On Sat, 22 Sep 2007 01:41:21 GMT, "Toller" wrote:

I think he is suggesting that the two tube be connected so that they form a
vacuum at the top. It wouldn't take much to make the sal****er evaporate to
fill the vacuum and condense over on the fresh water side.

Precisely right. I'm surprised Larry didn't catch that.

In article ,
Larry wrote:

Brian Whatcott wrote in
:


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


My deepest apologies to the engineers who may be rolling under their
desks, crushing their pocket protectors. It took me a while to stop
chortling. I nearly lost my Chinese dinner!

Psst...Brian....40'? What about the lake above 40', it's 400' deep and
above 40' ASL. It hasn't boiled away in millions of years from all that
pressure and lack of pressure.

Ummm...there is quite a difference between atmospheric pressure at 40'
ASL and a (near) vacuum. Presumably the connection at the top is
airtight and made with as little air as possible entering the tubes, and
presumably also the bottoms of the tubes open and submerged in some sort
of a vented container At sea level, atmospheric pressure will only
support somewhere in the vicinity of 40 feet of water, so the top of the
tubes will be approaching a vacuum. (This is why wells water wells
deeper than 35 or so feet require a pump in the well, rather than at the
top.)

I see no reason why this wouldn't work, at least to some degree,
although I do wonder how using a still of any sort differs from
distillation. I also wonder how easy it would be to make an effective
vertical solar collector on a boat that doesn't need constant climbing
about to fiddle and adjust.

--
Andrew Erickson

"He is no fool who gives what he cannot keep to gain that which he cannot
lose." -- Jim Elliot

On Sep 21, 10:15 pm, Andrew Erickson
wrote:
In article ,



Larry wrote:
Brian Whatcott wrote in
:

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

My deepest apologies to the engineers who may be rolling under their
desks, crushing their pocket protectors. It took me a while to stop
chortling. I nearly lost my Chinese dinner!

Psst...Brian....40'? What about the lake above 40', it's 400' deep and
above 40' ASL. It hasn't boiled away in millions of years from all that
pressure and lack of pressure.

Ummm...there is quite a difference between atmospheric pressure at 40'
ASL and a (near) vacuum. Presumably the connection at the top is
airtight and made with as little air as possible entering the tubes, and
presumably also the bottoms of the tubes open and submerged in some sort
of a vented container At sea level, atmospheric pressure will only
support somewhere in the vicinity of 40 feet of water, so the top of the
tubes will be approaching a vacuum. (This is why wells water wells
deeper than 35 or so feet require a pump in the well, rather than at the
top.)

I see no reason why this wouldn't work, at least to some degree,
although I do wonder how using a still of any sort differs from
distillation. I also wonder how easy it would be to make an effective
vertical solar collector on a boat that doesn't need constant climbing
about to fiddle and adjust.

--
Andrew Erickson

"He is no fool who gives what he cannot keep to gain that which he cannot
lose." -- Jim Elliot

hmmm, I wonder what the rate would be? One could assume that you do
not have to put in any heat to increase the temp so any heat input
would simply go into latent heat of water vapor. You would hav o
maybe use solar to heat the salt water side and cool the fresh water
side by immersing it in the ocean. Then the max rate would simply be
power in (whatever the heat from the sun would be in watts/m2 times
the area of your collector) which is Joules/sec which is roughly 4
calories/sec. Somebody look up the latent heat of water (I dont have
my handbook handy) and then you have grams/sec of fresh water (maximum
rate).

On Sat, 22 Sep 2007 01:21:39 +0000, Larry wrote:

[Brian]
The boiling point of water at the top of a sealed 40 ft column of
water is near ambient.

My deepest apologies to the engineers who may be rolling under their
desks, crushing their pocket protectors. It took me a while to stop
chortling. I nearly lost my Chinese dinner!
...
Larry

They say if you give a fool half a chance, he will rush in.
And so he did. TWICE! Chortling, at that.

Brian W

Brian Whatcott wrote:

On Sat, 22 Sep 2007 01:21:39 +0000, Larry wrote:

[Brian]

The boiling point of water at the top of a sealed 40 ft column of
water is near ambient.


My deepest apologies to the engineers who may be rolling under their
desks, crushing their pocket protectors. It took me a while to stop
chortling. I nearly lost my Chinese dinner!

..

