Heatsink Guide - The Basics of Cooling & Heatsink Technology

Radiation, as the name suggests, means that the heat is simply radiated away from the object, through electromagnetic radiation (photon transport). This effect is not bound to gas or other substances surrounding the heatsink. Radiation will even take place in a vacuum. How well an object can radiate heat depends on the material and the color (black is best). See fig. 1 for an illustration.

Conduction is the exchange of kinetic energy between molecules. Less energetic (lower temperature) particles gain kinetic energy by colliding with more energetic particles (through physical contact). Since direct contact is required, a heatsink (surrounded by air) cannot get rid of heat using conduction. However, conduction is the effect that's responsible for the heat transfer from the CPU to the heatsink.

Convection is heat transfer by movement of a heated substance (gas or liquid). This means that the heat is transferred to the molecules of the gas (or liquid) surrounding the hot object, and then transported away through movement of molecules. If the gas or liquid around the object is forced into movement (e.g. by a fan blowing air across a heatsink), then we're dealing with forced convection (see fig. 2).