Refrigeration Plant Operator B Practice Test

The propeller fan is not classified as a centrifugal fan because it operates on a different principle. Centrifugal fans move air by utilizing the centrifugal force generated when the fan blades rotate, effectively drawing air into the center and forcing it outwards, typically at a right angle to the intake. This design allows for high static pressure and efficient airflow in various applications.

In contrast, a propeller fan primarily relies on a direct thrust mechanism, where the blades push air in the direction of their rotation, producing a flow that is more linear than radial. This makes propeller fans suitable for applications requiring a large volume of air moved at relatively low pressure, such as ventilation systems or cooling applications, rather than the high pressure and velocity associated with centrifugal fans.

The other options—backward inclined, forward curved, and radial blade fans—are all types of centrifugal fans, as they operate on the principle of centrifugal force and involve the movement of air through a spinning action that results in an increase in air pressure. Each of these fan types has specific design features that contribute to their efficiency and application in different tasks within refrigeration and air handling systems.