Cb31516522

Prasanta Kumar Sen, Lal Gopal Das, Biswajit Halder / International Journal of Engineering
Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 3, Issue 1, January -February 2013, pp.516-522
The Characteristics of a Vertical Submersible Slurry Pump in
Transporting Dredged Slurry
Prasanta Kumar Sen*, Lal Gopal Das** & Biswajit Halder***
*
(PPE, CSIR-Central Mechanical Engineering Research Institute, Durgapur-713209, India)
**
(PPE, CSIR-Central Mechanical Engineering Research Institute, Durgapur-713209, India)
***
(ME, National Institute of Technology, Durgapur-713209, India)

ABSTRACT
The performance of vertical centrifugal of the centrifugal slurry pump depends on particle
slurry pump is quite different from clear water size, size distribution, shape, solid concentration,
pump due to presence of solid particles in water. solid specific gravity, pump speed and certainly on
An approach to derive the performance the pump geometry. The presence of solid particles,
behaviour of a vertical centrifugal pump used for specifically coarse particles, in the fluid always
transporting dredged slurry based on detail breaks fluid continuum. The bigger the particle size
hydraulic loss analysis has been presented in this worse is the effect. In most of the slurry pumping
paper. The derived analytical data has been system, particle size distribution is uneven, i.e., it is
compared with experimental results. mixed with fine, medium and coarse particles and it
Performance analysis of a vertical submersible is called heterogeneous slurry.
centrifugal slurry pump has been accomplished Previous researchers like Sellgren [1],
in two stages. At first, performance Gahlot, et al. [2] and many other eminent
characteristics of the centrifugal pump with clear researchers developed empirical formulae
water have been investigated considering an in- correlating head reduction ratio (RH) with solid
depth hydraulic loss analysis. Depending on the concentration by weight, solid specific gravity and
particle size distribution, the effect of solid particle size. Performance prediction utilizing
particles on the performance characteristics of empirical correlation carried out by them with the
centrifugal slurry pump has been investigated error band of ±12% to ±20 % for the test slurry.
considering volume fraction of particle size. The
homogenous slurry with fine particles has been Pump head with slurry, H s
treated as Newtonian fluid with slurry viscosity RH  1  (1)
and specific gravity. Additional hydraulic losses
Pump head with wate r, H w
due to coarse solid particle have been considered
for coarse slurry fraction. The performance of The present work has been conducted with
the vertical centrifugal slurry pump has been the objective of detail analysis of several hydraulic
predicted with the accuracies of about 87% and losses occurring in the pump. The fine slurry has
90 % for respective solid concentration of 18% been considered as Newtonian fluid. The same
and 10% by volume near the maximum efficiency hydraulic analysis method has been adopted for the
point. The drooping performance characteristics fine slurry with the slurry viscosity and specific
at low flow operation have been found gravity as presented for the centrifugal pump
deteriorating further with the increase of solid handling clear water. Additional hydraulic head
concentration. losses due to the presence of coarse solid particles
have been deducted from the fine Newtonian slurry
Keywords – Centrifugal, Diffuser, Impeller, Slurry head by applying the approach as postulated by
Roco, et al. [3]. The prediction of the performance
I. INTRODUCTION characteristics of the centrifugal slurry pump has
Centrifugal slurry pumps are mostly found been improved by considering the volume fraction
in transporting solid grains with carrier fluid through of the solid particles.
the pipe lines to the destined point in the process
industries like cement plant, petrochemical plants II. Test Rig & Experimentation
and fertilizer plants, etc. Performance characteristics The pilot seabed mining was carried out
of any centrifugal pump significantly differ in the from an anchor barge near the Kalvadevi bay of
presence of solid particles in the fluid from clear Ratnagiri, Maharashtra, India. The seabed mining
fluid characteristics. The slurry of uniform particle was carried out by a dredge head with water jets.
size is hardly found in industries, rather in most of The dredge head as shown in “Fig. 1” contains a
the application particle size varies from few microns water distributor (1) which provides pressurized
to the order of mm. The performance characteristics water to a series of nozzles (2) housed in an agitating

