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Imaginary Locomotives


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6 minutes ago, Clive Mortimore said:

An electrically heated steam loco would still need to exhaust its steam to draw the heat (hot air) through the boiler tubes to heat the water etc. just like one fired by wood or fossil fuels.

 

I don't follow that. Wouldn't it just have heating elements instead of the boiler tubes?

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2 minutes ago, Coryton said:

 

I don't follow that. Wouldn't it just have heating elements instead of the boiler tubes?

Yes you would as the loco has been proposed as being capable to being converted back to traditional means of firing. Elements along the tubes would greatly improve the ability to raise steam.

 

With a redesigned electrically heated boiler then no steam exhaust would be needed and could operate with a closed circuit steam/water system. As the steam leaving the cylinders is still under pressure, unlike that at the low powered end of a turbine, would it need to be condensed before being returned to the bolier? If so it would make a very inefficient loco having to carry around additional water to cool the steam.  

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‘Thermal Efficiency’ is irrelevant on a steam locomotive, as long as sufficient  boiler pressure can be maintained for the loco to do the work required.   Modern steam locos, superheated and at pressures above 200psi could easily achieve better than the 5/6% often quoted by diesel salesmen in the US in 40s and 50s, the source of these figures and hardly disinterested parties. 

 

In in order to assess the overall thermal efficiency when comparing steam, diesel, or electric traction, one must take into account the cost of thermal inefficiency in electricity generation, diesel refining from crude oil, and mining and transport of coal and oil. This is data that is difficult to compile with any meaningful degree of accuracy.  

 

Steam was was replaced by diesel or electric traction for sound operational reasons; availability, preparation time, manning, and driver’s forward visibility, not for any innate inferiority in terms of it’s ability to perform the work.

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1 hour ago, Clive Mortimore said:

Yes you would as the loco has been proposed as being capable to being converted back to traditional means of firing. Elements along the tubes would greatly improve the ability to raise steam.

 

With a redesigned electrically heated boiler then no steam exhaust would be needed and could operate with a closed circuit steam/water system. As the steam leaving the cylinders is still under pressure, unlike that at the low powered end of a turbine, would it need to be condensed before being returned to the bolier? If so it would make a very inefficient loco having to carry around additional water to cool the steam.  

Now I thought that to get the maximum thermal efficiency you had to condense the steam? To do this, you have to have the steam exhausting into something with negative pressure, i.e. below S.A.P.

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8 minutes ago, rodent279 said:

Now I thought that to get the maximum thermal efficiency you had to condense the steam? To do this, you have to have the steam exhausting into something with negative pressure, i.e. below S.A.P.

Could this be done without additional water by using cooling tubes like a fridge?

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The Wiki link on Condensing steam locomotives for any interested, the SAR class 25 looks a beast!

 

https://en.wikipedia.org/wiki/Condensing_steam_locomotive

 

It does mention in my quick look over that the big draw back is obviously the exhausted steam does not help draw more air through the fire box, but in the theoretical electrical element steam engine this would be less of an issue. Plus the electrical supply could used to drive big cooling fans on the condenser ;)

 

Thinking conventional steam for a moment, the other thing that springs to mind is given the size of that tender on the SAR 25 and the fact that in theory the water weight would not decrease over time as much, would it be a more suitable candidate to have driving wheels under the tender too? For example, high pressure cylinders at the front of the locomotive, they feed to low pressure cylinders for the drivers under the tender, and that then feeds into the condenser. (in theory, there's no reason why that couldn't be employed for the electrical version either, just imagine Corbs' electric 9f with a much bigger condensing tender sat on another 0-10-2 chassis).

 

 

Edit: just having a read up on the SAR 25, this sounds like an interesting solution to the firebox draught issue:

On the condensing locomotive, spent steam was recycled and condensed back to water for repeated use. Since the steam wasn't expelled up the chimney, the Class 25's smokebox contained a steam turbine-driven fan beneath the chimney to keep the draught going, with deflector plates that were supposed to prevent char from causing excessive wear on the fan blades

Edited by Satan's Goldfish
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16 hours ago, melmerby said:

The heaviest ever run was in Australia where BHP Billiton ran a train of nigh on 100000 tons with 8 AC6000s distributed down the train.

They normally run half this amount

 

The Guinness certified longest heaviest train in history on 21 June 2001. 

