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# Selection requirements and precautions of centrifugal fan.

Jul 31, 2019

Density: if the density is not given, the density of the working gas should be calculated or converted according to the working environment of the fan, such as altitude, local atmospheric pressure, working temperature, and the standard density of the gas.

Pressure: according to the given or calculated working condition density, the working condition pressure is converted to the fan standard state pressure. If the fan brings the intake box or muffler, its pressure loss should be considered, which can be calculated or estimated, and the estimated loss is generally between 100-300pa.

Flow rate: if the system requires the mass flow rate of the gas, the gas mass flow rate needs to be converted to the volume flow rate in the standard state of the fan. If the system requires the volume flow rate of the gas, the volume flow rate in the standard state of the fan is the same as that in the working condition.

Then there is the specific rotation number of the fan, because the calculation of the specific rotation number is an important step in the process of fan selection, and it is the main basis for judging the specific model of fan selection. According to the calculation formula of the performance parameters and the specific rotation number of the rotating speed converted to the standard state of the fan, different specific revolutions can be obtained according to different rotating speed. The first order specific rotation number is the basis of the single suction fan, and the second order specific rotation number is the basis of the double suction fan.

The model of centrifugal fan determines its performance curve, which is divided into dimensional curve and dimensionless curve. Dimensionless curve is the basis for judging whether or not to meet the requirements of the field, and dimensionless curve is the basis for describing fan characteristics. Dimensionless curve represents particularity and dimensionless represents universality. The dimensionless parameters commonly used are flow coefficient, pressure coefficient, internal efficiency and specific rotation. One of the flow coefficient and pressure coefficient can be used as the basis for calculating the fan number, the specific rotation number is the basis for selecting the fan model, and the internal efficiency is the basis for judging whether the model is an efficient fan or not.

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