A cutaway diagram showing a heat pipe and how it works.

A heat pipe uses a hollow receptacle (metal pipe) to transport heat directly from one point to another. The metal pipe is filled with fluid, 90 percent of which is distilled water; the remainder consists of special ingredients added to optimize the liquid's thermal transfer properties. Here's how it works: the liquid is subjected to a very low pressure, reducing the evaporation point to approximately 30 degrees Celsius. When cold, the pipe contains very little water. However, when the heat pipe contacts the CPU directly on one end, the water evaporates and transports the thermal energy to the cold end of the pipe.

The difference in temperature between the two end depends on the fluid used and the length of the heat pipe. On average, though, the difference amounts to about eight degrees. One important factor impacting efficiency is the position of the pipe when it is installed - the end dissipating heat must always be placed higher than the one collecting heat from the CPU. A heat pipe works best when placed in a perfectly vertical position. The heat pipe Shuttle installs in its mini PCs is up to 95 percent efficient - the heat-absorbing and heat-dissipating ends are perpendicular to each other at different heights.

How a heat pipe works.