Hi,
 
Does anyone know what working fluids are used in typical CPU GPU HSF Heatpipes?
 
Also what would the normal (Room Temperature) Pressure in the pipes be?  Atmospheric? Positive? Negative?
 
No one seems to list that sort of info.  They Just mention "fluid".  The Mechanical Engineer in me needs to know!
 
Cyborg

News to me that there is fluid in there...  
 
I always though the "fins" were thin pieces of metal for the heat to move out of faster...Seeing as water doesn’t dissipate heat it just transfers it, i don’t really see how it would be useful compared to a solid piece of metal.

LOL...I'm pretty sure there are 'legal' reasons a company doesn't list these specifics.  Something along the lines of, say, I don't know...product confidentiality???  
 
That point aside, I have heard somewhere it is an alcohol based fluid, but that could be completely wrong.

 
 
The fluid transfers heat, but does so by phase change inside the pipe rather than mass transfer/convection in water cooling.
 
Here is how they work and some of the possible working fluids.
 
http://www.cheresources.com/htpipes.shtml
 
http://en.wikipedia.org/wiki/Heat_pipe

Awesome, learned something new...

I was just reading about that a couple days ago too!
 
Owww, down goes another 3k Kaze. My poor pinkie! It tried to lop it off. Thank the gods that the blade broke off and only ripped a weird tear in my poor finger! Waaaaahhhh!
 
Thats Kaze # 2. Only have 3 left, lol!
 
--Lupi

That's why you buy fan grills, Lupi. Those things are dangerous.

 
i've read somewhere that it's either methanol or water under its own vapor pressure. so in the case of water, it's a vacumm (less than atm pressure) below 100 C or with methanol it's a vacuum below 64.7 C. these temps are the normal boiling points of the liquids. @ the boiling point temps, it's atm pressure, above these temps, it's positive pressure. the normal boiling point is defined as the temperature where the vapor pressure = atm.

HSF designs based on heatpipes have water as the main fluid with additive + decreased pressure (vaccume) to decrease the temperature in which it reaches vaporization (normal water =100C, but in HSFs this is around 32C. ) Methanol is also a possible candidate, but the Merit number for the water is higher. ( did a science fair project on heatpipes/ CPU heatsink design this year for science)

Wow, thanks, that is great info.
Please tell me this was a High School (or even College?) level project.  I dont think my ego (as a 30yo engineer) could take having something likethis explained to my by a kid in jr. high.
 
C.
 
Merit Number... Damn, there were too many of those X numbers, where X = some dead guy.  I Blew at thermo.

I read a bunch of articles on this as well now... Turns out there is a lot of science behind these heatpipes. the liquid is in a half/half state...liquid/vapor. The whole thing is nerdly interesting

Yes, that was for a science fair project in high school.
 
Merit Numbers:

 
Graph:

 
For more info see:
 
P.D. Dunn & D.A. Reay. (1994). Heat Pipes (4th ed.). UK: Pergamon.
 
A.D. Krauss. (1982). Analysis and Evaluation of Extended Surface Thermal Systems. Washington, D.C.: Hemisphere Publishing Co.  
 
F. Kreith. (2000). The CRC Handbook of Thermal Engineering. New York: CRC Press.  
 
Y.S. Touloukian & C.Y. Ho. (1970). Thermophysical Properties of Matter: Thermal Conductivity (Vol. 1). New York: Plenum Publishing Co.