离心风机的外文翻译.docx

. 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 composedof 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. 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 drivers. 2.1 Direct drive The fan wheel can be linked directly to the shaft of an electric motor. This meansthat the fan wheel speed is identical to the motor ’s 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 ;. . Belt drive 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 diameter of the motor sheave to the diameter of the fan wheel sheave and can be obtained from this equation: Where: fan wheel speed, revolutions per minute motor nameplate speed, revolutions per minute diameter of the motor sheave diameter of the fan wheel sheave Fan wheel speeds in belt-driven fans are fixed unless the belts slip. Belt slippage can reduce the fan wheel speed several hundred revolutions per minute (rpm). 2.2 Variable drive Variable drive fans use hydraulic or magnetic couplings (between the fan wheel shaft and the motor shaft) that allow control of the fan wheel speed independent of the motor speed. The fan speed controls are often integrated into automated systems to maintain the desired fan speed. An alternate method of varying fan speed is by use of an electronic variable-speed drive which controls the speed of the motor driving the fan. This offers better overall energy efficiency at reduced speeds than mechanical couplings. 2.3 Fan dampers ;. . Fan dampers are used to control gas flow into and out of the centrifugal fan. They may be installed on the inlet side or on the outlet side of the fan, or both. Dampers on the outlet side impose a flow resistance that is used to control gas flow. Dampers on the inlet side are designed to control gas flow and to change how the gas enters the fan wheel. Inlet dampers reduce fan energy usage