Liquid Heat Pipe Design, Orientation & Wicking Material

i am looking for some Senior Technical Guidance from a physicist and/or
engineer and/or anybody that is knowledgeable about heat pipe design
... or has taken a hack-saw to a high quality heat pipe.
here's some examples ... these heat sinks use heat pipes as part of the
thermal circuit from heat source to ambient air.
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here's an excerpt from a previous post on the same subject, where i
talk about the orientation of the heat pipe. (below)
basically, the heat pipes for computer heat-sink-fan assemblies are
usually used in a horizontal configuration (the part that is attached
to the heat sink fins is horizontal, when the heat-sink-fan is used on
a computer in a tower case.)
the "dogma" among computer enthusiasts is that "it doesn't matter too
much", the orientation that is.
this puts some reliance on the "wick" inside the heat pipe, in order to
get the thermal resistance down to a target .14 degrees C per watt.
thinking about it from the point of view of making my own heat pipes,
it seems like the placement of a wicking geometry will make it more
difficult for the fluid inside the heat pipe to circulate.
any references to technical papers or web pages that go into more
detail on this subject would be most appreciated !
so far i found this. the reference to usage in satellites (no gravity,
no horizontal or vertical) is interesting.
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dot com
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i am writing to ask for your help making sure that i am using the
heat-pipe technology correctly.
in my work as an engineer, when we used the term "heat pipe" it was
always for any construction that acted as a conduit for heat energy,
from the heat source, to a surface closer to the "cold-plate".
now, with PC's, like this
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Noctua heat sink, i believe that the heat pipes in it are filled with
some liquid. for example, ammonia, since it boils at a lower
temperature. this part is my imagination - the bubbles are lighter
than the surrounding liquid so they "go up". when they get to a cooler
part of the envelope to which they are restricted, they experience
another phase change back to liquid.
in each of those phase changes, from liquid to bubble and then from
bubble to liquid, there is a latent heat of evaporation & condensation
that is very effective in "moving heat".
OK but there's a big assumption in all of this - the ORIENTATION of the
heat sink.
i haven't taken apart the heatsinks like the Zalman and the Thermal
right and the Noctua. from the way they're pinched off, and from a lot
of the posts about them, i get the conclusion that they are liquid
filled and that the movement of the liquid inside the heatpipe
genuinely helps heat transfer, whether or not the liquid turns into
fizzy little bubbles in the process.
is the main part of this heat sink supposed to be vertical ?
this would mean that, when they are placed in a conventional tower
workstation, the end of the heat pipe away from the CPU, is horizontal.
so, how does the cooled-off fluid get returned to the CPU area of the
heat pipe for another dose of heat ? if the heat pipe is horizontal,
and it's a skinny heat pipe, it's not like pouring cold vodka into hot
chocolate, in which case it mixes real quick.
so i'm wondering, since most of us computer folks are using tower cases
of one kind or another, doesn't that leave these big beautiful heat
sinks operating in a sub-optimal orientation, with horizontal heat
pipes ?
have any of you experimented with your systems, like for example
measuring CPU temperatures with the case mounted horizontally and
vertically, to see if there's a difference ?
thanks for some good technical feedback. vodka-hot chocolate recipes
are appreciated too. :D
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I will share what little I have on heat pipes.
In order to provide thermal conductivity better than solid copper, it is necessary to operate a fluid near its change of state to gas from liquid. Water can be used - reduced pressure provides a lower operating point for temperature. A thin absorbant sheath at the inner tube surface provides a liquid path, while the center provides a gas path.
Brian Whatcott Altus OK
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Brian Whatcott
learn by doing.
did you do all the metal work yourself ?
Bernhard Kuemel wrote:
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And I learned about heat pipes only after I finished my work. That's why I called it vapor cooling and not heat pipe.
Yes, the sawing, drilling, grinding, polishing, glueing. I bought the aluminium pipe and the copper bar. Ohh, and I also cast the aluminium pieces that stopper the radiator pipe, using a piece of copper pipe as mould.
Reply to
Bernhard Kuemel
well, if i lived in *.at - that's austria ? - i'd invite you to come on over & have a brewski & melt some metal.
i still have most of my tools but if i fire up my kiln in the apartment i'm in now i have this idea that i'd be waving goodbye to getting my security deposit back.
i have some experience with investment casting for lost wax & vacuum casting.
i'd like to set up a larger vacuum casting set-up but not in a studio apartment !
Bernhard Kuemel wrote:
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