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I think I understand how heat pipes work, and thus the following one has me flummoxed:-

Chinese heat pipe

It's from a typical bulk order Chinese web site, but I've seem many similarly contorted arrangements. They are very common in the over clocking /modding community. There is never discussion as to which way the heat sink must be oriented for efficient operation.

My example seems ridiculous. With an U bend in the middle, I don't see how heat sinks like this can evaporate at the hot end and condense at the cold end. Surely the condensate will just pool in the U bend? Even with condensate wicking, it must be easier to wick downwards with gravity than upwards fighting gravity.

Are these types of heat sinks just a con? Overclocking /modding heat sinks are never spec'd with a deg. C /W rating or recommended orientation. This would not do in the engineering world. Can it work equally effectively in any orientation?

Community
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Paul Uszak
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3 Answers3

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Orientation does often matter. As Carl's answer mentions, the liquid can get from the condenser to the hot interface via capillary action, but most common heat pipes are designed assuming gravity will do the job.

Capillary action is much more effective in space where there is no gravity, but produces very little flow when it has to work against gravity. Therefore, even heat pipes designed to transport the liquid via capillary action in space need to be oriented correctly on earth.

Make sure the radiator is above the hot interface, especially where there is no datasheet available.

Olin Lathrop
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Orientation is in fact irrelevant. Heat pipes are used in space, among other places. Quoting from guess-what-reference-page,

At the hot interface of a heat pipe a liquid in contact with a thermally conductive solid surface turns into a vapor by absorbing heat from that surface. The vapor then travels along the heat pipe to the cold interface and condenses back into a liquid – releasing the latent heat. The liquid then returns to the hot interface through either capillary action, centrifugal force, or gravity, and the cycle repeats.

Carl Witthoft
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Orientation effects the Heatpipe's Qmax, the maximum watt that particular pipe can carry.

So, a well design Heatsink + Heatpipe system will stay below that. If you are below that in a well designed system, orientation will not affect it.

Transistor
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Lawrence L
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