 

https://www.youtube.com/watch?v=9LsuNWjRaAo

 

Cheers

David

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On 27/02/2019 at 11:36, 34theletterbetweenB&D said:

All the energy input required to heat the water from cold to boiling point and then to evaporate it as a gas - steam - is completely lost in the exhaust of a non-condensing steam engine. Once the engine and smokebox is warmed through the water leaves the pistons as steam - still in the gaseous state - and the water typically only reverts to vapour after it is exhausted to atmosphere. If the fire is achieving near complete combustion a small translucent zone can be observed above the chimney top, so there the exhaust is all gaseous, the condensation of the water content back to vapour occurring immediately above as the billowing white clouds. (A large condenser system - see power station cooling towers as an example - is required to obtain any useful output from this energy input. )

Remember steam is just a medium for getting energy from one place to another, so that the energy can be converted to work. As I remember from my college days; I#m going to get a rollocking from JJB, I suspect! Hot water at 100degrees C contains roughly 420 kiloJoules of energy. After you've added the energy to get to this point, you've got hot water just beginning to boil; the liquid water is turning into a vapour (steam). As you add more and  more heat, a greater proportion of the water is turned to steam. If I recall the amount of heat required to turn a mass of water into an equal mass of dry steam is around 2.2 MegaJoules, at 100 degrees C, and it's this latent heat of vaporisation which makes steam so useful. If you use the steam to move a piston in a cylinder, some of the energy is given up as work; if you cut off the steam inlet at a point before the end of the piston stroke, more energy is lost from the steam as the pressure drops. Obviously, the pressure cannot go below atmospheric, or the steam won't go up the chimney. As the steam expands, it cools,  and as it does so some of it will condense back to water, if it's not superheated. It's the very poor expansion ratio (1 to 5 is about the maximum you can get away with, IIRC) that gives the simple steam reciprocating engine/steam locomotive boiler combination its low efficiency. In a petrol engine, you can get away with 12 to 1 (?), and for a diesel it's even higher.

 

Edited by 62613
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30 minutes ago, 62613 said:

Remember steam is just a medium for getting energy from one place to another, so that the energy can be converted to work. As I remember from my college days; I#m going to get a rollocking from JJB, I suspect! Hot water at 100degrees C contains roughly 420 kiloJoules of energy. After you've added the energy to get to this point, you've got hot water just beginning to boil; the liquid water is turning into a vapour (steam). As you add more and  more heat, a greater proportion of the water is turned to steam. If I recall the amount of heat required to turn a mass of water into an equal mass of dry steam is around 2.2 MegaJoules, at 100 degrees C, and it's this latent heat of vaporisation which makes steam so useful. If you use the steam to move a piston in a cylinder, some of the energy is given up as work; if you cut off the steam inlet at a point before the end of the piston stroke, more energy is lost from the steam as the pressure drops. Obviously, the pressure cannot go below atmospheric, or the steam won't go up the chimney. As the steam expands, it cools,  and as it does so some of it will condense back to water, if it's not superheated. It's the very poor expansion ratio (1 to 5 is about the maximum you can get away with, IIRC) that gives the simple steam reciprocating engine/steam locomotive boiler combination its low efficiency. In a petrol engine, you can get away with 12 to 1 (?), and for a diesel it's even higher.

 

Hi 62613,

 

You are quite correct in your description of how and why steam is such a good medium for energy transmission.

 

The two things I would add are that, the drier the steam is the more energy it has per unit mass at what ever pressure is being worked and also that, expanded steam at the point of the valve opening to exhaust must indeed have positive pressure.

 

Hot dry steam, (a relativistic term), is the reason for the use of high degree super-heat, this comes at a cost of greater difficulties in the lubrication of the liners, piston and valve heads and rings and also the gland packings.

 

The main reason for positive pressure is that the steam has work to do in drawing the fire via the draughting arrangements.

 

The usual maximum exhaust pressure at the blast cap for a simple expansion, single chimney is around 12 psi irrespective of either maximum boiler pressure or steam chest pressure at any given cut off.

 

Any driver that thinks that he may develop more power by increasing the cut off beyond what the draughting arrangements will allow will only succeed in making lots of noise bye way of of increasing the back pressure of the locomotive ultimately lowering the power produced with the added expense of disrupting the fire bed and using more water that is necessary. That said certain idiots still give it a good go all the same !

 

Ask yourself what would happen, unlikely as this is, if the steam condensed in the cylinder and caused a vacuum.

 

Gibbo.

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18 minutes ago, melmerby said:

Surely you need to know the mass to know how much energy is contained therein?

 

One can only speak of changes in energy stored:

 

Energy transferred on heating or cooling = specific heat capacity x mass x change in temperature.

 

Also, in the SI, unit names are always spelled lower case: the unit of energy, named in honour of James Prescott Joule, symbol J, is written joule. This avoids the solecism of having a capital letter in the middle of a word when adding one of the SI prefixes, as, for example, kilojoule.

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18 minutes ago, melmerby said:

Surely you need to know the mass to know how much energy is contained therein?

Hi Kieth,

 

Hot water at 100*C atmospheric is 10.04lbs/gallon the same as it is at 250 PSI ( can't be bothered to look up my PVT tables to find temperature ! ).

 

When calculating steam production in locomotives and other steam plant, it is is done on a unit mass rate of water evaporated which directly translates as the unit mass of steam produced. The PVT graphs of the steam produced is how the efficiency is measured when put through the engine of what ever type you may wish to mention.

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1 minute ago, Compound2632 said:

 

One can only speak of changes in energy stored:

 

Energy transferred on heating or cooling = specific heat capacity x mass x change in temperature.

