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1、Chapter 4,Pumps,4.2 Pump Application and Classification,Para 1: Primary function: move liquids; Applications: the 2nd sentence .Fig.4.2-1/2 Para 2-5: Classification and mechanismsintake stroke 进气冲程/行程 counter-count line 2, para 4,Key term,Mechanisms: Dynamicaccelerate liquids axially ( in a straight
2、 line) or centrifugally (in circles); Positive displacementtransfer liquids using a rotary or reciprocating motion that displaces liquid on each rotation or stroke.,4.3 Internal Slip,Para 1: Definition of slip The difference between how much liquid a pump can move and how much it actually does move.
3、 Para 2: centrifugal pump100% slip, Fig 4.3-1;volute 蜗壳 line 5Para 3: PD pumpminimal slip.,Key term,4.4 Dynamic Pumps (Focus point),We already know that dynamic pumps are classified as centrifugal or axial. (Read the 2 Para),4.5 Centrifugal Pumps,WHAT IS CENTRIFUGAL PUMP? Convert the mechanical ener
4、gy into hydraulic energy by centrifugal force on the liquid； Constitute the most common type of pumping machinery； Used to move liquids through a piping system.,Working process: Please look at Fig 4.5-1 liquid encounters spinning impeller liquids propelled circular rotation that forces it outward in
5、to volute. Summary: centrifugal force and volute design convert velocity energy to pressure.,Liquid flow path inside a centrifugal pump,WORKING MECHANISM OF A CENTRIFUGAL PUMP,Simplest piece of equipment in any process plant； Energy changes occur by virtue of impeller and volute; Liquid is fed into
6、the pump at the center of a rotating impeller and thrown outward by centrifugal force; The conversion of kinetic energy into pressure energy supplies the pressure difference between the suction side and delivery side of the pump.,Basic Components Has two main components:1. Stationary componets, casi
7、ng, casing cover and bearings2. Rotating components, impeller and shaft Classified into three categories ： Radial Flow, Mixed Flow, Axial Flow,4.5 Centrifugal Pumps,Pump Design: Centrifugal pumps come in a variety of designs and applications: Vertical or horizontal (refers to shaft position); Single
8、 stage or multiple stage (refers to number of impellers, explain); Single or multiple suction inlets; Volute or diffuser; Axial flow, radial flow, mixed flow; Open, semi-open, closed impeller design. Pay attention: horizontal pumps are the most common type found in industry.And a useful term: bubble
9、 point line 7, Para 2,Impeller Design We have known that the simplest centrifugal pump is a single-stage pump, and it has only one impeller, so multistage pumps have more than one. Fig.4.4-1 Advantages and Disadvantages (versus PD pumps)head pressure 排出压力，水头压力 line 2, P75capacity range 扬程 line 3, P7
10、5,Key terms,Advantages less maintenance and space; Maintenance costs are lower operate with a constant head pressure over a wide capacity range; Simple in construction and cheapeasier to change the element( especially impeller); easier to change the driver; adaptability of the selected drivervariabl
11、e horsepower, fixed or variable speed. Handle liquid with large amounts of solids No metal to metal fits No valves involved in pump operation,Disadvantages not self-priming; 离心泵启动时，若泵内存有空气，由于空气密度很低，旋转后产生的离心力小，因而叶轮中心区所形成的低压不足以将储槽内的液体吸入泵内，虽启动离心泵也不能输送液体。此种现象称为气缚，表示离心泵无自吸能力，所以必须在启动前向壳内灌满液体。 Cannot handl
12、e highly viscous fluids efficientlyrespond poorly to viscous materials or variations in suction pressures; Cannot be operated at high heads; Maximum efficiency holds over a narrow range of conditions.,Head( Pressure) 1. Suction heads definition: the 2nd sentence; 2. Cavitations definition: The forma
13、tion and collapse of gas pockets around the impellers; How does it take place? The low pressure cause the liquid to boil; 3. NPSH: the minimum rating at which a centrifugal pump operates.净正吸入压头,Determining Differential Head Total Head Total head is equal to the discharge head minus the suction head,
14、 sometimes called differential head. PAY ATTENTION: Operators should know. Pump curvevalue line 3parameter line 2, Para2 The best operation condition for a centrifugal pump usually is indicated on the pumps efficiency curve. Fig 4.5-6,Key terms,Cavitation 泵的吸液作用是依靠0-0液面与泵吸入口截面1-1之间的势能（Z+p/g）差而实现的，也就
15、是说在泵的吸入口附近为低压区。当叶片入口附近的最低压力等于或小于输送温度下液体的饱和蒸汽压时，液体将在此处汽化或者是溶解在液体中的气体析出并形成气泡。含气泡的液体进入叶轮高压区后，气泡在高压作用下急剧地缩小而破灭，气泡的消失产生局部真空，周围的液体以极高的速度冲向原气泡所占据的空间，造成冲击和振动。在巨大冲击力反复作用下，使叶片表面材质疲劳，从开始点蚀到形成裂缝，导致叶轮或泵壳破坏。这种现象称为汽蚀。,Reduces the pump capacityCauses： metal removal，reduced flow，loss in efficiency，and noise； It occu
16、rs when suction pressure drops below NPSH. Homework: 4.6 Axial Pumps,REFERENCES,http:/en.wikipedia.org/wiki/Pump www.rpi.edu./dept/chem-eng/ Biotech-Environ/PUMPS/intro.html,4.6 Axial Pumps,Axial pumps can accelerate and transfer fluid by pushing it axially, or in a straight line.,特点： 轴流泵扬程低、流量大，适于吸送清水或物理及化学性质类似水的其它液体之用，主要供农田排灌、工业热电站输送循环水、城市给排水、船坞升降水位或其它水利工程用水，使用范围十分广泛。,
