Heatpipes - correct usage/orientation

[zybch]

There seem to be a lot of HSFs that are using heatpipes recently.

It is my understanding that the heatpipe principal works like this:
Liquid in the heatpipe is turned to vapor at the CPU end which rises to the other end when it gets cooled and then condenses on the walls of the pipe and moves (via a wick and gravity) back to the bottom to get heated again.

If this is the case, the orientation of the heatpipe must be so that they run in an up/down way.

This is just fine in desktop cases where the standard 'U' shaped pipes are still in an up/down orientation, but what happens when you use these same sinks in a tower case the the 'U' shape then isn't in this orientation?

Isn't the effectiveness reduced a great deal by not having the 'hot end' located at the bottom and the 'cool end' at the top? For the vapor to have to move down, and then around a 180degree bend and then up (or up briefly, then do a 180 then down) seems pretty stupid, thermally illogical and innefficient to me.

Am I missing something here, or are heat pipes in towers cases a bit of a con?

[Midknyte]

http://www.cheresources.com/htpipes.shtml

It consists of a sealed aluminum or copper container whose inner surfaces have a capillary wicking material. A heat pipe is similar to a thermosyphon. It differs from a thermosyphon by virtue of its ability to transport heat against gravity by an evaporation-condensation cycle with the help of porous capillaries that form the wick. The wick provides the capillary driving force to return the condensate to the evaporator.

[zybch]

All of the HSFs that I've seen do better when used in desktop-PC orientation.

[The Lodge]

This may seem like a stupid question. What is the difference between a desktop case and a tower case? Obviously you’re not referring to a case that sits on its side. If anything, it would depend on the orientation of the socket on the mb.

[zybch]

Thats exactly what I'm refering to.
In a tower case, with the CPU mounted vertically, no matter which way round the socket is, the heat source is at the side and the heatpipes either go down 1st then up, up then down, or at best have a slight incline to one (the ones with dual pipes) but a decline to the other.
Its only in desktop cases with the CPU monted horizontally where the pipes consistently are in the up/down orientation.

Midknyte, thanks for the info, however do you really believe that the majority of HSF makers out there will use the right liquid/wicking material? It doesn't take much googling to see that quite a few just use a hollow copper tube sealed at both ends and call it a heat pipe.

[Midknyte]

Believe what you want. Don't buy 'em then. :p

[Happy Joe]

I saw between a 3 and 5 C rise in temps when i moved my sp97 from horizontal to vertical orientation. Thermalright also specifies recommended and non recommended orientations (probably for effieciency resons). so, yes I believe that the orientation has an effect, especially when the pipes are U shaped.
Enjoy!

[zybch]

Vindication! :)

[Midknyte]

All right. Pure physics say that it should work (liquid/gas in a vacuum), but gravity does seem to make a difference. I don't think it's a con. If the pipes are parallel to the ground, then it should perform adequately.

if you think it's a con then just get a heatsink without heatpipes like a Zalman.

This is right off Thermalright's website:
Question 3: Does how heat pipes are oriented truly affect performance?

Answer: Due to the multiple heatpipes we use on the design to minimize the gravitation effect on Heatpipe performance, we at Thermalright tested only 0.03 celeius/W on an open case environment for best/worst scenario with Panaflo FBA09A12H.

[zybch]

They still work better with the hot bit at the bottom, a desktop case will still be the best option.