I give up. My Masters degree in Physics is of no value here. My
Bachelors degree in Math is of no value here. My 20 years with the
university (retired) means nothing. Someone with an opinion (however
false) instead of facts of physical science, seems to be more able to
swing the belief of the uninformed.

I will try to explain it again.

The vacuum will hold the column of water in the tube.

Dont believe it?
Test this statement, take a simple soda straw stick in in a glass of
water put your finger over the end and lift it out. The 8" column of
water stays in the straw because of the vacuum in the top of the
straw. Now remove your finger and the water drops out. So, it
doesn't TAKE a 32' column of water, but that is the tallest column of
water that will be suspended, a simple law of physics.

Thats why a lift pump like the old rocker handle pitcher pumps have to
be replaced with either submerged or Jet pumps in deeper wells. A
lesser column WILL work however. At the top is a vacuum. If its 32
feet, thats the greatest vacuum you can create. There is salt water
on one side and fresh water on the other. The salt water will boil
earlier because of the salt content.

Now test that statement.
Put a pot on the stove and then before it comes to a boil add salt.
Voila, it begins to boil.

The fresh water column is sealed at the bottom and fresh water, as it
builds a higher column, can be drawn off WITH A PUMP. You cannot open
the bottom of the tube to get the water out or you will break the
vacuum. As you draw fresh water off WITH THE PUMP you will draw salt
water into the bottom of the other end (which is under the surface of
the salt water the boat is floating in) to replace the salt water that
has been boiled off. Obviously you will have to be careful that you
don't pull off enough fresh water to cause the sal****er column to
overflow into and contaminate the fresh water column. Also, I make no
representation as to the efficiency of such a system, only that it
WILL work.

Now, I have nothing more to say on the subject as I don't have the
time to waste. I didn't realize I would have to go into such
miniscule detail. I have been casting my pearls before swine and I
dont have the time for that. If someone with an appropriate education
and who has done the above experiments as I outlined, would like to
contact me off list I would be willing to discuss it. BUT...if you
are supposing, without knowledge, using feelings for facts, DONT
bother me.

On Sep 29, 12:04 pm, Keith Hughes wrote:
jim wrote:

"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.

This is just plain wrong. As a *unit of measure* 32 feet of water
column equals about 13.9 psi. Meaning, if you pumped a 40' column up to
a 39' height with water, equalized the headspace to atmospheric pressure
(assuming 14.7psia), sealed it, then allowed gravity to *drain* the
water column to a height of 2', the resulting pressure in the headspace
will be about 0.8psia. Now you also have 33' of empty evacuated column.

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.

Sorry, this makes no sense. Putting water in does not cause it to "pull
down". Yes, you have supply makeup water to maintain column height lost
to evaporation.

The fresh water distills off the top of the
sal****er column then migrates

Yes, and this "migration" is simple diffusion. *And* you have (in the
example above) 33' of column it has to diffuse through on the seawater
side, and however many feet of column on the freshwater side it has to
traverse prior to condensation. If both columns (fresh and sea) are
referenced to the same height, then the evacuated column height on both
sides will be the same, and that diffusion path will be up to 66'. That
does not happen quickly.

In reality, though, the columns won't be referenced to the same level,
with the freshwater column being referenced (i.e. the bottom is opened
to) the deck height on the boat. So the freshwater column will be, say
8' higher than the seawater column. The diffusion path is still the
same, but the evacuated seawater column would then be 37', with 29' on
the freshwater side.

as steam to the other side and distills
in the fresh water side....also creating a vacuum.

No, this does *not* create a vacuum in the sense you seem to mean. It
maintains an equilibrium pressure by lowering the partial pressure of
water vapor generated by the 'boiling' process on the seawater side.

This relates to the critical rate-limiting feature of the system -
maintaining pressure. When you evaporate, or sublime, water into the
headspace, the pressure in the headspace increases. Condensation on the
other side lowers the pressure, and an equilibrium pressure will
eventually be established. For any given temperature, the evaporation
rate is going to be limited by the partial pressures at the
headspace/water-surface interface. It's a feedback loop, More
evaporation - more water vapor molecules liberated to the headspace -
more pressure in the headspace - slower evaporation until the pressure
is reduced. And to reduce the pressure, those molecules have to diffuse
up to 66'.

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.

Yes, VERY slowly. You can increase *throughput* by increasing the column
diameters, but how practical is that on a boat?



It works but does it work as well as other methods that are simpler and
easier to implement. Also if you have no fresh water on hand to start
with there is no way to make it work.

Not quite true...you can seal the 'freshwater' column, using only the
column walls for condensation surfaces, until you have sufficient
condensate collected to allow the freshwater column to be opened.

I can see someone getting a
"Darwin Award" by accidentally spilling all there existing freshwater
supply in a failed attempt to get this contraption going.

It doesn't *have* to be that way, BUT.... :-)



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.

