On 2007-10-08 18:17:58 -0400, Mark Borgerson said:

Getting rid of the disssolved gases in the headspace and as bubbles
forming on the sides of the tube is going to be a major headache.

Not a headache, an impossibility (they're not really dissolved at that
point though) :-) That, and the increase in pressure due to water vapor
will make this an oscillating, self-quenching system. It'll require
more and more heat as the partial pressures of the non-condensables
increases, and the column heights will drop as the pressure goes up,
with the diffusion path increasing the whole time.

I agree with that part---except for the oscillation part. I think the
processes are slow enough and the thermal and physical masses are high
enough that the oscillations will be damped out and you will see a slow
change to equilibrium with little or no overshoot.

Though I consider this whole discussion impractical, I haven't seen
anyone mention that the fresh-water side will be drawn down fairly
regularly. And, of course, the sea water side will be replenished from
time to time.

Suck hard enough on the fresh-water side and you get even better
"vacuum" at the top. (Dissolved gasses are likely to be a problem,
though.) Cool the fresh-water side and water vapor will condense there
-- the whole point of the exercise.

Thinking only momentarily on a problem that I have little interest
in... if the fresh-water side is evacuated to the point that the
salt-water side is slightly below the top, every once in a while (or
perhaps often), the fresh-water side will be empty and only the
previously-dissolved gasses evacuated.

The required evacuation pumps and one-way valves sound like the problem
at the moment.

--
Jere Lull
Tanzer 28 #4 out of Tolchester, MD
Xan's new pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI pages: http://homepage.mac.com/jerelull/BVI/