what exactly constitutes a troll?

mike regish wrote:

This thing has me curious. I just found this little tidbit. See what you
think.

It comes from the work done compressing the gas in the cylinder.

The Temperature changes in response to compression due to addition of
more molecules of air to the closed, fixed-volume cylinder. Work is
produced. Temperature rises.

The temperature must change by following Ideal Gas Law:

P V = N k T

Where P = pressure, V = volume, N = number of gas molecules, k = is
Boltzman's constant and T is Kelvin.

The equation must balance. Pick any system of gasses at a specific
pressure, temperature and volume. Change any of those four conditions,
the others must change proportionately.

See also, http://scienceworld.wolfram.com/phys...ealGasLaw.html

mike

"Matt Whiting" wrote in message
...

mike regish wrote:


But temperature *is* a measure of energy.

It is a partial measure of energy. It doesn't measure potential energy.

Matt

Yes, so what is your point with respect to temperature as a measure of
energy?

Matt

Not a thing.

mike

Yes, so what is your point with respect to temperature as a measure of
energy?

Matt

mike regish wrote:
Not a thing.

mike

Yes, so what is your point with respect to temperature as a measure of
energy?

Matt

OK, I was trying to figure out the connection and didn't see one. :-)

Matt

My point was that I don't understand where the confusion is as to where the
heat comes from in filling a scuba tank. You are cramming a whole crapload
of molecules into a confined space and it makes heat. If you cram those
molecules into that space quickly (with respect to how fast you can
dissipate that heat) you get a VERY hot tank. This formula just explains it
better to me, though it doesn't seem to satisfy some as an explanation. It's
the same as a deisel engine except that rather than increasing the number of
molecules of air, the deisel decreases the volume of a fixed number of
molecules. It does it rapidly, so there's no time to dissipate the generated
heat through the cylinder walls, and the air heats up enough to ignite the
fuel when it's added by the injector. If you filled up the scuba tank very
slowly, giving it time to give up its heat to the surroundings (they're
filled in a water tank, no?), then it would not get so hot. I'm guessing
that they are filled from a pressurized tank. That TANK will get cold due to
the decreasing number of molecules in it as the scuba tank fills.

I guess I just don't get where all the confusion comes from. What do scuba
tanks get filled to? Something like 2 or 3 THOUSAND psi, no?

mike

"Matt Whiting" wrote in message
...
mike regish wrote:
Not a thing.

mike

Yes, so what is your point with respect to temperature as a measure of
energy?

Matt

OK, I was trying to figure out the connection and didn't see one. :-)

Matt

My point was that I don't understand where the confusion is as to where the
heat comes from in filling a scuba tank. You are cramming a whole crapload
of molecules into a confined space and it makes heat.

Yes, but you are cramming a whole crapload of =cold= molecules into that
space. The heat generated seems like it wouldn't be enough to
compensate for the cold of the inflowing gas.

That gas is cold because it expanded from the other tank, which was
under even higher pressure.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

"Jose" wrote in message
et...
My point was that I don't understand where the confusion is as to where the
heat comes from in filling a scuba tank. You are cramming a whole crapload of
molecules into a confined space and it makes heat.

Yes, but you are cramming a whole crapload of =cold= molecules into that
space. The heat generated seems like it wouldn't be enough to compensate for
the cold of the inflowing gas.

That gas is cold because it expanded from the other tank, which was under even
higher pressure.

The gas in the tank that is expanding has all of the cold being produced, shared
among all of the gas in the tank, not just the gas that is leaving the tank.

If the cold was contained in, and limited to just the molecules that were
leaving, then the tank being compressed might not get hot. That is not
happening though, and much of the cold is left behind in the now, very cold
tank.
--
Jim in NC

The gas coming in isn't cold. The gas left in the filling tank is cold. The
gas coming into the scuba tank isn't expanding all that much...a little
through the lines, and a little as it comes into the lower pressure scuba
tank, but no that much.

mike

"Jose" wrote in message
et...
My point was that I don't understand where the confusion is as to where
the heat comes from in filling a scuba tank. You are cramming a whole
crapload of molecules into a confined space and it makes heat.

Yes, but you are cramming a whole crapload of =cold= molecules into that
space. The heat generated seems like it wouldn't be enough to compensate
for the cold of the inflowing gas.

That gas is cold because it expanded from the other tank, which was under
even higher pressure.

Jose
--
"Never trust anything that can think for itself, if you can't see where it
keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

"mike regish" wrote in message
...
(they're filled in a water tank, no?),

That practice tends to be discouraged these days... It has been determined
that a slow fill is better... There are some that say that especially with
aluminum tanks, the water tank method is especially bad since the
temperature of the surface of the metal might be radically different than
the temperature of the inner metal thus increasing the chance of fractures
in the metal...

That makes sense. It's been a while since I got mine filled, but they did it
in a water tank.

In researching this, I found scuba divers complaining about "hot fills"
where the tank is filled too rapidly and when it cools down they are left
with a less-than-full tank.

mike

"Grumman-581"
"mike regish" wrote in message

(they're filled in a water tank, no?),

That practice tends to be discouraged these days... It has been determined
that a slow fill is better... There are some that say that especially with
aluminum tanks, the water tank method is especially bad since the
temperature of the surface of the metal might be radically different than
the temperature of the inner metal thus increasing the chance of fractures
in the metal...

"mike regish" wrote in message
. ..
In researching this, I found scuba divers complaining about "hot fills"
where the tank is filled too rapidly and when it cools down they are left
with a less-than-full tank.

I suspect that the water bath approach just results in the skin temperature
of the tank being cooler whereas the gas hasn't really decreased that much
in temperature... Thus, they're still getting "hot fills", they just don't
notice it... The easiest solution to hot fills is to just fill it higher
than normal and when it cools, it's at the target pressure... Or you could
just do it right and slowly fill the tank...