Some years ago I acquired some multiplex telephone linking equipment
made by SR Telecom Inc. here in Canada. It operated around 1400 MHz as
I recall but that is not important. These units were installed in
completely sealed, cast aluminum outdoor enclosures. To remove the heat
from the final stages, they used a heat pipe. It consisted of a length
of copper tube sealed at both ends and about one half of its length
partially flattened. The other half had a large number of copper fins
attached to the tube. There was a gasketed disk attached to the center
that searved to seal the connection where the heat pipe passed thru the
wall of the enclosure. The flattened end of the heat pipe was clamped
against the bottom of the final amp assembly with some heatsink compound
to ensure good thermal contact.
I don't know what the working fluid in the heat pipe was but someone
suggested it was just water operating in a partial vacuum to lower the
boiling point. It could be any liquid with a suitable boiling point and
a high latent heat of vaporization.
For those who don't know the principles of operation of heat pipes, let
me explain briefly. A heat pipe is just a sealed tube partially filled
with a working fluid, and containing a wick that passes from one end to
the other. There may also be an expansion chamber to relieve the
increased pressure when the fluid is heated. When one end is heated, the
working fluid is vaporized and the vapor flows to the cold end where it
condenses. The liquid is then forced back to the hot end with the wick.
No moving parts to wear out, it can never get colder than the ambiant
air of the cold end (hence no condensation), it is totally silent and is
quite inexpensive.
It is far more efficient than an equivalent length of solid copper.
Tests using infra-red photography shows that when heat is applied to one
end, the whole length of the tube rapidly becomes warm, 10 to 100 times
faster than a solid copper bar of the same diameter.
There endith the lesson for today :-) Have fun with your experiments.
Burt VE2BMQ>>>
Dave VanHorn wrote:
> At 01:35 PM 6/4/2005, Alexander Tubonjic wrote:
>
>
>>>>>The first thing that comes to mind is how to dealing with the
>>>>>condensation created during the heating and cooling of the
>>
>>refridgerant.
>>
>> What if you were to place the radio vertical with the heatsink
>>facing the ground and place a drip pan under the radio? Condensation
>>on the heatsink shouldnt effect the performance of the radio? Same for
>>the power supply, just mount it upside down with the heatsink facing
>>the ground.
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