And what's 'practical' for useability, is impractical for functionality.
There are no 'soft tubing' materials I'm aware of that have anything
approaching decent heat absorbance, conduction, or emissivity
properties, so that will be another very significant rate limiter in the
system.



That makes no sense. You are going to have a hard time pumping water out
of the fresh water side any faster than gravity can deliver it.

You actually *can't* pump faster than gravity, unless you want to suck
seawater up the column on the other side.

The
salty side OTOH, if you rely only on gravity to feed it, will become a
solid block of salt once you have evaporated enough water from it.

Doubtful that you'd ever get a solid chunk of salt (and short of having
a bypass circulation loop - cooling the column and further reducing
efficiency - I don't see how a pump could even help the situation), but
of course as the salinity increases, the boiling point increases, and at
some point the process will just stall. The heat input won't be
sufficient to boil the brine solution. Then you have to stop, drain,
clean, and start over. How quickly this happens will depend on column
heights and diameters, but it'll happen at some point. Just another
rate-limiting feature.

All these rate limiters are natures way of saying that there is no
thermodynamic free lunch. A low energy input system will have a low
output (in terms of whatever work you want the system to do).

Keith Hughes

In rec.boats.cruising jim.isbell wrote:
:I give up. My Masters degree in Physics is of no value here. My

Not if you think salt water has a lower boiling point than fresh, no.

Dear jim.isbell:

"jim.isbell" wrote in message
ups.com...
I give up. My Masters degree in Physics is of
no value here. My Bachelors degree in Math
is of no value here. My 20 years with the
university (retired) means nothing. Someone
with an opinion (however false) instead of facts
of physical science, seems to be more able to
swing the belief of the uninformed.

Someone with this much experience must know that the ignorant
will always trample the carpet of wisdom. Why do you waste your
time responding to them?

The entire comedy is misinterpretation of wording, and argument
about strawmen. Relax and have what is left of a weekend. For
they (in this case) are as right as you are... just about
different things.

David A. Smith

Wow, Pearls! Let this swine take a look and see if he can root them out...

jim.isbell wrote:
I give up. My Masters degree in Physics is of no value here. My
Bachelors degree in Math is of no value here. My 20 years with the
university (retired) means nothing. Someone with an opinion (however
false) instead of facts of physical science, seems to be more able to
swing the belief of the uninformed.

I stand (sit actually) abashed in the light of your professed achievements.


I will try to explain it again.

The vacuum will hold the column of water in the tube.

Pearl #1? Hmmm, no. No one claimed otherwise. continued rooting sound

snip irrelevancies related to above statement

Thats why a lift pump like the old rocker handle pitcher pumps have to
be replaced with either submerged or Jet pumps in deeper wells. A
lesser column WILL work however. At the top is a vacuum. If its 32
feet, thats the greatest vacuum you can create. There is salt water
on one side and fresh water on the other. The salt water will boil
earlier because of the salt content.

Pearl #1? Hmmm, alas no. Physics relating ionic strength and boiling
point of water must have changed since your education. continued
rooting sound

Now test that statement.
Put a pot on the stove and then before it comes to a boil add salt.
Voila, it begins to boil.

Pearl #1? Hmmm, no dice here either. It's called *nucleation*. Ever
notice the water *stops* boiling as soon as the salt is fully dissolved?
And doesn't boil again until the new, higher, boiling point is
reached? Try it. continued rooting sound


The fresh water column is sealed at the bottom and fresh water, as it
builds a higher column, can be drawn off WITH A PUMP. You cannot open
the bottom of the tube to get the water out or you will break the
vacuum.

Pearl #1? Hmmm, not yet. Of course you can pull water from the BOTTOM
of the freshwater column - if its end is below the freshwater reservoir
level. Just like the seawater side is. Elevate the freshwater
reservoir, decant to maintain column height. No pump needed. How hard
was that? continued rooting sound

snip

Also, I make no
representation as to the efficiency of such a system, only that it
WILL work.

Pearl #1? Hmmm, well, maybe a tiny, dull one - well, maybe not, no one
said it wouldn't work. And if you think the 'perpetual motion'
reference was to this system, then learn to read. That post was about
*RO* and using this system as a hydraulic pump mechanism. continued
rooting sound

Now, I have nothing more to say on the subject as I don't have the
time to waste. I didn't realize I would have to go into such
miniscule detail. I have been casting my pearls before swine and I
dont have the time for that. If someone with an appropriate education
and who has done the above experiments as I outlined, would like to
contact me off list I would be willing to discuss it. BUT...if you
are supposing, without knowledge, using feelings for facts, DONT
bother me.

OK Mr. Oyster. Oh, and by-the-by, *you* choose to be bothered or not, we
don't do that for you. Have fun in bivalvia...

Keith Hughes

On Sep 30, 9:13 am, "jim.isbell" wrote:
... The salt water will boil
earlier because of the salt content. ...

http://en.wikipedia.org/wiki/Boiling-point_elevation

-- Tom.

