Re: ATM Cooling thought...

[Aart Olsen <aolsen@prairienet.org>]

I toyed with a "cold trap" years ago, fashioned after laboratory
apparatus that removes moisture from a gas stream.  I took a round
plastic garbage can and coiled about 15 feet of flexible 3 inch diameter
aluminum tube inside of it, the kind of tubing you use to vent a clothes
drier.  This was coiled inside the can along the inner wall.  A fan
pushed air through the tubing, the far end of which went to my
telescope.  I filled the bottom of the garbage can with a bag of ice
cubes that covered maybe 1/3 of the tubing.  The ice initially cools the
air but it then rewarms because the coil is surrounded by ambient air,
drawn into the garbage can by the fan.  During the cooling phase the ice
causes the moisture to condense inside the coil, and during the
rewarming phase the air's relative humidity drops below the ambient. 
The end of this tubing was duct taped to the bottom of my telescope tube
(a 12.5 inch with a 15 inch diameter aluminum solid tube).  The device
worked, sort of -- the telescope cooled real fast and the inside of the
telescope, including the secondary, didn't dew up.  However, the outside
of the telescope absolutely dripped, because the air flow didn't rewarm
quite enough and the telescope got too cold.  You could actually see the
cold air pouring out of the tube, which wasn't so good for seeing.  The
coiled tubing filled with condensed water too, and I had to put a little
weep hole in the bottom to keep that empty.  It was all too much trouble
of course, but it was "really cool".

-- 
Aart Olsen
aolsen@prairienet.org