化工四大化学(专业)review88Transportationandmeteringoffluid(课堂讲义)

1、1 Chapter 8 Transportation and metering of fluid 1. Transportation of fluids, both liquids and gases. 2. Metering of fluid: flowmeters 2 Energy needed to transport fluid 22 22 aa a a f bb b b p V gZ p h V gZ p W g V Z g p g h g V Z g p g W aa a a f bb b b p 22 22 22 22 aa aaf bb bbp V gZph V gZpW J/

2、kg J/N,m Pa, J/m3 3 Classification of transportation devices: Transporting Liquid: pump Centrifugal pump离心泵 Positive-displacement pump正位移泵 Transporting Gas: Fan 通风机 Blower 鼓风机 Compressor 压缩机 Vacuum pump 真空泵 4 1. Centrifugal pump n1.1. Centrifugal pump n1.2. Performance characteristics and characteri

3、stic curves n1.3. Variation of pump characteristic curves n1.4. Piping system characteristic curve and Operating point (Duty point) n1.5. Flow rate control n1.6. How to select a pump and operate the pump correctly.(air binding, cavitation) 5 1.1. Centrifugal pump nStructure and main parts of a centr

4、ifugal pump nStructure: impeller, volute, shaft gland, suction inlet, discharge outlet 6 1.2. Performance characteristics and characteristic curves Performance characteristics特性参数 1. (volumetric) flow rate, capacity q ( m3/s, m3/h) 流 量 2. (actual) head H (J/N, m) 压头，扬程 3. Shaft power (consumption) P

5、B (W) 轴功率 HgqWmp pf gqH Wmp pB Required power 4. Efficiency 效率 B f P P 7 Best Efficiency Point (BEP) high efficiency region characteristic curve of a centrifugal pump max 92. 0 8 1.3. Variation of pump characteristic curves nChange of density nChange of viscosity nChange of impeller diameter nChange

6、 of impeller speed(RPM) 9 1.4. Piping system characteristic curve and Operating point (Duty point) nPiping system characteristic curve He: J/N, m qe: m3/h gA KKK D L fB fce 2 36002 1 4 g p ZK 2 ee BqKH 10 q H a b p P: Operating point 11 1.5. Flow rate control Usually the valve on the discharge line

7、is used to control capacity of a centrifugal pump. The method of adjustment the flow rate: (1) Change characteristic curve of flow system. (2) Change characteristic curve of the pump. (3) Connect two pumps 12 Adjust the valve in discharge line K Bqe2 13 in parallelin series Connect two pumps 14 Comp

8、are the two kind of connecting manner Low friction loss piping High friction loss piping 15 1.6. How to select a pump and operate the pump correctly. (air binding, cavitation) nSelect a pump nInstall a pump (Suction lift and Cavitation) nOperate a pump 16 Suction Lift and Cavitation g p g p g V NPSH

9、 va a a 2 2 g pp H aa s Net positive suction head 允许吸上真空度 17 nSuction lift: NPSHh pp g Z fs va a 1 g h g V HZ fs a a sa 2 2 (suction from an open tank) 18 2. Positive-displacement pump正位移泵 n1. Self-priming, not subject to air binding; n2. H is nearly independent of q n3. Adjust flow rate by bypass l

10、ine with a pressure relief valve n4. Usually used in situation required high developed head, low flow rate. 19 The performance characteristics of a reciprocating pump n1. Volumetric flow rate,capacity q (m3/s) n2. Developed head H or H (J/N or m) n3. Mechanical efficiency n4. Power input, shaft powe

11、r PB (W) 20 3. Fans nS t r u c t u r e a n d p e r f o r m a n c e characteristics n (1) Standard cubic feet ft3/h or m3/h 风 量 n (2) Fan total head(fan total pressure), J/m3, Pa or N/m2. 全风压 n (3) Shaft power, W or kW轴功率 n (4) Efficiency, 效率 21 22 4. Compressor Compression of an ideal frictionless g

12、as 理想压缩循环： 吸气阶段：41 压缩阶段：12 排气阶段：23 23 Actual compression process 实际压缩循环： 吸气阶段：41 压缩阶段：12 排气阶段：23 膨胀阶段：34 24 Clearance factor 余隙系数 %100 31 3 VV V Capacity factor 容积系数 31 41 0 VV VV 11 1 0 k a b p p 25 5. Flowmeters nVenturi meter（文丘里流量计） nOrifice meter（孔板流量计） nRotameters（转子流量计,变截面流量计 ） nPitot tube（测速

13、管） 26 nEXAMPLE A gear pump with efficiency of 80% is used to deliver the liquid from an open tank to a closed vessel and the liquid level for both tanks is maintained unchanged. The readings of pressure gauge in the top of the vessel is 30103Pa. The flow is adjusted by the bypass shown in the attach

14、ed figure. The flow in main pipe with a diameter 663mm, and length 80m(include equivalent length for all kinds of friction loss) is 14m3/h. 27 nFor bypass pipe, which the diameter is322.5mm, the flow is 5m3/h, and the pipe length is 20m(include equivalent length for all kinds of friction loss except

15、 the valve). Flow regime of liquid are the same for both pipes, energy loss from liquid surface of open tank to the branch point of main and bypass pipes can be neglected. The liquid viscosity is 50mPa.s and the density is 1100kg/m3. Calculate: (1) shaft power of pump (2) loss factor for the valve i

16、n bypass. 28 29 nEXAMPLE Water (1000 kg/m3)is delivered by a centrifugal pump from a reservoir to an open tank. The level of the tank is 13m above the level of the reservoir. Friction loss of this pipe system is 3105q2 (q is in m3/s). Flow is complete turbulence. Head-capacity curve of the pump is: nH=28-2.5105q2 (q is in m3/s). 30 n(1) calculate the flow rate, head and shaft power of the pump. (2) if the same system is used to pump alkali solution with density 1250m3/kg,