You can apparently get a good effect in drying air by passing the air
through a helical coil of copper tube immersed in a bucket of
ice-and-water. Water will condense out of air at low temperature and
remain in lowest region of pipe at that point, giving dry air emerging
out of the helix.
This hint given to my by pneumatics shop I use. Apparently a customer
does that frequently and is very happy. Would be useful if
occasionally did moisture-affect process. Would be a bit of a pain to
use all the time. I gather a lot of commercial drying systems for
compressed air are an inbuilt refrigeration system.
Ice idea - would be even bigger effect if threw salt into bucket, as
that would lower temperature even more, to -10C or less.
ben carter wrote:
It would get more water out, but that could backfire, due to frost
buildup inside the coil. With icewater, the condensate can run downhill
to a trap you provide for it at the bottom. If you were building the
system for semi-constant use, you'd want a drain leg hanging off the
bottom of the bucket (and unless you had a lot of free ice, you'd want
to pick up an icechest or the like for use as the "bucket"). Could be
set up relatively low-hassle, pretty good for a home shop where a
full-on airdryer is far too costly.
You could also build something involving a refrigerator (rather than
ice), if there's one leaving the premises because it's not the right
color, rather than becasue it does not work well.
On 14 Dec 2004 06:50:55 -0800, email@example.com wrote:
So you take air, and blow it down a narrow pipe part-full of water.
Then you expect the air to be _drier_ ?
There are several problems with this idea. One is simply the
thermodynamics of it - too much air is flowing over too little surface
at too high a temperature to condense effectively.
Secondly, there's no separation of condensate and flow. You need to do
this, otherwise you simply shift the equilibrium a little. Your air
might be drier, but it won't be dry.
If you want to dry air, do it the way that air driers always do it -
drop the pressure by sudden expansion, and provide mechanical (spin or
gravity) separation to take the condensate away afterwards.
A sealed drier can't possibly work either, unless you operate some
sort of batch blow-down process.
Always remember to sprinkle the elephant-preventive dust when
travelling by bus.
Forget it - still not cold enough. If you really want to do this
(it's a common thing in vacuum systems) then use dry ice and a large
surface baffle, like a louvred blind.
The coiled tube in a bucket is not "pure snake-oil" but close. A
refrigerant dryer has a regenerative heat exchanger that takes warm wet
high pressure air and cools it. A refrigerator then finishes cooling the
air to about 35 F (2 C) where the water that has condensed falls out and
is remove via a drain. The cold saturated air now goes back through the
regenerative heat exchanger to warm itself up and cool down the incoming
air. The exiting air now has a dew point that is well below freezing,
and will not condense in your torch, paint gun, etc.
In your coil in a bucket system it will work if you need only a small
amount of air for a very short time. As soon as the tubing fills with
water it will carry over and go down the line as a slug of water. Also
as the air coming out of the bucket is at about 32 F it may cool enough
by expansion and dump what water it is carrying.
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