"DC Fan" blower to achieve the purpose, the need for static and dynamic pressure. Total pressure and static and dynamic pressure algebra, total pressure refers to the difference between the total pressure of the fan given by the amount of increase in the total pressure, the fan between exports and imports. In practice, the nominal value of the maximum wind is not blowing the actual amount of fan heat sink obtained, air volume, ventilation does not mean that ability. Due to air flow, air flow in its path will encounter obstruct fan heat protracted sheet or element, the impedance will limit the free flow of air. That is when the air volume increases, air pressure decreases. Therefore, there must be a working optimum operating point, the intersection of the fan performance curve and drag the curve. At the operating point, the slope of the characteristic curve of the fan to a minimum, and the change of the system characteristic curve was the lowest. Note that at this time the fan static efficiency (air volume × Pressure ÷ Power consumption) is the best. Of course, sometimes in order to reduce the impedance of the system, even the choice of a smaller size fan, can achieve the same amount of wind.