外文翻译--离心风机-精品(共8页)

1、Centrifugal fanA centrifugal fan (also squirrel-cage fan, as it looks like a HYPERLINK /wiki/Hamster_wheel o Hamster wheel hamster wheel) is a mechanical device for moving HYPERLINK /wiki/Air o Air air or HYPERLINK /wiki/Gas o Gas gases. It has a HYPERLINK /wiki/Fan_(mechanical) o Fan (mechanical) f

2、an HYPERLINK /wiki/Wheel o Wheel wheel composed of a number of fan HYPERLINK /wiki/Blade o Blade blades, or HYPERLINK /wiki/Ribs o Ribs ribs, mounted around a hub. As shown in Figure 1, the hub turns on a HYPERLINK /wiki/Driveshaft o Driveshaft driveshaft that passes through the fan housing. The gas

3、 enters from the side of the fan HYPERLINK /wiki/Wheel o Wheel wheel, turns 90 degrees and HYPERLINK /wiki/Accelerate o Accelerate accelerates due to HYPERLINK /wiki/Centrifugal_force o Centrifugal force centrifugal force as it flows over the fan blades and exits the fan housing. HYPERLINK /wiki/Cen

4、trifugal_fan l cite_note-EPA-0#cite_note-EPA-0 1 Figure 1Centrifugal fans can generate pressure rises in the gas stream. Accordingly, they are well-suited for HYPERLINK /wiki/Industry o Industry industrial processes and HYPERLINK /wiki/Air_pollution o Air pollution air pollution control systems. The

5、y are also common in central heating/cooling systems.1. Fan componentsThe major components of a typical centrifugal fan include the fan wheel, fan housing, drive mechanism, and inlet and/or outlet HYPERLINK /wiki/Damper o Damper dampers.2. Types of drive mechanismsThe fan drive determines the speed

6、of the fan wheel (impeller) and the extent to which this speed can be varied. There are three basic types of fan drives. HYPERLINK /wiki/Centrifugal_fan l cite_note-EPA-0#cite_note-EPA-0 12.1Direct driveThe fan wheel can be linked directly to the shaft of an HYPERLINK /wiki/Electric_motor o Electric

7、 motor electric motor. This means that the fan wheel speed is identical to the motors HYPERLINK /wiki/Rotation o Rotation 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 bel

8、t driveBelt driven fans use multiple belts that rotate in a set of HYPERLINK /wiki/Sheave o Sheave 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 d

9、epends upon the HYPERLINK /wiki/Ratio o Ratio ratio of the diameter of the motor sheave to the diameter of the fan wheel sheave and can be obtained from this equation: HYPERLINK /wiki/Centrifugal_fan l cite_note-EPA-0#cite_note-EPA-0 1 where:rpmfan= fan wheel speed, revolutions per minuterpmmotor= m

10、otor nameplate speed, revolutions per minuteDmotor= diameter of the motor sheaveDfan= diameter of the fan wheel sheaveFan 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).2.2Variable driveVaria

11、ble drive fans use HYPERLINK /wiki/Hydraulic o Hydraulic hydraulic or HYPERLINK /wiki/Magnetic o Magnetic 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 HY

12、PERLINK /wiki/Automate o Automate automated systems to maintain the desired fan wheel speed. HYPERLINK /wiki/Centrifugal_fan l cite_note-EPA-0#cite_note-EPA-0 1An alternate method of varying the fan speed is by use of an electronic variable-speed drive which controls the speed of the motor driving t

13、he fan. This offers better overall energy efficiency at reduced speeds than mechanical couplings.2.3 Fan dampersFan 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

14、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 due to their ability to affect the airflow pattern into the fan. HYPERLINK /wiki/Centrifugal_fan

15、l cite_note-EPA-0#cite_note-EPA-0 13. Backward-curved bladesBackward-curved blades, as in Figure 3(b), use blades that curve against the direction of the fan wheels rotation. The backward curvature mimics that of an airfoil cross section and provides good operating efficiency with relatively economi

16、cal construction techniques. These types of fan wheels are used in fans designed to handle gas streams with low to moderate particulate loadings. They can be easily fitted with wear protection but certain blade curvatures can be prone to solids build-up.Backward curved fans can have a high range of

17、specific speeds but are most often used for medium specific speed applications- high pressure, medium flow applications.Backward-curved fans are much more energy efficient than radial blade fans and so, for high horsepower applications may be a suitable alternative to the lower cost radial bladed fa

18、n.4. Straight radial bladesRadial fan blades, as in Figure 3(c), extend straight out from the hub. A radial blade fan wheel is often used on particulate-laden gas streams because it is the least sensitive to solids build-up on the blades, but it is often characterized by greater noise output. High s

19、peeds, low volumes, and high pressures are common with radial fans, and are often used in HYPERLINK /wiki/Vacuum_cleaner o Vacuum cleaner vacuum cleaners, pneumatic material conveying systems, and similar processes. Figure 35. Centrifugal fan ratingsRatings found in centrifugal fan performance table

