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Old September 6th, 2009, 01:33 PM
hochung hochung is offline
Ho Chung
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Join Date: Sep 2003
Location: Rancho Palos Verdes, CA
Posts: 2,006
Aside from the cooling effect John describes, there's another cooling effect that takes place right at the regulator. The Joule-Thomson effect.

This effect is the drop in temperature of a gas as it expands from inside the tank (800 - 1000 psi) to the open atmosphere through a small opening.

CO2 has a particularly high Joule-Thomson coefficient, so the cooling effect is greater.

for comparison, Nitrogen's JT coefficient isn't as high, so you wouldn't see the same amount of "freezing" on the regulator under similar conditions.

I believe this is the principle behind refrigerators and automotive A/C systems that use CFC gases, with unusually high JT coefficients.

For info, look up Boyle's Law and Joule's Laws, and you'll better understand how your Power Tank works.
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