Potable Water - The Third Way.

External Since: Jul 11, 2007 Posts: 225

On Sat, 29 Sep 2007 14:42:17 -0000, "jim.isbell"
<jim.isbell.TakeThisOut@gmail.com> wrote:

>
>>
>> Ah well, another great idea skuppered by dat old devil science Smile

>>
>> 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
>saltwater 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

External Since: Jul 11, 2007 Posts: 225

On Sat, 29 Sep 2007 13:57:27 -0500, Brian Whatcott
<betwys1.RemoveThis@sbcglobal.net> wrote:

>(That would however take a hand pump capable of supplying a flow
>at 15 psi plus. Like a bicycle pump, or better? )

Grease guns are, some of them, capable of at least. hundreds of psi.
I happen to own a 0-5000 psi gauge. Bought it to check tractor
hydralic systems. I forget just what a grease gun pumped it up to, but
it was a lot.
There is a reverse osmosis watermaker intended for liferaft use, with
a hand pump, and RO takes hundreds of psi. That is what you want, if
you actually need high pressure.

Casady