Instructions: Regarding an earlier email concerning frosty propane tanks, most all of the elements and many compounds (including propane gas) can be made to exhibit changes in phase (solid/liquid/vapor) by varying temperature and pressure. Ice melts into water as temperature rises above freezing (32 F.), and then the water turns to steam as the
temperature rises above boiling (212 F.) (both examples at standard atmospheric pressure.). An automobile cooling system operates under pressure to prevent the coolant from boiling at temperatures higher than 212 F (increases efficiency); whereas ice skates work because the extreme pressure under the edge of the blade turns a thin layer of ice into water, only to refreeze once the skater passes and the pressure is removed.

In the case of LP gas stored in the tank of, lets say, your barbecue grill, the undisturbed gas is at the same temperature as its surroundings, but under a fair amount of pressure. If one reduces the pressure rapidly enough to cause the gas in the tank to boil, say by opening the valve wide into the air, the temperature of the tank would indeed drop, even forming frost on the valve. This is the principle by which evaporative refrigeration works.

However, the conditions arent nearly met in the normal use of a gas grill.

The volume of gas being used is minuscule... There are companies manufacturing self-adhesive liquid-crystal tank level gauge strips which one merely sticks to the side of the tank, and then pours hot

(boiling?) water over the tank and gauge. The liquid level is revealed because the empty part of the tank doesnt lose heat as fast as the part in contact with the LP, which sinks off (absorbs) the heat rapidly. The gauge reveals this difference in temperatures.

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