Flow Through Orifices - Hydraulics

Flow Through Orifices, Orifice, Types of Orifice according to Shape Size Edge Discharge, Jet, Venacontracta, Hydraulic Coefficients, Coefficient of Contraction,Coefficient of Velocity, Coefficient of Discharge, Coefficient of Resistance, Hydraulic Coefficients by Experimental Method, Discharge Through a Small rectangular orifice, Discharge Through a Large rectangular orifice, Discharge Through a Fully Drowned orifice, Discharge Through Partially Drowned orifice, Mouthpiece and its types. By Engr. M. Jalal Sarwar

2. ORIFICE
•Anopening,inavesselorcontainer,through
whichtheliquidflowsoutisknownasan
Orifice.
•TheholeoropeningiscalledOrifice,solongas
theleveloftheliquidontheupstreamsideis
abovethetopoftheorifice.
•Theusualpurposeofanorificeisthe
measurementofdischarge.
•Anorificemaybeprovidedintheverticalside
ofthevessel/containerorinthebase.
BY ENGR. M. JALAL SARWAR

3. TYPES OF ORIFICE
•Therearemanytypesoforifices,dependingupontheirsize,shape&
natureofdischarge.Butthefollowingareimportant:
1)TypesAccordingtoSize:
a)SmallOrifice:IftheheadoftheliquidfromthecenterofOrificeismore
thanfivetimesthedepthoftheOrifice,calledSmallOrifice.
b)LargeOrifice:Iftheheadoftheliquidislessthanfivetimesthedepthof
Orifice,calledLargeOrifice.
2)TypesAccordingtoShape:
a)CircularOrifice
b)RectangularOrifice
c)TriangularOrifice
d)SquareOrifice
BY ENGR. M. JALAL SARWAR

4. TYPES OF ORIFICE
3)TypesAccordingtoEdge:
a)SharpEdgedOrifice
b)SquareEdgedOrifice
c)Bell-MouthedOrifice
BY ENGR. M. JALAL SARWAR

5. TYPES OF ORIFICE
4)TypesAccordingtoDischarge:
a)FreeOrifice:Iftheheightoftheliquidsurfaceondownstreamsideisdown
fromtheOrifice,itiscalledFreeOrifice.
b)FullyDrownedOrifice:Iftheheightoftheliquidsurfaceondownstream
sideishigherthantheOrifice,thenitiscalledFullyDrownedOrifice.
c)PartiallyDrownedOrifice:Iftheheightoftheliquidsurfaceon
downstreamsideishigherthanthebaseoftheOrificebuttheOrificeisnot
fullysubmergedintheliquid,thenitiscalledPartiallyDrownedOrifice.
BY ENGR. M. JALAL SARWAR

6. TYPES OF ORIFICE
BY ENGR. M. JALAL SARWAR

7. TECHNICAL TERMS
1.Jet:
•Thecontinuousstreamofliquid,thatcomesoutorflows
outofanOrifice,isknownastheJetorJetof
Water/Liquid.
2.Vena-contracta:
•WhentheliquidpassesthroughtheOrificeintheformof
Jet,itlosesomeenergy.Ithasbeen,thus,observedthat
thejet,afterleavingtheOrifice,getscontracted.The
maximumcontractiontakesplaceatasectionslightlyon
thedownstreamsideoftheOrifice,wherethejetmore
orlesshorizontal.SuchsectionisknownasVena-
contracta.
3.VelocityofApproach:
•Velocityofaliquid,whenitapproachesatOrifice,is
calledVelocityofApproach.
BY ENGR. M. JALAL SARWAR

8. HYDRAULIC COEFFICIENTS
•TheratioofActualQuantity(velocityordischargeetc.)&
TheoreticalQuantity(velocityordischargeetc.)iscalled
HydraulicCoefficients.
•ThefollowingfourcoefficientsareknownasHydraulic
CoefficientsOROrificeCoefficients.
1.CoefficientofContraction
2.CoefficientofVelocity
3.CoefficientofDischarge
4.CoefficientofResistance
BY ENGR. M. JALAL SARWAR

