centrifugal pump - fkm.utm.mysyahruls/resources/skmm2323/4-cp-1.pdf · pressure difference across...
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CENTRIFUGALPUMP
BASICEQUATIONRotationalspeed
= = ?@ =ABC
60
= = linearvelocityinm/s? = radiusinm@ = angularvelocityinrad/sB = diameterinmC = rotationperminutePowerOPQR? = S ∙ U = O ∙ V ∙ U = WXℎ ∙ VU = WXℎ ∙ Z
OPQR? = WXZ ∙ ℎ
[P?\ = Torque×AngularvelocityWork
[P?\ = Force×Distance
TURBOMACHINESTurbomachines are the commonly employed devicesthateithersupplyorextractenergyfromaflowingfluidbymeansofrotatingpropellersorvanes.PUMP:Pumpaddsenergytoasystem,withtheresultthatthepressureisincreased.Italsocausesflowtooccuroritincreasestherateofflow.TURBINE:Aturbineextractsenergyfromasystemandconvertsittosomeotherusefulform,typically,toelectricpower.Hydroturbine:isamachinethatgeneratespowerfromhigh-pressure water; relatively large conduits ortunnels deliver fluid to closed turbines in order togeneratepower.Anotherexample:steamturbineandairturbine.
PUMPCLASSIFICATION
CENTRIFUGALPUMPAcentrifugalpumpconsistsoftwoprincipalparts:(1) Impeller: which imparts a rotarymotion to the
liquid.(2) Housing or casing:which directs the liquid into
theimpellerregionandtransportsitawayunderahighpressure.
Theimpellerismountedonashaftandisoftendrivenbyanelectricmotor.The casing includes the suction anddischargenozzlesand houses the impeller assembly. The portion of thecasingsurroundingtheimpelleristermedthevolute.Liquidentersthroughthesuctionnozzletotheimpellereye and travels along the shroud, developing a rotarymotionduetotheimpellervanes.
It leaves the volute casing peripherally at a higherpressurethroughthedischargingnozzle.Somesingle-suctionimpellersareopen,withthefrontshroudremoved.Double-suctionimpellershaveliquidenteringfrombothsides.
HEADOFPUMP(Manometrichead)This isdefinedbyBritishStandardsas the sumof theactuallift(H)+thefrictionlossesinthepipes(hf)+thedischargevelocityhead.
rs = r + ℎt +Uuv
2X=Ov − OxWX
+Uvv − Ux
v
2X
However, for special pumps allowance must also bemadeforthevelocityofflowtowardsthesuctionintakeandanypressuredifferencesatthewatersurfacesinthesupplyandreceivingtanks.Commonly thesuctionanddeliverypipesareofequaldiameter.Inwhichcase:
rs =Ov − OxWX
VELOCITYTRIANGLE
Legend:Atinlet(1)=x = ?x@ = Tangetialvelocityofimpeller{x = Absolutevelocityat|xtotangent{}x = {x − =x = RelataivevelocitytoimpellerbladeComponentvelocityfor{x:{~x = Whirlvelocity{tx = Radialflowvelocity�x = InletbladeangleAtoutlet(2)=v = ?v@ = Tangetialvelocityofimpeller{v = Absolutevelocityat|vtotangent{}v = {v − =v = RelataivevelocitytoimpellerbladeComponentvelocityfor{v:{~v = Whirlvelocity{tv = Radialflowvelocity�v = Inletbladeangle
BLADETYPE1. Forwardblade2. Radialblade3. Backwardblade
FORWARDBLADE
RADIALBLADE
BACKWARDBLADE
THEEFFECTOFBLADETYPECentrifugalpumpsdonotalwayshavebackwardcurvedvanes. Butwhen they do, it ismostly for fluids in theincompressibleregimeofoperationsuchaswater.Forcompressible operation of fluids such as air, forwardcurve-vanedcentrifugalpumpsareused.Thenetidealheaddevelopedbyacentrifugalpumpisgivenby:
rÇuÉÑÖ = V − ÜZZ = volumeflowrateattheimpelleroutletV, Ü = constantforagivenimpellerrunningatagivenspeed
Additionally,Ü ∝ cot �v .
Donotethatthevalueoftheactualheaddevelopedbythepumpwillbe lower than this idealvalueowing toshocks
ràâäãå = çx Zu − Zv
Zu = designvolumeflowrateZ = actualvolumeflowrate
Frictioncanbecalculatedby:
ℎt = çvZv
whichtogetherconstitutehydrauliclosses.
The power required to drive the pump to provide agivenflow-rateisgivenas:
O = WXZ ∙ rÇuÉÑÖTherepresentativecurvesaregivenbelow.
