ppt后习题答案Word文档下载推荐.docx

ppt后习题答案Word文档下载推荐.docx

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105Pa,p2=-33332Pa

Problem4作业1.3

ppt1-2

InaNewtonianfluid，therelationshipbetweenthesheartressandshearrateis（

）

●Keepingthepressureconstant，theviscosityofagaswill（increase）asthetemperaturerising,andtheviscosityofaliquidwill（decrease）asthetemperaturerising

●theeffectofthesolidboundaryontheflowisconfinedtoalayerofthefluidimmediatelyadjacentto（wallofsolid）

●Atlowflowratesthepressuredropinthefluidisproportionaltothe（velocity）;

athighratesitincreasesasthe（squareofthevelocity）.

●Mechanicalenergyisfinallyconvertedto（heat）wheneddiesinfluidareobliteratedbyviscousaction,whichmayleadtoalarge（friction）lossinthefluid.

●Potentialflowhastwoimportantcharacteristics:

（1）neithercirculationsnoreddiescanformwithinthestream

（2）frictioncannotdevelop

ppt1-3

Ø

Bernoulli'

sequationhasfollowingrestrictions

1）idealfluid

2）densityisconstant

3）steady-stateflow

Thetotalenergybalanceisnotoftenusedwhen（appreciableenthalpy）changesoccuror（appreciableheat）isexchangedbetweenthesystemandtheenvironment.

Mechanicenergyincludes（workterm）,（potentialenergy）,（kineticenergy）,and（flowworkpart）oftheenthalpyterm.

4．ExperimentontheconversionofmechanicalenergyshowninFig..

作业1.5

Waterfromthereservoirflowsthroughthepipe,whichthethroatdiameterisd.theratioofDtodequals2,theverticaldistancehbetweenthetankAandaxisofthepipeis1m.

HowmuchtheHisneededifthewateratthetankAislefttothethroatofthepipe?

Assumingthatfluidflowisapotentialflow.

作业1.8

Movingthewaterfromonecontainerintotheotherplacebymeansofapipeofconstantcross-sectionalareaisshownasinfigure.Find

（1）ThevelocityatstationA,B,C,D

（2）ThepressureatstationA,B,C,D

（3）ThemechanicalenergyinstationA,B,C

Assumingthatthewaterflowsthroughthepipewithoutfrictionlosses.

Solution：

1）towriteBernoulliequation1.3-26fromstation1tostationD

simplifying

Andgives

VD=9.9m/s

Fromcontinuityequation

VA=VB=VC=VD=9.9m/s

2）gaugepressurePD=0

writingBernoulliequationbetweenstationsc-dgives

，

PC=-3×

9.81×

1000=-294300Pa

Similarly

PB=1×

1000=9810Pa

PA=-4×

1000=-392400Pa

Totalmechanicalenergymaintainconstantwhenthefluidflowsfromthecontainertotheexit

5=49.05J/kg

ppt1-4

Theaveragevelocityis（0.5）timesthemaximumvelocityatthecenterforlaminarflow.

Theaveragevelocityis（0.8）timesthemaximumvelocityatcenterforturbulentflow

Themaximumvalueofthemomentumfluxoccurs（attheinterfacebetweenthefluidandthewallofsolid）foralaminarflow.

Themaximumvalueofthevelocityoccurs（atthecenterofthetube）foralaminarflowinpipe.

Inlaminarflowthevelocitydistributionwithrespecttoradiusis（parabola）withtheapexatthecenterlineofthepipe

Thepressuredropis（proportional）totheaveragevelocityforthelaminarflow

ppt1-5

•Forlaminarflow,theaveragevelocityinapipeismaximumvelocity,forturbulentflowaveragevelocityismaximumvelocity.

•Forlaminarflowinapipe,theflowrateisconstant,whendiincreases,thefrictioncoefficientwill（increse）,andfrictionlosswill（reduce）.

•Whenthepipeinstallationchangesfromhorizontaltoverticalpositionandthevelocitykeepsunchanged,thefrictionallosswillbeC.

A）.increased;

B）.decreased;

C）.thesame;

D）.uncertain

•Inlaminarflow,thevelocitydistributionwithrespecttoradiusis（）atthecenterlineofthepipe

•Roughnesshas（noeffect）onthefrictionfactorforlaminarflowunlesskisverylarge.

•Forlaminarflow,thefrictioncoefficientisproportionaltoa（reciprocalofRe）

•Forturbulentflow,thefrictioncoefficientisafunctionofboth（roughnessandRe）

•Forcompletelyturbulentflow,thefrictioncoefficientisafunctionof（relativeroughness）

1250cm3/sofwateristobepumpedthroughasteelpipe,25mmdiameterand30mlong,totank12mhigherthanitsreservoir.Calculateapproximatelythepowerrequired.Whatpowermotor（inkW）wouldyouprovide?

