The centrifugal fan is based on the principle that kinetic energy is converted into potential energy. The high-speed rotating impeller accelerates the gas, then decelerates and changes the flow direction, so that the kinetic energy is converted into potential energy (pressure). In a single-stage centrifugal fan, gas enters the impeller from the axial direction, the gas changes to radial direction as it flows through the impeller, and then enters the diffuser. In the diffuser, the gas changes the direction of flow and the cross-sectional area of the pipe increases to slow the flow. This deceleration converts kinetic energy into pressure energy. The increase in pressure mainly occurs in the impeller, followed by the expansion process. In a multistage centrifugal fan, a return flow is used to direct the gas flow to the next impeller, resulting in higher pressure.
The working principle of the centrifugal fan is basically the same as that of the turbo compressor, because the gas flow rate is low and the pressure does not change much. Generally, it is not necessary to consider the change of the specific volume of the gas, that is, the gas is treated as an incompressible fluid.
Centrifugal fans are available in both right-handed and left-handed versions. Front view from the side of the motor: the impeller rotates clockwise, called the right rotary fan; the impeller rotates counterclockwise, called the left rotary fan. Used in cooling towers.