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Selection of roots blower, standard air volume formula for calculating the air volume of roots blower, how to measure the actual air volume?

Source: Roots blower manufacturer Published on: February 15, 2022 Hits:

Roots blower is a type of displacement fan. There are two three blade impellers that rotate relatively in the space sealed by the casing and wall panel. Since each impeller is involute or the envelope of the epicycloid, the three blades of each impeller are identical, and the two impeller are also identical, which greatly reduces the processing difficulty. Numerical control equipment is used during impeller processing to ensure that a certain minimum clearance can be maintained no matter where the two impellers rotate, under the condition that the center distance between the two impellers is constant, so as to ensure that the gas leakage is within the allowable range.

The two impellers rotate in opposite directions. Because the clearance between impellers and impellers, between impellers and casings, and between impellers and wallboards is very small, a vacuum state is formed at the air inlet. The air enters the air inlet chamber under the action of atmospheric pressure. Then, two of the blades of each impeller form a sealed chamber with wallboards and casings, The sealing chamber formed by two blades is constantly taken to the exhaust chamber, and because the impellers in the exhaust chamber mesh with each other, the air between the two blades is squeezed out. In this way, the air is continuously transmitted from the air inlet to the air outlet, which is the whole working process of Roots blower.
Roots blower has high pressure compared with ordinary blower, and can maintain constant flow under the condition of large pipeline resistance, so it is widely used in sewage treatment, pneumatic conveying, ironmaking, chemical industry and other fields! However, in the application process, the air volume is sometimes insufficient. The main factors affecting the air volume are as follows.
1. There are obstacles or blockages at the inlet or outlet of the fan. At this time, the blockages should be cleared in time to keep the inlet and outlet unblocked.
2. The clearance between the impeller and the casing is too large, resulting in insufficient pressure. At this time, it is necessary to adjust the impeller clearance. If the impeller clearance is too large due to friction, it is the most effective and simple method to replace the impeller. Excessive impeller clearance will also cause the internal temperature of the fan to be too high, affecting the service life of the fan.
     

Selection of Roots blower, standard air volume formula for calculation of Roots blower air volume

3. The belt slips and the tension is insufficient. At this time, it is necessary to replace the belt, increase the belt tension, and ensure that the output power of the motor is not lost.
4. The pipeline is rusted, causing ventilation leakage. At this time, the pipeline needs to be repaired or replaced.
5. The motor has overcurrent, but the fan regulating valve has not been fully opened.
In addition, if the fan regulating valve has been fully opened, but still cannot meet the system requirements, it may be the reason for model selection, installation, or unreasonable system piping layout. Manufacturing process and level are also important reasons that affect the fan air volume. It is recommended that customers choose regular manufacturers for selection and purchase!
Air volume formula of Roots blower
The air volume of Roots blower refers to the air volume under the standard air inlet state. The so-called standard state is the temperature of 20 ℃, the pressure of 101.3kpa, and the relative humidity of 65%.
The air volume of roots blower under the reference state (temperature 0 ℃, absolute pressure 101.3kpa) is generally expressed in Nm3/min. When the inlet air pressure is the same, the following formula can be used to convert the air volume to the standard state:
Qs=QN * 1.0332 Qs: standard state air volume QN: reference state air volume
The following formula can be used to convert the air volume in the exhaust state to the air volume in the standard state
       Qs=Qd*(1.0332+Pd)/1.0332*(273+ts)/(273+td)
Qd: air volume in exhaust state (m3/min)
Pd: exhaust pressure (kpa)
Ts: inlet air temperature td: exhaust air temperature
1. The exhaust pressure of the air volume calculated from the above structure, and then the fan model, diameter, speed and required power can be calculated according to the performance table.
2. The selection range of model parameters of some fans is repeated. From the perspective of cost, it is recommended to select fans with relatively small models, and from the perspective of noise and upgrade space, it is recommended to select fans with relatively large models.
Main parameters of Roots blower
Fan diameter: 50~350A Air volume: 0.4~180m3/min Pressure: 9.8~98kpa Motor power: 0.75~350kw
I believe that after reading the above contents, you should also know the air volume formula of Roots blower. I hope it will be helpful to you.