Cooling in refrigeration is accomplished by adiabatic expansion of the
refrigerant gas - a rapid increase in the entropy due to the phase change from
liquid to gas.  From the ideal gas laws, P1V1/T1 = P2V2/T2   Change the pressure
and volume, and the temperature changes as a consequence.  See "Carnot cycle".

> I find this explanation neat, although I am not entirely satisfied
> somehow. Imho the problem resides in the fact that the liquid is a
> compressed gas which will want to expand as soon as there is a
> possibility for it.

That's irrelevant once the pressure differential between the two containers is
equilibrated.  What evaporated into gas can be recompressed back into liquid.

> I dimly remember that refilling a lighter often gave
> frustrating results as it was impossible to refill up to the initial
> level... with the exception of the use of a /pressurised/ filling mechanism.
>
> Thomas

Yes, when refilling with butane the filling container is obviously pressurized.

I believe that there are several interrelated issues here.

First, most people hold the butane refiller to the refilling valve, depress, and
then it's over and done with.  The system has not been given a chance to attain
equilibrium.

Second, there is likely to be a mixture of gases at play -

From http://lighterreviews.com/butane/  :

"Butane, is either of two isomeric flammable gaseous alkanes C4H10 usually
obtained from petroleum or natural gas and used as a fuel. Most butane for cigar
lighters is a mixture of of butane as noted above, isobutene , propane and a
small amount of air (yup the stuff we breath everyday). "

When you use the lighter, the butane flows from the bottom, through a "dip
tube".
http://www.inpharmix.com/jps/_images/exploded%20lighter%20labeled.jpg

Which means that the less volatile components, the ones that tend to remain
liquid as the lighter gets used, are pushed out by the headspace gas - composed
of the comparatively less liquifiable components.  After several
discharge/refill cycles, the lighter becomes filled with a higher proportion of
less liquifiable compounds, and so requires either more pressure to complete the
same fuel transfer, or venting of the more volatile components.

You could hold down the fuel lever to vent these gases before refilling, or more
effectively, hold the partially full lighter upside down while doing so -
causing the expansion of the less volatile components to push the more volatile
ones out the dip tube (which is now at the top).
You could then refill the lighter which has been depleted of those other
components.

To enhance filling, you could heat the butane refiller while filling with warm
water or a towel soaked in hot water.  Alternatively, you could chill the
lighter in the freezer before filling.

And, you could just wait and keep the filler depressed against the lighter for
far longer than most people do so that equilibrium can be more closely achieved.

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