离心风机英文文献

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 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 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 sheave Dfan 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 2Variable 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 wheel speed 1 An 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 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 due to their ability to affect the airflow pattern into the fan 1 3 Backward curved blades Backward curved blades as in Figure 3 b use blades that curve against the direction of the fan wheel s rotation The backward curvature 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 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 fans and so for high horsepower applications may be a suitable alternative to the lower cost radial bladed fan 4 Straight radial blades Radial 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 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 3 5 Centrifugal fan ratings Ratings 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 m with the barometric pressure at sea level of 29 92 inches of mercury 101 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 air 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 Centrifugal 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 moves 1 000 ft min 28 m min at 70 F 21 C it will also move 1 000 ft min 28 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 centrifugal 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 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 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 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 离心风机离心风机 离心风机 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 1 1 1 风机组件风机组件 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 2 类型的驱动机制类型的驱动机制 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 12 1 直接驱动直接驱动 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 除非是可调的电机 转速 2 1 12 1 1 带传动带传动 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带轮的直径风扇轮轮和可从 该方程 1 其中 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 2 2 2 2 2 变频驱动器变频驱动器 可变液压驱动风扇使用或磁性联轴器 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 32 3 范减震器范减震器 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 3 向后弯曲叶片向后弯曲叶片 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 介质流应用 向后弯曲的球迷更能源效率比径向叶片风扇 因此 对于大功率的应用可能是一个合适的替代成本更低径向叶片风扇 4 4 径向直叶片径向直叶片 径向风扇叶片 如在图 3 c 项 扩大直接从枢纽 径向叶片风扇车 轮