Dear Glen Walpert:

"Glen Walpert" wrote in message
...
On Thu, 27 Sep 2007 13:54:13 -0000, "jim.isbell"
wrote:

On Sep 22, 10:39 pm, OldNick wrote:
On Sat, 22 Sep 2007 10:55:52 -0500, Brian Whatcott
wrote stuff
and I replied:

But what is the cheap source of getting the vacuum?
I figured there had to be a vacuum, although it was
not said. But how do you get it?


Gravity.

Wishful thinking. Where are you going to get the
feedwater containing no noncondensible gasses in
solution? In all real distillation plants a continuosly
operating vacuum pump is required to maintain
vacuum and prevent the condensers from filling with
noncondensible gasses. There is no way you are
going to eliminate the vacuum pumps with any kind of
inverted tube arrangement.

But they don't have to be large, and they don't even have to run
continuously (just frequently). There are also going to be
controls...

You could even run it without a vacuum pump until it shut itself
down, drop and purge the gas bubble, then "forklift" your pipes
back up.

And do it at less than the melting point of plastic (should that
be important).

For reasonable efficiency real distillation plants
are multi-stage, where the latent heat of
condensation from one stage is used to boil
feedwater in the next stage, with up to 5 stages
being used in larger plants (in the days before
reverse osmosis made them uneconomical by
comparison).

Scaling is real problem too...

Sucessive stages operate at lower pressures, and
corresponding lower temperatures. The 1100 or
so BTU required to boil one pound of water can
thus boil up to 5 pounds of water instead.

You still need enough thermal gradient to get the
heat to flow through all those heat exchangers.
By using low thermal differentials between the hot
and cold ends you either reduce capacity to a
pittance or require huge and expensive heat
exchangers, in either case not competitive.
TANSTAAFL.

.... a characteristic article ...
http://www.hcn.org/servlets/hcn.Arti...ticle_id=17136
This was not proposed to be a source of free energy, violate the
second law of thermodynamics, or poke fingers in anyone's eyes.

I think it was something that someone could do fairly cheaply, to
get drinkable water from salt water. In other words "a graduate
or undergraduate college project".

I just wonder if you get any improvement in what is left in the
brine, vs. what also evaporates at the lower temperatures...

David A. Smith