What does it take to be a Transport Correspondent?
 

On 23/04/2011 10:38, d wrote:
On Fri, 22 Apr 2011 09:55:48 -0700 (PDT)
wrote:
On Apr 22, 5:50=A0pm, wrote:


I fear that entropy enjoyed an early triumph in his cognitive processes.

Water turning to ice can crack stone or raise objects increasing their
potential energy. It requires heat to be removed for this to happen, not =
added.
So where does that leave your simplistic 19th century argument now?


You really REALLY R-E-A-L-L-Y do need to study thermodynamics.

When you do, you will realise where entropy comes into all that and
what we are talking about.

So fill me in then. If heat is required to do work why does removing
heat from water to form ice also do work.

Heat will spontaneously flow from a high temperature to a low
temperature, but not in the other direction (this is the "Zeroth law of
thermodynamics").

If you want to create ice when the ambient temperature is above 0 deg C,
then work is needed to pump the heat "uphill" from the water you are
freezing to the surroundings. That's what the motor does in a
refrigerator. The work used to pump the heat need not come from a heat
source itself, it could come from hydro power, for instance.

But the work done by water expanding as it freezes will be considerably
less than the work needed to freeze the water in the first place.

In pumping heat in this way, the entropy (degree of disorder) of the
universe is increased.

Thermodynamics is a very important subject for understanding how the
technological world works. If you don't understand thermodynamics, then
a relatively simple book which explains it (without all the differential
equations that are usually found in thermodynamics textbooks) is "The
refrigerator and the universe: understanding the laws of energy" by
Martin Goldstein and Inge F Goldstein, published by the Harvard
University Press in 1993.

--
Jeremy Double {real address, include nospam}
Rail and transport photos at
http://www.flickr.com/photos/jmdoubl...7603834894248/

What does it take to be a Transport Correspondent?
 

On Sat, 23 Apr 2011 11:12:36 +0100
Jeremy Double wrote:
Heat will spontaneously flow from a high temperature to a low
temperature, but not in the other direction (this is the "Zeroth law of
thermodynamics").

If you want to create ice when the ambient temperature is above 0 deg C,
then work is needed to pump the heat "uphill" from the water you are
freezing to the surroundings. That's what the motor does in a
refrigerator. The work used to pump the heat need not come from a heat
source itself, it could come from hydro power, for instance.

But the work done by water expanding as it freezes will be considerably
less than the work needed to freeze the water in the first place.

I'm not talking about in a fridge - I'm talking about water sitting outside
on a cold night with the heat disappearing off into space. No energy is
being used to remove the heat yet the water freezes and the ice can do work
on anything nearby as it expands.

If what is being claimed is true - ie that heat is always required to do
work then this should be impossible. Clearly it isn't so that rule is wrong
in this instance just as it doesn't apply inside a car cylinder which was
my initial statement.

B2003

What does it take to be a Transport Correspondent?
 

On Fri, 22 Apr 2011, bob wrote:

On Apr 21, 7:18*pm, Tom Anderson wrote:
On Thu, 21 Apr 2011, Capt. Deltic wrote:
On 21 Apr, 09:58, wrote:
On Thu, 21 Apr 2011 09:33:41 +0100

Graeme Wall wrote:
Pedantically they have motors, not engines. �The latter being those
nasty infernal combustion thingies. �Motors run on nice clean electrickery.

Tell that to Arthur Daley!

To be even more pedantic, an engine generates power, while a motor
consumes power.

What? *What*?

'Generates' power? 'Consumes' power? Has that small matter called the
first law of thermodynamics passed you by?

I assume Uncle Roger means "shaft power" as used in the context of the
second law applied to a control volume (ie work rather than heat).

I'm afraid i'm not familiar with the term "shaft power"; a quick google
suggests it means the mechanical power at the drive shaft, but i don't see
how that's relevant here. Is that what you meant? In what way does an
electric motor consume it?

