Re: Potable Water - The Third Way.

There's another neat way you can demonstrate this with minimal equipment.

Take a tight fitting jar and get the water boiling vigerously in it with the
cap on loose enough to let the steam out.  When it is full of dense steam
and about 1/3 boiling water, remove instantly from heat and tighten cap.

When everything is cooled to room temperature, put an ice cube against the
jar and the water will start to boil.  The ice condenses the water vapor
further, reducing the pressure to the point where the water will boil at
room temperature.

I've seen it done and it looks like the ice cube is boiling the water.

My father won a science fair doing this back in the 1930's.

--
Roger Long

Well, at least this respondent Jim, is operating at shall we say the
7th grade level of science/engineering insight.    Like so many other
products of the domestic school system, he seems to have a severe
case of self-esteem syndrome.  

 Still, he may be retrievable, starting with a science demonstration
he may have missed.   Place a beaker of water in a bell-jar and pump
the air out.

When 99% of the air has been pumped out, the water in the beaker is
boiling vigorously, until, in the usual way, the beaker boils dry.
The beaker feels cool to the touch, naturally.

To quote him: "unless I have a cheap source of heating this won't
work..."

    For the $64 prize:   NOW do you get it?

Brian Whatcott    Altus OK

Well no, he obviously hadn't figured that out. Nor can anybody figure
out what is going to hold a column of water 40 ft high as was stated in
the original post. The tubes may be 40 feet but the column of water will
be considerably less. How much less will depend on how much energy is
heating on the hot side and how much energy is cooling on the cool side.
The total amount of energy needed is not going to be any different than
any other distilling method.
    Unless you have the free or cheap sources of cooling and heating at
specific temperatures this isn't going to work any better either.

-jim

Dear Larry:

What Brian left to the reader's imagination, is that the head
space of the tubes is at a near perfect vacuum, flooded only with
water vapor.  You might recall that a perfect vacuum will lift a
column of water about 32 feet, on a high pressure day.  Or had
you not figured that out?

David A. Smith

dlzc <dlzc1@cox.net> wrote in news:1190415672.506271.93890
@k79g2000hse.googlegroups.com:

http://en.wikipedia.org/wiki/Boiling_point

"The boiling point of water is 100 °C (212 °F) at standard pressure. On
top of Mount Everest the pressure is about 260 mbar (26 kPa) so the
boiling point of water is 69 °C. (156.2 °F)."

AT 40' ASL, the boiling point must be down to...to....211.95F!

Larry

Dear Brian Whatcott:

There are ship-board distiller units that use an engine to pull a
vacuum, and the engine's waste heat to boil that water, to generate
drinking water.  A little shorter...

David A. Smith

You've heard all about distilling water, and you've heard all about
reverse osmosis,  but you haven't heard about low-cost, low energy
stills: they are brand new.

Briefly:
Take one forty ft vertical tube filled with saline.
Take one forty ft vertical tube filled with fresh water.
Connect them with a little engineering help - at the top.

The boiling point of water at sea level pressure is about 100 deg C

The boiling point of water at the top of a sealed 40 ft column of
water is near ambient.
So, it doesn't take much heat to boil the brackish water, and have it
pass to the fresh column where it is slightly cooled to hold the near
vacuum conditions at the boiling level.

[An engineering effort of a U of Utah group I think]

Brian Whatcott   Altus OK