Relationship Between Air Pressure, Air Volume, Power, and Rotational Speed in Coaxial Duct Centrifugal Fans

Typically, the rotational speed of a coaxial duct centrifugal fan (usually denoted by the letter n) can be directly measured using instruments, expressed in revolutions per minute (rpm). In contrast, smaller coaxial duct centrifugal fans typically operate at higher speeds and are often directly connected to the motor. Larger coaxial duct centrifugal fans generally rotate at lower speeds and are typically belt-driven, connecting to the motor via a pulley system. This allows adjustment of the fan's rotational speed by altering the pulley diameter. This relationship can be expressed as n1/n2 = d2/d1. In this formula, n1 and n2 represent the motor speeds, while D1 and d2 denote the diameters of the fan and motor pulleys. In summary, to alter the speed of a coaxial duct centrifugal fan unit, simply modify the diameter of the pulleys on either the fan or the motor. After altering the fan speed, the fan's characteristic parameters and performance curve will correspondingly change. Furthermore, the fan possesses distinct characteristic curves for each speed state. In practice, when the speed changes, the variations in the centrifugal fan's characteristic parameters Q, H, and N can be calculated using the following formulas: Q/Q' = n/n', H/H' = (n/n')², N/N' = (n/n')³. When fan speed changes from N to air pressure, the variation is proportional to the square of the speed ratio. Force changes are proportional to the cube of the speed ratio. Therefore, when the rotational speed of a coaxial duct centrifugal fan changes, its output must be recalculated, and the original motor's overload capacity must be reevaluated. Furthermore, these performance parameters of coaxial duct centrifugal fans are not fixed; all are determined by specific internal connections.