Re: Propane Question


"Jeff Wisnia" <jwisnia@xxxxxxxxxxxxxx> wrote in message news:131cpoohfaiboe6@xxxxxxxxxxxxxxxxxxxxx
This is a question I once wondered about and now I don't remember ever
if I ever got an answer.

Take two identically sized and shaped propane tanks, one nearly full of
liquid and the other nearly empty, coupled together with a tube between
their tops.

If they are left undisturbed long enough in a constant air temperature
environment of say 70 F, will the liquid levels in the two containers
eventually equalize on their own?

If it doesn't change immediately, why should it change at all?
If the tube reaches the bottom of the tanks then expect a syphon,
but I'll assume that is not the case.


And if they won't, will they if the
air temperature surrounding them periodically cycles up and back down
again a few degrees.

Yes, eventually, but theoretically only at t = infinity.

What's the physics governing this?

Start at the extreme, one entirely filled with gas, the other
with liquid. Now cool both. Nothing happens to the level
in the full cylinder, but SOME vapour condenses to liquid in
the empty cylinder.
Now heat both. SOME liquid in the full cylinder vaporises and
flows into the empty cylinder.
Continue with the cycle and a balance is eventually reached,
but it is not a linear function of time. It has a "half-life" where
if 1/4 the liquid has been transferred in a week of continuous
cycling then 1/8 will transfer the next week, 1/16 the week after,
1/32 the week after that and so on. So it approaches the
same level in both but never quite reaches it until the end of
time. In practical terms, however, the difference soon becomes
too small to measure.
http://www.kettering.edu/~drussell/Demos/SHO/damp.html
Does the damped oscillation ever stop entirely?





Thanks guys,

Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.


.

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