Calling one an engine and one a motor is a matter of convention. It's
preposterous to ascribe a fundamental meaning to the distinction.

The distinction is related to the second law. A motor converts "work"
to other "work" while an engine converts heat to work (and some left
over heat).

There's no difference between what a combustion and an electric engine do
he matter flows from a place where it has a high potential to where it
has a low potential, increasing entropy as a result, and that flow is
harnessed to turn a shaft. In a combusion engine, the matter is steam or
combustion gases, and the potential is of the heat-and-pressure kind. In
an electric engine, the matter is electrons, and the potential is of the
electrical kind.

To get another angle on it, do you think a watermill is a motor or an
engine? What about a piston engine driven by pressurised water?

IMHO, the whole heat/work dichotomy has been really unhelpful since it did
its part in getting thermodynamics started. There are states with
different potentials, and various amounts of stuff in those states. Stuff
wants to flow from high-potential states to low-potential states, and you
can harness such flows. There's no value in drawing a distinction between
potentials where the states are is in the same place in space (eg chemical
potential, electron potential in an atom) and those where they aren't
(primarily heat gradients).

tom

--
If I want consciousness expansion, i go to my local tabernacle and i SING!

What does it take to be a Transport Correspondent?
 

On 22/04/2011 11:57, Capt. Deltic wrote:
On 21 Apr, 17:36, Graeme wrote:
On 21/04/2011 15:58, Capt. Deltic wrote:

While we're OT let's have a test of other interests. The diesel
engines include two Oliver Tigers. Does that mean anything to anyone
in this NG? No remarks about sad gits going in circles, please.

Dredging my memory, isn't that a very old model aircraft engine?

From another sad git.

--
Graeme Wall
This account not read, substitute trains for rail.
Railway Miscellany atwww.greywall.demon.co.uk/rail

Thanks for confirming my general exoperience that however recherche
the topic, someone on UKR will iknow about it.

Indeed, diesel engines hand made by Mr John Oliver. Which somehow
combined easy starting, good 'throttleability' with lots of power.

Never had one myself but friends used to swear by them

not to be confused with the Italian Super Tigre (got one of those
too?.

Death to glow-plugs.


Aforesaid friends used to swear at them! Me I never really moved on
from rubber bands, preferred gliders myself.


--
Graeme Wall
This account not read, substitute trains for rail.
Railway Miscellany at www.greywall.demon.co.uk/rail

What does it take to be a Transport Correspondent?
 

On Sat, 23 Apr 2011 10:20:22 +0000 (UTC), d put
finger to keyboard and typed:

On Sat, 23 Apr 2011 11:12:36 +0100
Jeremy Double wrote:
Heat will spontaneously flow from a high temperature to a low
temperature, but not in the other direction (this is the "Zeroth law of
thermodynamics").

If you want to create ice when the ambient temperature is above 0 deg C,
then work is needed to pump the heat "uphill" from the water you are
freezing to the surroundings. That's what the motor does in a
refrigerator. The work used to pump the heat need not come from a heat
source itself, it could come from hydro power, for instance.

But the work done by water expanding as it freezes will be considerably
less than the work needed to freeze the water in the first place.

I'm not talking about in a fridge - I'm talking about water sitting outside
on a cold night with the heat disappearing off into space. No energy is
being used to remove the heat yet the water freezes and the ice can do work
on anything nearby as it expands.

The energy being used is the heat from the sun which liquifies the water to
begin with. That energy is stored in the water in liquid form, and used up
when the water reverts to ice.

If it were not for the heat applied in the first instance, water would
never be liquid at all. The natural (ie, non-energetic) form of water is
ice. The only reason we assume that the normal form is a liquid is because
we live in an environment where heat is being continuously applied to it in
order to keep it that way.

Mark
--
Blog: http://mark.goodge.co.uk
Stuff: http://www.good-stuff.co.uk

What does it take to be a Transport Correspondent?
 

