Fog Chiller - Part 2
The Heat Exchanger
Metal "stove pipe" duct material.
I bought three lengths of galvanized
metal duct - 4" diameter x 24" length.
The image at left shows aluminum
duct (which was replaced.)
The 26 ga. galvanized variety costs a little
more, and is harder to assemble, but the
finished product is very strong.
The cage
The cage will be used to support thecopper coil. If you intend to use aluminum
duct, this cage will also provide some
degree of strength.
The cage is made of 1/2" hardware cloth.
The welded cloth is easier to find and
more affordable than the woven
(decorative) variety.
The copper coil
I made single coils out of3/8" "soft" copper tubing.
Any bigger and it would be difficult to
bend around a 2" form.
Any smaller and the (water) flow might
be overly restricted.
3/8" tubing is a happy medium for
this project.
Assembly
Fashion a "tube" of hardwarecloth slightly smaller than the
inner diameter of the metal duct.
Test the fit.
Be sure to bend the cut ends of the wire
so that the overlapping edges latch on to
one another. This will aid in the shaping
process, and will also minimize the
possibility of future snags.
For this project I made three coils.Each coil used 25 feet of 3/8"
copper tubing.
A small rolling pin made an ideal
form for this procedure.
Be sure to leave a short length
of tubing at each end of the coil.
This will be used for future connections.
I made small hooks out of bare copper wire.These hooks will be used to suspend the
coil from the hardware cloth cage, while
centering the coil within the metal duct.
This will allow the fog to travel
through, over, or under the coils.
Carefully straighten the ends of the coiland insert it into the hardware cloth cage.
Attach the coil to the cage by threading
the copper hooks through the cage and
bending them back. (...needle nose pliers...)
Work carefully, and center the coil
within the cage. The copper hooks are
much easier to bend than similar hooks
made of steel.
I used three rows of three hooks.You could use more, but three rows
makes centering easier, and will
certainly hold the weight of the coil
when filled with water.
Carefully insert this new assembly
into the metal duct.
This completes the "heat exchanger
sub-assembly" part of this project.
Putting things together.
Run a bead of siliconedown the length of each seam before you
assemble the metal duct.
After you fight with the joint long enough,
it will snap into place and you can run
a second bead of silicone on the outside
of the joint.
The entire cooling chamber needs to
be water tight.
I chose to make the "loops" out ofpoly tubing. You could use copper,
but remember that it isn't very
forgiving, and kinks easily.
This reinforced tubing won't kink as easily
as soft vinyl tubing, and bends easier
than the rigid "white" variety.
Pipe clamps at each joint
guarantee a leak-free recirculating
system.
The short length of copper tubing in
the photo at right will be the segment that
exits the cooling chamber.
I used 4" p.v.c. 90 degree ellsto join the sections of metal duct.
A short piece of 4" pipe was used
to cement the two ells together.
The coils were connected with a
short length of poly tubing, and the p.v.c.
ells were installed and sealed with
(a generous amount of) silicone.
The "in" and "out" portionsof the cooling chamber are also made
of p.v.c. pipe - the green pipe.
Everything is assembled dry.
Once the fit is satisfactory, the pieces
are disassembled, silicone is applied,
and the parts are re-assembled.
The joints are held together with
duct tape until the silicone cures.
(approx. 24 hours.)
The cooling system is finished, with the exception
of the pump installation. It's strong enough to easily support
the weight of the ice. The total length of the cooling chamber
is slightly more than 9 feet (six feet of metal heat exchanging
surface area) The over all dimensions of the finished assembly are;
32" long x 16 1/2" wide x 4 1/2" high.
--- --- --- Side notes ( or... information without visual support) --- --- ---
Test as you go, especially the recirculating system.
Pump water through the entire system before gluing everything together.
At this stage, any leaking joints would be easy to repair. Once the silicone sets,
the same job will be far less enjoyable.
Use thin walled pipe (sewer pipe)
Thin walled pipe and fittings are cheaper than schedule 40 products.
Use heavy gauge metal duct. You only want to build this thing once.
Con someone else into forming the copper coils.
25 feet isn't so bad.
50 feet is a somewhat like work.
75 feet is a chore.
Buy good silicone. (again, you only want to build this once.)
GE brand silicone II has excellent adhesive properties , and will remain
flexible after curing. Metal will expand and contract with changes
in temperature, and a water-tight seal is very important to the
design of this project.
Don't buy flexible metal ells based on the theory that metal is a good conductor.
The joining process used in the fabrication of these fittings produces
a surprisingly weak joint.
If you have access to one-piece metal ells, consider yourself Blessed
and buy four of them. Metal IS a good conductor and will help
cool the fog,.
If you will be buying a pump, buy a "strong-ish" one.
The model I purchased is rated at 170 gallons per hour.
I wouldn't go much smaller than this. (you'll be pushing through
75 feet of 3/8" o.d. copper tubing with nothing but resistance.)