On 2012-03-13, Bob La Londe wrote:
Ok... I'm still mulling over the possibility of a Hilsch tube on one of my
machines as the coolant and to blow chips away from the cutter. I see many
commercial ones are made out of stainless, but that just isn't in my plans
if I make one. Stainless is beyond my easy working level.

I have some large aluminum bar stock laying around, (left over from another
project) and I was thinking I could turn one out of it. My quandry is in
this. I only ran across a few mentions of heat sinking in regards to Hilsch
tubes. One article said to heat sink the whole thing. I think they just
meant the whole heat separator/exchangers side of it. It would be counter
intuitive to heat sink the cold air outlet tube. I would think you would
want to insulate that. The thing is the physics of it is beyond me. I get
the basics of both principle said to be at work. It's the details.

I could easily turn heat sink fins on the outside. I just wonder if that
will provide a lower ouput temperature, or if somehow it might reduce the
efficiency of the design somehow?

The primary benefit of heat sinking the hot output side (the
only part which *I* see as benefiting from that) would be the reduction
of heat conducted to the cold side and heating the air coming through
that.

A secondary benefit would be reducing the discomfort of
accidentally contacting the hot output side with your hand when working
around it.

If you put styrofoam insulation around the cold tube, you would
reduce the heat gained by condensing water onto the tube and thus
improve the efficiency somewhat. (Note that this will consume a *lot*
of air, so I hope you have a good air compressor -- and good hearing
protection. :-)

BTW That might be a benefit of using stainless as the material too
lower thermal conductivity.

But, FWIW, I made one once (as an experiment) in which the
vortex was formed by a machined piece of brass (the only thing that I
was then sure that I could machine), the housing was made from an old
pipe union. The two output tubes were 1/2" copper tubing -- both of the
same size, but the output end of the hot side had to be pinched down to
about the diameter of the cold hole in the vortex assembly.

If I were to make one today, I think that I might make the
vortex forming assembly and the housing from Delrin -- minimize the
conduction of heat in both directions. Perhaps the same (or PVC) for
the cold tube. Copper or aluminum and heat sink fins for the hot tube.
And ideally, some kind of muffler on at least the hot side, which is
pointed out into the human space of the working environment. Make the
hot tube significantly larger than the cold tube, which also benefits
with better thermal conduction to the air, and only restrict the output
end (a few inches downstream) of the hot tube to the diameter of the
cold hole in the vortex assembly.

Good Luck,
DoN.

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