"220V Cooling Fan" leaf number and spacing of the blades have opposing relationship, the more the number of blades, blade pitch to be reduced, so that the increase in the number of blades left to narrow, in addition to increased friction, the blades each other more obvious influence of interference ??? So the turbulence will also rise, while the spacing between them is the noise of the fan blade aerodynamics and "220V Cooling Fan" the impact, blade pitch is too small, it increases the chance of friction surface of the blade, resulting in fan efficiency reduce, relative blade spacing is too large, the separation phenomenon is the pressure loss becomes large. Efficiency of several cooling fan model is very close, so, in this little traffic. Found that "220V Cooling Fan" leaf number 7 best static characteristics. When the flow is greater than 0.008 cubic meters per second, the opposite is true, then the efficiency of the leaf number 7 and 4, 5 and 6 is greater than efficiency. This is because the total pressure efficiency related, in this flow, the total pressure of 4 7 and higher, and therefore high efficiency.