It Yourself Heat-Pipe Fabrication Using Simple Fabrication Methods
And Readily Available Materials
have built a heat pipe, from scratch, to transfer captured
Solar Energy out of my Evacuated (vacuum)Solar Thermal Energy
I soldered a sealed tube with a condenser bulb (made from
a standard ½ inch copper "Stub-Out" fitting
and a ½ to ¼ inch reducer fitting) at the top
and a 42 inch long X ¼ inch ID copper boiler tube that
extended down the inside of the Evacuated Solar Thermal Energy
Capture Tube. Before sealing the tube I had added 0.078 fluid
ounces of acetone as a heat pipe heat transfer working fluid.
The idea was to boil the acetone into acetone vapor, thereby
cooling the inside of the Solar Thermal Energy Capture Tube
by using the large heat-of-vaporization of the acetone working
The design looks like this (NOTE: Selective Coating rendered
transparent for clarity):
wrapped two stretched out pads of "Brawny" Stainless
Steel Pot Scrubbers (total cost$1.98) around the boiler tube,
and inserted them into the bore of the Evacuated Solar Thermal
Energy Capture Tube, so that the stainless Steel wool was
in thermal contact with both the acetone heat pipe boiler
tube and the solar heated inner wall of the energy collector
tube. The purpose of the stainless steel wool, was to form
a permanent, intamate heat transfer medium, that is both rugged,
and cheaper than the brass or copper wools, that would not
rust or corrode, at continuous high operating temperatures.
I placed the heat pipe Solar Thermal Energy in the sunlight,
and slipped a piece of thermal foam pipe insulation, over
the condenser bulb, and slipped a 60 - 250 F meat thermometer
into the foam, along side the condenser bulb. After 15 to
20 minutes, I returned, and was stunned, to find that the
thermometer read off-scale at 250 F, and the thermal foam
had melted due to the very high temperatures being given off
by the heat pipe condenser bulb, as the vaporized acetone
condensed, and gave up is heat of condensation, to became
a liquid once again, and was returned to the boiler, by gravity
to re-vaporize again, and begin another rapid heat energy
is a picture of the heat pipe condenser after the thermal
insulation foam was melted by the hot Solar Energy Capture
Tube Heat Pipe Condenser Bulb!
type of thermal pipe insulation foam is in common use, on
hydronic (radiators or hot-water floor or baseboard) heating
systems world-wide that operate continuously at 180-200 F.
So to melt such a high temperature foam, the condenser bulb
had to be well above the 250 F scale limit on the meat thermometer.
home brew DIY heat pipe worked very well, the first time I
DIY heat pipe exceeded my initial expectations for both ease
of fabrication, and long term operating performance.
fabrication was very simple and straightforward, and I plan
to make a LOT more of these easy to assemble and use heat
pipes, not only to use with my solar thermal energy collection
tubes, but also, to modify some ammonia propane boilers in
RV refrigerators, to operate on captured Solar Thermal Energy
instead of a propane flame.
Speople have asked for more information and updates, so here
used copper throughout, since acetone will not attack copper,
stainless should work OK.
an ammonia based heat pipe would need stainless.
The first version I built had a huge 6 inch long x ½
condenser bulb, but empirically, I found that when I cooled
1½ inches with a water jacketed cooling manifold, then,
the top 4.5
inches immediately dropped to the water cooling ambient.
So only a small portion of the 6 inch long condenser bulb
was actually condensing any acetone under these conditions.
So, I just reduced the size of the copper bulb to 1.25, need
far less costly copper, in the heat transfer region.
That makes the manifolds much lighter and thus far less costly
in copper content.
Thermally they are just as efficient as the old larger one.
So, this copper size reduction, was just an optimization,
rather than a cost compromise.
important lesson learned, is that the heat transfer is so
fast and efficient, that much smaller manifold sizes are possible,
compared to our intuitive experience, based on moving large
amounts of heat around by weakly vibrating molecules, hopelessly
a solid phase metal crystal lattice.
Thus, a tiny amount of acetone vapor, can move heat around,
of times faster, and far more efficiently, than even an expensive
pure silver bar or rod!
I was astonished how easily the heat pipes can be designed
and built by a DIY who can sweat solder copper.
Some care is required, if using flammable working fluids like
acetone, so this sweat soldering should be done outdoors,
with a water source nearby.
Cotton clothing with no polyester content should be worn.
With a water
hose running nearby.
Eye protection should also be worn but that is true any time
The amount of working fluid used is so tiny, that there is
little danger involved.
I purposely lit off some of the acetone vapor with my propane
torch just after I had purged out the oxygen/nitrogen/ during
the purging step, and it just burned off like a small blow
So, the average DIY experimenter can make simple heat pipes
even using flammable working fluids safely if simple precautions
are taken, and good construction practices are used.
when I think about it, the uses for inexpensive DIY heat-pipes,
are almost unlimited!
of manifold construction
Flux to fittings with brush
11 Dec. 2006
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