"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 For each "220V Cooling Fan", all with the increase in traffic efficiency are first increased then decreased. When the flow is less than 0.006 cubic meters per second, the blade 5 and 6 of these two cooling fans than the other two models is high, this is because the small number of blades, less gas flowing, "220V Cooling Fan" The total pressure is low, thus resulting in less efficient: When an increase in the number of blades, the increased generation of eddy currents. Causing the blade lift coefficient decreased, so that the flow path within the flow losses rise rapidly decreased efficiency.