heatpipe cooling upside down

loldrup · Post by **loldrup** » Sat Jun 21, 2008 6:22 pm

Hi
I am builing a HTPC where the motherboard will be placed upside down, so the CPU cooling fan will suck air in from below.
Do any of you know if this will rule heatpipe based CPU coolers out of the game? They work by vaporisation of a liquid. When the liquid is near the CPU it vaporises and the vapor should drift upwards towards the cooling fins (because vapor is lighter than liquid), where it will cool down again. That's how I have understood the heat pipe principle.
But when the fan is upside down, the vapor will already be at the upper most part of the heatpipe - it can't escape to the fins. Is this true? I hope not..

/Jon, Denmark

Stravos · Post by **Stravos** » Sat Jun 21, 2008 6:28 pm

I think the pipes fill up with vapor quickly enough that it wouldn't really be a problem. The wicking material *should* keep the liquid distributed throughout the pipe as well.

cmthomson · Post by **cmthomson** » Sat Jun 21, 2008 6:31 pm

No, modern heat pipes don't rely on gravity. The working fluid evaporates from whatever part of the pipe is hot, and condenses on whatever part is cool. The wicking on the inside of the pipe spreads the liquid more or less evenly regardless of temperature or orientation.

So the short answer is: yes, modern heat pipes work just as well "upside down" as "right side up".

EndoSteel · Post by **EndoSteel** » Mon Jul 07, 2008 8:21 am

The operability of a heatpipe oriented upside down depends on it's length (or the length of it's vertical section, i.e. how high does the wick structure have to pump the condensed fluid). 10cm - you doubtly notice any difference, 30cm - your temps go ski-high.

They make special pipes for upside-down operation, with a very thick wick (this widens the pipe's outer diameter to 8mm while the vapour chanel stays similar to that of a 6mm standard pipe) and even then the heat transfer capacity is lower than that of a standard 6mm pipe oriented normally.

colm · Post by **colm** » Mon Jul 07, 2008 9:24 am

a popular heat pipe vid card cooler proves to me upside down doesn't matter. path of least resistance loses gravity. Heatsinks and upside down cpus may be an oddity, as cpus aren't normally upside down. Vid cards are...
then again, most cpus are sideways, vertical and heatsinking through anything attached.