1、Unit 21 Pumps 1. Introduction Pump, device used to raise, transfer, or compress liquids and gases. Four general classes of pumps for liquids are described below t In all of them , steps are taken to prevent cavitation (the formation of a vacuull1), which would reduce the flow and damage the structur
2、e of the pump, - pumps used for gases and vapors are usually known as compressors . The study of fluids in motion is called fluid dynamics. 1介绍泵是提出，转移或压缩液体和气体的设备。下面介绍四种类型的泵。在所有的这些中，我们一步步采取措施防止气蚀，气蚀将减少流量并且破坏泵的结构。用来处理气体和蒸汽的泵称为压缩机，研究流体的运动的科学成为流体动力学。Water Pump, device lor moving water from one location
3、to another, using tubes or other machinery. Water pumps operate under pressures ranging from a fraction of a pound to more than 10,000 pounds per square inch. Everyday examples of water pumps range from small electric pumps that circulate and aerate water in aquariums and fountains to sump pumps tha
4、t remove Water from beneath the foundations of homes. 水泵是用管子或其他机械把水从一个地方传到另一个地方。水泵的操作压力从一磅到一万磅每平方英尺。日常生活中，泵是很多的，有用于在鱼池和喷泉使水循环和向水中充气的电泵，还有用于从住宅处把水引走的污水泵。Two types of modern pumps used to move water are the positive-displacement pump and the centrifugal pump. Positive-displacement pumps use suction cr
5、eated by a vacuum to draw water into a closed space. An example of this type of pump is the lift, or force, pump used commonly in the rural United States until the mid-1900s. The lift pump is operated by raising a handle that is attached to a piston encased in a pipe. Lifting the piston creates a pa
6、rtial vacuum beneath it in the pipe, causing water to be drawn from a well below , through the pipe, and into a chamber in the pump. A one-way valve closes after water is pumped into the chamber, keeping the water from flowing back down into the well. Subsequent pumps of the piston pull more water i
7、nto the chamber, which eventually overflows, spilling water out of a spout. Centrifugal pumps use motor-driven propellers that create a flow of water when they rotate. The blades of the propeller are immersed in the water to be pumped. As the propeller turns, water enters the pump near the axis of t
8、he blades and is swept out toward their ends at high pressure. An alternative, early version of the centrifugal pump, the screw pump, consists of a corkscrew-shaped mechanism in a pipe that. when rotated, pulls water upward. Screw pumps are often used in waste-water treatment plants because they can
9、 move large amounts of water without becoming clogged with debris. In the ancient Middle East the need for irrigation of farmland was a strong induceDlent to develop a water pump. Early pumps in this region were simple devices for lifting buckets of water from a source to a container or a trench. Gr
10、eek mathematician and inventor Archimedes is thought to have devised the first screw pump in the 3rd century Be. Later, Greek inventor Ctesibius developed the first lift pump. During the late 17th and early 18th centuries AD, British engineer Thomas Savery, French physicist Denis Papin . and British
11、 blacksmith and inventor Thomas Newcornen. contributed to the development of a water pump that used steam to power the pump s piston. The steam-powered water pumps first wide use was in pumping water out of mines. Modern-day examples of centrifugal pumps are those used at the Grand Coulee Darn on th
12、e Columbia River. This pump system has the potential to irrigate over one million acres of land. 现在，两种典型的排水泵是容积泵和离心泵。容积泵通过由真空产生的吸力把水引到一个紧凑的地方。这种类型泵的一个实例就是提升或压力泵，在20世纪中叶美国农村普遍使用。提升泵的操作是通过一个与被管子包住的活塞手柄来进行的。当我们提升活塞时在管子下部产生一个局部的真空，这样我们就用管子从下面的取水，并且送到泵的一个空间。当水被泵吸入时，单向阀关闭，阻止水流回到井下。接着泵的活塞吸入更多的水进入泵的膛体中。这样最后
