Around "220V Cooling Fan" is nothing more than a few of several factors that the main factor of voltage, current, power, speed, noise and the like. I believe that many customers want to buy low noise, large air volume of axial cooling fan, but in practice, the nominal value of the maximum wind not blowing fan heat sink to get the actual amount of wind capacity, not on behalf of ventilation ability. "220V Cooling Fan" 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 wind increases, air pressure decreases. Therefore, there must be an optimum working point operations, namely the intersection of the fan performance curve and drag the curve. In the operating point, the slope of the "220V Cooling Fan" characteristic curve is minimal, and the change of the system characteristic curve was the lowest. Note that at this time the fan static efficiency (the amount of wind power ÷ × pressure) is the best. Of course, control to this point is very difficult, no longer experience simply will not be completed.