XinFeng Classroom | Ventilator Series: Centrifugal Fan Selection Considerations Expansion Department, XinFeng Ventilators December 26, 2023, 7:00 PM

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Centrifugal Fan

       Centrifugal fans are mechanical devices that convert electrical energy into mechanical energy. They utilize the pressure differential created by rotating blades to draw in and expel fluids. These fans are widely used in workshops, coal mines, power generation facilities, and buildings.

 Selecting the correct and appropriate centrifugal fan is a crucial step in ensuring the normal and economical operation of ventilation and pneumatic conveying network systems. How should one choose the right centrifugal fan?

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Principles for Selecting Fans

    1. The operating point of the fan must be within the high-efficiency zone     When selecting a fan, the primary requirement is that its air volume and pressure meet the ventilation network's specifications. Additionally, its operating point should fall within the optimal efficiency or economical operating range, meaning the efficiency at the operating point should not be less than 90% of the maximum efficiency.

2. Ventilators must exhibit excellent regulation performance. For ventilation and dust removal networks, a relatively flat fan performance curve is required; however, for pneumatic conveying networks, a steeper curve is preferable. This is because in pneumatic conveying systems, when material flow rates change during operation, network resistance also fluctuates significantly. Only ventilators with steep performance curves can maintain stable airflow output despite resistance variations.

3. The motors equipped with ventilators are not prone to overload. Fans with backward-curved blades do not overload because their maximum power occurs at the rated airflow. For forward-curved and radial-bladed fans, power consumption increases linearly with airflow volume, accelerating at an increasingly rapid rate. Therefore, when selecting forward-curved fans for pneumatic conveying systems, special attention must be paid to prevent empty-running of material pipes when dampers are open, as this poses a risk of motor overload. 4. Ventilators must accommodate the properties of conveyed gases     Different fan types are required for conveying air with varying properties. For instance, when air contains exceptionally high dust concentrations, dust extraction fans with wear-resistant blades that resist dust accumulation should be selected. When pairing fans with dryers, high-temperature-resistant fans must be chosen.

5. Ventilators must meet environmental protection requirements and operate at low noise levels. Under identical conditions, low-noise ventilators should be prioritized. Generally, peak noise frequency is proportional to fan rotational speed. Therefore, while meeting network pressure and flow requirements, low-speed ventilators should be used whenever possible. Typically, fan rotational speeds should not exceed 3000 r/min.

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Steps for Fan Selection

     1. Design Matching

     Equipment serves the process. Before selecting suitable centrifugal fans, calculate the actual air pressure H`T required by the conveying system using Bernoulli's equation based on pipeline layout and process requirements. Then convert this value to the experimental air pressure HT using conversion formulas.

2. Selection-Based Type     After determining the required airflow range for the selected process design, the fan type should be further specified based on the properties of the conveyed gas (e.g., clean air, flammable, explosive, or corrosive gases, and dust-laden gases) and the required pressure range.

3. Model Identification

     Centrifugal fan model codes typically consist of six components: name, model, size, drive type, rotation direction, and discharge position. Understanding the model allows for quick assessment of a centrifugal fan's fundamental performance characteristics. (Click here for details)

4. Design Calculation After determining the appropriate centrifugal fan model, the shaft power must be calculated based on the experimental static pressure HT and the required actual airflow (calculated at the fan inlet condition). This calculation should be performed using the performance table or characteristic curve provided in the fan catalog.