I’ve always been interested in atmospheric effects, especially for theater, concert, and film use.  Low fog is traditionally done with dry ice, CO2, ice cubes, or expensive high power refrigeration units.

My favorite is this one: Glaciator X-Stream

Here are some of my own experiments.  These are all using the special “molecular” fog fluid designed for chillers.

The first thing I tried was a dorm room refrigerator.  This was a small 1/8Hp compressor with R-134a.  It got really cold, well below freezing.  The problem was that it did not have the surface area or the heat capacity to chill the fog effectively.  More of a low lying haze machine.  Most of the chilling took place in the metal tube leading into the chamber.  The evaporator was a U shaped piece of steel with the passages molded into it.  Biggest problem hear was no fins so the surface area was very low.

The next idea I tried was a device I had read about for industrial vapor cooling.  Basically it sprays water in a fine mist into a chamber that also has the fog.  The water, having a higher heat capacity the air, absorbs most of the heat and cools the fog rapidly.

This sure worked, but because I was using water there was no way to cool the fog below the dew-point.  Thus I had almost perfectly neutraly-boyant fog right a waist level.  Weird.  The water also made a bit of a mess and it’s size was impractical.  For high temperature vapors however, this system was very effective.

The last thing I tried was your typical 5000 BTU window air conditioner I got for $10 at a garage sale.  I had high hopes for this as it was firstly designed to cool vapors, and secondly had a much higher heat capacity then the dorm refrigerator system.  The compressor was considerably more powerful and the heat exchanger had aluminum brushes on it.  Not ideal, as the brushed caught and condensed a lot of the fog, but very high surface area.

This system worked very well.  I calculated my fogger would need at least 4500 BTU to cool the fog, and this seems to be very close to what actually happened.  I zig-zaged the fog through the coils to maximize it’s time in contact with the evaporator.  The dual-rotor fan was removed to make room for the fog, and the two chambers sealed off.  I then used a $10 fan to cool the condenser.  We were running the compressor kinda hard, but it only refused to start once and never shut down on us.  I figure for $20 it’s a pretty good start at a closed loop refrigeration system for fog effects.

The next step will be to build it into a more insulated and controlled enclosure (no duct-tape!) and see what we can get out of it before it dies.  Then I’ll grab something like a 25,000 BTU unit and really freeze that fog!