In general, firms in the cost considerations, to design "220V AC Cooling Fan" of the air volume, it is necessary to sacrifice some of the pressure. If the fan can bring a large amount of air flow, but the pressure is small, the wind not blowing the radiator at the bottom (which is why a high number of fan speed, air volume is large, but the cooling effect is not good reason), conversely, it often means big pressure on the small amount of wind, there is not enough cold air and the heat sink for heat exchange, the cooling effect will be bad. General requirements for aluminum fin heat sink fan pressure is large enough, and the copper heat sink fin fan air volume is required to be large enough; more dense fin heat sink fins less dense compared to the heat sink, the need greater pressure fan, otherwise poor flow of air between the fins, the cooling effect will be greatly reduced.