Re: liquid air for concentrating HTP?

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.


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Jerry Durand, Durand Interstellar, Inc.  www.interstellar.com
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