In article . com,
says...
I give up. My Masters degree in Physics is of no value here. My
Bachelors degree in Math is of no value here. My 20 years with the
university (retired) means nothing. Someone with an opinion (however
false) instead of facts of physical science, seems to be more able to
swing the belief of the uninformed.

I will try to explain it again.

The vacuum will hold the column of water in the tube.

Dont believe it?
Test this statement, take a simple soda straw stick in in a glass of
water put your finger over the end and lift it out. The 8" column of
water stays in the straw because of the vacuum in the top of the
straw. Now remove your finger and the water drops out. So, it
doesn't TAKE a 32' column of water, but that is the tallest column of
water that will be suspended, a simple law of physics.

Thats why a lift pump like the old rocker handle pitcher pumps have to
be replaced with either submerged or Jet pumps in deeper wells. A
lesser column WILL work however. At the top is a vacuum. If its 32
feet, thats the greatest vacuum you can create. There is salt water
on one side and fresh water on the other. The salt water will boil
earlier because of the salt content.

Now test that statement.
Put a pot on the stove and then before it comes to a boil add salt.
Voila, it begins to boil.


BZZZZT!!! FALSE!!!


Salt water DOES NOT boil at a lower temperature than fresh water. It
boils at a higher temperature. When you add salt to heated water,
it appears to boil because the water is superheated near the bottom of
the pan and the salt crystals provide "nuclei" that start the boiling
process. You can easily verify this by starting with two pans
of water, one salty and one fresh and heating them to their respective
boiling points and measuring the temperature. More explicit
instructions, aimed at middle school students are at:

http://aquarius.nasa.gov/pdfs/prop_fresh_sea.pdf


snip


Mark Borgerson






SNIP

Boiling Point Elevation
The boiling point of a solution is higher than that of the pure
solvent. Accordingly, the use of a solution, rather than a pure
liquid, in antifreeze serves to keep the mixture from boiling in a hot
automobile engine. As with freezing point depression, the effect
depends on the number of solute particles present in a given amount of
solvent, but not the identity of those particles. If 10 grams (0.35
ounces) of sodium chloride are dissolved in 100 grams (3.5 ounces) of
water, the boiling point of the solution is 101.7°C (215.1°F; which is
1.7°C (3.1°F) higher than the boiling point of pure water). The
formula used to calculate the change in boiling point ( Tb) relative
to the pure solvent is similar to that used for freezing point
depression:

Tb = i Kb m,

where Kb is the boiling point elevation constant for the solvent
(0.52°C·kg/mol for water), and m and i have the same meanings as in
the freezing point depression formula. Note that Tb represents an
increase in the boiling point, whereas Tf represents a decrease in
the freezing point. As with the freezing point depression formula,
this one is most accurate at low solute concentrations.

From:
http://www.chemistryexplained.com/Ce...roperties.html

On Mon, 08 Oct 2007 05:33:39 -0700, Keith
wrote:

Boiling Point Elevation
The boiling point of a solution is higher than that of the pure
solvent. Accordingly, the use of a solution, rather than a pure
liquid, in antifreeze serves to keep the mixture from boiling in a hot
automobile engine.....
From:
http://www.chemistryexplained.com/Ce...roperties.html


Actually, no. Ethylene glycol in its pure liquid state boils near
200 degC
http://www.dow.com/ethyleneglycol/about/properties.htm

It is usually cut to 50% dilution for use as an antifreeze.

Brian Whatcott Altus OK

Brian Whatcott wrote:
On Mon, 08 Oct 2007 05:33:39 -0700, Keith
wrote:

Boiling Point Elevation
The boiling point of a solution is higher than that of the pure
solvent. Accordingly, the use of a solution, rather than a pure
liquid, in antifreeze serves to keep the mixture from boiling in a hot
automobile engine.....
From:
http://www.chemistryexplained.com/Ce...roperties.html


Actually, no. Ethylene glycol in its pure liquid state boils near
200 degC
http://www.dow.com/ethyleneglycol/about/properties.htm

It is usually cut to 50% dilution for use as an antifreeze.

Brian Whatcott Altus OK

Since he used the term "solvent", the assumption, at least on my end, is
that he's talking about a solvent/solute system, not a solution of
miscible liquids.

Keith Hughes

In article , betwys1
@sbcglobal.net says...
On Mon, 08 Oct 2007 05:33:39 -0700, Keith
wrote:

Boiling Point Elevation
The boiling point of a solution is higher than that of the pure
solvent. Accordingly, the use of a solution, rather than a pure
liquid, in antifreeze serves to keep the mixture from boiling in a hot
automobile engine.....
From:
http://www.chemistryexplained.com/Ce...roperties.html


Actually, no. Ethylene glycol in its pure liquid state boils near
200 degC
http://www.dow.com/ethyleneglycol/about/properties.htm

It is usually cut to 50% dilution for use as an antifreeze.

True---when mixing liquids, the boiling point is somewhere between
the boiling points of the two.

Radiators and cooling systems are pressurized so that the system
can have an elevated boiling point.


Mark Borgerson