Fan is widely used in civil and industrial buildings. It is a kind of machinery which uses the interaction of rotating blade and gas to compress and transfer gas.
Fans can be divided into different categories according to different classification criteria. The following is a brief introduction to the smoke control system in the common several fans.
When the air is inhaled from the axial inlet of the fan and enters the impeller by 90 °turn, the gas in the clearance of the impeller is rotated and the centrifugal force is obtained. The gas moves towards the shell because of the centrifugal force and produces a certain positive pressure. From the volute gathering and leading along the tangential direction to the exhaust outlet, the impeller forms a negative pressure due to the departure of the gas, so that the gas is continuously sucked in by the air inlet in the axial direction, thus forming the continuous suction and pressure of the gas. The flow process of expulsion.
Low pressure centrifugal fan: total pressure not exceeding 1000pa
Medium pressure centrifugal fan: total pressure between 1000-3000pa
High pressure centrifugal fan: total pressure greater than 3000pa
Axial flow fan
The blades of the axial flow fan are installed on the rotating hub. When the impeller is driven by the motor, the airflow is inhaled from the axial direction, the gas is pushed by the blade and the pressure is increased, and the axial flow is formed, because the direction of the air flow in the fan is always along the axial direction. So called axial flow fan.
Low pressure axial fan: full pressure less than 500pa
High pressure axial flow fan: full pressure not less than 500pa
Mixed flow fan
The shape of the mixed flow fan (also known as the inclined flow fan), the structure of which is between the centrifugal fan and the axial fan, is the fan between the axial fan and the centrifugal fan, and the high speed rotation of the impeller of the inclined flow fan allows the air to be centrifuged. The axial movement, that is, the centrifugal force of centrifugal fan and the lifting force of axial flow fan, are produced. The movement of air in the casing mixes the axial flow and centrifugal motion.
Comparison of centrifugal fan , axial flow fan and mixed flow fan ( equivalent external dimension , rotating speed ) :
1)Pressure: centrifugal fan > mixed fan > axial fan
2)Air volume: centrifugal fan < mixed fan < axial fan
Low pressure centrifugal fan, medium pressure centrifugal fan, axial flow fan or mixed flow fan are generally used in smoke control system.
The exhaust fan of smoke exhaust system generally adopts centrifugal fan, axial flow fan or mixed flow fan.
The difference between the exhaust fan and the pressurized fan is that the exhaust fan should be able to work continuously for 30 min under 280 °ambient conditions.http://www.jnblower.com/