20、s and curves are based on standard air SCFM. Fan manufacturers define standard air as clean, dry air with a density of 0.075 pounds mass per cubic foot (1.2kg/m), with the barometric pressure at sea level of 29.92 inches of mercury (101.325kPa) and a temperature of 70F (21C). Selecting a centrifugal

21、 fan to operate at conditions other than standard air requires adjustment to both static pressure and brake horsepower. The volume of air will not be affected in a given system because a fan will move the same amount of air regardless of the air density.If a centrifugal fan is to operate at a non-st

22、andard density, then corrections must be made to static pressure and brake horsepower. At higher than standard elevation (sea level) and higher than standard temperature, air density is lower than standard density. Centrifugal fans that are specified for continuous operation at higher temperatures n

23、eed to be selected taking into account air density corrections. Again, a centrifugal fan is a constant volume device that will move the same amount of air at two different temperatures.If, for example, a centrifugal fan moves 1,000 ft/min (28 m/min) at 70 F (21 C) it will also move 1,000 ft/min (28

24、m/min) at 200 F (93 C). Centrifugal fan air volume delivered by the centrifugal fan is not affected by density. However, since the 200 F (93 C) air weighs much less than the 70 F (21 C) air, the centrifugal fan will create less static pressure and will require less brake horsepower. Selecting a cent

25、rifugal fan to operate at conditions other than standard air requires adjustment to both static pressure and power. When a centrifugal fan is specified for a given CFM and static pressure at conditions other than standard, an air density correction factor must be applied to select the proper size fa

26、n to meet the new condition. Since 200 F (93 C) air weighs only 80% of 70 F (21 C) air, the centrifugal fan will create less pressure. To get the actual pressure required at 200 F (93 C), the designer would have to multiply the pressure at standard conditions by an air density correction factor of 1

27、.25 (i.e., 1.0 / 0.8) to get the system to operate correctly. To get the actual power at 200 F (93 C), the designer would have to divide the power at standard conditions by the air density correction factor.离心(lxn)风机离心风机(fn j)（也鼠笼式风扇，因为它看起来像仓鼠轮）是一种机械装置移动空气或气体。它有一个风扇轮组成若干风扇叶片，或肋骨，装在一个枢纽。如图1所示，该中心将在驱动

28、轴，穿越风扇住房。气体进入从侧面的风扇方向盘，把90度，并加快由于离心力因为它流动的风扇叶片和出口风扇住房。 1 离心式风机可产生压力上升(shngshng)气流。因此，他们非常适合工业加工和空气污染控制系统。他们还共同在中央供暖/冷却系统。 图11.风机组件主要组成部分典型的离心式风机包括风扇轮，风扇住房，驱动机制，进口和/或出口闸。 2类型的驱动机制 风扇驱动器决定的速度，风扇轮（叶轮）以及在何种程度上这样的速度可以多种多样。有三种基本类型的风机驱动器。 1 2.1直接驱动 风扇轮可以直接联系的骨干一个电动马达。这意味着，风扇轮速是相同的电机转速。这种类型的风机驱动机制，风扇转速不能更改，

29、除非是可调的电机转速。 2.1.1带传动图2 ：离心风机用皮带驱动风扇driveBelt使用多重皮带旋转的一套滑轮安装在电机(dinj)轴和风扇轮轴。 这种类型的驱动机制是描绘在图2 。皮带传递机械能的电机风扇。 风扇轮速取决于比例的直径电机(dinj)带轮的直径风扇轮轮和可从该方程： 1 其中(qzhng)： rpmfan =范轮速，每分钟的革命rpmmotor =电机铭牌速度，每分钟的革命Dmotor =直径电机轮Dfan =直径风扇轮轮范车轮速度皮带驱动风扇是固定的，除非带滑。带滑移可以降低风扇轮速几百革命每分钟（每分钟转速）。 图22.2.变频驱动器 可变液压驱动风扇使用或磁性联轴器（

30、范之间轮轴与电机轴） ，使控制风扇轮速独立的电机转速。该风扇转速控制常常被纳入自动化系统，以保持理想风扇轮速。 1 替代的方法不同的风扇速度是使用电子变速驱动器的速度控制的电机驱动风扇。这提供了更好的整体能源使用效率，同时降低速度比机械联轴器。 2.3范减震器范减震器是用来控制气体流量流入和流出的离心式风机。他们可能会被安装在入口旁或出口一侧的风扇，或两者兼而有之。阻尼器的出口方面实行流动阻力，用于控制气流。阻尼器的进气口一侧的目的是控制气体流量和改变气体进入风机轮。 范进闸减少能源使用量，由于他们有能力影响气流的模式风扇。 1 3.向后弯曲叶片后向弯曲的刀片，在图3 （ b ） ，使用该曲线对叶片的方向风扇轮的自转。落后的曲率模仿(mfng)的翼型截面，并提供良好的运营效率相对经济的施工技术。这些类型的风机轮毂中使用的风扇设计来处理天然气流与低到中等颗粒负荷。他们可以很容易地安装的抗磨损保护，但某些刀片曲率可以容易固体建设。 向后弯曲的球迷可以有很高的一系列具体的速度，但往往是用于具体的高速应用中-高压力，