Newly restored "Flying Scotsman" back in service - ongoing discussion

[whole diary]

[bradshaw]

The water cools the copper because it has a high specific heat. That is it takes a lot of heat to boil the water.
In my distant teaching past I used to boil water using a paper tray and Bunsen burner! The students would not believe it could be done but it usually worked.
It is the same when water is used to douse a fire; it takes the heat away

[stuving]

The water cools the copper because it has a high specific heat. That is it takes a lot of heat to boil the water.

To be even more - well, specific -
The specific heat capacity of liquid water is 4.2 kJ/kg.K at all temperatures. That's big, compared to most liquids; the next highest common one is ethanol at 2.5. But if that's big, just wait -
The specific latent heat of evaporation (or vaporisation) of water to steam at 1 atmosphere is 2260 kJ/kg. That's huge.

Put another way, to boil water into steam needs as much energy as heating it through 540 K.

I suspect it's one of those "not at all well-known facts", but it should be as it helps to explain the weather. Condensing water vapour falls as rain (or ice) and leaves behind a lot of energy to heat the air and make it rise. Since the specific heat of air is lower, the equivalent temperature rise is bigger (about 2300 K). So even a water vapour content of 1% or less in the air heats it up by several degrees as part of it condenses.

These strong updraughts are the motive power of storms of all kinds, whether inside them or over larger area by generating pressure differences. Finally, the maximum (saturation) water vapour content of water goes up by 6.7% for a 1 K higher temperature. Hence the potential of rising temperatures to increase both rainfall and storm intensity, directly and quite apart from any changes in claimate or weather patterns.

Note: SI units are used above, so 1 K is the unit of temperature difference and 1 degree C = 1 K. 

[Gordon the Blue Engine]

Interesting.

Copper has a high heat conductivity of course, and the outside of the firebox will always be water at no more than its boiling point of about 250 deg C at 220 psi.  So I can see that that the copper surround of the firebox will remain well below its melting point.  I presume calculations exist to show the temperature gradient across it when the fire is at maximum output. 

I read somewhere that the copper used for FS^s firebox was a special type of copper, presumably an alloy of some sort.  Whether this is to increase hardness, or strength or melting point I do not know - but I bet someone else does.

[Red Squirrel]

But if that's big, just wait...

Shameless digression, but I heard somewhere that when a Tesla P85D does its 'insane mode' party trick of accelerating from 0-60 in 3.2s, it does so essentially by converting the mass of one electron into energy. One electron weighs 9.1 x 10^-31 kg.

[stuving]

But if that's big, just wait...

Shameless digression, but I heard somewhere that when a Tesla P85D does its 'insane mode' party trick of accelerating from 0-60 in 3.2s, it does so essentially by converting the mass of one electron into energy. One electron weighs 9.1 x 10^-31 kg.

I think that would be more of an "interesting coincidence of numbers" - if true. But it isn't, you'd need a lot of electrons. Like 10¹⁹ of them - so not even an exotic heavy particle is going to do it.

The power it needs is 250 kW - which is impressive itself, and about what you'd find in a single (not very fast) EMU^▸ (Electric Multiple Unit) carriage (to disdigress a little).

[TonyK]

I've now found the Daily Mail link.....

http://www.dailymail.co.uk/news/article-3477601/Ultimate-guide-Flying-Scotsman-4-2million-renovation-classic-locomotive-finally-tracks.html

That is truly a splendid cutaway drawing, reminiscent of those in one of the comics of the 1960s - was it Eagle?

[JayMac]

That is truly a splendid cutaway drawing, reminiscent of those in one of the comics of the 1960s - was it Eagle?

May I suggest this on the shopping list then (available to purchase from 31st March 2016):

https://haynes.co.uk/catalog/general-interest-manuals/rail/flying-scotsman-manual

[eightf48544]

As has been said the trick is to keep the crown of the firebox covered in water which makes the injectors the second most important fittings on a steam loco after the brake. But there is an additional safety  fitting called  a fusible plug in top of the firebox which is made of lead so melts well below 1000 and will allow the steam and water in the boiler to escape into the firebox. It was virtually a sackable offence to have a plug go, unless both injectors had failed and it wasn't possible to drop the fire quickly enough.

[Red Squirrel]

As has been said the trick is to keep the crown of the firebox covered in water which makes the injectors the second most important fittings on a steam loco after the brake. But there is an additional safety  fitting called  a fusible plug in top of the firebox which is made of lead so melts well below 1000 and will allow the steam and water in the boiler to escape into the firebox. It was virtually a sackable offence to have a plug go, unless both injectors had failed and it wasn't possible to drop the fire quickly enough.

I did an engine driving taster course on the West Somerset a few years ago. There were a couple of blokes in my group who had retired from Hinkley; they found it very hard to get their heads round the concept of a boiler where the water level changed for so many reasons - not just the fact that the water's being boiled away but things like line gradient, pressure changes caused by opening and shutting the regulator, and the chilling effect of injecting fresh (cold) water. Busy person, the firer.

From what they told me, I think it is fair to say that dropping a fusible plug at Hinkley was taken quite seriously too.

[TonyK]

From what they told me, I think it is fair to say that dropping a fusible plug at Hinkley was taken quite seriously too.

The stuff of nightmares with an advanced gas-cooled reactor design, much less so with a Thorium molten salt plant. At least in theory.

[Red Squirrel]

But it isn't...

So:

The battery loses mass according to E = mc²

A Tesla P85D has a mass of 2239kg so we need about 806kJ to accelerate it to 60mph. The mass equivalent of this if 806000 / 299792458² = 8.9x10^-12kg

If one electron has a mass of 9.1 x 10^-31 kg, so we lose the equivelent of 9.7 x 10¹⁸ of them.

Gosh, that's remarkably close to your calculation. I will concede!

[chuffed]

Looks as if we might have to start raising 'Ein Stein' to the budding mathematicians and physicists on this forum !

[stuving]

Gosh, that's remarkably close to your calculation.

If taking reliable values for physical quantifies, and doing the same calculation, doesn't give the same answer then clearly this isn't proper science. It could be engineering (including coarse back-of-an-envelope science) if the answers are "close enough for our current purposes" - the textbook definition of "approximate."

Of course it could easily be politics or journalism. And these days, more worryingly, economics or psychology (and some other medical fields) are getting the same reputation.

[GBM]

Looks as if we might have to start raising 'Ein Stein' to the budding mathematicians and physicists on this forum !

Is Rick his brother?

[TonyK]

So:

The battery loses mass according to E = mc²

A Tesla P85D has a mass of 2239kg so we need about 806kJ to accelerate it to 60mph. The mass equivalent of this if 806000 / 299792458² = 8.9x10^-12kg

If one electron has a mass of 9.1 x 10^-31 kg, so we lose the equivelent of 9.7 x 10¹⁸ of them.

Gosh, that's remarkably close to your calculation. I will concede!

You spelled "equivalent" wrong, Proffesser.