How Not To Make A Fog Chiller

The hot fog from a glycol fogger billows out and up - giving a "pea soup" effect. Everybody agrees that the cure is a fog chiller. It is hotter than the surrounding air, so tends to rise.

Everybody on the e-mailing lists said "It's easy - just cut two holes in an old cooler!" But we found out it can be a log more complicated than that.

This is the story of our first fog chiller, built in 1998. It's quite educational, in a painful sort of way...

Outside

Outside view of the chiller immediately shows two problems: it's made of unprotected styrofoam, and it's small. The internal dimensions are approximately 12x7x12".

[photo] This is one of the outputs; the naked end of a piece of PVC pipe. Normally you would put a coupler on each side and hook up your distribution manifold. If you really only want a little fog, you can cap the other end.

Fog Flow

Looking inside, you see something seldom done: the chiller is also a fog distribution system with two outputs.

Fog comes in the big pipe on the left and exist through the two smaller pipes on the right. [Actually, it's a single pipe with the half facing into the cooler cut away. The remaining pipe gives strength to the two snippets that stick out.]

The hardware cloth over the input and output holds up the ice load, keeping it from collapsing into the holes and blocking for flow.

Fog Induction

The fog induction is clever. Pity it didn't work that well.

The inlet is a 4-inch diameter Y that mixes fog and air. Ideally, the fog machine is on a timer that shoots occasional bursts of fog into the cooler. When the fogger is off, a fan blows air into the chiller to slowly dispense the fog.

Ambient air is blown in from the side - the black thing is a muffin fan attached to a piece of pipe that fits the Y. This can be used to pressurize the box of fog and blow out any fog that is sitting in there.

The fog enters from the straight path. Note that the fog enters through a long snout. This means that the fog enters the Y mixing chamber after the air, which pushes the fog along. If the fog came straight into the Y, it might either (a) flow back through the fan if the fan is off (b) get blown against the wall of the Y if the fan is on.

Ideally, this setup could be used several ways:

With fogger on and the fan off, the Y acts as a venturi, sucking in air to mix with the fog.
With fogger on and the fan on, you get a boost to the air flow.
With the fogger off, the fan can inject air to push out fog that is stored in the chiller.

[photo] This is the fog induction rig snugly in place.

Note that the fogger inlet is small. In fact, it was sized to fit the output nozzle of the fogger.

Problems

So, what went wrong?

The cooler is much too small to afford long contact between fog and ice. Simply using a larger cooler might have helped a lot!
In order to be a permanent construct, the styrofoam should be protected against both wear and tear (outside) and fog (inside).
The "fog after air" injection scheme wasn't a bad idea, but violated the 4-inch rule. There needs to be some kind of expansion area, with plenty of ambient air that can be draw in with the fog.

Understand: We actually tried using this, and it did work a little. But it is probably quite easy to get some results. The problem is getting good results.