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Compressed air

A recent post to the List suggested that air supplied to our fish tanks from
an air compressor would have an "elevated temperature."  Yes and no.

 Yes, when you compress any gas, the temperature rises.  However, when you
release the gas and it "decompresses," it gets COLDER. The Law of
Conservation of Energy. This is how your refrigerator (and your air
conditioner) work!  The gas in the system is compressed, which raises its
temperature. The hot gas is circulated through coils, so it can release that
temperature rise. As it cools, it becomes liquid.  Then, the cooled liquid is
released into the "inner works" of the refrigerator, the cooling coils
inside.  The expanding gas from the evaporating liquid drops in temperature,
thus absorbing energy from the refrigerator inner space, cooling the food.
The now slightly warmed gas is then circulated through the compressor,
starting the whole cycle over again.

Yes, the "blowers" DO raise the temperature of the air slightly  as they
compress it. And, yes, the air bubbling through the tank IS cooler than it
was before it was compressed by the blower. Not enough to matter, though! :-)

It does not take much pressure to bubble air from 18 to 24 inches deep in our
tanks, and at such low pressures blowers are LOTS more efficient, IOW they
cost less to run than the piston type compressors.  You pays your money, and
takes your choice. Both kinds of air supply are really NOISY!!!

Hope this helps.