13、形成溢流，水从管口处流出。而离心泵时使用了一种螺旋推进器，旋转时使水流动，而且推进器的切片是在泵送水时侵入水中的。而且，当推进器旋转时，水进入位于刃片的轴部的间隙并且以很高的压力甩向底部。与它类似，离心泵的早期形式，螺杆泵，通过一个管子螺丝钉的组成，当旋转时，把水提升上去。螺旋泵经常用在污水处理厂中，因为他们可以运输大量的水，而不会因为碎片而堵塞。在远古的中东，因为对农场进行灌溉的需求，所以有一种强大的动力去推进水泵的进程。在这些区域里，早期的泵是为了将水一桶一桶的从水源或河渠中提升到容器中。古希腊的发明家和数学家的阿基米德泵认为是公元前3世纪首先提出螺旋泵的发明家。之后，古希腊发明家发明了第
14、一个提水泵。在十七世纪末和十八世纪初，英国的工程师ThomasSavory，法国的物理学家DenisPapin，和英国的铁匠和发明家TomasNewcomen,它们发明了用蒸汽驱动活塞的水泵。蒸汽驱动的水泵首先广泛的被应用在从煤矿往外输水过程中。现在离心泵使用的例子，可以是在哥伦比亚河上使用的大古利水坝。这个泵有超过灌溉一百万英亩的土地能力。2. Reciprocating PumpsReciprocating pumps consist of a piston moving back and forth in a cylinder that has valves to regulate th
15、e flow of liquid into and out of the cylinder. These pumps may be single or double acting. In the single acting pump, the pumping action takes place on only one side of the piston, as in the case of the COD1ll1on lift PUDlP, in which the piston is moved up and down by hand. In the double acting pump
16、, the pumping action takes place on both sides of the piston, as in the electrical or steam-driven boiler feed pump, in which water is supplied to a steam boiler under high pressure. These pumps can be single-stage or multistaged, Multistaged reciprocating pumps have multiple cylinders in series.2.往
17、复泵往复泵有一个在圆筒中上下移动的活塞，可以使水规则的流入或流出圆筒。这些泵可以是单作用的，也可以是双作用的。在单作用的泵中，泵的作用仅仅发生在活塞的一侧，典型的例子就是升液泵。在升液泵中，活塞通过手上下移动。在双作用的水泵中，泵的作用发生在活塞的两侧，比如说电动的或气动的锅炉给水泵，水以高压通过蒸汽锅炉供给。这些泵可以是单级的也可以是多级的。多级的往复泵的泵系列有多个刚体。3. Centrifugal Pumps Also known as rotary pumps, centrifugal pumps have a rotating impeller, also known as a bl
18、ade, that is immersed in the liquid. Liquid enters the pump near the axis of the impeller , and the rotating impeller sweeps the liquid out toward the ends of the impeller blades at high pressure. The impeller also gives the liquid a relatively high velocity that can be converted into pressure in a
19、stationary part of the pump , known as the diffuser. In high-pressure pumps , a number of impellers may be used in series, and the diffusers following each impeller may contain guide vanes to gradually reduce the liquid velocity. For lower-pressure pumps, the diffuser is generally a spiral passage,
20、known as a volute, with its cross-sectional area increasing gradually to reduce the velocity efficiently. The impeller must be primed before it can begin operation, that is, the impeller must be surrounded by liquid when the pump is started. This can be done by placing a check valve in the suction l
21、ine, which holds the liquid in the pump w-hen the impeller is not rotating. If this valve leaks, the pumps may need to be primed by the introduction of liquid from an outside source such as the discharge reservoir. A centrifugal pump generally has a valve in the discharge line to control the flow an
22、d pressure. For low flows and high pressures, the action of the impeller is largely radial. For higher flows and lower discharge pressures, the direction of the flow within the pUD1P is more nearly parallel to the axis of the shaft, and the pump is said to have an axial flow. The impeller in this ca
23、se acts as a propeller. The transition from one set of flow conditions to the other is gradual, and for intermediate conditions, the device is called a mixed-flow pump. 3离心泵离心泵被认为是旋转泵，它是有一个旋转地叶轮，也有刃片，刃片是侵入液体中。液体也是由叶轮轴向进入泵，并且旋转的叶轮将液体甩向叶片根部。同时叶轮也给液体一个较高的过度，这个过度能够使泵的一个固定部件转化成压力。我们一般称为扩压器。在高压泵里，很多叶轮可以被系
24、列选用，并且在一个叶轮后有一个扩压器，也可能含有导轮，可以逐渐的降低液体的过度。对于低压泵来说，扩压泵一般就是一个螺旋形的通道，成为蜗壳，作用原理是拦截面逐渐增加可以有效降低流体的过度。在泵工作前，叶轮必须被灌注，也就是在泵启动时，叶轮必须被液体包围。也可以通过在吸入线上放另一个截止阀来实现，截止阀在泵停止工作时是液体保留在泵内。如果阀泄露了，泵可以通过阀的入口，从外面的水源比如说蓄水池来取水灌注。一般离心泵在排水线也有一个阀控制流体和压力。对于小流量和高压力来说，叶轮作用很大部分是放射状的。对于高速流体和低压排水压力，泵中流体的方向可以近似于与轴的轴向平行，这时泵有一个轴流。这时叶轮就近似于
25、螺旋推进器。从一种流的状态转换到另一种流的状态是渐进的，对于中间状态，设备可称为混流泵。4. Jet PumpsJet pumps use a relatively sznall stream. of liquid or vapor, moving at high velocity, to move a larger flow of fluid. As the high-velocity stream passes through the fluid, it carries some of the fluid out of the pump; at the same time, the hig
