離心風(fēng)機(jī)英文文獻(xiàn)

1、wordCentrifugal fanA 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 throug

2、h 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 1Centrifugal fans can generate pressure rises in the gas stream. Accordingly, they are well-suited for indust

3、rial processes and air pollution control systems. They 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 dampers.2. Types of drive mechanismsThe fan drive

4、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.12.1Direct driveThe fan wheel can be linked directly to the shaft of an electric motor. This means that the fan wheel speed is identical to the motor's rot

5、ational speed. With this type of fan drive mechanism, the fan speed cannot be varied unless the motor speed is adjustable. Belt drive Figure 2: Centrifugal fan with a belt driveBelt driven fans use multiple belts that rotate in a set of sheaves mounted on the motor shaft and the fan wheel shaft.This

6、 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

7、 wheel speed, revolutions per minuterpmmotor= motor 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 revo

8、lutions per minute (rpm).2.2Variable driveVariable 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

9、 the desired fan wheel speed.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 the fan. This offers better overall energy efficiency at reduced speeds than mechanical couplings.2.3 Fan dampersFan dampers are us

10、ed 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 chang

11、e 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.13. Backward-curved bladesBackward-curved blades, as in Figure 3(b), use blades that curve against the direction of the fan wheel's rotation. The backward curv

12、ature mimics that of an airfoil cross section and provides good operating efficiency with relatively economical 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

13、 but certain blade curvatures can be prone to solids build-up.Backward curved fans can have a high range of 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 fa

14、ns and so, for high horsepower applications may be a suitable alternative to the lower cost radial bladed fan.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 lea

15、st sensitive to solids build-up on the blades, but it is often characterized by greater noise output. High speeds, low volumes, and high pressures are common with radial fans, and are often used in vacuum cleaners, pneumatic material conveying systems, and similar processes. Figure 35. Centrifugal f

16、an ratingsRatings found in centrifugal fan performance tables 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/m³), with the barometric pressure at sea level of 29.92 inches of mercury (1

17、01.325kPa) and a temperature of 70°F (21°C). Selecting a centrifugal 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 ai

18、r regardless of the air density.If a centrifugal fan is to operate at a non-standard 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. Centrif

19、ugal fans that are specified for continuous operation at higher temperatures need 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 mo

20、ves 1,000 ft³/min (28 m³/min) at 70 °F (21 °C) it will also move 1,000 ft³/min (28 m³/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 le

21、ss than the 70 °F (21 °C) air, the centrifugal fan will create less static pressure and will require less brake horsepower. Selecting a centrifugal fan to operate at conditions other than standard air requires adjustment to both static pressure and power. When a centrifugal fan is specifie

22、d 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 fan 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 p

23、ressure. 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 1.25 (i.e., 1.0 / 0.8) to get the system to operate correctly. To get the actual power at 200 °F (93 °C),

24、 the designer would have to divide the power at standard conditions by the air density correction factor.離心風(fēng)機(jī)離心風(fēng)機(jī)也鼠籠式風(fēng)扇，因?yàn)樗雌饋硐駛}鼠輪是一種機(jī)械裝置移動(dòng)空氣或氣體。它有一個(gè)風(fēng)扇輪組成假設(shè)干風(fēng)扇葉片，或肋骨，裝在一個(gè)樞紐。如圖1所示，該中心將在驅(qū)動(dòng)軸，穿越風(fēng)扇住房。氣體進(jìn)入從側(cè)面的風(fēng)扇方向盤，把90度，并加快由于離心力因?yàn)樗鲃?dòng)的風(fēng)扇葉片和出口風(fēng)扇住房。 1 離心式風(fēng)機(jī)可產(chǎn)生壓力上升氣流。因此，他們非常適合工業(yè)加工和空氣污染控制系統(tǒng)。他們還共同在中央供暖/冷卻系統(tǒng)。 圖1

