pumps, fans, compressors, water turbines, etc. all belong to fluid machinery. The so-called fluid machinery refers to machinery that uses fluid as working medium to convert energy, that is, machinery that converts energy between mechanical energy possessed by fluid and work done by machinery. Fan is a kind of fluid machinery that converts the work done by the prime mover into the pressure potential energy and kinetic energy of the transported fluid, and the one that transports the liquid is called pump; Those who transport gas are called fans. Generally speaking, a Fan is a rotating shaft equipped with two or more blades to push the airflow. The blades convert the rotating mechanical energy applied to the shaft into an increase in pressure to push the airflow, and this conversion is accompanied by the movement of the fluid. The use of fans can be roughly divided into two categories: civil ventilation and air exchange, which is used to ventilate the inside and outside of civil public buildings, to send fresh air into the buildings (air supply fans) or to exhaust the dirty old air in the buildings to the outside, and at the same time, a separate preset air inlet is responsible for compensating the fresh air (air exhaust fans). For example, ventilation in venues, cinemas, commercial buildings, culverts, tunnels and other occasions are all necessary auxiliary functions, which are currently realized by fans; Ordinary smoke exhaust is used to remove cooking fumes in public dining places (smoke exhaust fans), such as Infineon CUS series fans used in McDonald's, which are typical cases of such fans.