 

Also, in the SI, unit names are always spelled lower case: the unit of energy, named in honour of James Prescott Joule, symbol J, is written joule. This avoids the solecism of having a capital letter in the middle of a word when adding one of the SI prefixes, as, for example, kilojoule.

What is wrong with British Thermal Units ???

 

Base ten metric units are for thickies that can't count !!!

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Most of the rest of the world doesn't use BTU's anymore. And why make life difficult for yourself? Best keep everything coherent, rather than use conversion factors. It only complicates things and adds scope for error.

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14 minutes ago, Gibbo675 said:

What is wrong with British Thermal Units ???

 

Base ten metric units are for thickies that can't count !!!

 

Principally the fact that you've written it in bold italic and capitalised the t and u. International convention on units is that they are written in unemphasised upright script or type. There's no problem in using traditional units in the appropriate context, provided that the can be expressed in tems of SI units when the need to communicate with folk outside one's specialism. I'm perfectly happy using the absurdly mixed unit scale ratio of 4 mm/ft - fit for purpose as the prototype is generally dimensioned in round imperial units (at least, rounded to the nearest 1/16"!) while my steel rule and vernier micrometer are marked in millimetres.

 

Base ten units are for those who want to avoid unnecessary complication in multiplication, rather than merely in counting. There is a valid argument that abandoning LSD de-incentivised primary school children from learning maths.

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22 minutes ago, Gibbo675 said:

What is wrong with British Thermal Units ???

 

Base ten metric units are for thickies that can't count !!!

Base ten metric units are for people with ten fingers and toes.  I've always assumed those who hanker after outdated weights and measures must have their own reasons for preferring other numbers....

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32 minutes ago, Northmoor said:

Base ten metric units are for people with ten fingers and toes.  

 

The Babylonians counted in base 60. I suppose this to be an anti-fraud measure, ensuring that there are always at least three people present at audit.

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41 minutes ago, Compound2632 said:

Base ten units are for those who want to avoid unnecessary complication in multiplication, rather than merely in counting. There is a valid argument that abandoning LSD de-incentivised primary school children from learning maths.

 

It took me a moment to realise that in this context LSD is pounds, shillings and pence.

 

I hope!

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41 minutes ago, rodent279 said:

Most of the rest of the world doesn't use BTU's anymore. And why make life difficult for yourself? Best keep everything coherent, rather than use conversion factors. It only complicates things and adds scope for error.

 

29 minutes ago, Compound2632 said:

 

Principally the fact that you've written it in bold italic and capitalised the t and u. International convention on units is that they are written in unemphasised upright script or type. There's no problem in using traditional units in the appropriate context, provided that the can be expressed in tems of SI units when the need to communicate with folk outside one's specialism. I'm perfectly happy using the absurdly mixed unit scale ratio of 4 mm/ft - fit for purpose as the prototype is generally dimensioned in round imperial units (at least, rounded to the nearest 1/16"!) while my steel rule and vernier micrometer are marked in millimetres.

 

Base ten units are for those who want to avoid unnecessary complication in multiplication, rather than merely in counting. There is a valid argument that abandoning LSD de-incentivised primary school children from learning maths.

 

27 minutes ago, Northmoor said:

Base ten metric units are for people with ten fingers and toes.  I've always assumed those who hanker after outdated weights and measures must have their own reasons for preferring other numbers....

Why do railway modelers take such a pedantic view of life, did none of you spot that what I wrote was a mickey take ?

 

Why is science taken as the "new religion" that may not be questioned by heretics such as myself ?

 

Now here is a question for you all to see if you can answer;

 

How, when a locomotive comes into light steam, 5 psi or less, would you go about changing a leaking fusible plug, bearing in mind that the water level is and will remain above the top of the crown sheet without letting any of the water out of the boiler ?

 

All in good sport,

 

Gibbo.

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10 minutes ago, Gibbo675 said:

Why do railway modelers take such a pedantic view of life, did none of you spot that what I wrote was a mickey take ?

 

How, when a locomotive comes into light steam, 5 psi or less, would you go about changing a leaking fusible plug, bearing in mind that the water level is and will remain above the top of the crown sheet without letting any of the water out of the boiler ?

 

 

I used to be involved with committees that discussed such things - railway modellers are easy-going, let-anything-pass types in comparison.

 

Now, I suppose it might be possible to heat the alloy in the fusible plug to a temperature at which it is sufficiently soft that the water, under the residual boiler pressure, will force it back into a tight fit in the housing but not so soft that the alloy will simply run out?

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4 minutes ago, Compound2632 said:

 

I used to be involved with committees that discussed such things - railway modellers are easy-going, let-anything-pass types in comparison.

 

Now, I suppose it might be possible to heat the alloy in the fusible plug to a temperature at which it is sufficiently soft that the water, under the residual boiler pressure, will force it back into a tight fit in the housing but not so soft that the alloy will simply run out?

The plug is to removed and replaced, think of your PVT graphs, cold water and the injector overflow pipe.

 

I've done it upon two occasions.

 

Gibbo.

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