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chamber (3). The pressurized water is supplied
through feed line (4) and distributed to the nozzles. Table -1
Water jets from the nozzles cut the seabed Pump Details
resulting formation of slurry in the dredge head. The Rated Capacity 240 m3/hr
solid concentration in the dredge head is varied by Head 25 m
controlling the nozzle jet velocity. Capacity Range 75 – 400 m3/hr
The test rig of the seabed dredging system Motor Power 35 HP
is as shown in “Fig.-2” .The dredge head (1) is
Speed 2,900 rpm
suspended from a crane (2) and placed on seabed.
No. of stage single
The horizontal centrifugal pump (3) mounted on the
equipment barge (4) sucks sea water through flexible No of vanes in impeller 4
hose (5) and discharges high pressure water through Impeller blade inlet angle 18o
delivery pipe (6) to the dredge head(1). Impeller blade outlet angle 22.5o
The pressurized water released from a set Impeller diameter 198 mm
of nozzle cuts seabed resulting formation of solid- No. of vane in diffuser 8
water slurry in the agitation chamber of the dredge Water Properties
head (1).The vertical submersible slurry pump (7) Pumping water Sea water
mounted on the dredge head (1) sucks slurry from Temperature 0 – 20 oC
the dredge head and delivers through discharge Specific gravity of clear sea 1.028 – 1.034
flexible hose (9) and slurry pipe to the hopper barge water
(8). A by pass line (10) with flow control valve (11) Kinematic viscosity (m2/s) 1.83x10-6 to 1.05x10-6
regulates the pressurised water supply to the dredge Solid Properties
head without disturbing the performance
characteristics of the water supply pump(3). Power
to the equipment is supplied by 320 kVA Diesel Type Seabed sand
Generator Set mounted on the equipment barge.
Data Acquisition System for recording
online data in computer has been installed. Magnetic Specific gravity 2.7 to 3.5
flow meter (14), pressure transmitter (15), and Particle size (mm) 0.035 to 0.350
ultrasonic solid concentration meter (16) mounted on
slurry pipe line. Pressure transmitter (17) &
magnetic flow meter (18) are installed on the clear
water pipe line (6). Signal conditioner circuitry
converts signal sensed by the respective transducer
in to electrical signal which is transferred to a master
controller via RS 485 communication port. Master
controllers transmit Data to a personal computer via
RS 232 –C port for on line display and recording in
the hard disk. The investigated pump is single stage
centrifugal impeller and diffuser type casing. The
details of the pump and characteristics of sea water
and sea bed sand are listed in Table- 1

III. Performance Characteristics with Clear
Water
III.1 Eulers Head
The energy imparted to the pumping fluid per unit
weight of the fluid with infinite number of blades is
popularly known as Euler’s pump head.
u 2 c 2 - u 1c 1
H th  (2)
g
Considering zero inlet pre-rotation of fluid in the
design.
u 2 c 2
H th  (3)
g

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Fig 1 Dredge Head

Fig 2 Test Rig

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III.2 Slip Table. 2 Hydraulic losses
Fluid rotates in the reverse direction of Local Hydraulic Losses
impeller rotation at the impeller speed after Shock 2
entering into the rotating impeller from stationery Losses, w θi
h inc  k inc ,
condition. Thus, a reverse circulation is set-up in Conrad et 2g
blade to blade flow passages. These relative eddies al. [5]
kinc = 0.5 to 0.7
at the outer edge of the impeller will have (6)
circumferential velocity (cөs) in the opposite
Mixing hmix 1  1   wake   B 
 1 
1   wake  
Losses,
Johnston et ci 1 i 
direction of the outlet whirl velocity (c Ө2) and is 2

known as slip velocity (cөs)
al. [6], 2g
Mizuki et (7)
c
al. [7]  i  2
cm 2
1 w2
 wake  1 
0.45 wm ax
Secondary Hydraulic Losses
Blade 2
2 u2
Loading hbl  0.05D f (8)
Losses, 2g
Galvas [8] 0.75H th1
D f  0.3 
w1 z  D  D
1  1   2 1
 D 
Fig. 3. Outlet effective velocity triangle with slip u2   2  D2
velocity
It is depicted in “Fig. 3”. It has been
studied by many researchers that Weisner’s[4] slip u 2 c 2
model gives realistic slip factor and same has been
H th1  2
u2
considered for the present work.
Friction
c
 f  1  s Skin 1 2 L
u2 Friction, hf  wm  (10)
Musgrave 2 dh
sin  2 (4)
 f 1 [9] 1 w d 
z 0 .7  2 log 10  m hm    0.8
u c - c  (5)
   
