Select a fan with a head of 2500 Pa. What will happen if the system resistance exceeds this value? !
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Two fan manufacturers have two different opinions. A said that the air volume would decrease and the motor current would also decrease. B said that if the air volume does not change much, the motor current will increase, and eventually the motor will burn out. A coupling motor. B belt motor. It was what a technician said. It was said by Business Person B. Which one is correct? !
Are you sure? The fan has a performance curve.
Based on the pipeline characteristic curve and the power curve, the flow rate will decrease, the effective power will drop slightly, and the current will also decrease slightly.
But the rated power of the motor is right there. If the current increases, doesn’t the power also increase? Power = Voltage × Current.
If the power is reduced in all cases, how can fan surge occur? !
A centrifugal fan is essentially a variable-flow, constant-pressure device. When the rotational speed is constant, the pressure-flow theoretical curve of a centrifugal fan should be a straight line. Due to internal losses, the actual characteristic curve is curved. The pressure generated in centrifugal fans is greatly affected by changes in inlet temperature or density. For a given volume of air intake, the lowest pressure is achieved at the highest intake temperature (when the air density is lowest). For a given pressure-flow characteristic curve, there is a corresponding power-flow characteristic curve. When the blower operates at a constant speed, the power required for a given flow rate increases as the intake temperature decreases.
Centrifugal fans are used when the load requires a constant pressure effect. Since centrifugal fans are constant-pressure fans, their main operating parameter is air pressure; the volume of air delivered varies with changes in the ductwork and load, while the air pressure remains relatively constant. Centrifugal fan, with low air pressure. The compression of air is usually carried out through several working impellers (or stages) under the action of centrifugal force.
Surge occurs when the flow rate decreases, causing the pressure behind the fan or pump to be lower than the pressure in the subsequent system