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Lately I've been looking at HSFs for a new machine and I can't help but notice the seemingly rapid proliferation of heat pipes. It seems they're putting them in everything these days, whether they're needed or not. Kind of like blue LEDs.

Heat pipes rely on phase change (boiling) to transfer heat from the base of the pipe to the top. If a heat pipe cooler is mounted horizontally, this would distribute the liquid through the pipe and it would then have to be less efficient at transferring heat. Most of the pipe coolers I've seen also have the pipes bent upward at a 45 degree angle or so from the base before bending again and going vertically into the main fin assembly, and this would mean that half the pipes would have their liquid sitting in the fins rather than near the source of heat - which would be worse.

So my question is: If I mount a heat pipe HSF in a tower case so that it is sitting horizontally, what sort of performance hit in cooling can I expect, and would I be better off buying a standard non-heat-pipe cooler in such a situation?

There must be some performance hit there.

I don't have the money to do this myself, but maybe someone should take a few of the latest pipe HSFs and mount them on Chernobyl - and test what they do vertically vs. horizontally. It could be an eye-opener.

Daryl

Answer:
You're right, if you're talking about the most basic kind of heat pipe, which is just a sealed tube with some liquid in it.

Heat pipes made for use in various orientations, though, have a wicking material around the inside of the tube, which allows liquid refrigerant to flow back to the hot end by capillary action.

Heat pipes with a wick can point any way you like, which is why coiled ones work.

Wicked heat pipes aren't as efficient in the vertical orientation as unwicked ones, and wicked pipes also do, indeed, often work not quite as well if they're horizontal or upside down. But the difference isn't large (at least, not for CPU cooling purposes, which are pretty low performance), and there's no liquid-lock problem.