Nitrogen shock

I got a tin of genuine A&W rootbeer for Christmas. Been saving it
until I've got the time to create an A&W-type burger to go with it.

 

The would be your combined gas law innit. Or Boyle's. Or somesuch.

 

Adiabatic expansion. Boyle leaves me cold though.

 

Heat extraction from the surroundings (including finger).

 

According to Boyle, the gas will increase in volume in inverse proportion to
the pressure ie, 1litre of gas@ 10bar will expand to 10litres@ 1bar.
AFAICS temperature remains the same. Or am I missing something?

 

A tube!! Heretic! All, Hail The Tin.

 

<googles>

Aha, I thought I might be missing something.
Like the compression stroke on a diesel only in reverse?

 

Have you never a) discharged a CO2 fire extinguisher, b) re-filled a
gas lighter, c) used a can of spraypaint? If so, you may have noticed
how cold things get around the nozzle. This happens whenever a
compressed gas expands, and is the subject of one or more gas laws I
learnt in school.

The opposite situation occurs when you compress a gas, and can easily
be demonstrated by pumping up a bicycle tyre using an old-fashioned
pump with a rubber tube, which will get very hot as you force the air
through it (decreasing its volume).

 

But there's no phase change when compressed nitrogen expands so you
don't have the latent heat of evaporation that you get in a and b above.
And I don't think that a paint aerosol nozzle gets cold at all.
Have you got any other examples?

 

According to Boyle, in a closed system then volume is inversely
proportional to pressure _if_temperature_remains_constant_.

In a non-closed system, with no constraints on any one variable, all
three will change. In this case, pressure goes down, volume and
temperature both go up.

 

Wotcha.

Not so much the nitrogen, but pre-historic pingfuckits which would leap out
and remove limbs ;-)

http://sackheads.org/~caseyc/triumph/reference/Mark 2.jpg

 

Don't you mean pressure and temperature go down and volume goes up?

 

All those examples involve evaporation/sublimation and thus latent heat of
evaporation, which I knew. I was wondering about a simple change in gas
volume.

I had always assmed that the venturi effect of forcing the air through the
tube increased its velocity such that friction produced heat. The air in the
tyre does not, after all, get significantly warmer.
I reckon the compression stroke of a diesel is a better example, a 20:1 CR
will raise the temp by at least 500deg C.

 

The can itself does get colder but I hink that is due to the LPG propellant
evaporating.

 

I think he means pressure and temperature goes down, volume goes up...

 

You can try it for yourself. With your mouth open wide breathe
forcefully onto your hand. You'll feel a warm breeze on it. Now blow
hard on your hand, but regulate the flow, to similar to what it was
before, by pursing your lips. You'll find the air feels considerably
cooler on your hand, even though the amount and velocity is the same
as previously. The air is cooler because it is expanding as it leaves
your mouth.

 

That is total bollocks.
I suggest you pierce your cheeks and insert a thermometer and manometer
before repeating the experiment.

 

Not as obvious as letting the nitrogen out of a damper, given the thread
subject. ;-)

 

So what's your explanation?

 

Some refrigerators work on a gas cycle, where no phase change is
involved - simply a heat exchanger.