Larry


They say if you give a fool half a chance, he will rush in.
And so he did. TWICE! Chortling, at that.

Brian W


And your point was???

On Sat, 22 Sep 2007 01:04:55 -0500, cavelamb himself
wrote:

Brian Whatcott wrote:

The boiling point of water at the top of a sealed 40 ft column of
water is near ambient.

They say if you give a fool half a chance, he will rush in.
And so he did. TWICE! Chortling, at that.

Brian W

And your point was???

Put this pointy hat on, and go stand in the corner
with that other fellow.
I'll tell you when to sit down again.

Brian W

Larry, I think you are confusing the pressure/pull of a standing/
suspended 40 ft water column and that of a 40 ft air column.

Chris


of a On Sep 21, 6:21 pm, Larry wrote:
Brian Whatcott wrote :





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

My deepest apologies to the engineers who may be rolling under their
desks, crushing their pocket protectors. It took me a while to stop
chortling. I nearly lost my Chinese dinner!

Psst...Brian....40'? What about the lake above 40', it's 400' deep and
above 40' ASL. It hasn't boiled away in millions of years from all that
pressure and lack of pressure.

In Tehran, Iran, my apartment was about 7000' ASL. Water DID boil at a
lot lower temperature. Making a cake at 7000' altitude is simply
amazing! ONE little cake mix makes 4 cakes!.....er, ah, after you clean
out the oven from putting ALL the cake mix in the pan, filling the oven!

But, alas, even at 7000', the water in my glass didn't boil itself at
ambient temperature, even at 110F out on the lawn!

Every engineering firm across the planet is going to be a jolly place
after hearing about this on Monday...(c;

Larry
--
Sure glad it doesn't work that way! We'd all be DEAD!

Brian Whatcott wrote:
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 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,

A nice idea, but unfortunately, the vast bulk of the energy used by the
distiller is not used in heating the water to the boiling point, but in
performing the phase change from liquid to gas. I believe this is a
constant regardless of the surrounding pressure.

The same principle works with ice keeping things cold. It is not so
much the fact that the ice is colder than your drink that keeps it cold
for so long, but rather that the energy required to accomplish the phase
change from solid to liquid requires a bunch of energy.

- Dan best

On Sat, 22 Sep 2007 08:29:57 -0700, Dan Best
wrote:

...the vast bulk of the energy used by the
distiller is not used in heating the water to the boiling point, but in
performing the phase change from liquid to gas. I believe this is a
constant regardless of the surrounding pressure....

- Dan best

As it happens, you believe wrongly.

But you might be surprized if you took a moment to look up enthalpy of
water, or refer to steam tables, or whatever....

Brian Whatcott Altus OK

Brian Whatcott wrote:
On Sat, 22 Sep 2007 08:29:57 -0700, Dan Best
wrote:

...the vast bulk of the energy used by the
distiller is not used in heating the water to the boiling point, but in
performing the phase change from liquid to gas. I believe this is a
constant regardless of the surrounding pressure....

- Dan best

As it happens, you believe wrongly.

But you might be surprized if you took a moment to look up enthalpy of
water, or refer to steam tables, or whatever....

Brian Whatcott Altus OK

Actually, do a search on "triple point" and look at the phase diagram
for water. That gives a good graphical depiction of the
pressure/temperature/phase relationships.

But, as to what the original poster claimed, i.e. that:

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.

And that:

The boiling point of water at the top of a sealed 40 ft column of
water is near ambient.

is simply wrong as stated. If you filled each vertical tube with water,
venting the air at the u-tube connection, then sealed the u-tube *and*
allowed the water to drain down about 30 feet, then you'd pull a
sufficient vacuum. The water, however, would not be anywhere near the
"top of a sealed 40 ft" column.

So, this system will certainly work, but you need to heat the entire
length of the 40' seawater column (to prevent column refluxing). You
also need to cool the condenser side of the system if you want any
efficiency.

Bottom line, you can use a system like this to save energy, but you have
to run it very, very slowly. When the seawater evaporates, the
headspace pressure rises, quenching the process until the condensation
on the other side reduces the headspace pressure again, and that steam
has to travel 60 feet, so it's slowwwww. Diffusion is all you've got to
work with here.

There ain't no free lunch. You want to speed it up, you need more energy
input, either on the heating side, the cooling process, or in the
evacuation process.

Keith Hughes