1、1第四章顆粒流體兩相流動 Chapter 4Particle-fluid two-phase flow2Fluidized bed granulator dust to secondary collectorproductover-size particlespart productfinesliquid + gaspowders1234567895101 lift 2 feeder 3 fluidized bed 4 cyclone 5 transfer screw 6 sprayer7 product screw 8 sieve 9 blower 10 breaker 3Fluidized

2、 granulator4Pneumatic transportDefinition using gas (often air) to suspend and transfer particles in pipes.Suitable for fines or particles with sizes from microns to a few millimeters.advantages high efficiency；particles keep clean and no pollution; easily automation； particles can be treated during

3、 transfer (drying, coating or reaction).disadvantages high energy consumption; particles, equipment and pipeline breakage or abrasion. 5Pneumatic transport system氣源顆粒進料與加速段穩(wěn)定輸送段氣固分離裝置blowerhopperentry stageacceleratestageexpansion dense phasedilute phaseelbow highabrasionG-S separation6Flow pattern

4、for vertical transportFlow pattern in pneumatic transport This two-phase flow shows several flow patterns and subjected to transition in between.vertical transportEffect parameter gas velocityResult pressure drop in pipepower consumption can be a function of flow patterncan be in dense or dilute pha

5、sesuniformlittleaggregateaggregate slugging Pressure drop for vertical transport 壓降最低曲線 densedilute“哽噎”速度 appearance velocity, u ABabcdeeeeeaaabbbbccccdddd1G2G3G4G5G0Gp/LMinimum P7Flow pattern in pneumatic transportHorizontal transportIn this process, the gravity is perpendicular to the flow and the

6、 force to suspend particles is buoyancy from the flow. The flow pattern is usually in dense phase.Flow pattern for horizontal transportuniform dilute particle aggregation deposit velocity sand hill flow blocking Pressure drop for horizontal transportdead velocity appearance velocity, u D p/L12345Min

7、imum pressure drop8The pressure drop in this system comes from transport pipe, dust collecting section, pipe parts and valves. wherepf friction between pipe wall and gaspa particle accelerationpr particle suspension and rising pi collision and friction between particle and pipe wallIn straight pipes

8、Pressure drop in pneumatic transport9Modeling of pneumatic transporttwo-phase model流體相 Considering particle and gas as two interaction phases，balance the momentum in a differential length L in a pipe，respectively.顆粒相u, c average velocities of two phasesmg , mp masses of two phases in C. V.If the voi

9、dage is ，then For particle phaseFor gas phase 10Modeling of pneumatic transporttwo-phase modeldrag of fluid to particle, Fdinter-phase relative velocityFriction in fluid phase, Ff,g (let free section fraction as Friction in particle phase, Ff,p can be expressed asThe forces in two phases from pressu

10、re drop, Fp,g and Fp,p are11Modeling of pneumatic transporttwo-phase modelAll the dynamic factors and p are related with voidage and the voidage is strongly affected by the feed rate and the velocities of gas and particles.then, the feed mass ratioLet particle and gas mass flow rates G and qm, respe

11、ctively, = 15 is often used as the criterion for flow pattern. Actually，even with same ，the flow pattern can be different for different velocity and particle properties. or volume ratio 12Modeling of pneumatic transporttwo-phase modelUnder uniform distribution, the relationship between , c and u1 ar

12、e The key of two-phase model is the inter-phase force, Fd , but it is difficult to predict in practice. Therefore, the usefulness of this model is limited at some situations.13Virtual homogeneous phase modelConsidering the system as a single phase and omitted the inter-phase force, Fd . The system i

13、s simplified and the result is correct in dilute phase situation. In steady section where the accelerations are zeroFor horizontal, the first two terms can be omittedThe particle velocity, c can be calculated with IGT (Institution of Gas Technology) correlation Konno & Saito Eq. Where friction facto

14、r in gas phase p friction factor in particle phase14Types and installations of transport systemDilute phase ( 15） For transfer operated in negative pressure, dilute phase are more common.The system can be divided as two typesfansuction head15Types and installations of transport systemFor positive pr

15、essure operations, they can be divided as：low pressure 100 kPa；middle pressure300 kPa；high pressure1000 kPa blowervent16Types and installations of transport systemCombine systemblowerdistribution valve17Types and installations of transport systemSelection of blowersThe blower character curve should

16、meet the pressure drop curve in the figure.When feed is G1 , blowers II and I meet the operation condition.When feed is increased to G2 , blower I can not meet the dilute transport condition.As for feed G3 , both blowers can not meet the condition. If slope of the blower character curve is large, the adjustment range of feed is wide. 18Types and installations of transport system Feeder selection Several factors should be considered, as particle properties (size, shape, and sphericity, etc.),