The centrifugal fan is based on the principle of converting kinetic energy into potential energy, using a high-speed rotating impeller to accelerate the gas, then decelerate, change the flow direction, and convert kinetic energy into potential energy (pressure). In a single -stage centrifugal fan, the gas enters the impeller from the axial direction, changes to the radial direction when the gas 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 decelerate the gas flow. This deceleration effect converts kinetic energy into pressure energy. The increase in pressure mainly occurs in the impeller, followed by the expansion process. In a multi-stage centrifugal fan, a refluxer is used to make the air flow into the next impeller, generating higher pressure.