At 10:02 AM 3/7/2006, Alexander Mikhailov wrote:
This should probably be looked at as an exercise in
thermodynamics, but still might be interesting.
It's known that air cools, when released from a highly
pressurized volume. Say, today you can reasonably easy
get air compressed to 200-300 bars.
The question is, how much the air can cool when
expanding from 300 bars to 1 bar, starting from normal
(300K) temperature?
I've seen liquid air devices that pressurize air, chill it and then
let that expand into an insulated bowel in an insulated chamber. The
air is circulated in a loop with makeup air and some chilling. After
a while you wind up with liquid.
Basic two-stage cooling system, the ones we used in semiconductors
used two types of fluorocarbon gas. The first stage has an
air-cooled condenser and the evaporator cools the condenser for the
second stage. The evaporator for the second stage cools the device
being tested (normally at -55C). These are very common in testing electronics.
For some items, we used a different method. We had a tank of methol
alcohol with a coil of pipe in it. We poured liquid nitrogen into
the alcohol until it was a slush (lower than -55C). We then
circulated fluorocarbon (I think it was FC-66) through the pipe and
then over a heater to get it to exactly -55C. The items to be tested
would be dropped into the fluorocarbon and would be at temp VERY
quickly (thermal shock).
Not the most efficient, but it worked and liquid nitrogen is
cheap. We made our own.
Of course, now you'd have to use something environmentally friendly
in place of the FC-66.
--
Jerry Durand, Durand Interstellar, Inc. www.interstellar.com
219 Oak Wood Way, Los Gatos, California 95032-2523 USA
tel: +1 408 356-3886, USA toll free: 1 866 356-3886
Skype: jerrydurand
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