Depending on the required flow rate you may be able to use a peristaltic
pump.
Bruce
Bob Camp wrote:
Hi
A heat pipe might work if the fluid had a sufficiently low boiling point. The
rubidium isn't terribly tolerant of high temperatures, and I'm going to pick up
some heat rise as I put it inside some baffles / shields. You need to find
something that fits a fairly narrow window.
I suspect that a recirculating water loop is a more practical approach to carry
away the heat. It's got a pump to move the water, but the rest of it is fairly
simple.
Bob
On Dec 24, 2009, at 2:49 PM, Joe Gwinn wrote:
A dodge occurs to me - a homebrew heat
pipe:<http://en.wikipedia.org/wiki/Heat_pipe>.
Make the cold plate of copper, to which is soldered a meandering piece of
copper tubing, which tubing is also soldered to a copper radiator plate that is
above the coldplate, forming a closed loop with a fill tube attached by a T.
Braze all tubing connections, as for freon refrigeration systems. (Soft solder
is too porous to work for the joints, but is OK for attaching tubes to plates.)
Insulate the two tubes running between coldplate and radiator plate from one
another.
Put enough working fluid into the system to fill the tubing that is soldered to
the coldplate, but no more. Warm the system up so the vapor drives all the air
out, pinch the fill tube off and fold it back, and braze the end shut. (It's
not critical to get absolutely all the air out.)
Making the radiator plate be above the coldplate (the boiler) implements what
amounts to an oldtime two-pipe water vapor heating plant. Vapor goes up one
pipe, condensed fluid returns via the other. I lived in a house with such a
system. The difference between a vapor plant and a steam plant is pressure:
the vapor plant runs below atmospheric pressure, while the steam plant runs at
or slightly above.
Make sure that things are arranged so the returning fluid does not pool
anywhere but in the coldplate, or the heat pipe will bang like an old steam
heating system.
There is a brazing filler metal intended for copper-to-copper joints that is widely
used for freon
systems:<http://www.uniweld.com/catalog/alloys/silver_brazing_alloys/phos_copper.htm>.
The zero silver phos stuff is adequate, cheap and widely available. While
copper-to-copper needs no flux, copper-to-brass does, so also get the flux. Plumbing
supply houses and welding equipment stores are likely sources. You will also need a
torch or pair of torches able to raise the tubing joints to an orange heat in a
reasonable length of time.
Depending on the chosen working fluid, the cold plate temperature will not rise
above the boiling point of the fluid unless the system is too small (in
radiator heat removal capacity) to easily handle the 10 or 20 thermal watts
that are passing through.
What fluid to use? Anything common and thermally stable that does not attack
copper. Alcohol (methyl or ethyl) and water are common choices, as are the
various freons. I bet acetone would also work. Anyway, one controls the
coldplate temperature by a combination of choice of working fluid and internal
pressure.
I have seen commercially made heat pipes for cooling Intel CPUs advertised, but
I don't know that these units can be adapted.
Anyway, a heat pipe system will stabilize the coldplate temperature fairly
accurately despite variations in thermal load, has no moving or electrical
parts, and may be sufficient by itself. If not sufficient, it can be used as
the outer stage in a two-stage ovening scheme.
Joe Gwinn
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