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 Post subject: Re: Tek Tube Internally Finned XID Boiler Tube
PostPosted: Wed Aug 09, 2017 7:24 pm 

Joined: Thu May 24, 2012 1:37 pm
Posts: 869
Just as a note: the Cleaver Brooks "aluFer" tubes have an aluminum (!) insert that blocks a substantial amount of the free lumen of the tube, with very long and comparatively thin fins. Aside from being soot magnets (they are normally used in industrial units with a modulating "Fecralloy" burner) and targets for corrosion and ash-impingement wear, these would, I think, suffer rather quickly from edge melt and distortion in conventional locomotive firing. I do not think it would take much slumping to destroy the required gas throughput in these tubes when run with locomotive induced draft...

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Last edited by Overmod on Thu Aug 10, 2017 2:48 am, edited 1 time in total.

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 Post subject: Re: Tek Tube Internally Finned XID Boiler Tube
PostPosted: Wed Aug 09, 2017 9:45 pm 

Joined: Sat Aug 31, 2013 4:11 pm
Posts: 270
R. Hahn wrote:
TimReynolds wrote:
Where multi-pass boiler designs ever tried on a steam loco?


At least one, but it isn't exactly modern steam.

Roger


Well that answers that. And fascinating stuff on the Franco-Crosti design too


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 Post subject: Re: Tek Tube Internally Finned XID Boiler Tube
PostPosted: Thu Aug 10, 2017 4:26 am 

Joined: Wed Nov 23, 2016 7:05 pm
Posts: 63
R.M. -
Agreed it wouldn't take much slumping to destroy proper draft, but are aluFer inserts pure aluminum or a high temp alloy like Y alloy or an Al-3Fe eutectic? That looks like it would get you up into high temp region that should work at locomotive boiler temps. Hoval uses them in boilers up to 2300 HP, so they must be able to take some heat. I also note that in the CB literature it appears the ends of their inserts have a tapered fin entrance - I assume to improve flow and reduce sharp edges that would burn quickly. Other thoughts are to use them only in loco boilers with combustion chambers to remove more heat pre-flue, have very capable blowers, and use Porta or cyclone nozzles in the front end to even out the draft a bit if you have clean fuel. One would probably want to keep a basket nozzle for cleaning effect if using dirty fuel. I note the CB down-draft boilers have a very large combustion chamber around the burner screen and seem to recall that the fans are programmed to follow the heat curve (instead of lead it) to slow the gas as much as possible for better heat extraction. The same situation in a loco firebox might preclude solid fuel.

Anyway I still wouldn't try anything like that with anything but the cleaner liquid fuels, and would still start trials with a shallow spiral-finned tube style first. Maybe an amusement park burning LPG would be a good trial for the aluFer.

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 Post subject: Re: Tek Tube Internally Finned XID Boiler Tube
PostPosted: Fri Aug 11, 2017 12:13 pm 

Joined: Thu May 24, 2012 1:37 pm
Posts: 869
Quote:
"are aluFer inserts pure aluminum or a high temp alloy like Y alloy or an Al-3Fe eutectic? That looks like it would get you up into high temp region that should work at locomotive boiler temps. Hoval uses them in boilers up to 2300 HP, so they must be able to take some heat ..."


These are all interesting questions.

Reading between the lines, it seems to me that the boilers using the aluFer inserts are either condensing boilers or multiple-pass reflux, where good heat transfer under fairly steady-state conditions without either excessive turndown or overfiring conditions are typical. In my opinion, the quality and temperature of combustion gas impinging on the inserts will be very different in locomotive boilers under even 'normal' heavy operation conditions. Ross might care to comment on the 'crazy high' superheat he has observed at some points during high-speed operation with substantial load; the gas characteristics, especially near the rear tubeplate, associated with these temperatures are the things of greatest concern to me.

I do think it is highly likely that the inserts have metallurgy similar if not identical to what you describe. As an additional point, it might be remembered that the inserts will normally run with some sort of Orsat analytical control of combustion, and there may be periods both of significant oxidation or reduction away from what would be achieved in a stationary plant under industrial loading. That may not be significant but it should be remembered in analysis.

As implicitly noted elsewhere in the Cleaver-Brooks material, even slight waterside deposits can have a radical effect on heat-transfer effectiveness and thereby on the temperature in conductive elements -- notably, the portions of elements with perhaps relatively low heat-transfer coefficient that are located out at the end of thin sections depending on conduction for their 'cooling'. That is really the situation I'm concerned with, combined with the relative lower-than-atmospheric gradient down the tube during induced draft operation (I cannot think offhand of a locomotive in the last century using forced draft that has operated cost-effectively...)

Equalizing gas flow across flues and tubes matters far more to peak steam generation than it does to peak gas temperatures -- the combination of peak temp and mass flow being the thing that will distort or decrement the aluminum elements.

Likely these boilers are fed with gas or flutter burners -- modern industrial low-NOx practice. There aren't many cost-effective approaches to use these on locomotives of any size that takes advantage of the net 'economy' offered by the elements -- in my opinion.

I wouldn't hesitate to try using these on a park engine burning LPG, with the appropriate process implementations and precautions, in fact before messing around with complicated spiral or Serve tubes. That's in the size and load range of proven implementations. The question becomes whether the additional efficiency of heat uptake provides net operating benefit after capital charges for the provision of the aluFer tubes in the first place, and then their periodic maintenance. (As I noted, I'm certain Cleaver-Brooks will provide you a coherent cleaning and inspection plan for a given installation of these tubes, and advise what special equipment and techniques will need to be obtained and used.)

Evening out the draft won't matter any more than it does on a coal-burning engine at high speed. There is marginal 'brightening' at the peaks of induced maximum acceleration but I suspect the actual heat release is comparatively slight and of course is 'cooled' below peak level within no more than a couple of milliseconds. Likewise, nothing that happens to the gas after it transits the tubes/flues matters to the inserts. Porta of course thought you could arrange cyclonic flow in the firebox itself to remove some of the potential ash content that might erode, plug, or perhaps react with the elements -- personally, I don't think that approach would work most of the time on any locomotive used in regular railroad service.

The extended question hanging here is whether these elements might be useful in some larger (but still relatively "small") tourist-type locomotives, which will never be used faster than 25 to 40mph or see a combination of high exhaust volume and heavy draft. They would certainly seem preferable, in the long run, to any externally-finned approach even with Porta-McMahon treatment... I'm still uncertain whether the thermodynamic gain would pay for the exercise.

I am assuming that the elements are made as one extrusion, and two of them are pressed into the tube by some reasonably easy to estimate fabrication method.

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