Centrifugal fans operate based on the principle of converting kinetic energy into potential energy. They use a high-speed rotating impeller to accelerate the gas, then decelerate and change its flow direction, thereby converting kinetic energy into potential energy (pressure). In a single-stage centrifugal fan, the gas enters the impeller axially, changes to radial flow as it passes through the impeller, and then enters the diffuser. In the diffuser, the gas changes its flow direction, causing deceleration. This deceleration converts kinetic energy into pressure energy. The increase in pressure mainly occurs in the impeller, followed by the diffuser process. In a multi-stage centrifugal fan, a return vane is used to direct the airflow into the next impeller, generating higher pressure. Fans have a long history. Many years before the common era, China had already produced simple wooden windmills for grinding grain, whose working principle was basically the same as that of modern centrifugal fans.