Asisevidentfromthepower-dischargecharacteristicsof the radialand forwardvanedcentrifugalpump, thepower requirement increases monotonically with anincreaseindischarge.Hence,ifthepumpmotorisratedformaximumpower,thenitwillremainunder-utilizedformostoftheoperatingtime,andresultinanincreasedcost due to its higher rating. On the other hand, if amotor is rated at the design point, and due to somereasontheflow-rateexceedsthedesignflowrate,thenthepowerrequirementwillshootup(incaseofforwardandradialvanesonly),causingoverloadingandmotorfailure.However,forbackwardcurve-vanedcentrifugalpumps,if the flow-rate exceeds the design flow rate (occursquiteclosetothemaximaofthepower-dischargecurve),thencontrarytotheearliercase,thepowerrequirementdropsdownasevidentfromthecurves.Thisenablesthemotorwhichisratedatthedesignpowertohandletheentire range of flow-rates without any problems. Theactualdesignpointislocatedcorrespondingtotheflow-rateatwhichmaximumefficiencyoccurs.
EULERHEADTorque=kadarperubahanmomentumsudutMomentumsudut=(jisim)×(halajutangen)×(jejari)
Momentumsudutmasuk = è{~x?x
Momentumsudutkeluar = è{~v?v
è = kadarjisimmengalirsesaatKadarperubahanmomentumsudut:
ê = è{~v?v − è{~x?x
è = WVU = WZ
ê = WZ {~v?v − {~x?x
Diketahuipowerialah:
O = ê@
O = WZ {~v?v − {~x?x @Diketahui:
= = ?@
=x = ?x@
=v = ?v@
?x =ëíìand?v =
ëîì
Diketahuipowerialah:
O = WZ {~v?v − {~x?x @
= WZ {~v=v@− {~x
=v@
@
= WZ {~v=v − {~x=x
Powerjugabolehditulissebagai:
O = WXZ ∙ ℎ
Jika power adalah maksimum, nilai h ialah nilaimaksimum, iaitu niai power dalam keadaan tiadakehilangantenaga(losses,friction,etc).Nilaihbolehditulissebagairñ(Eulerhead)
O = WXZ ∙ rñ = WZ {~v=v − {~x=x
rñ =1
X{~v=v − {~x=x
IakenalisebagaiEulerhead(turusEuler).Unitnyadalammeter(m).Ia adalah turus ideal yang dihasilkan oleh impeller(pendesak)dalamsystempam.
PUMPEFFICIENCY(kecekapanpam)Manometricefficiency
ósÑòä =Kuasaairyangdihasilkan
Kuasaimpeller
=WXZ ∙ rsWXZ ∙ rñ
=
WXZ ∙ rs
WXZ ∙1X {~v=v − {~x=x
ósÑòä =Xrs
{~v=v − {~x=x
Mechanicalefficiency
ósÉãâ =Kuasaimpeller
Kuasayangdiberikankepadasyaf
ósÉãâ =
1X {~v=v − {~x=x
OÇòôëö
Overallefficiency
óä =Kuasaairyangdihasilkan
Kuasayangdiberikankepadasyaf
óä =WXZ ∙ rsOÇòôëö
CENTRIFUGALPUMPTUTORIALO1
QUESTION1A centrifugal pump is driven by an electricmotor at 1450 rpm.Outletdiameterofblade,outletbladewidthandoutletbladeangleare600mm,400mmand30o,respectively.Inletdiameterofblade,inletbladewidthandinletbladeangleare300mm,80mmand20ᵒrespectively. Pressure at suction pipe and delivery are positive13.5 bar and negative 0.5 bar, respectively. Assume that thediameter for suction and delivery pipes is equal. The flowrateinsidethepumpis0.3m3/s.Determine:i. Themonometrichead,Hmii. Themanometricefficiency,WXiii. Powerrequiredbyelectricmotorifoverallefficiencyis98%.QUESTION2Acentrifugalpumphasinletandoutletdiameterof30cmand60cm,respectively.Impellerwidthatoutletis12cm.Bladethicknessoccupied10percentofthecircumference.Bladeisbackwardwithinlet and outlet blade angle is 30ᵒ and 40ᵒ, respectively. Theflowrateis0.5m3/s.Assumetherearenowhirlatinletandvelocityofflowisconstantdetermine:i. Therotationofpumpinrpmii. Theoutputpowerifmanometricefficiencyis85%iii. Thepressuredifferenceacrosstheimpeller
QUESTION3Centrifugalpumpsupplieswaterattherateof400liter/sandthepressuredifferenceacrossthepumpis200kN/m3.Outletdiameterandoutletwidthare40cmand10cm,respectively.Bladethicknessoccupied10%ofthecircumference.Impellerinletdiameterishalfof theoutletdiameter.Assume losses in casingand impellerarenegligible and zero whirl at inlet. The diameter of suction anddeliverypipesisequal.Ifthebladesareradial,determine:i. Thepumppowerinputinhorsepowerifoverallefficiencyis
80%ii. Theimpellerspeedinrpmiii. TheinletbladeangleifvelocityofflowisconstantQUESTION4Theinletandoutletimpellerdiameterofcentrifugalpumpare200mmand400m,respectively.Impellerwidthatinletandoutletare15mmand8mm,respectively.Bladesarebackwardwithangleof38ᵒ. Pump operates at 1500 rpm. The flowrate is 15 liter/s.Determinethepressurechangesintheimpeller.Assumenoenergylosses.
QUESTION01
QUESTION02
QUESTION03
QUESTION04