25、1.風(fēng)機(jī)組件主要組成局部典型的離心式風(fēng)機(jī)包括風(fēng)扇輪，風(fēng)扇住房，驅(qū)動(dòng)機(jī)制，進(jìn)口和/或出口閘。 2類型的驅(qū)動(dòng)機(jī)制 風(fēng)扇驅(qū)動(dòng)器決定的速度，風(fēng)扇輪葉輪以及在何種程度上這樣的速度可以多種多樣。有三種根本類型的風(fēng)機(jī)驅(qū)動(dòng)器。 1 2.1直接驅(qū)動(dòng) 風(fēng)扇輪可以直接聯(lián)系的骨干一個(gè)電動(dòng)馬達(dá)。這意味著，風(fēng)扇輪速是相同的電機(jī)轉(zhuǎn)速。這種類型的風(fēng)機(jī)驅(qū)動(dòng)機(jī)制，風(fēng)扇轉(zhuǎn)速不能更改，除非是可調(diào)的電機(jī)轉(zhuǎn)速。 帶傳動(dòng)圖2 ：離心風(fēng)機(jī)用皮帶驅(qū)動(dòng)風(fēng)扇driveBelt使用多重皮帶旋轉(zhuǎn)的一套滑輪安裝在電機(jī)軸和風(fēng)扇輪軸。 這種類型的驅(qū)動(dòng)機(jī)制是描繪在圖2 。皮帶傳遞機(jī)械能的電機(jī)風(fēng)扇。 風(fēng)扇輪速取決于比例的直徑電機(jī)帶輪的直徑風(fēng)扇輪輪和可從該方程：

26、 1 其中： rpmfan =范輪速，每分鐘的革命rpmmotor =電機(jī)銘牌速度，每分鐘的革命Dmotor =直徑電機(jī)輪Dfan =直徑風(fēng)扇輪輪范車輪速度皮帶驅(qū)動(dòng)風(fēng)扇是固定的，除非帶滑。帶滑移可以降低風(fēng)扇輪速幾百革命每分鐘每分鐘轉(zhuǎn)速。 圖22.2.變頻驅(qū)動(dòng)器 可變液壓驅(qū)動(dòng)風(fēng)扇使用或磁性聯(lián)軸器范之間輪軸與電機(jī)軸 ，使控制風(fēng)扇輪速獨(dú)立的電機(jī)轉(zhuǎn)速。該風(fēng)扇轉(zhuǎn)速控制常常被納入自動(dòng)化系統(tǒng)，以保持理想風(fēng)扇輪速。 1 替代的方法不同的風(fēng)扇速度是使用電子變速驅(qū)動(dòng)器的速度控制的電機(jī)驅(qū)動(dòng)風(fēng)扇。這提供了更好的整體能源使用效率，同時(shí)降低速度比機(jī)械聯(lián)軸器。 2.3范減震器范減震器是用來控制氣體流量流入和流出的離心式風(fēng)機(jī)

27、。他們可能會(huì)被安裝在入口旁或出口一側(cè)的風(fēng)扇，或兩者兼而有之。阻尼器的出口方面實(shí)行流動(dòng)阻力，用于控制氣流。阻尼器的進(jìn)氣口一側(cè)的目的是控制氣體流量和改變氣體進(jìn)入風(fēng)機(jī)輪。 范進(jìn)閘減少能源使用量，由于他們有能力影響氣流的模式風(fēng)扇。 1 3.向后彎曲葉片后向彎曲的刀片，在圖3 b ，使用該曲線對(duì)葉片的方向風(fēng)扇輪的自轉(zhuǎn)。落后的曲率模仿的翼型截面，并提供良好的運(yùn)營效率相對(duì)經(jīng)濟(jì)的施工技術(shù)。這些類型的風(fēng)機(jī)輪轂中使用的風(fēng)扇設(shè)計(jì)來處理天然氣流與低到中等顆粒負(fù)荷。他們可以很容易地安裝的抗磨損保護(hù)，但某些刀片曲率可以容易固體建設(shè)。 向后彎曲的球迷可以有很高的一系列具體的速度，但往往是用于具體的高速應(yīng)用中-高壓力，介質(zhì)流應(yīng)用。向后彎曲的球迷更能源效率比徑向葉片風(fēng)扇，因此，對(duì)于大功率的應(yīng)用可能是一個(gè)適宜的替代本錢更低徑向葉片風(fēng)扇。 4.徑向直葉片徑向風(fēng)扇葉片，如在圖3 c 項(xiàng)，擴(kuò)大直接從樞紐。徑向葉片風(fēng)扇車輪上經(jīng)常使用的顆粒拉丹天