Tech geekery: heat pipes

For the last four years, I've been working on thermal management products - mostly materials and devices designed to keep hot things cool.  I've become familiar with heat pipes and vapor chambers and I think they're cool as hell (NPI).

There are heat pipes in most laptops these days, carrying heat from your CPU to the edge of your computer.  A heat pipe looks like a ~1/4" copper tube, maybe somewhat flattened, and it's usually attached to a solid block at one end (which sits on the heat source) and has fins on the other end to radiate the heat.  A heat pipe can conduct more heat than a piece of solid copper of the same size - but how?  Copper has the second-highest thermal conductivity of any metal!

from http://www.xoticpc.com/8800m-installation-guide-sager-notebook-np579x-a-41.html

Remember that heat is carried by convection, conduction, and radiation.  A solid chunk of copper uses conduction, but a heat pipe replaces that with convection, or more accurately, gas flow.  The heat is carried in the form of a hot wind.  The pipe does it, ingeniously, by evaporating a liquid at the hot end and allowing it to re-condense at the cold end.  The liquid is carried from the cold end back to the hot (providing more to evaporate) by a wick.  That's pretty much it:  it's a hollow tube lined with a wick, and partially filled with alcohol or water.  Hot air goes one way and liquid goes the other way, and in some cases the airflow can be supersonic!  It'll carry as much heat as you can dump into it, as long as the wick can carry the liquid back to the evaporation point.  If the evaporator dries out, though, it quits in a hurry. 

There are variations - vapor chambers for heat spreading, Variable Conductance Heat Pipes, etc.  These things are like magic, I'm just amazed that they work.