Q: Heat pipes need gravity - do they work better vertically

deadbolt · Post by **deadbolt** » Sun Sep 02, 2007 4:03 pm

The way I understand heat pipes is that they perform a phase change causing a liquid to evaporate. As the gas comes into contact with a cooler metal part it looses energy and condenses. Gravity carries the liquid back to the heating element and the cycle continues.

So if gravity is needed how can a heat pipe placed on its side operate efficiently or at all ?

I am particularly interested in the Ninja and Thermalright Ultra because they appear to have pipes that extend below the heating surface of the CPU when mounted in a tower case.

aaa · Post by **aaa** » Sun Sep 02, 2007 5:32 pm

I get the feeling many are just soild copper...

Elixer · Post by **Elixer** » Sun Sep 02, 2007 6:25 pm

This has been gone over quite a few times here on the forums. Do a couple of searches and you should find them. The basic conclusions are:

Heatpipes used today use wicks, so turning them in any direction does not significantly affect their ability, except where they are very long, ie some of today's motherboards. The wick carries the fluid from the cool end to the hot end, allowing the heatpipe to operate in any direction. It also varies depending upon the heatpipe used. I think some heatsinks with heatpipes can be shown to have a 1-2C difference when turned the wrong direction, but some also show no change whatsoever. With the new motherboards, some people have reported problems when running them upside down (ie in Lian Li and some other case designs) and this may be due to the long length and/or quality of the heatpipes used.

Howard · Post by **Howard** » Sun Sep 02, 2007 10:45 pm

Heat pipes by definition have internal wicks. The ones without wicks are called thermal syphons.

aaa; if they were solid copper, heatsinks with heat pipes would perform worse than the ones without.

deadbolt · Post by **deadbolt** » Mon Sep 03, 2007 3:47 pm

Thank you for the insightful replies. Yes I should have searched and can see the importance on very busy boards. Is it all that critical on quieter boards when activity inspires more frequent visits ? Some boards look pretty stagnant even though they do contain pertinent information.

I am still left wondering how the hotter portion of the pipe would attract the condensed fluid or gas. I will perform a search and have previously visited a manufacturers web page that has a FAQ but it still does not answer how it works without gravity.

Post by **NeilBlanchard** » Mon Sep 03, 2007 4:40 pm

Greetings,

Here's an article on heatpipes:

http://www.silentpcreview.com/article647-page1.html

HueyCobra · Post by **HueyCobra** » Mon Sep 03, 2007 9:06 pm

You might also like to see Ask Dan: Which way up for motherboard heat pipes?