26、h-velocity stream creates a vacuum that pulls fluid into the pump. Jet pumps are often used to inject water into a steam boiler. Jet pumps have also been used to propel boats, particularly in shallow water where a conventional propeller might be dam.aged. 4射流泵射流泵是通过一个流量相对较小的液体或蒸汽，以较高速度移动到较大的液流。因为高速流
27、体要通过液体，它从泵里带走液体一部分，同时，高速流产生一个真空，这个真空又把液体吸入泵内。射流泵经常给蒸汽锅炉注水。另外，也应用来推动的船只，特别是在正常的推进器可能被破坏的浅水里。5. Other pumps A variety of positive-displacement pumps are also available, generally consisting of a rotating member with a number of lobes that move in a close-fitting casing. The liquid is trapped in the sp
28、aces between the lobes and then discharged into a region of higher pressure. A common device of this type is the gear pump, which consists of a pair of meshing gear. The lobes in this case are the gear teeth. A simple but inefficient pump can also be constructed by having a screw turning in a casing
29、 and pushing the liquid along. A similar pump was first invented by the Greek mathematician and physicist Archimedes sometime after 300 Be. In all these pumps the liquid is discharged in a series of pulses and not continuously, so care must be taken to avoid resonant conditions in the discharge line
30、s that could damage or destroy the installation. For reciprocating pumps, air chambers are frequently placed in the discharge line to reduce the magnitude of these pulsations and to make the flow more uniform.5其他类型的泵仍然存在其他很多类型的容积泵，一般用带有很多保密配合的圆形突出的回转件。液体被收集在耳朵之间，而且被转送到一个压力较高的区域。这种泵的一个典型设备是齿轮泵，包含有一对网
31、状齿轮，在齿轮泵里耳朵就是齿牙。也可通过一个在外壳旋转的螺杆来构造一个简单而低效的泵，螺杆推动也提前进。一个相似的泵在公元前3世纪被希腊数学家和物理学家阿基米德发明了。在所有的泵里，液体被一些列脉冲排出，并且不连续。因此我们必须注意在排除线上来避免共振，因为共振可能会损伤或破坏整个设备。对往复泵来说，真空经常放在排除线上，可以减少振动，并使流动均衡。Unit 22 Pumping Equipment for Gases Essentially the same basic types of mechanical equipment are used for handling gases and
32、 liquids, though the construction may be very different in the two cases. Under the normal range of operating pressures, the density of a gas is considerably less than that of a liquid so that higher speeds of operation can be employed and lighter valves fitted to the delivery and suction lines. Bec
33、ause of the lower viscosity of a gas there is a greater tendency for leakage to occur, and therefore gas compressors are designed with smaller clearances between the moving parts. Further differences in construction are necessitated by the decrease in volume of gas as it is compressed , and this mus
34、t be allowed for in the design. Since a large proportion of the energy of compression appears .as heat in the gas, there will normally be a considerable increase in temperature which may limit the operation of the compressor unless suitable cooling can be effected. For this reason, gas compression i
35、s often carried out in a number of stages and the gas is cooled between each stage. Any gas which is not expelled from the cylinder at the end of compression (the clearance volume ) must be expanded again to the inlet pressure before a fresh charge can be admitted. This continual compression and exp
36、ansion of the residual gas results in loss of efficiency because .neither the compression nor the expansion can be carried out completely reversibly. With liquids this factor has no effect on the efficiency because the residual fluid is not compressed. Unit22气体的泵设备对于处理戒指为气体或液体来说，虽然设备在结构上有很大差异，但这两种设备
37、在本质上属于相同基本类型的机械设备。在正常操作范围内，因为气体的密度比液体小，所以对气体的操作可达到较高的速度，而且在吸入线和排出线上可使用较轻的阀。因为气体的粘度小所以它们容易发生泄露。因此气体压缩机的移动部件之间的间隙被设计的非常小。因为气体压缩过程中体积减小，因此与液体相比在结构上存在差异，而且这个差异在设计中也要考虑。压缩机中很大一部分能量要被转换成热能。因此在没有合适的冷却措施时将会限制压缩机的操作。也因为这个，气体压缩机分为多级完成，而且每一级中可分别冷却。任何在压缩机中没有被排出缸体的气体，再重新充入时要膨胀到入口的压力。残余的气体连续压缩和膨胀导致效率下降，因为不管是压缩还是膨