On 23/04/2011 11:20, d wrote:
On Sat, 23 Apr 2011 11:12:36 +0100
Jeremy wrote:
Heat will spontaneously flow from a high temperature to a low
temperature, but not in the other direction (this is the "Zeroth law of
thermodynamics").

If you want to create ice when the ambient temperature is above 0 deg C,
then work is needed to pump the heat "uphill" from the water you are
freezing to the surroundings. That's what the motor does in a
refrigerator. The work used to pump the heat need not come from a heat
source itself, it could come from hydro power, for instance.

But the work done by water expanding as it freezes will be considerably
less than the work needed to freeze the water in the first place.

I'm not talking about in a fridge - I'm talking about water sitting outside
on a cold night with the heat disappearing off into space. No energy is
being used to remove the heat yet the water freezes and the ice can do work
on anything nearby as it expands.

If what is being claimed is true - ie that heat is always required to do
work then this should be impossible.

Heat isn't always required to do work _directly_: hydro-power uses the
potential energy of water flowing downhill to perform work, for
instance. But in that case the energy that moved the water from the
seas to the hills to allow it to perform work came from the heat of the sun.

If work is performed using heat as the energy source, then the laws of
thermodynamics apply, and there is a limit to the amount of work that
can be got out of a certain quantity of heat, which can be calculated
from the ratio of the absolute temperature of the heat source to the
absolute temperature of the heat sink.

Clearly it isn't so that rule is wrong
in this instance just as it doesn't apply inside a car cylinder which was
my initial statement.

You originally wrote:

Internal combustion engines don't convert heat to work. The work is done
by the pressure of the gas from the chemical reaction. Heat is a useless
byproduct of this reaction that has to be got rid of.

Internal combustion engines _are_ a type of heat engine, they do convert
heat to work. The laws of thermodynamics apply to them just as they do
to a steam engine or steam turbine. The only difference is that the
heat is created inside the cylinder, not outside.

The fuel burns in the air charge, converting chemical energy to (mostly)
heat and a small amount of work. The heat causes the gases to expand,
allowing them to do work and move the piston. Almost all of the
expansion of the combustion gases is due to the heat liberated by
combustion, not due to the increased number of moles of gas (for
instance, 1 mole of carbon burning uses 1 mole of oxygen to give 1 mole
of carbon dioxide). Remember that most of the gas in the cylinder of an
engine is nitrogen from the charge air (air is about 79% nitrogen).

You are right that there is some useless heat created in combustion,
which has to be got rid of. That is a consequence of the second law of
thermodynamics, which says that there is a limit to the amount of heat
that can be converted to work. The useful work depends on the ratio of
the temperatures of the heat source (i.e. the combustion temperature of
the fuel) to the heat sink (i.e. the temperature of the exhaust gas).

If you need to understand this better, I suggest you read the book I quoted.
--
Jeremy Double {real address, include nospam}
Rail and transport photos at
http://www.flickr.com/photos/jmdoubl...7603834894248/

What does it take to be a Transport Correspondent?
 

On 23/04/2011 11:12, Jeremy Double wrote:

Thermodynamics is a very important subject for understanding how the
technological world works. If you don't understand thermodynamics, then
a relatively simple book which explains it (without all the differential
equations that are usually found in thermodynamics textbooks) is "The
refrigerator and the universe: understanding the laws of energy" by
Martin Goldstein and Inge F Goldstein, published by the Harvard
University Press in 1993.


Or there is Flanders & Swann, definitely no calculus.


--
Graeme Wall
This account not read, substitute trains for rail.
Railway Miscellany at www.greywall.demon.co.uk/rail

What does it take to be a Transport Correspondent?
 

On Apr 23, 11:25*am, Tom Anderson wrote:
On Fri, 22 Apr 2011, bob wrote:
On Apr 21, 7:18�pm, Tom Anderson wrote:
On Thu, 21 Apr 2011, Capt. Deltic wrote:
On 21 Apr, 09:58, wrote:
On Thu, 21 Apr 2011 09:33:41 +0100

Graeme Wall wrote:
Pedantically they have motors, not engines. �The latter being those
nasty infernal combustion thingies. �Motors run on nice clean electrickery.