9. HYDRAULIC COEFFICIENTS
1.COEFFICIENTOFCONTRACTION:
•TheratioofareaoftheJet,atVena-contracta,totheareaofthe
Orifice,isknownasCoefficientofcontraction.
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•Thevalueofthecoefficientofcontractionvariesslightlywiththe
availableheadoftheliquid,size&shapeoftheOrifice.
•AnaveragevalueofC
cisabout0.64.
BY ENGR. M. JALAL SARWAR

10. HYDRAULIC COEFFICIENTS
2.COEFFICIENTOFVELOCITY:
•Theratioofactualvelocityofthejetatvena-contracta,tothe
theoreticalvelocityisknownascoefficientofvelocity.
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•ThevalueofC
vistaken0.95–0.99,where0.97isconsideredas
averagevalue.
BY ENGR. M. JALAL SARWAR

11. HYDRAULIC COEFFICIENTS
3.COEFFICIENTOFDISCHARGE:
•TheratioofactualdischargethroughanOrificetothetheoretical
dischargeisknownasCoefficientofDischarge.
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•Anaveragevalueofcoefficientofdischargevariesfrom0.60–0.64.
BY ENGR. M. JALAL SARWAR

12. HYDRAULIC COEFFICIENTS
4.COEFFICIENTOFRESISTANCE:
•Theratiooflossofhead(lossofK.E)intheOrificetotheheadof
water(actualK.E)availableattheexitoftheOrificeisknownas
CoefficientofResistance..
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•ThelossofheadintheOrificetakesplace,becausethewallsofthe
Orificeoffersomeresistancetotheliquidasitcomesout.
•TheC
risgenerallyneglected,whilesolvingnumericalproblems.
BY ENGR. M. JALAL SARWAR

13. HYDRAULIC COEFFICIENTS BY EXPERIMENTAL METHOD
Inlaboratories,HydraulicCoefficientscanbefound.Itsexperimentalmethod
isgivenas:
•Consideratankcontainingwaterataconstantlevel,maintainedbya
constantsupply,asshowninFig.
•LetthewaterflowoutofthetankthroughanOrifice,fittedinonesideof
thetank.ConsideraparticleofwaterinthejetatP.LetthesectionC-C
representthepointofvena-contracta.
BY ENGR. M. JALAL SARWAR

14. HYDRAULIC COEFFICIENTS BY EXPERIMENTAL METHOD
Let H= Constantwaterhead
x= HorizontalDistancebetweenC-CandP
y= VerticalDistancebetweenC-CandP
v= Velocityofthejet,
t= Time(Second)takenbytheparticletoreachfromC-CtoP
Where�=
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& �=??????×??????
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BY ENGR. M. JALAL SARWAR

15. HYDRAULIC COEFFICIENTS BY EXPERIMENTAL METHOD
Substitutingthevalueof“t”inequation(i)
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Thisisanequationofaparabola.Itis,thus,obviousthatthepathofajetisalso
aparabola.Wealsoknowthatthetheoreticalvelocityofaparticleis,
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BY ENGR. M. JALAL SARWAR

16. HYDRAULIC COEFFICIENTS BY EXPERIMENTAL METHOD
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Thesimplestmethodofdeterminingthecoefficientofdischargeisby
measuringtheactualquantityofdischargethroughtheOrificeinagiven
time.Thisactualdischargemay,then,bedividedbythetheoretical
discharge,whichwillgivetherequiredvalueofthecoefficientof
discharge.Mathematicallycoefficientofdischargeis
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BY ENGR. M. JALAL SARWAR

17. HYDRAULIC COEFFICIENTS BY EXPERIMENTAL METHOD
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Nowthecoefficientofcontractionmaybefoundoutbymeasuringthe
actualareaofthejetatvena-contractaandthendividingbytheareaof
thejet.Mathematicallycoefficientofcontractionis
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Themeasurementofareaofthejetatvena-contractaisabitdifficult,as
itrequiresalotoftimeandpatience.Thecoefficientofcontractionmay
alsobeeasilyobtainedbytherelation,
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BY ENGR. M. JALAL SARWAR

