All electronic components generate heat during their operation. This heat increases the temperature of the components and if not dissipated at a proper rate will burn the component or reduce substantially the component's service life.
To remove the generated heat, air is generally used. The heat dissipation rate depends on air velocity, surface area in contact with the flowing air and temperature difference between air and the hot surface in contact with the air.
To generate air flow, fans or blowers are usually used with are referred to generally as air moving devices.
The fan or blower utilize a motor-rotated impeller to generate air flow at a specific range of volume and at a specific range of air pressure.
The axial fan generates a rotating cone of axially flowing air, the blower generates an airflow with a cross section in accordance with the cross section of the air outlet from the blower. Axial fans generate low pressure and high air flow while blowers generate high pressure and low air flow. The operation of air moving devices are according to their operating curves which show the pressure VS. air flow and operating laws which defines the relation between airflow and air pressure to dimensions of the air moving device, its rotating velocity and the power consumption of the motor
With airflow totally blocked air flow is zero and pressure is maximal, with free air flow into an open space without any obstacle to block the airflow the air flow is maximal and pressure is zero. In practice for an minimally packed enclosure cooled by the fan the pressure developed by the fan will be low and air volume high while for a densely packed enclosure the opposite will prevail.
In many cases the surface area of the component in contact with the air is too small to remove the generated heat at the permitted temperature difference between the component surface and the air. To increase the surface area in contact with the flowing air a heat sink is used. When the largest practical heat sink is not sufficient to cool the component at natural convection an air moving device is used in association with the heat sink. The air moving device is either remotely disposed in respect to the heat sink, such as on the enclosure wall while in other cases such as with CPU COOLERS the air moving device is mounted on the heat sink above the fins, blowing the cooling air directly on the fins and base.