*Update*
Ok, so I apologize to you guys. My earlier posts were not very clear because I was confused myself. Hopefully, THIS post will clear up the distinction between what exactly is a heat pipe, and what is called a "heat pipe" by marketers but is actually not (further explanation follows).
Link #1 1: Heat Pipe Technology: Passive Heat Transfer for Greater Efficiency
http://www.thermacore.com/thermal-basics/heat-pipe-technology.aspx
"Heat pipes are the most common passive, capillary-driven of the two-phase systems." Note this manufacturer says that heat pipes have "TWO-PHASE" systems. This is important.
"Key Components of a Heat Pipe
The three major components of a heat pipe include:
A vacuum tight, sealed containment shell or vessel
Working fluid
Capillary wick structure"
OK, so in order to be a true heat pipe, it must have 3 components right? Those are: A VACUUM TIGHT, sealed containment shell. A working FLUID. And a CAPILLARY wick structure. These 3 are the components of a heat pipe.
Link #2: Passive Two-Phase Devices
http://www.thermacore.com/products/two-phase-heat-transfer-devices.aspx
Remember, Thermacore states that heat pipes are two-phase systems. So this link takes us away from the theoretical and shows us the actual two-phase heat pipe devices for sale. The one we want is under " Heat Spreader Solutions: Remote Dissipation"
"Remote heat pipe heat sinks, using cost-effective coolants like methanol or water, can move hundreds of watts of heat and stand up to extreme variations of temperature. A Thermacore remote dissipation cooling system for Navy radar cooling performed successfully after 200 cycles between -40° C and 70° C, and its simple, rugged construction stood up to heavy shock tests without faltering."
So this heat pipe is used in Navy radar cooling, stands up to hundreds of watts in extreme variations in temperature.
Link #3:
http://www.enertron-inc.com/enertron-products/heat-pipe-selection.php
On this page what you want to look at is "Table 1: Typical Operating Characteristics of Heat Pipes." For ranges between 5-230 degrees celsius, typically the working liquid is WATER, under a vacuum tight shell.
So what I'm getting at, is that in order to be a true heat pipe, it must be a two-phase change device, with liquid inside, and under a vacuum.
Now, the question becomes: is what cpu cooler manufacturers call a "heat pipe" a true heat pipe?
In order to be yes, it would have to contain a liquid inside. Also, I can't imagine how they would decrease the pressure inside the shell enough so that water boils around 70 celsius (70 the average temp of a processor) without having some sort of valve there, can you? So I would think it would be logical to look for some valve to "charge" the heat pipe and apply a vacuum pump, otherwise how could they apply vacuum?
Finally, lets take a closer look at some cpu coolers and what are called "heat pipes."
http://www.pcper.com/reviews/Cases-...0-HP-600W-Modular-Heat-Pipe-Cooled-PSU-Review
This is a typical marketing phrase that shows a product described as "heat pipes." The reviewer in fact makes a blatant error, in that he describes the science of "two-phase system" heat pipes, but doesn't provide any evidence that said product contains them. No liquid shown. No evident valve or any mechanism for charging or applying vacuum.
More openings:
1. Post by Phoenix: "You'll also notice there's nothing dripping out of it." Notes there is no liquid inside the pipe.
2.
http://www.frostytech.com/articleview.cfm?articleID=2616. Cuts open a Zalman "heat pipe" cooler. Note there is no liquid inside.
So, in conclusion, there is a lot of confusion surrounding the term "heat pipe" in both the enthusiast and aftermarket community. CPU coolers are called "heat pipes," but they do not contain the components of a true "two-phase change heat pipe." What they are in fact are heatsinks, which may be "pipe-shaped," or even hollow. But they are certainly not phase change, and rely on thermal conductivity instead.
Further reading on phase change cooling, the concept and implementation:
http://www.overclockers.com/build-your-own-phase-change-pc-cooling-system/