18. DISCHARGE THROUGH A SMALL RECTANGULAR ORIFICE
•AnOrificeisconsideredtobesmall,iftheheadofwaterismorethan5times
theheight/depthoftheOrifice.
•InasmallerrectangularOrifice,thevelocityofwaterintheentirecross-
sectionofthejetisconsideredtobeconstant.
•ThedischargethroughsuchanOrificeisgivenbytherelation:
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WhereC
d=CoefficientofdischargefortheOrifice
a=Cross-sectionalareaoftheOrifice
h=HeightoftheliquidabovethecenteroftheOrifice
b=WidthoftheOrifice
d=DepthoftheOrifice
BY ENGR. M. JALAL SARWAR

19. DISCHARGE THROUGH A LARGE RECTANGULAR ORIFICE
•AnOrificeisconsideredtobelarge,iftheheadofwaterislessthan5
timestheheight/depthoftheOrifice.
•InlargerectangularOrifices,thevelocityofvariousliquidparticleswill
notbeconstant,becausethereisaconsiderablevariationofhead
alongtheheightofanOrifice.
•Thevelocityofliquidvarieswiththeavailableheadoftheliquid.
BY ENGR. M. JALAL SARWAR

20. DISCHARGE THROUGH A LARGE RECTANGULAR ORIFICE
•ThedischargethroughalargeOrificeisgivenby:
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WhereQ = Discharge through a large Orifice
h
2= Head above the bottom of Orifice
h
1= Head above the top edge of Orifice
C
d= Coefficient of Discharge
b = Width of Orifice
g = Gravitational Acceleration
BY ENGR. M. JALAL SARWAR

21. DISCHARGE THROUGH FULLY DROWNED ORIFICE
•SometimestheentireoutletsideoftheOrificeisundertheliquid.Itisknownasa
whollysubmergedOrificeasshowninFig.InsuchOrifice,thecoefficientof
contractionisequaltoone.
•ThedischargethroughafullydrownedOrificeisgivenby:
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Q=Discharge
h= Difference of water levels either side of the Orifice
h
2= Head above the bottom of Orifice
h
1= Head above the top edge of Orifice
C
d=CoefficientofDischarge
b=WidthofOrifice
d=DepthofOrifice
BY ENGR. M. JALAL SARWAR

22. DISCHARGE THROUGH PARTIALLY DROWNED ORIFICE
•IftheoutletsideofanOrificeispartlyunderwater,itisknownas
partiallydrownedorpartiallysubmergedOrificeasshowninFig.
•ThedischargethroughapartiallydrownedOrificeisobtainedby
treatingthelowerportionasadrownedOrificeandtheupperportion
asanOrificerunningfree,&thenbyaddingthetwodischargesthus
obtained.
BY ENGR. M. JALAL SARWAR

23. DISCHARGE THROUGH PARTIALLY DROWNED ORIFICE
Weknowthatdischargethroughthefreeportionis
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&dischargethroughthedrownedOrificeis
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Nowtotaldischargeis
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BY ENGR. M. JALAL SARWAR

24. MOUTHPIECE
•SometimeswithOrifice,ashortpipeisfitted,whichwillincreasethe
valueofcoefficientofdischarge.
•Asweknowthattheincreaseinthevalueofcoefficientofdischarge
willincreasethedischargethroughtheOrifice.
•Suchapipe,whoselengthisgenerallymorethan2timesthediameter
oftheOrificeandisfitted(externallyorinternally)totheOrifice,is
knownasaMouthpiece.
•Mouthpieceisusedformeasuringtherateofflowofliquid.
BY ENGR. M. JALAL SARWAR

25. CLASSIFICATIONS OF MOUTHPIECE
•Dependingupontheirpositionwithrespecttothetanktheyare
classifiedas
ExternalMouthpiece
InternalMouthpiece
BY ENGR. M. JALAL SARWAR

26. CLASSIFICATIONS OF MOUTHPIECE
•Dependingupontheirshapethey
areclassifiedas
CylindricalMouthpiece
ConvergentMouthpiece
Convergent-Divergent
Mouthpiece
•Accordingtothenatureof
dischargeattheoutletof
mouthpiecetheyareclassifiedas
MouthpiecesRunningFull
MouthpiecesRunningFree
BY ENGR. M. JALAL SARWAR