O.T. electric cars - do they have gearboxes?

[The Natural Philosopher]

Typical modern steam power station 37%. More with supercritical steam Typical diesel. 25%.

No use telling harry anything. The thermodynamics are all well understood, but not by harry

Exatamondo. I cant remember what the law is called, but the hotter the working fluid (steam in this case) is to start with, and the colder the final exhaust, the more efficient is the engine.

Which is why a combined cycle gas turbine that starts with 1000C gases in the jet engine, then heats a boler to get steam, and has a final after condenser temp of around 50C, willnet you over 60% thermal efficiency.

Whether you call that an IC or a steam engine is up to you.

[Tim Streater]

One of the laws of thermodynamics IIRC - efficiency is related to the difference between input and output temps - in degrees K, not C. We derived it in one of the courses I did at Uni, but, sadly, I've not kept the notes I took at the time.

Looks like it's:

E = (Tin - Tout) / Tin

[Chris Hogg]

Carnot cycle or Carnot's law.

Not to be confused with Fred Karno, who had an 'army' IIRC!

[The Natural Philosopher]

Anything *seems* to be possible if you know nothing.

I have often said - and it bears repeating - that my education in hard science and engineering doesn't tell me ultimately how to build stuff that works, but it is incredibly effective at telling me what cannot work, so I don't waste time trying.

This 'negative knowledge' is hugely useful.

Greens call it 'being negative' :-)

[The Natural Philosopher]

That's the bugger!

[Dave Plowman (News)]

A steam locomotive generally operates under carefully controlled conditions. Like all railways.

Cars don't.

[charles]

my elementary physics suggests that if you are only refering to a temperature difference the answer is the same in °K and in °C.°

[Nightjar]

That looks like it. I only recall the publicity of its launch and didn't follow up on what happened to it. However, MIT and Stanford University have both demonstrated low energy water splitters that can run from low voltage sources.

[Tim Streater]

Nice try. But the difference is then divided by the Tin temp, also measured in K. As I then went on to say.

[Chris Hogg]

Splitting water only requires 1.23v in theory. If it's low energy, as opposed to low voltage, you only get low amounts of H2 and O2. And with the usual systematic energy losses, you'll get even lower amounts of energy back when you recombine them. The idea that you can split water, recombine the products, and get more energy out than you put in, is pure fantasy, like the thinking on any other perpetual motion machine.

[Tim+]

"Didn't follow up" is a lame excuse for believing in fairies! Do you believe in other perpetual motion machines?

Tim

[dennis]

You can split water with an AAA battery, the voltage doesn't matter much its how much energy it takes.

Rule one: you cannot get more energy out than you put in.

This means that all these split water put it through a fuel cell and re-split it while taping off energy are scams, every one. There are no exceptions no matter how many youtube likes they get.

I know its hard to understand but its the truth, in this reality anyway.

[The Natural Philosopher]

well I am sorry, but unless the laws of physics have changed the energy required to split a molecule of water into hydrogen and oxygen is the same whatever method you use, and about three times what you are likely to get back recombining them to make mechanical or electrical power.

[The Natural Philosopher]

Well its not actually the temperature difference, its the *ratio* of the temperatures.

The total input energy in heat is proportional to the absolute temperature.

The lost output energy as heat is proportional to the output temperature in absolute degrees.

Theres a bit of a fudge in that you start with ambient to do your heating of course.

[Chris Hogg]

A simple paraphrasing of the laws of thermodynamics that I remember:

1st law: You can't ever win, you can only ever break even. 2nd law: You can only break even at absolute zero. 3rd law: You can't reach absolute zero.

It always sup rises me that seemingly intelligent people who claim to have invented the perpetual motion machines that they proudly display on Youtube, aren't multi-millionaires, having solved the world's energy and AGW problems at a stroke with their carbon-free, non-nuclear methods of electricity generation, such as cars that run on water or spinning magnet arrangements to make electricity.

The fact that they aren't multi-millionaires says it all.

[Dave Plowman (News)]

Rather like someone trying to sell you a money making scheme. If it were good, they'd keep it to themselves, and make all the money they want.

[Johnny B Good]

The main benefit of using deg K instead of Deg C is the complete and utter absence of negative numbers by which to confuse the mathematics. :-)

It's true enough that as far as steam engines are concerned, this is unlikely to effect calculations involving deg C, but there are other heat engines designs based on fluids with much lower freezing and boiling points than zero deg C (the triple point of water to within an accuracy of one decimal place).

[Tim Streater]

The formula for efficiency *requires* K.

[harry]

Total drivel. Steam locomotive efficiency, typically 5%.

The most efficient power stations use rejected heat for district heating. But that only applies in Winter. In Summer the heat is dumped. And it only works if the heat is needed nearby. Higher steam temperatures results in less efficient boilers because the exiting combustion gases can be at no lower temperature than the stem.

If you look at the picture, there are cooling towers. What do you suppose they are for? (Clue,dumping excess heat)

The problem of what to do with rejected low grade heat has proved insurmountable.

Flash steam boilers are suited for rapid start up, cheapness and low weight. But are notoriously inefficient, high maintenance and short life. Yes,I have run these too.

[harry]

You don't get anything for nothing. In theory it take the same amount of energy to split hydrogen and oxygen as you get burning the hydrogen. In practice, splitting the hydrogen is very inefficient. So the whole concept is/was doomed.