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# Matters needing attention in selection of centrifugal Fan

May 29, 2018

Centrifugal fan selection, First of all, confirm the flow, pressure, density of the gas, these are the three elements of centrifugal fan selection process.

Flow: if the system requires the mass flow of gas, it is necessary to convert the mass flow of gas into the volume flow in the standard state of the fan. If the system requires the volume flow of the gas, the volume flow in the standard state of the fan is the same as the volume flow in the working condition.

Density: if the density is not given, it is necessary to calculate or convert the density of the operating gas according to the operating environment of the fan, such as altitude, local atmospheric pressure, working temperature, gas density.

Pressure: according to the given or calculated working condition density, the working pressure is converted into the fan standard state pressure. If the fan has 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.

The next step is to calculate the specific rotation number of the fan because the calculation of the specific rotation number is an important step in the selection process of centrifugal fan and the main basis for judging the selection of the specific model of the fan. According to the formula of calculating the performance parameters and rotational speed in the standard state of fan, different specific rotation numbers can be obtained according to different rotational speeds. The first order specific rotation number is the basis of single suction fan, and the second order specific rotation number is the basis of double suction fan

The model of centrifugal fan determines its performance curve. The performance curve is divided into dimensionality curve and dimensionless curve. The dimensionless curve is the basis for determining whether or not to meet the requirements of the scene, while the dimensionless curve is the basis for describing the characteristics of the fan, the dimensionality represents the particularity, and the dimensionless dimension represents the universality. The commonly used dimensionless parameters are flow coefficient, pressure coefficient, internal efficiency and specific rotation number. One of the factors of flow coefficient and pressure coefficient can be used as the basis for calculating the fan machine 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.

According to the calculated specific rotation number, the model of the fan is selected and the corresponding points are judged whether the fan is in the high efficiency region, for example, in the high efficiency region, the fan's machine number is preliminarily calculated according to the corresponding flow coefficient or pressure coefficient.

According to the known density, rotational speed, model and roundness of the coarse calculated fan machine number, using the drawing function of the software, the dimensional performance curve of the fan can be expressed. At the same time, the working point of the fan can be calibrated, and the dimensional performance table can also be listed. Calibrate the location of the operating point. Furthermore, the inner power of the fan can be calculated according to the actual working condition performance.

After the above three stages, centrifugal fan selection is basically over, we only need to follow the above steps to ensure that you can choose the correct fan.http://www.jnblower.com/