H th  2  2 s Clearance Flow
g Clearance q  zsLu
cl cl
losses, (1
Augier Pcl
III.3 Hydraulic losses in the impeller u cl  0.816 1)
The fluid while passing through the [10] 
impeller or diffuser flow passages encounters Qr2 c 2  r1c1 
several hydraulic losses which reduces the effective Pcl 
head developed by the pump. Roco et al [6] zrb
classified the hydraulic losses as local hydraulic r  r 
r 1 2 b
b1  b2 
losses, secondary hydraulic losses and frictional 2 2
losses. The optimum hydraulic loss model has been
considered in the present study which is shown in
Table-2.
IV. Property of Homogeneous Solid Liquid
Mixture:
III.4 Diffuser Losses
It has been experimented that particles of
Hydraulic losses in the diffuser are
size below 70 µm remains suspended
calculated in the similar manner as impeller but a
homogenously in water. Viscosity of such fine
stationary frame of reference is considered.
solid liquid homogeneous mixture has been
calculated using Thoma’s [11] correlation and
mixture specific gravity as listed below.

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2

 
v* 1
m  w 1  2.5Cv  10.5Cv
2 2
(12) Frsl 
ad p ( s  1)  s l
2
100 c
m  (13) Where, a  2 ,
C w (100  Cw ) r2

s w c'
v* 
 b 
V. Effects Of Solids on Pump Performance 5.98  5.75 log10  2 
The centrifugal pump behaves in a quite  2kimp 
 
different manner in presence of solid particles in 0.5
the pumping fluid. Solid particles can slip from the a
carrier fluid, i.e., the particles move at a slower or a W (a, C v )  Wo   (1  C v ) E
g
faster velocity than the carrier fluid or it can move  
with same velocity as carrier fluid depending on The value of E is taken from E vs. Particle
the particle size, particle specific gravity and solid Reynolds Numbers curve as given by Gandhi, et al.
concentration. [12]
Roco, et al. [6] considered the additional
head losses due to presence of solid particles in the H  f
 1100Cw(s  1)
gd p Wo (17)
H 
sl
fluid. They classified the hydraulic losses in three
classes, viz., local losses, secondary losses and f f
c2 c
frictional losses. The additional hydraulic losses
due to the presence of solid particles have been VI. Experimental Uncertainty.
estimated by correlation with three non- Table. 2 Uncertainty of the instrument
dimensional numbers namely, particle Reynolds Instruments Make % of
number, Froude number and pump specific speed. Error
It has been observed that the solid particle sizes Magnetic Flow Manas 0.75%
below 70 µm remain homogenously suspended in Meter Microsystems Pvt
the fluid and such particles are treated as fine Ltd, India
particles. Homogenous slurry of fine particles in Pressure WIKA 0.50%
which particles are evenly distributed behaves like Transmitter Instruments India
a clear continuum liquid and it can well be treated Pvt. Ltd
as Newtonian fluid with its specific gravity and Ultrasonic Solid Rhosonics 0.10%
viscosity. Coarse particles (70 to 350 µm) are Concentration Analytical BV,
unevenly distributed in the fine homogeneous meter Netherland
slurry. The analysis has been done considering
coarse particle mean size, d50 = 250 µm and that of
the fine particles are of 50 µm. The hydraulic
VII Results and Discussion
The performance test of a vertical
losses have been estimated considering two volume
submersible slurry pump has been accomplished
fraction of particles as described above. In brief,
hydraulic losses occurred in the pump flow passage with 18 % and 10 % solid concentration by volume
are caused by fine homogenous slurry fraction and and same has been done analytically. It has been
the additional losses by the coarse slurry fraction. observed that analytical performance curve
Hydraulic losses (HL) for centrifugal slurry pump matches very closely to experimental curve at the
best efficiency point (bep) ( 254 m3/ hr.) with the
are analysed as below.
accuracy of about 87% and 90% for solid
concentration by volume (C v) of 18% and 10%
 HL total   HL f   HLsl
(14) respectively. The present experimentation has been
H  Re sl
conducted from minimum to maximum flow rate
 297C v ( s  1)
sf sl with clear water as well as with slurry by opening
H sf f
Ns
(15)
the discharge valve gradually. It has been observed
that the predicted and the experimental
H loc sl 10.8Cv  s  1 performance curve intersect at some flow rate
 (16)
H loc  f Frsl towards the left of the best efficiency point and
these curves closely match in the region from bep
w(a, cv )d p to intersection point. As the pump flow reduces
Re sl  from bep operating conditions or in other words the
 flow velocity reduces, hydraulic head losses as well
as the additional head losses due to solid particles

