the tubes the same. I chose Tich because it is about the smallest viable loco capable of hauling more than its driver. Any difference in performance will be immediately obvious. LBSC used superheaters often involving some complication even when boasting that Anne Bodie could build her. How much LBSC was a slave to his own grand design aspirations and how much he found superheaters necessary/valuable by "scientific" experimentation I don't know. What I can say is that if I was looking for the most basic and simplest beginners loco I would look at Barry Potter's Blowfly design. Thick plate frames requiring no horns, slip eccentric, simple boiler and surprise, surprise, NO superheater. As designed Blowfly can pull 12 adults up grades of 1:50. That said, there heve been two revisions to the Blowfly design, each time the grate area was increased. Would that be necessary if Blowfly had been superheated? |
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greensands
Part of the e-furniture
Building a Don Young 5" Black Five
Posts: 409
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Post by greensands on Nov 5, 2014 22:23:18 GMT
Julian - Could you please provide the link to your thread on STEPNEY where reference is made to making and fitting of concentric superheaters.
Reg
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Post by Deleted on Nov 5, 2014 22:56:48 GMT
I notice that steam4ian has fallen for that old myopia trick of mis-reading that which has been clearly printed in front of him...........I used the word W-A-S-T-E ...... and those cooling towers to illustrate the heat energy literally going up in STEAM...................You won't find the word POLLUTION in MY post as that was never the subject matter in the first place ( A trick the media like to employ, apparently )....Incidentally, as the young Hagley spent his Apprentice Years and then some RN service time on the Marine version of that complete photo you can rest assured he knows the basic difference 'twixt steam and FFO exhausting..( Economisers, feedwater pre-heaters etc ).......................My understanding as to the reason why Superheaters are fitted is mainly one of ECONOMY ( Roger has hit the nail square on the head with }----"Throwing away water you've boiled but failed to expand to steam is clearly wasteful". )....Hence my photo.... It's not the water thrown away that concerns us but the heat energy still contained within it .....steam4ian's two TICH locos will give comparable results BUT the Superheated one will be using less coal to achieve it.......... Do have a thorough read of this..I've posted it before but how many actually READ it ?? >>>>>>>>>>>>>>>> en.wikipedia.org/wiki/Superheater |
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Post by Deleted on Nov 5, 2014 23:53:02 GMT
Roger said} "Presumably some shunting locomotives didn't bother with superheaters because efficiency was of little importance to them."....Quite so...remember that photo of 1501's open smokebox door showing it to be a saturate loco ??.. ie}--No superheater......The class of ten locos spent the majority of their life shunting ECS movements in and around Paddington.......
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chrisb
Part of the e-furniture
Posts: 355
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Post by chrisb on Nov 6, 2014 0:50:19 GMT
Interesting that Hagley chose a pic of my former place of work.
Yes it does indicate heat loss but that isn't steam as such, power station water steam cycles use a closed circut of ultra pure water. Imagine how soon a power station boiler would become scaled up if tap water were used!
So the steam from the turbines is exhausted into a condenser to go round the feed heating and boiler circuits once more. Where it reaches a pressure of around 165bar (2400psi) and is superheated to approx 565degC this is then fed to the HP turbine before being returned to the boiler for reheat and then into an IP turbine and exhausting into LP turbines before finding its way back to the condenser.
The circulating water used in the condenser is river water, this is pumped from the river into the cooling tower ponds and pumped though the condenser and out to the cooling tower where a proporton will be purged back to the river. What you are seeing from the top of the cooling tower is water vapor from the cooling process of the water being sprayed out through a matrix of nozzles about 1/4 the way up the tower and falling over special packing to spread the heat transfer from the upward natrural draught of the air.
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