As the density of transistors in a microprocessor increases, the amount of heat disipated increases. A Pentium 4 processor (180 nm running at 2GHz) disipates, 55 Watts of power as heat. Its area is just 131 mm2. This gives a 55 W/(131/(102)) = 42 W cm-2. In comparison a steam iron is 5 Wcm-2.
One solution is the heat pipe. As its name suggests, it transfers heat from high temperature regions to lower temperature regions where there is more space for heat sinks or cooling fans.
Inside a heatpipe
Although it just looks like a sealed metal pipe, there is a wick or porous material and a liquid with a high latent heat of vaporization. When the pipe is heated the liquid uses the heat to evaporate and changes into a gas, the gas moves to a colder region of the heat pipe where is condenses and uses the latent heat to change back into a liquid. Heat pipes are a reliable and cost effective solution for laptop computers where fans would reduce battery life.
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