The axial flow fan blade curvature in a certain range, the greater curvature of the blade, the same speed, the gas kinetic energy is bigger, the air volume and pressure increased; at the same time, the blade force is greater, the greater the torque motor. When the camber / chord ratio exceeds 0.1, the lift coefficient will no longer increase linearly, so the "range" of 0.05< / <0.1 arc height chord.
Axial fan blade angle: the greater the tilt angle, the greater the pressure difference between the upper and lower surfaces of the blade, the greater the wind pressure at the same speed; but the upper surface pressure is too large, may produce reflux phenomenon, but reduce the fan performance. Therefore, the blade inclination should also be increased to a certain extent.
The axial flow fan blade pitch: the distance between the blade is too small, will cause the airflow disturbance, increase the friction of the blade surface, reducing the efficiency of the fan blade; the distance is too large, it will lead to insufficient air pressure and pressure loss increases.
Number of blades: cross section curves and inclination angles of fan blades of various specifications, the width of each blade often depends on the height of fan blade. In order to ensure that the blade spacing is not too large and the wind pressure is affected, the fans with smaller diameter are more compensated by increasing the number of blades. Whether the number of blades is much less, the number of blade axial fan is always 3, 7, 11 odd, this is because if the even shape symmetrical blades, and no adjustment of balance, it is easy to make the system resonance occurs, if the blade material is unable to resist fatigue due to vibration, will make the blade or the spindle is broken, so the odd fan blade design on asymmetric multi axis design. This principle applies to a wide range of fan blades, including some helicopter propellers.
Blade clearance: how to adjust the clearance between the fan blade and the outer frame is a difficult problem in the fan design. The gap is too small will make the air flow and the blade frame, friction, increase the noise; increase the gap is due to the influence of airflow flyback ear low fan efficiency -- the gap increases 1%, while the total pressure power decreased by about 2%.
Blade curvature: the fan blade does not extend straight along the radial direction in addition to a certain curvature in the plane, but is slightly curved in the direction of rotation, showing a certain radian. If the leaves along the radial straight stretch, driven by the rotation of the fan airflow in the air outlet side will be scattered, blowing distance is short, and "power" is not centralized; if the current version of a product radian, can ensure the blowing airflow concentrated in the cylindrical space in front of the air outlet, increasing air and distance air pressure.
Spindle diameter: as a result of the existence of motor and bearing, the main part of the main shaft of the axial fan must have no blind area through which the air flow passes, and the diameter of the main shaft determines the size of the blind area. The motor shaft diameter mainly depends on the fan motor power -- power to the stator windings larger, will occupy more space, not in the longitudinal expansion of the case, I had lateral extension.
Leaf smoothness: This is an indicator of non design factors that basically depend on the producer's die forming and finishing processes. Outside the design curve, unevenness on the blade causes turbulence in the rotation, increases friction, reduces fan efficiency, fan performance, and increases work noise. Therefore, the smoothness of the blade surface should be strictly controlled, and if the purchased products are not handled properly, the subsequent test should be compensated by hand grinding and other follow-up methods.