On Sat, 29 Sep 2007 14:42:17 -0000, "jim.isbell"
wrote:



Ah well, another great idea skuppered by dat old devil science :-)

Bruce in Bangkok
(brucepaigeATgmailDOTcom)


A 32' column of water is a continuous vacuum pump. As long as you put
water (salt water) into the column it will pull down and keep a vacuum
in the top of the column. The fresh water distills off the top of the
sal****er column then migrates as steam to the other side and distills
in the fresh water side....also creating a vacuum. You draw off the
fresh water on one side and pump salt water into the other side. The
salt water side is painted black to absorb sun heat and the fresh
water side is painted white to reflect the suns heat. You only need a
few degrees difference for distillation and the vacuum creates the
boiling at low temperatures...even ice will change state to steam in a
vacuum. The idea works.

In a practical sense, I would use soft tubing for the sides and a
solid "U" shaped piece of copper tubing for the top center with a ring
soldered to it so it could be hoisted up the mast of a sailboat. It
would take a 30 to 40 foot mast to do the job. The bottom end of the
salt water tube could go to a through hull for a continuous supply of
salt water and the bottom end of the fresh water tube could go to a
small pump to remove the water without breaking the vacuum.

What you describe is just a still, and a 32 ft inverted U will change
nothing. Solar stills are not new. A very tall boiler connected to a
very tall condenser is all you describe.

Why don't you build one and let us know just how it is superior to any
other solar still, especially ones without all the windage and
topweight.

By the way, it takes about 1100 BTU's evaporate a pound of water, and
this does not vary with pressure. How much sunlight is your still
going to intercept? Sunlight is a maximum of about 1400 watts per sq
meter, or, according to the 'calculator that takes no prisoners', the
HP48, about one eighth of a BTU /sq ft/sec.
Something like half a pound of water evaporated per hour, per sq ft.
This assumes that the collector is squarely aimed at the sun, at all
times. What you want is the largest possible shadow. A rectangle 1 in
by 32 ft is about 2,66 sq ft., by the way. A tube is not a very
efficient shape for a solar collector, of course, but it simplifies
aiming it, since a vertical cylinder looks the same from every
horizontal angle. Your vertical tube will face the sun nice and square
at sunrise and sunset.

Casady