外文翻译--离心风机-精品.doc

Centrifugal fan A centrifugal fan (also squirrel-cage fan, as it looks like a hamster wheel) is a mechanical device for moving air or gases. It has a fan wheel composed of a number of fan blades, or ribs, mounted around a hub. As shown in Figure 1, the hub turns on a driveshaft that passes through the fan housing. The gas enters from the side of the fan wheel, turns 90 degrees and accelerates due to centrifugal force as it flows over the fan blades and exits the fan housing.[1] Figure 1 Centrifugal fans can generate pressure rises in the gas stream. Accordingly, they are well-suited for industrial processes and air pollution control systems. They are also common in central heating/cooling systems. 1. Fan components The major components of a typical centrifugal fan include the fan wheel, fan housing, drive mechanism, and inlet and/or outlet dampers. 2. Types of drive mechanisms The fan drive determines the speed of the fan wheel (impeller) and the extent to which this speed can be varied. There are three basic types of fan drives.[1] 2.1Direct drive The fan wheel can be linked directly to the shaft of an electric motor. This means that the fan wheel speed is identical to the motors rotational speed. With this type of fan drive mechanism, the fan speed cannot be varied unless the motor speed is adjustable. 2.2.1 Belt drive Figure 2: Centrifugal fan with a belt drive Belt driven fans use multiple belts that rotate in a set of sheaves mounted on the motor shaft and the fan wheel shaft. This type of drive mechanism is depicted in figure 2. The belts transmit the mechanical energy from the motor to the fan. The fan wheel speed depends upon the ratio of the diameter of the motor sheave to the diameter of the fan wheel sheave and can be obtained from this equation:[1] where: ? rpmfan = fan wheel speed, revolutions per minute rpmmotor = motor nameplate speed, revolutions per minute Dmotor = diameter of the motor sheav