陜西科技大學過程裝備與控制工程過程裝備雙語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 進氣沖程/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 蝸殼 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 排出壓力， 水頭壓力 line 2, P75 capacity range 揚程 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; 離心泵啟動時，若泵內(nèi)存有空氣，由于空氣密度很低，旋轉(zhuǎn)后產(chǎn)生的離心力小，因而葉輪中心區(qū)所形成的低壓不足以將儲槽內(nèi)的液體吸入泵內(nèi)，雖啟動離心泵也不能輸送液體。此種現(xiàn)象稱為氣縛，表示離心泵無自吸能力，所以必須在啟動前向殼內(nèi)灌滿液體。 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.凈正吸入壓頭,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液面與泵吸入口截面1-1之間的勢能（Z+p

15、/g）差而實現(xiàn)的，也就是說在泵的吸入口附近為低壓區(qū)。當葉片入口附近的最低壓力等于或小于輸送溫度下液體的飽和蒸汽壓時，液體將在此處汽化或者是溶解在液體中的氣體析出并形成氣泡。含氣泡的液體進入葉輪高壓區(qū)后，氣泡在高壓作用下急劇地縮小而破滅，氣泡的消失產(chǎn)生局部真空，周圍的液體以極高的速度沖向原氣泡所占據(jù)的空間，造成沖擊和振動。在巨大沖擊力反復(fù)作用下，使葉片表面材質(zhì)疲勞，從開始點蝕到形成裂縫，導(dǎo)致葉輪或泵殼破壞。這種現(xiàn)象稱為汽蝕。,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.,特點：

17、軸流泵揚程低、流量大，適于吸送清水或物理及化學性質(zhì)類似水的其它液體之用，主要供農(nóng)田排灌、工業(yè)熱電站輸送循環(huán)水、城市給排水、船塢升降水位或其它水利工程用水，使用范圍十分廣泛。,4.6 Axial Pumps,4.7 Jet Pumps,Function：lifting the water； Venturi（effect/tube) 2. Basic components: Shown in Fig.4.7-1,圖1 可調(diào)式水噴射泵結(jié)構(gòu)原理圖1.引射水入口 2.調(diào)節(jié)噴針 3.引水室 4.被引射水口 5.混合室 6.擴散段 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 重質(zhì)烴 Application: the most widely used PD pumps;,C Handle viscous fluids Used mainly in, heavy hydrocarbon, paint, slurries, oil burners, soaps and cosmetics(化妝品）, sugars, syrup, and molasses（糖蜜）, dyes, ink, bleac

20、hes(增白劑）, 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 脈動，間斷 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