What Is the Difference Between Centrifugal Fan and Radial Fan
Centrifugal and radial fans differ in blade design, airflow patterns, and applications, despite their similar appearance.
Centrifugal fans are widely used in various industrial applications for moving air or gases. To select the right centrifugal fan for a specific application, it is essential to determine the required airflow rate, typically measured in cubic feet per minute (CFM). Calculating the CFM of a centrifugal fan involves considering several factors such as the fan’s dimensions, speed, and static pressure.
Manufacturers provide performance curves for their centrifugal fans, which plot the relationship between CFM and static pressure at various fan speeds. To determine the CFM using a performance curve:
In the absence of a performance curve, you can estimate the theoretical CFM using the fan’s dimensions and speed. Use the following formula:
CFM = (π × D × W × N × C) / 4
Where:
For example, consider a centrifugal fan with a wheel diameter of 18 inches (1.5 feet), a wheel width of 6 inches (0.5 feet), and a speed of 1,750 RPM. Using a coefficient of 0.6, the estimated CFM would be:
CFM = (3.14159 × 1.5 × 0.5 × 1,750 × 0.6) / 4 ≈ 981
Keep in mind that this is a theoretical estimate, and actual CFM may vary due to factors such as static pressure and system losses.
For the most accurate determination of a centrifugal fan’s CFM, field measurements can be conducted using specialized instruments such as anemometers or pitot tubes. These devices measure air velocity at various points across the fan’s inlet or outlet, which can then be used to calculate the average velocity and CFM.
To measure CFM using an anemometer:
For example, if the average air velocity across a 2 square foot inlet is 1,200 feet per minute (FPM), the CFM would be:
CFM = 1,200 FPM × 2 ft² = 2,400 CFM