520 | P a g e

decreases although the pump fluid flow remains in
the turbulent region (Re ~ 6 x 105 ) with least
friction factor. So, in the region from bep to
intersection point, predicted performance curves
closely match with the experimental curves. It is
indicated in Fig.2 and Fig.3. It is also found that
from intersection point to the end of the curve,
head of the predicted performance curve is higher
than the experimental curve for slurry application.
The predicted heads are 24% and 15% higher than
the experimental heads at the flow rate of 300 m3/
hr. for Cv of 18% and 10% respectively. The
excessive additional head losses due to the
presence of coarse solid particles at high flow
Fig. 3. Performance Curve (18% solid Conc.)
region may cause this deviation, which could not
be captured accurately in the presented analytical I: Experimented with clear water
technique.
A drooping (stall) performance II: Predicted with clear water
characteristics in both the experimental and the III: Predicted with seabed sand slurry
predicted performance curves have also been (Conc. 10% by volume)
observed at an operating point in the reduced flow IV :Tested with seabed sand slurry
region. It happens due to steep divergence in blade (Conc. 10% by volume)
to blade flow passages. Fluid moves against the
positive pressure gradient which thickens the
boundary layer and finally it separates from the
impeller wall surfaces. Eddy formation takes place
in the separated region which causes huge
hydraulic losses and it is further deteriorated due to
presence of solid particles. The pump again tries to
develop higher head to match with the discharge
pressure which further increases hydraulic losses.
As a result, the head developed by the pump again
falls and the pump operation at this flow rate is
unstable.
These unsteady flow fluctuation
propagates throughout the impeller and diffuser
flow passages and the pump experiences stall. Fig. 4. Performance Curve (10% solid Conc.)
Pump performance at this low flow region is also .
found to deteriorate further with the increase of VIII. Conclusion
solid concentration, i.e., it is more prominent when Analysis of performance characteristics of
the pump handles slurry of solid concentration by centrifugal slurry pumps considering the volume
volume 18% than that of 10%. The dotted lines in fractions of solid particle depending on particle size
Fig. 2 and Fig. 3 show the expected performance and particle distribution gives improved results
curves at reduced flow rate while the experimental than considering a mean particle size. The
curves deviate from it. presented method gives reasonably accurate results
around the best efficiency point. However, further
research, in-depth study and experimentation is
I: Experimented with clear water really needed for performance analysis of
II: Predicted with clear water centrifugal slurry pump when it handles highly
III: Predicted with seabed sand slurry coarse slurry with varied particle size.
(Conc. 18% by volume)
Acknowledgement
IV :Tested with seabed sand slurry The work has been conduced in network
(Conc. 18% by volume) project of Capacity Building of Coastal Placer
Mining led by Council of Scientific & Industrial
Research, New Delhi, India. Authors are duly
acknowledged to the Director, CSIR–Central
Mechanical Engineering Research Institute,
Durgapur, India for his kind support and permitting
to publish this paper.

