Many people now think that the three-bladed rotor blower has one more leaf than the two-bladed rotor Roots blower and simply believes that the two-bladed rotor blower has a larger exhaust volume than the three-bladed blower under the same center-to-circle radius Great, this is a wrong view.
For involute impellers, since the area utilization coefficient is not related to the number of impeller heads, that is, when involute impellers are used, the displacement of the two- and three-leaf roots blowers is the same when the main parameters are the same. identical.
Comparison of noise and vibration
In the working process of Roots blowers, the gas countercurrent compression generates strong air impact dynamic noise. In order to reduce this noise, the volume of a single effective volume V is reduced without changing the entire effective volume, thereby reducing the Holmheim resonance To achieve the purpose of reducing noise. Changing the two-leaf type into the three-leaf type, thereby changing the effective volume from two equal parts to three equal parts, reducing the pulsation of the output air pressure, and reducing the volume of the gas returned to the intake chamber through the impeller gap. The disturbance of the gas is reduced and the pulsating pressure of the gas is reduced, so that the vibration of the blower is reduced. Pressure pulsation is the main noise source of Roots blowers. Three-lobe blowers can effectively reduce noise by 5dB.
Comparison of internal leaks
When the gap size and working conditions are the same, the internal leakage flow of the three-leaf blower is often smaller than that of the two-leaf. The element volume V is located between the leakage gap and the air inlet, and has a certain blocking effect on the internal leakage flow. For a two-bladed blower, the volume V remains closed within a small angular range, and the barrier effect is not great. The basic volume of the three-leaf blower has a closed rotation process of at least 60 °, and the blocking effect is significant, which can improve the volumetric efficiency of the blower. A three-blade rotor and a counter-current cooling blower are used. The gas in the enclosed volume is at the intermediate pressure of suction and exhaust. In this way, the leakage through the top and end surfaces of the impeller is not directly from the exhaust pressure to the suction pressure. For a three-blade twisted-blade rotor, when the exhaust ports are arranged diagonally, combined with the characteristics of the gradual meshing of the twisted-blade rotor, the twisted-blade rotor does not make the element volume completely communicate with the exhaust port when it works as a straight blade Before the communication with the exhaust port, the gas in the element volume can generate a certain internal compression when the rotor in the casing rotates, which is smaller than the direct leakage of the two-blade rotor under the same conditions, and the volume specific energy It is also reduced accordingly.
Comparison of rotor mechanical properties
Due to the differences in the airfoil structure of the three-blade impeller and the two-blade, in general, the mechanical properties of the three-blade rotor are better than those of the two-blade. With the same impeller size and gas pressure difference, the maximum resultant force of the three-blade rotor is smaller than that of the two-blade rotor, which is about 80% of the two-blade rotor. The structure of the three-blade rotor is more rigid than the two-blade rotor. And, with the same center distance, impeller radius, and impeller length, and the same materials are used, the quality of the third leaf is slightly lighter than that of the second leaf. Therefore, the three-blade rotor has more advantages in ensuring the clearance between the impeller and the casing and the clearance between the impellers.