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 Originally Posted by OngBonga
But when I'm filling my lighter up, the liquid gas that escpaes into the air and evaporates causes a significant cooling to the point it freezes the bottom of the lighter and cools the fingers where it holds the lighter to the point it almost hurts. I can see condensation having the opposite effect to this.
Sounds like you're talking about a butane lighter (as opposed to a Zippo-type, which generally burns Naptha). The butane is a gas at STP, so it must be contained in a pressure vessel.
The butane is held above atmospheric pressure, so that it can be stored as a liquid. The liquid is much more dense than the gas, so this method allows much more efficient use of volume.
When you release that pressure, the temperature of the fluid drops according to the ideal gas law.
PV = nRT
If I simplify this to mere expansion, and ignore the fact that the number of particles in the pressure vessel is changing, then I get the result by re-writing the equation as this
P/T = nR/V
then I acknowledge that nR/V is the same in the before and after pictures, so I can equate (P/T)_before = nR/V = (P/T)_after.
P_1/P_2 = T_1/T_2
where P_1 is the starting pressure, P_2 is the ending pressure, T_1 is the starting temperature, and T_2 is the ending temperature.
Which means that if the pressure goes down by X%, then the temperature goes down by X%, and vise-versa.
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It gets a bit ugly and confusing for the purposes of this post to acknowledge that the number of particles in the pressure vessel goes down, too. It's hard to make generalizations with the added two variables.
I could be persuaded to do a full write-up of a hypothetical case of butane released from a pressure vessel. Then we could compare actual values of the temperature change due to the pressure change, then compare that temp change to the temp change caused by subsequent evaporation.
I.e.
If I have a full butane container with X grams of butane, and I spray 0.5 grams of butane on a surface...
What is the temperature of the butane as it is deposited on the surface?
(Note that this will vary over time as the pressure changes during the spraying.)
What is the temperature of the last butane molecule to evaporate?
These two question should indicate the initial temp and final temp of both the sprayed butane and the deposited butane.
(These questions will require some calculus to solve.)
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