PRESENTATIONON

CENTIFUGAL PUMPS

FLUID POWER ENGINEERING

SUBMITTED BY:

HIMANSHI GUPTA (140120119057)/ ME/A2PRACHI SHARMA(140120119216) / ME / A2

(2151903)

GANDHINAGAR INSTITUTE OF TECHNOLOGY

CENTRIFUGAL PUMPS

PUMP:• The hydraulic machine which converts the mechanical

energy into hydraulic energy (form of pressure energy).

CENTRIFUGAL PUMP:• The hydraulic machine which converts mechanical

energy into pressure energy by means of centrifugal force acting on the fluid.

• Purpose: • To increase pressure energy• To impart kinetic energy• To lift and circulate• To exhaust or extract liquids

CLASSIFICATION OF PUMPS

1) Positive displacement pumpi. Reciprocating pumpsa) Piston pumpsb) Plunger pumpsc) Bucker pumpsii. Rotory pumpsa) Gear pumpsb) Vane/lobe pumpsc) Screw pumps

2) Roto-dynamic pumpa) Radial flow pumpb) Axial flow pumpc) Mixed flow pump3) Other type of pumpsa) Jet pumpb) Air lift pump

MAIN PARTS OF CENTRIFUGAL PUMP

ImpellerCasing• Volute casing• Vortex casing• Casing with guide bladesSuction pipe with a foot valve and a strainerDelivery pipe

CLASSIFICATION OF CENTRIFUGAL PUMPS

1) According to shape of impeller and casinga) Volute or spiral casing type pumpb) Vortex (whirpool) casing type pumpc) Diffuser type pump2) According to type of impellera) Closed or shrouded impellerb) Semi-open impellerc) Open impeller3) According to working heada) Low head centrifugal pumpb) Medium head centrifugal pumpc) High head centrifugal pump

4) According to number of stagesa) Single stage centrifugal pumpb) Multi-stage centrifugal pump• Impeller in series• Impeller in parallel5) According to direction of flow through impellera) Radial flow pumpb) Axial flow pumpc) Mixed flow pump6) According to number of entrances to the impellera) Single suction pumpb) Double suction pump7) According to specific speed of pumpa) Low specific speed pumpb) Medium specific speed pumpc) High specific speed pump

VELOCITY DIAGRAM AND WORK DONE BY IMPELLER

• Centrifugal pump acts as a reversed of an inward radial flow reaction turbine.

• Assumptions made for analysis are:-1. Liquid enters the impeller in radial direction2. No energy loses in impeller due to friction

and eddy formation3. Liquid enters without shock

VELOCITY DIAGRAM

WORK DONE BY CENTRIFUGAL PUMP

• u1= ω R1, u2 =ω R2

• Mass of water striking /sec = (

• Momentum of water striking the vanes at Inlet = ( Vw1 , Outlet = ( Vw2

• Angular Momentum of water striking the vanes at inlet = ( Vw1 x R1 (Vw1= V1 cos α )

at Outlet = ( Vw2 x R2 (Vw2= V2 cos β)

• T = Rate of change of Angular Momentum = ( Vw1 x R1 – ( Vw2 x R2 ) = (

• Work done/sec = T x ω = x ω = =

WORK DONE BY CENTRIFUGAL PUMP

• Work done/sec/unit weight of water/sec = x

• Work done/sec/unit weight of water/sec = – • Work done/sec/unit weight of water/sec = - = - (Vw1 = 0)

WORK DONE BY CENTRIFUGAL PUMP

HEADS OF CENTRIFUGAL PUMP

where : Vs = Velocity of fluid in the suction pipe. Vd = Velocity of fluid in the delivery pipe hs = Suction head. hd = Delivery head. hfs = head losses in the suction pipe. hfd = head losses in the delivery pipe.

hst = static head

EFFICIENCIES OF A CENTRIFUGAL PUMP

1- Hydraulic Efficiency (ζh)

)()('

eh HHeadEuler

HHeadTotalsPump

22UVgH

wh

2- Manometric Efficiency(ζm)

)()('

e

mm HHeadEuler

HHeadManometricsPump

22UVgH

w

mm

3 -Volumetric Efficiency (ζv)

QQQ

v The normal value lies between 97% to 98%

4- Mechanical Efficiency (ζ)It is due to losses in the shaft, coupling, and other operation losses as vibration

shafttheatPowerimpellerthetoinPower

ShaftPowerUVQQ w

)( 22

The normal value is 95% - 98%

5 - Overall Efficiency (ζo)

.T

QHPP

in

outo

hQQQH

PP

PP

PP

lin

t

in

t

t

outo

)(

hvmo The normal value is 71% - 86%

LOSSES IN CENTRIFUGAL PUMP

1) Hydraulic losses2) Mechanical losses3) Leakage losses

TYPES OF IMPELLERS

• There are three main categories of impeller due type of impeller’s vane, which are used in the centrifugal pumps as;

1. Radial vanes, Fig. (a).2. Backward vanes, Fig. (b).3. Forward vanes, Fig. (c).

MINIMUM SPEED FOR STARTING A CENTRIFUGAL PUMP

• When a centrifugal pump is started, it will start delivering liquid only if the pressure rise in the impeller is more than or equal to the manometric head.

• Flow will commence only if ≥Hmano

• For minimum speed ,we must have: = Hmano ……………(1)

2 22 1

2u ug

2 22 1

2u ug

2 22 2

mano manomano

wW

H gHV uV u

g

2 2

11 60

wmano mano

V uH

gD Nu

22 60

D Nu

Substitute the value in eqn. 12 2

22 1 212 60 60 60

wmano

VD N D N D Ng g

2 22 1 2 2120 mano w

N D D V D

2 2

min 2 22 1

120 mano wV DND D

CAVITATION IN CENTRIFUGAL PUMP

• Cavitation begins to appear in centrifugal pumps when the pressure at the suction falls below the vapour pressure of the liquid. The intensity of cavitation increases with the decrease in value of NPSH.

• In a centrifugal pump , the pressure is lowest at the inlet of the impeller and hence vapour bubbles are formed in the suction region.

• These bubbles are carried along with the flowing liquid to higher pressure region near the exit of impeller where these vapour bubbles collapse.

• Due to sudden collapsing of bubbles on metalic surface the high pressure is created, which cause pitting action on metalic surface and produces noise and vibrations.

CAVITATION• Factors responsible for cavitationi. High impeller speedii. Small diameter of suction pipe and inlet of impelleriii. Too high specific speediv. Required NPSH > Available NPSHv. High temperature of flowing fluid

• The harmful effects of cavitation are:-i. Pitting and erosion of surfaceii. Sudden drop in head, efficiencyiii. Noise and vibration.

CAVITATIONThomas cavitation factor is used to indicate the onset of cavitation.

2

2

atm v s

mano mano

ss s fs

atm

H H HNPSHH H

VH h hg

H

atmospheric pressure head

Thank You