No, not a misspell of 'dessert ice' (not this time anyway)...
Poser-of-the-Day: Can anyone imagine making real ice, as in
solid-water ice, but in the desert, using zero electricity and
only natural forces?
The question arose out of this interesting thread on Slashdot,
based on a recent
Time Magazine article, telling us how Dave Williams is trying to
make ice for third-world applications using the Hilsch-Ranque
vortex-tube effect. As all on Vo know - this mechanical device was
developed in 1930 by G.J. Ranque, using swirling air in a tube,
such that the counter-rotating vector components split the air
stream into hot and cold components.
Well, lo-and-behold, as it turns out: It is possible that the
ancient Egyptians did something even more remarkable, without a
vortex tube. If you build a solar reflector, and employ it at
night, especially in a dry environment, the items inside a
reversed focal point can be induced to become very cold, and can
attain temperatures below freezing, even if the previous day-time
temp was 120 - since desert nights can be quite chilly.
And that is a further interesting prospect of having a solar farm.
Use the solar concentrators at night to create cold water and
store it for air conditioning. I wonder how quick I can get this
idea to the patent office?
BTW here is what you use your solar concentrators for during the
day - zinc refining ! Yes, the hydrogen economy (or zinc-air
battery economy) being run from free solar energy (with a little
bit of biomass):
http://www.isracast.com/tech_news/090905_tech.htm
The cooling part doesn't work as well on cloudy nights but this is
desert, remember? You are essentially 'beaming' the low grade heat
away and back into the great heatsink called space). Perfect for
Las Vegas... and with their rate of growth, Hoover Dam may not be
enough.
A slashdot contributor named Adam (the original contributor ?)
sez:
"In September 1999, we placed two funnels out in the evening, with
double-bagged jars inside. One jar was on a block of wood and the
other was suspended in the funnel using fishing line. The
temperature that evening (in Provo, Utah) was 78 F. Using a Radio
Shack indoor/outdoor thermometer, a BYU student (Colter Paulson)
measured the temperature inside the funnel and outside in the open
air. He found that the temperature of the air inside the funnel
dropped quickly by about 15 degrees, as its heat was radiated
upwards in the clear sky. That night, the minimum outdoor air
temperature measured was 47.5 degrees - but the water in both jars
had ICE. I invite others to try this, and please let me know if
you get ice at 55 or even 60 degrees outside air temperature
(minimum at night). A black PVC container may work even better
than a black-painted jar, since PVC is a good infrared radiator -
these matters are still being studied.
I would like to see the "Funnel Refrigerator" tried in desert
climates, especially where freezing temperatures are rarely
reached. It should be possible in this way to cheaply make ice for
Hutus in Rwanda and for aborigines in Australia, without using any
electricity or other modern "tricks." We are in effect bringing
some of the cold of space to a little corner on earth. Please let
me know how this works for you."
------
This is an experiment you can conduct yourself if you are in the
right kind of location. It may be that without advanced insulation
(but maybe using straw ?) one can indeed have desert ice, for
dessert, following your post impala-steak dinner on Safari... is
it possible?
Jones
BTW should have added that there are several ways to move heat
energy for cooling. One is the gas-fired refrigerator which has
been discussed here before, along with Fred's "swampper." The
method being demonstrated in this post is differential infrared
radiation. All other things being equal, if an object is rejecting
more infrared heat photons than it is absorbing, then it looses
heat. Focused mirrors can speed up the process in both directions.
Since the clear night sky contributes little incoming radiation to
the earth's surface, but is instead a giant heat sink, things can
cool off more quickly than expected using mirrors. By using
reflectors one can increase the surface area of the radiation
dramatically and gain greater active cooling, just as solar
collectors with reflectors can gain greater heat energy with the
focused sun shining on them.
At least that portends the interesting prospect of having a solar
farm - and using it at night also.
