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Axial Fan Performance Impact

Nov 02, 2017

The radial clearance of the axial fan is the gap between the blade tip and the inner wall of the casing, and the axial gap refers to the gap between the two blades of the impeller. The size of the two gaps has an impact on the performance of the fan.

Axial fan radial clearance is too large, negative pressure is high, it is bound to cause the blade tip and the chassis gap on both sides of the larger pressure difference, the pressure difference is the main reason for axial leakage. Leakage and leaves were withdrawn, discharged to the atmosphere, forming a "circulating air", this part of the air power is consumed in vain, so the fan efficiency.

The rotor tells the rotor that the air is advancing in the axial direction, because the air itself has the weight and moisture contained in the air and the dust particles are told to rotate the blades around the air, the air is densely packed near the case, The anterior spiral flow increases the airflow density and the negative pressure in the radial direction. In this case, the radial gap is too large to change back along the gap around the casing to produce a large number of cylindrical air flow in the axial reverse flow, with the normal air flow impact, so that the air flow in vain, thereby reducing efficiency The

When designing an axial fan, maintain a certain axial clearance between the cascades, mainly to ensure that the subsequent cascade has a uniform intake, to eliminate the impact between each other, otherwise it will worsen the respective working conditions. Uneven airflow may act as a vibration source, causing subsequent blade vibrations. On the contrary, the axial clearance is too large, will make the axial size is too long. Therefore, the size of the axial gap on the fan noise, vibration and axial size have an impact.

Single-stage axial fan-level in the form of the following:

Single stage impeller grade

Level only impeller, which is characterized by lower pressure and efficiency. Since there is no rear deflector, the part of the kinetic energy for the speed of the outlet of the ventilator is not utilized and lost in vain. Single-stage fan full-pressure coefficient is small, but the structure is simple, easy to manufacture, mainly for low pressure and low power consumption of low-pressure axial fan, its specific speed range is usually 205-490. The wheel hub is also smaller than usual.

2. Impeller + rear deflector and

The ventilator is equipped with a rear deflector at the rear end of the impeller, which is intended to be able to partially or even use the impeller outlet to rotate east to improve the pressure of the ventilator and to increase the efficiency of the ventilator accordingly. It is characterized by a large single-stage full-pressure coefficient, generally 0.15-0.72; high efficiency, so this level in the axial fan is widely used. This type of axial flow fan speed is usually 90-305. Ventilator can be in the case of downtime or operation, with the change in the impeller blade installation angle of the adjustment of the working conditions.

3. Front deflector + impeller grade

The ventilator has a blade mounting angle adjustable and fixed front deflector at the front of the impeller. So that a negative winding speed is generated before the impeller inlet, and the winding speed of the airflow at the impeller outlet is zero. As the front deflector deteriorates the velocity field and pressure field of the impeller inlet airflow and increases the average relative velocity of the impeller, the fan loss increases and the efficiency decreases. In addition, this type of axial fan noise has also increased.

4. Front deflector + impeller + rear deflector

This type of axial fan has its front deflector blade mounting angle designed to be adjustable. This type of fan is characterized by: high pressure, the single-stage fan full pressure coefficient is small, about 0.33-0.84; pre-flow regulator structure is simple, easy to adjust, easy to automate, and can change Impeller blade installation angle combined to adjust to improve the operation of the fan economy. The drawback is: fan machine axial size is relatively large, the noise should be larger.