Active heat-sink:

For most electronics projects that require some form of cooling we make use of the classic heat-sink which employs the principle of passive or natural convection. In today's computers, the processor is cooled by means of a heat-sink which uses active convection. By adding a miniature ventilator, such a processor heat-sink achieves a thermal resistance which is very low relative to its size. This article shows how a lowcost CPU cooler may be used for different applications, and how its thermal resistance may be measured empirically.