陕西科技大学过程装备与控制工程过程装备双语Chap4-Pumps.ppt

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 mechanisms intake stroke 进气冲程/行程 counter-count line 2, para 4,Key term,Mechanisms: Dynamicaccelerate liquids axially ( in a straig

2、ht 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 mov

3、e. Para 2: centrifugal pump100% slip, Fig 4.3-1; volute 蜗壳 line 5 Para 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 e

4、nergy 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

5、 into 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 in

6、to 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,

7、casing, casing cover and bearings 2. 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); S

8、ingle 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:

9、bubble 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, P75 capacity range 扬程 l

10、ine 3, P75,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 driv

11、ervariable 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。 Can

12、not handle 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:

13、The formation 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 suct

14、ion head, sometimes called differential head. PAY ATTENTION: Operators should know. Pump curve value line 3 parameter 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

15、/g）差而实现的，也就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 capacity Causes：metal removal， reduced flow， loss in efficiency， and

16、noise； It occurs when suction pressure drops below NPSH. Homework: 4.6 Axial Pumps,REFERENCES,/wiki/Pump ./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：

17、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。,4.6 Axial Pumps,4.7 Jet Pumps,Function：lifting the water； Venturi（effect/tube) 2. Basic components: Shown in Fig.4.7-1,图1 可调式水喷射泵结构原理图1.引射水入口 2.调节喷针 3.引水室 4.被引射水口 5.混合室 6.扩散段 7.混合水出口,Key term,3. Another common jet

18、 pump: the jet assembly forms a suction chamber that creates a vacuum.,4.8 Positive Displacement Pumps,Rotary pumps-rotary-motion gears, screws, vanes, lobes; Reciprocating pumps-diaphragm, piston, plunger. never be blocked in on the discharge side until the pump is turned off-unless damage-pressure

19、 relief valve.,Note：,4.8 Positive Displacement Pumps,4.9 Rotary Pumps,heavy hydrocarbon 重质烃 Application: the most widely used PD pumps;,C Handle viscous fluids Used mainly in, heavy hydrocarbon, paint, slurries, oil burners, soaps and cosmetics(化妆品）, sugars, syrup, and molasses（糖蜜）, dyes, ink, bleac

20、hes(增白剂）, vegetable and mineral oils.,Key term,Mechanism：using a rotary motion; Characteristic: combine the rotary motion and the positive displacement feature. High pressure, high efficiency Liquids must be free of solids Types: last sent.,4.9 Rotary Pumps,Single-screw Rotary Pumps ( Progressive ca

21、vity Pumps） pulsation 脉动，间断 line 5 turbulence 湍流 line 6 Mechanism：only one moving part, the rotor;,4.9 Rotary Pumps,Key terms,Basic components: Rotor and stator, universal joints, seals and bearings.,4.9 Rotary Pumps,Application: metering, heavy or viscous fluid, fluid with solid.,Screw pumps carry

22、fluid in the spaces between the screw threads. The fluid is displaced axially as the screws mesh.,4.9 Rotary Pumps,2. Multiple-screw Rotary Pumps Characteristic: have either 2 or 3 screws, and 2 or 3 rotors; Functions: provide high flow rates and excellent suction and to pump virtually(有效地） any flui

23、d.,3. Gear Pumps External gear pumps,As the teeth come out of mesh, liquid flows into the pump and is carried between the teeth and the casing to the discharge side of the pump; The teeth come back into mesh and the liquid is forced out the discharge port.,Internal gear pumps,4. Sliding Vane Pumps:

24、Consist of spring-loaded or non-spring-loaded vanes attached to a rotor, or impeller, that rotates inside an oversized circular casing. An eccentric cam rotates the circular plunger (shown in gray) around the edge of the casing, fluid is swirled around the edge to the outlet port.,5. Flexible Vane p

25、umps: have a soft elastomer impeller They are frequently used in vacuum service. 6. Lobe Pumps,Fluid is carried between the rotor teeth and the pumping chamber; The rotor surfaces create continuous sealing.,4.10 Reciprocating Pumps,Primary Function: to transfer small volumes of liquid at relatively high pressures; Based on two stroke principles: High pressure, high efficiency Self-priming Small quantity, vibration, physical dimension, uneven