38、胀都不能被可逆操作。The principal types of compressors for gases are described as follows.而对液体，间隙容量不会影响效率的，因为残余液体不可压缩。Reciprocating piston compressor往复式活塞压缩机 This type of compressor which may consist of from one to twelve stages is the only one capable of developing very high pressures, such as for example ov
39、er 350 M;N 1m2 as required for polythene manufacture. A single-stage, twocylinder unit, shown in Fig. 5. 4, operates at relatively slow speed and is being replaced wherever possible by the centrifugal type Which can now develop all but the very highest pressures .这种压缩机可以包含112级，是唯一可以达到较高压力的设备，比如在乙烯工业
40、中所需水的压力达到超过350万牛/每平方米，图5.4是单级双缸的压缩机，操作速度低，在操作压力较低时可以用离心压缩机取代。 Rotary blowers and compressors 旋转式鼓风机和压缩机These can be divided into two classes-those which develop a high compreseion ratio and those which have very low ratios. The former include the sliding-vane type) in which the compression ratio is
41、achieved by eccentric mounting of the rotor (Fig. 5. 5) and the Nash Hytor pump (Fig. 5. 6) in which the compression ratio is achieved by means of a specially shaped casing and a liquid seal which rotates with tile impeller. 这种压缩机可以分为较高压缩和较低压缩两种类型。前者包含滑片式，它的压缩比是通过离心转子来实现的。NashHytor泵是通过特殊形状的刚体和叶轮同时旋转
42、的液体密封来实现的。In the sliding-vane unit the rotor is slotted to take the sliding blades which subdivide the crescent-shaped space between the rotor and cylinder. On rotation the blades move out trapping the gas which is compressed during rotation and discharged at the delivery port as shown. 在滑片式压缩机通过在壳体
43、上开槽夹住叶片，而叶片将转子和缸体之间的月牙空间分成一片一片的。在旋转时，刃片滑片拦住气体但气体在旋转式被压缩，并且在端口被排出。The Nash Hytor (Fig. 5. 6) type, which is also known as the liquid-ring pump; is a positive displacement type with a specially shaped casing and a liquid seal which rotates with the impeller. The shaft and impeller are the only moving
44、parts and there is no sliding contact, so that no lubricants are required and the gas under compression is riot contaminated.NashHytor泵也可以分为液环泵，属于容积泵类型而且带有一个特殊形状的壳体和一个与叶轮同时旋转的液体密封。轴和叶轮是没有移动部件而且没有滑动触点，所以不需要润滑剂，而且被压缩的气体不会受到污染。 With this arrangement the liquid leaves and re-enters the impeller cells in
45、 the manner of a piston. The service liquid is supplied at a pressure equal to the discharge pressure of the gas and is drawn in automatically to compensate for that discharged Irornt he ports. During compression the energy is converted to heat so that this is a nearly isothermal . process. Downstre
46、am the liquid is separated from the gas and recirculated with any .necessury make up. 在这种压缩机中，液体通过活塞离开和重新进入叶轮单元。工作液体的进口压力与出口压力相等，而且工作液体自动被吸入来补偿出口的液体。在压缩中，能量转化成热，因此这个工艺接近于等温工艺。在下液，液体从气体中分离出来通过必要的构造进行再循环。A different kind of unit is represented by the cycloidal or Rootes blower. In this type, compressi
47、on is achieved by the rotation of two elernents. These rotors turn in opposite directions so that, as each passes the inlet, it takes in air which is compressed between impeller and the wall and is than expelled outwards. 还有其他类型，比如摆线型或罗茨鼓风机。在这种类型的压缩机是通过两个部件的旋转来实现的。转子以相反的方向移动，它们通过入口时，带入空气，并将空气在叶轮和壳体之
48、间受到压缩和排出。Centrifugal blowers and compressors; including turbocompressors 离心式鼓风机和压缩机，包括涡轮压缩机These depend on the conversion of kinetic energy into pressure energy. Fans are used for low pressures, and can be made to handle very large quantities of gases. For the higher pressure ratios now in demand, m
49、ultistage centrifugal compressors are mainly used, particularly for the requirements of high capacity chemical plants. Thus in catalytic reforming, petrochemical separation plants ( ethylene manufacture), ammonia plant-s with a production rate of 12 kg/s, and for the very large capacity needed for natural gas fields, this type of compressor is now supreme. These units now give flowrates up to 140 m3/s and pr
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