Theroughnessofasteelpipewillbetakenas0.045mm;

theefficiencyofthepumpis50%

turbulentflow

frommoodyfigure

作业1.9

Liquidflowsthroughthetube,showninFig.thelengthofabequalscd，andthediameterandroughnessoftubearesame.Find:

（1）theexpressionsofΔpab/（ρg）,hfab,Δpcd/（ρg）andhfcd,respectively.

（2）therelationshipbetweenreadingsR1andR2intheUtube.

两水池的水位差H=24m，l1=l3=l4=100m，d1=d2=d4=100mm，

d3=200mm，沿程阻力系数λ1=λ2=λ4=0.025，

λ3=0.02，除阀门外，忽略其他局部阻力。

（1）阀门局部阻力系数ζ=30，求管路中的流量；

（2）关闭阀门，其他条件不变，求管路中的流量。

解：

假设2、3的l相等

1）由

得

流量

总摩擦阻力损失

故u3=0.575m/su1=3m/sQ=0.024m3/s

2）

得u1=2.5m/sQ=0.0196m3/s

ppt1-7

●orificeandventurimetersmeasuretheaveragevelocityoftheentirestreamoffluid

●Thepitottubemeasuresthelocalvelocityoffluid.

●Rotametermustbeverticallyinstalledinthepipeline,andthefluidmustflowupwardthroughthetaperedtubeandsuspendsfreelyafloat.

vIntheorificeandventurimeter,thevariationofvelocitythrough（constant）areageneratesa（variable）pressuredrop.

vIntherotameter,thevariationofflowratethrough（variable）areageneratesa（constant）pressuredrop.

vForaorifice,nozzleandventurimeter,whentheReynoldsnumberisgreaterthancriticalRe,thenorificecoefficientCois（onlydependent）oftheReynoldsnumberforagivenβ

Sulphuricacidofspecificgravity1.3isflowingthroughapipeof50mminternaldiameter.Athin-lippedorifice,10mm,isfittedinthepipeandthedifferentialpressureshownbyamercurymanometeris10cm.Assumingthattheleadstothemanometerarefilledwiththeacid,calculate（a）theweightofacidflowingpersecond,and（b）theapproximatepressuredropcausedbytheorifice.Thecoefficientoftheorificemaybetakenas0.61,thespecificgravityofmercuryas13.6,andthedensityofwateras1000kg/m3

（a）themassflowratemisgivenby

Or,where

isapproximatelyunity,m=0.268kg/s

（b）theapproximatepressuredropcausedby（13600-1300）×

0.1=12066.3Pa

Waterflowsthroughanorificeof25mmdiametersituatedina75mmpipeattherateof300cm3/s.whatwillbethedifferenceinlevelonawatermanometerconnectedacrossthemeter?

Taketheviscosityofwateras1mNs/m2.

Thevelocityflowingthroughhole

velocityflowingpipe

theratioofarea:

m=0.11

so

Co=0.61

R=51.2mm

Wateristransportedbyapumpfromreactor,whichhas200mmHgvacuum,tothetank,inwhichthegaugepressureis0.5kgf/cm2,asshowninFig.Thetotalequivalentlengthofpipeis200mincludingalllocalfrictionalloss.Thepipelineis57×

3.5mm,theorificecoefficientofCoandorificediameterdoare0.62and25mm,respectively.Frictionalcoefficientis0.025,Find:

DevelopedheadHofpump,inm.（thereadingRofUpressuregaugeinorificemeteris168mmHg）

Pr=-200×

13.6×

9.81=-26683.2PaPt=49035Pa，

PressuredropinU

∆p=0.168×

（13600-1000）×

9.81=20765.8Pa

fromcontinuityequation:

1.6m/s

skinfrictionloss

developedhead

ppt2-1

●Ifacentrifugalpumpoperatesonair,then,itcann’tdrawliquidfromaninitiallyemptysuctionline。

●Positive-displacementpumpsarenotsubjecttoairbinding.

●Beforeacentrifugalpumpstartsup,closethevalveindischargeinotherto（reduce）thestart-uppowerrequired

●Whenthetemperatureoffluidtobetransportedincreases,themaximumliftofsuctionwill（B）.Ifthevelocityofsuctionpipedecreases,themaximumsuctionliftwill（A）.Iftheflowrateremainsconstantbutthediameterofsuctionpipedecreases,themaximumsuctionliftwill（B）

A）increase;

B）decrease;

C）keepthesameD）beuncertain

●Whenthesuctionpressureis（close）tothevaporpressure,thecavitationwilloccur

●Thedifferencebetweenthetheoreticalandactualcurvesresultsfrom（shockloss）;

（frictionloss）;

and（recirculationloss）.

•Whenhigherdevelopedheadisrequired,thebestselectionis（B）.

A）operationinseriesB）multistagecentrifugalpumpC）throttledbyvalve

●（×

）OnepumpcandevelopmoreHthanthattwosamepumpswhichworkinseries.

●Themethodsofadjustingvolumeflowrateofcentrifugalpumpare

（1）changesinrevolutionofpump;

（2）changeofdiameterofimpeller;

（3）adjusttheopeningof