Tell that to Arthur Daley!

To be even more pedantic, an engine generates power, while a motor
consumes power.

What? *What*?

'Generates' power? 'Consumes' power? Has that small matter called the
first law of thermodynamics passed you by?

I assume Uncle Roger means "shaft power" as used in the context of the
second law applied to a control volume (ie work rather than heat).

I'm afraid i'm not familiar with the term "shaft power"; a quick google
suggests it means the mechanical power at the drive shaft, but i don't see
how that's relevant here. Is that what you meant? In what way does an
electric motor consume it?

That is the derivation of the term, but thermodynamically things like
electricity and magnetic forces Behave in the same way. It is a
general term for energy entering a system that does not have an
associated entropy change with it.

Calling one an engine and one a motor is a matter of convention. It's
preposterous to ascribe a fundamental meaning to the distinction.

The distinction is related to the second law. *A motor converts "work"
to other "work" while an engine converts heat to work (and some left
over heat).

There's no difference between what a combustion and an electric engine do
he matter flows from a place where it has a high potential to where it
has a low potential, increasing entropy as a result, and that flow is
harnessed to turn a shaft. In a combusion engine, the matter is steam or
combustion gases, and the potential is of the heat-and-pressure kind. In
an electric engine, the matter is electrons, and the potential is of the
electrical kind.

The difference is entropy. In a control volume type analysis, shaft
work (electrical power) adds no entropy to the system, heat transfer
does. If you have a motor, you put some work in and get some work out
(in the case of hydraulics the difference in work is the pressure x
volume pumping work to get it in or out). In a heat engine (including
all combustion engines) the second law places constraints on the
engine behaviour requirig a heat rejection as well as heat input and
work input in order to do work. It all comes down to entropy.

To get another angle on it, do you think a watermill is a motor or an
engine? What about a piston engine driven by pressurised water?

Water mill: work done by a falling weight is converted to work in a
shaft. No heat.
Hydraulic motor: work done pumping water in is converted to work in
the shaft. No heat.

IMHO, the whole heat/work dichotomy has been really unhelpful since it did
its part in getting thermodynamics started. There are states with
different potentials, and various amounts of stuff in those states. Stuff
wants to flow from high-potential states to low-potential states, and you
can harness such flows. There's no value in drawing a distinction between
potentials where the states are is in the same place in space (eg chemical
potential, electron potential in an atom) and those where they aren't
(primarily heat gradients).

But to ignore the difference between these is to ignore entropy and to
therefore ignore the second law of thermodynamics. The entire basis
of the second law is the difference between heat and work, the
relation between heat and temperature, and the limitations on things
like the maximum efficiency of heat engines (motors can be100%
efficient, heat engines can not).

Robin

What does it take to be a Transport Correspondent?
 

"bob" wrote in message
...
[...]

It's not just the "Standard". Christian Wolmar, writing in Friday's "Times"
states that an HST "has a locomotive at one end". Last time I checked, it
was one at each end.

A pity, since his basic premise that it is nuts to transport dead diesel
engines round under the wires (in bi-mode IEP) was sound.

Regards

Jonathan

What does it take to be a Transport Correspondent?
 

On Sat, 23 Apr 2011 13:11:36 +0100, Jonathan Morton wrote:

"bob" wrote in message
news:7087ab16-d6c1-45c5-b5b6-
...
[...]

It's not just the "Standard". Christian Wolmar, writing in Friday's
"Times" states that an HST "has a locomotive at one end". Last time I
checked, it was one at each end.

Maybe he was thinking back to the period when the HSTs were being re-
numbered, and some sets would have had something in the 43xxx range at
one end and something in the 254xxx at the other - a locomotive at one
end and a DEMU driving motor brake at the other?

;-)

--
From the Model M of Andy Breen, speaking only for himself