On Mon, 12 Feb 1996, REICHLE, CHRISTOPHER wrote:
>
> *****
> Air expands not fuel. A change in temperature from cool night to warm day in
> a tank with little gas in it could build up a bit of pressure from the
> expanding air if not properly vented.
>
> Chris Reichle
>
Correct on both counts - and there's a third factor - vapor pressure. As
the temperature increases, more gasoline evaporates, adding to the number
of molecules banging around in that space, creating pressure. PV=NRT
V stays essentially constant, so as N and T increase, P must increase!
To demonstrate this idea of vapor pressure (no LBC content, but
this is really _fun_!) put a small amount of water in an empty aluminum
beverage can, and boil the water for a while on your kitchen range. The
water vapor will essentially drive all the air out of the can, leaving
only water vapor in there. Now (Here's the fun part) pick up the can with
some sort of tongs or a hot pot holder and quickly invert it into a pan
of cold water, so that the open top is submerged. The water vapor will
quickly condense back to a liquid, leaving a pretty good vacuum inside
the can - but not for long! The outside air pressure almost instantly
crushes the can. Try it, you'll like it! Use about half an inch of water
in the can to start with, and be careful not to spill boiling water on
anyone when you invert the can!
Len Bugel '50 TD
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