Heat pipes effective when mounted horizontally?

[halofx]

I understand the heat pipes work on the concept of fluid vaporizing, and rising to pull away heat. Once the fluid cools it condenses and sinks back down. I see this working just fine on something like the Scythe Ninja on a horizontally mounted board. But does it loose effectiveness once the board is mounted vertical in a tower case and the pipes are laying horizontal? There is no where for the vapor to rise to.

I am looking at the XP-90 or the Ninja to cool a pair of Opterons. The XP-90 looks like it would be even less effective once mounted in a tower since the vapor would have to make a U turn.

Has anyone compared temps when the case is up right verses on its side with these heatpipe coolers?

 

[zbuddah]

don't use the word "rises" its more like capilary action through the use of a wick. If you used a hollow heatpipe, then yes using it in any orientation other than vertical will reduce the heatpipes effectiveness. Because most heatpipes use a wick the fluid is transferred through the wick from hot to cold. Think celery stalks and food coloring. It won't be as effective but it still works. look for intels papers on thermal solutions, decent reads on heatpipes.

Q. Do heat pipes work against gravity?
A. Yes, a heat pipe is said to be operating against gravity when the evaporator is located above the condenser. In this orientation, the working fluid must be pumped against gravity back to the evaporator. All heat pipes have wick structures that pump the working fluid back to the evaporator using the capillary pressure developed in the porous wick. The finer the pore radius of a wick structure, the higher against gravity the heat pipe can operate. A thermosyphon is similar to a heat pipe, but has no wick structure and will only operate gravity aided.

The sintered wick is uniquely capable of returning working fluid to the evaporator against gravity by using capillary pumping action. Screen and grooved wick structures are not capable of returning the working fluid against gravity at angles greater than -5°.

The finer the pore radius of a wick structure, the higher against gravity the heat pipe can operate.

What we've found at Neoseeker during our reviews is that whether a heatpipe based cooler is standing upright, or standing on its side, the cooling performance difference is less than 1 degree Celsius - so in our real world testing that sort of orientation difference does not seem be a huge factor. Temperature differences resulting from orientation were slight and are likely the result of variations in the test environment.

 

[Miller]

However, despite all that, if oriented upside-down the temperatures ARE affected greatly, yes?

I ask because I have the Asus A8N-SLI Premium, and in my searching for a new case, I was somewhat forced to avoid the V-series Lian-Li cases because of their motherboard orientation and the fact that I'm too lazy to replace the heatpipe with an active cooler of some sort.