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Nomenclature [3] M.C. Roco, M. Marsh, G.R. Addie, and
a characteristics local acceleration (m/s2) Maffett, , Dredge pump performance
J.R.
bep best efficiency point prediction, J. Pipelines 5(1985) 171-190
b impeller width (m) [4] F.J. Wiesner, A review of slip factors for
Cv concentration of solids in the slurry by volume incentrifugal impellers, ASME J. Eng. for
decimal fraction
Cw concentration of solids in the slurry by weight(%) (1967) 558—576
Power, 89
c velocity of flow (m/s)[5] O. Conrad, K. Raif and M.Wessels, The
dp solid particle size (m) calculation of performance maps for
d50 particle size, 50% by weight passing through
centrifugal compressors with vane-island
the sieve diffusers. In Proceedings of the 25th
dhm hydraulic mean diameter (m) ASME Annual International Gas Turbine
D impeller diameter (m) Conference and the 22nd ASME Annual
Df diffusion factor Fluids Engineering Conference on
Fr Froude number Performance Prediction of Centrifugal
s clearance gap width (m) Pumps and Compressors, New Orleans,
ρ specific gravity Louisiana (1980) 135–147.
v* friction velocity (m/s)
[6] J. P. Johnston and Jr, R. C.Dean, Losses in
c’θ corrected whirl velocity (m/s) vaneless diffusers of centrifugal
w relative velocity (m/s) compressors and pumps.
Wo unhindered particle settling velocity (m/s)
Analysis,experiment, and design, Trans.
W(a,Cv) modified particle settling velocity(m/s) at ASME, J. Engg Power 88(1966) 49–62
local acceleration (a) and solid concentration(Cv) [7] S. Mizuki, I. Ariga and I. Watanabe,
z no of vanes Prediction of jet and wake flow within
g gravitational acceleration(m/s2) centrifugal impeller channel, In
u impeller peripheral speed (m/s) Proceedings of the 25th ASME Annual
hinc incidence head losses (m) International Gas Turbine Conference
hmix mixing head losses (m) and the 22nd ASME Annual Fluids
hbl blade loading losses (m) Engineering Conference on Performance
hf frictional head loss (m) Prediction of Centrifugal Pumps and
L blade mean streamline meridional length (m)
Compressors, New Orleans,
kinc incidence loss coefficient Louisiana(1980) 105–116.
kimp impeller flow coefficient
[8] M. R. Galvas, Analytical correlation of
Ns pump specific speed (SI) centrifugal compressor design geometry
∆pcl clearance pressure loss (N/m2) for maximum efficiency with specific
Q pump flow rate (m3/s) speed, NASA Technical Note T.N.-
Q flow rate (m3/s) D6729(1972)
r impeller radius (m) [9] D.S. Musgrave., The prediction of
Re Reynolds number design and off design efficiency for
β blade angle centrifugal compressor impellers, In
λ friction coefficient Proceedings of the 25th ASME Annual
εwake width of wake (dimension less) International Gas Turbine Conference
ν kinematic viscosity (m2/s) and the 22nd ASME Annual Fluids
Subscripts Engineering Conference on Performance
1 impeller inlet f fluid, fine slurry Prediction of Centrifugal Pumps and
2 impeller outlet s slip, solid Compressors, New Orleans, Louisiana
Ө sl slurry tangential (1980) 185–189.
cl sf secondary flowclearance [10] R. H. Augier, Mean Streamline
aerodynamic performance analysis of
References centrifugal compressors, Trans ASME,88
[1] A., Sellgren, Performance of Centrifugal (1966) 49 – 62.
Pumps When Pumping Ores and Industrial [11] D.G. Thomas, Transport properties of
Minerals, Proc. Hydro transports-6, suspensions: VIII. A note on the viscosity
Paper G1, BHRA Fluid Engineering of Newtonian suspensions of uniform
(1979) 291-304. spherical particles. J. Colloid Science, 20,
[2] V. K. Gahlot, V. Seshadri, and R.C. 267-277 (1965).
Malhotra, Effect of Density, Size, [12] B. K Gandhi, S.N Singh, and V. Seshadri,
Distribution and Concentration of Solid on Improvement in the prediction of
the Characteristics of Centrifugal Pumps, performance of centrifugal slurry pumps
Trans. ASME, J. of Fluid Engg., Vol 114 handling slurries, Proc. Instn. Mech.
(1992) 386-389. Engrs Vol 214, part-A (2000) 473 -486

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Cb31516522

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