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Post by joanlluch on Oct 12, 2015 23:16:42 GMT
Hi Pete, I'm on M series BMW's these days. I've my second one already. Form the many brands I have tried, that's the one that most satisfies me, yet you can do whatever you want with the car and it never breaks. The Ford Cosworth has become a classic over the years, i regret having sold it, but frankly the car was absolutely torn in pieces when I sold it. Even as new, the car didn't sustain my continuous throttle/braking on a mountain road for more than several minutes without ejecting the radiator water out. And forget about German autobhans or asphalt circuits with that car. This has never been a problem with my two BMWs so far. I made 360.000Km with my old M3 before selling it and it didn't even consumed 1 litre of engine oil between official checks. Totally amazing for what I was used to before.
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Post by joanlluch on Oct 13, 2015 10:21:54 GMT
if Joan ... i will send him Jim Ewin's paper on firebox crown height, and his objections to co-axial superheaters. Hi Julian, Before you send me that paper, I have spend some time at looking again at the figures provided by Jim Ewins on boiler temperatures. He states that a parallel tube like superheater reaches steam temperatures in excess of 700 C at the tip of it (firebox side). However, steam temperature at the cylinder chest gets down to about 300C. This suggests to me that the return pipe of the superheater cools it down significantly. My point about coaxial superheaters is that by insulating the return pipe, you'll avoid steam cooling down. Temperature at the tip of the superheater should be about the same, but then you'll prevent most of that temperature being lost through the return pipe. Insulation of the inner tube can be performed by just inserting it in a Silica or Ceramic fibre sleeve of the same diameter before soldering it to the outer tube.
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pault
Elder Statesman
Posts: 1,497
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Post by pault on Oct 13, 2015 19:12:36 GMT
Hi Joan I think the 700 degree temperature is the metal temperature of the element. Assuming you are looking at the same drawings I am temperatures H & J should be the other way round if it is steam temperature. It is highly unlikely the steam temperature would be dropping in a radiant element whilst still in the fire box.
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Post by joanlluch on Oct 13, 2015 19:50:55 GMT
Hi Pault. Yes, we are looking at the same drawings. My understanding of this drawing is that J is the temperature -presumably of the steam- at about the tip of the superheater. Temperature at H is even higher because steam is still circulating thought a section of the superheater that is IN the firebox, so it keeps heating. At point H, steam reaches its maximum temperature. Then the superheater return pipe continues inside one of the fire tubes to the smoke box and finally it gets the cylinder steam chest. It is from point H to point N where steam looses temperature because tubes are surrounded by smoke at much lower temperatures. So i pressure that if you have a way to insulate section H to N they you'll have more efficiency and less water consumption. A coaxial superheater is an ideal arrangement to applying this idea.
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pault
Elder Statesman
Posts: 1,497
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Post by pault on Oct 13, 2015 21:14:56 GMT
Hi Joan, the temperature drops between J and H and so is dropping inside the firebox. I believe that the drawing and notation are very clear, both in text and the position of the dots which represent where the temperature is measured.
N is described as steam temperature and the dot is within the steam pipe to the cylinders H&J are described superheater temperature (not steam temperature)and the dots are on the wall of the superheater.
Measuring the steam temperatures at H and J would mean putting two thermocouples inside the element, not touching the wall of the element, which whilst It can be done would be tricky.
There probably is a drop in temperature towards the smokebox but not that great. The gas temperatures are still relatively high until part way down the tubes.
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jma1009
Elder Statesman
Posts: 5,901
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Post by jma1009 on Oct 13, 2015 22:25:25 GMT
hi joan,
Jim Ewins was a scientist employed at Imperial College London. as Paul points out there is nothing wrong with Jim's findings as published - what you would expect of a scientist. everything Jim did was meticulous and thorough.
what you need is the cylinders, especially for a valve gear being notched up and used with a short cut off and expansive working, is to avoid condensation of the steam. the steam pressure is what does the work, but this is hindered if condensation occurs in the cylinders. there are other factors such as increased fluidity, but the above will do for the time being.
the text of Jim's research made it quite clear that the exhaust steam was above the condensation temperature. having driven myself the loco that Jim made and tested i can vouch for it's superb qualities!
Both Paul and Jim Scott have published on here findings with modern thermocouples with superheaters that accord to Jim's findings in the late 1960s.
cheers, julian
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Post by joanlluch on Oct 14, 2015 7:03:49 GMT
Hi Paul,
Ok, I see your point. I haven't looked at the drawing carefully enough. However, test No 3 has a higher temp at point H than point J, so there's some sort of contradiction about what actually happens at that site.
My point though is still the same. I regard the superheating system as (1) a countercurrent flow heat exchanger on the input tube, followed by (2) a parallel flow heat exchanger on the return pipe. If you analyse both elements then you find that (1) is clearly acting as a heating device, while (2) will act as a heating or cooling device depending on (T) the actual steam temperature at the tip of the superheater. It T is low then steam temperature will keep increasing through the return pipe. If T is already high, then steam temperature will decrease. Whether it cools down or it heats depends on what is called the mean temperature difference that in turns depends on the input and output temperatures of both fluids being interchanged.
So given this, I can think on a setup that favours heat exchange during (1) and prevents cooling down during (2). And that's what a coaxial superheater with insulated return pipe does. That's just my way of seeing this, of course. This is why I asked whether the idea of insulating the inner pipe or a coax superheated has been actually attempted or tested by someone.
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Post by joanlluch on Oct 14, 2015 7:09:49 GMT
Hi Julian,
I have never discussed or disputed Jim Ewins work if that's what you mean, In fact I am using his data to take my own concussions. Also, I'm fully aware of what you mentioned regarding how a steam loco works. That's out of any doubt, and I think I have clearly shown that.
Still, I am interested in what Pault and Jim Scott have published, which I am aware.
Please, could you point me to the right place for me to have a look?.
Thank you very much.
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