SPPU Question Papers
Class: TE Mechanical (2015 Course)
Subject: Turbo Machines
Unit V: Centrifugal Pump
May 2015
Q. 5. a)
Define specific speed of a hydrodynamic pump. Derive expression for the same. [8 marks]
Q. 5. b)
A centrifugal pump running at 800 rpm is working against a head of 20.2 m. The
external diameter of impeller is 480 mm and its width is 60 mm. If the vane
angle at exit is 40° and manometric efficiency is 70% find: [10 marks]
i)
Flow velocity at outlet
ii)
Absolute velocity of water leaving the vane
iii)
Angle made by the absolute velocity at outlet with direction of motion at the
outlet
iv)
Discharge
v)
Specific speed
(OR)
Q. 6. a)
Explain effect of blade angle (outlet) on discharge in centrifugal pump. [6 marks]
Q. 6. b)
A three stage centrifugal pump has impeller diameter 400 mm and 20 mm wide. The
vane angle at outlet is 45° and the area occupied by the thickness of vane is
8% of total area. Inner diameter of impeller is half of outer diameter and
inlet width is twice that of outlet. The pump discharge is 3.6 m3
per minute & runs at 920 rpm. Flow velocity is constant from inlet to
outlet. Find: [12 marks]
i)
Power output of pump in kW
ii)
Total manometric head
iii)
Specific speed
iv)
Shaft power
v)
Vane angle at inlet
Take
mechanical efficiency = 88%, Manometric efficiency = 77%
December 2015
Q. 5. a)
Explain the Priming and Cavitation of Centrifugal pump? [8 marks]
Q. 5. b)
A centrifugal pump having outer diameter equal to two times the inner diameter
and running at l000 rpm work against total head of 40 m. The velocity of flow
through the runner is constant and equal to 2.5 m/s. The vanes are set back at
an angle of 40° at outlet. If the outer diameter of the impeller is 50 cm and
width at outlet is 5 cm, Determine:
i)
Vane angle at inlet
ii)
Work done by impeller on water per second
iii)
Manometric efficiency. [10
marks]
(OR)
Q. 6. a)
Derive an expression of minimum starting speed of centrifugal pump? [8 marks]
Q. 6. b)
A centrifugal pump running at 900 rpm is working against a head 20 m. The
external diameter of the impeller is 460 mm and outlet width is 50 mm. If the
vane angles at outlet is 40° and manometric efficiency is 70 %, determine: [10 marks]
i)
Flow velocity at outlet
ii)
Absolute velocity of water leaving the vane
iii)
Angle made by the absolute at outlet with the direction of motion at outlet
iv)
Rate of flow through the pump
May 2016
Q. 5. a)
Define the maximum suction lift. State the expression to calculate it. What
factors affect its values? [6 marks]
Q. 5. b)
Following data relates to centrifugal pump: Eye and rim diameter = l0 cm and 20
cm respectively, outer width = l.25 cm, vane angle at outer rim = 25°, speed =
3000 rpm, constant flow velocity = 3 m/s, manometric efficiency = 78% and
overall efficiency = 72%. Determine: [12
marks]
i)
Inlet vane angle
ii)
Discharge
iii)
Manometric head and
iv)
Shaft Power
v)
Mechanical efficiency
(OR)
Q. 6. a)
Derive an expression for rise in pressure through impeller of a centrifugal
pump. [6 marks]
Q. 6. b)
Power input to centrifugal pump is 50 kW at the shaft while running the pump at
l440 rpm. The impeller tip diameter is 30 cm and the blade width at the tip is
l.5 cm. The water flow rate is ll0 lit/s. The vacuum gauge reading at the
suction flange is – 20 cm of mercury and at the delivery flange the pressure
gauge reading is 370 kPa. The blade outlet angle is 65°. Calculate: [12 marks]
i)
Theoretical head
ii)
Ideal head
iii)
Hydraulic efficiency
iv)
Mechanical efficiency
v)
Overall efficiency
vi)
Specific speed of the pump
Assume
radial entry and constant flow velocity.
December 2016
Q. 5. a)
Derive an expression for the minimum speed for starting a centrifugal pump. [6 marks]
Q. 5. b)
Explain different types of casing used in centrifugal pump. [4 marks]
Q. 5. c)
A centrifugal pump delivers l800 lit/min against a total head of 20 m. Its
speed is l450 rpm. Inner & outer diameters of impeller are l20 mm & 240
mm respectively and the diameter of suction & delivery pipes are both l00
mm. Determine the blade angles of the impeller vane at inlet & outlet
respectively if the water enters radially. Assume manometric efficiency is 0.90.
[8 marks]
(OR)
Q. 6. a)
Derive an expression of specific speed of centrifugal pump? [6 marks]
Q. 6. b) Write
a short note on Priming of a centrifugal pump. [4 marks]
Q. 6. c)
A three stage centrifugal pump has impellers 50 cm diameter and 3 cm width at
outlet. The thickness of the blades has reduced the circumferential area by
l0%. The manometric efficiency is 90%, overall efficiency is 80%, whirl
velocity at outlet is 20 m/s, velocity of flow at outlet is 2.25 m/s and speed
is l000 rpm. Calculate: [8 marks]
i)
Head generated
ii)
Discharge
iii)
Exit vane angle
iv)
Shaft power
May 2017
Q. 5. a)
Explain the different types of casing used for centrifugal pump. [6 marks]
Q. 5. b)
Derive an expression of minimum starting speed of centrifugal pump. [6 marks]
Q. 5. c)
Discuss the influence of blade angle on the performance of centrifugal pump. [6 marks]
(OR)
Q. 6. a)
An impeller of inside diameter l5 cm and outside diameter 40 cm having a width
at inlet 4 cm and width at outlet 2 cm is running at l440 rpm. The inlet and
outlet blade angles are 25° and l5° respectively. The whirl velocity at inlet
is zero. Determine:
i)
Flow rate in LPM
ii)
Power of impeller
iii)
Absolute velocity at outlet. [10 marks]
Q. 6. b) Write
a short note on Priming & Cavitation of Centrifugal pump. [8 marks]
December 2017 (2012 Pattern)
Q. 5. a)
Explain manometric head, manometric efficiency, mechanical efficiency and
overall efficiency of a centrifugal pump.
[8 marks]
Q. 5. b)
A three stage centrifugal pump has impellers 30 cm diameter and l.5 cm width at
outlet. The velocity of water at inlet is radial, the vanes are curved back at
an angle of 30º to the tangent at outlet and occupy 8% of the outlet area.
While running at l000 rpm, the pump delivers 40 lit/sec with 85% manometric
efficiency and 75% overall efficiency. Calculate the head generated by the pump
and the input power. [10 marks]
(OR)
Q. 6. a)
A centrifugal pump with a discharge l565 lit/sec against a mean lift of 6.l m
when the impeller rotates at 200 rpm. The impeller diameter is l2 cm and area
of the outlet periphery is 6450 cm2. If the vanes are set back at an
angle of 26º at the outlet, find: [12
marks]
(i)
Hydraulic efficiency
(ii)
Power required to drive the pump
If
the ratio of external to internal diameter is 2, find the maximum speed to
start pumping.
Q. 6. b) What
is multi staging in a centrifugal pump? Describe the methods used for multi
staging. [6 marks]
December 2017 (2015 Pattern)
Q. 7. a)
Explain with neat sketch any two types of impellers used in centrifugal pump. [6 marks]
Q. 7. b)
The impeller of the centrifugal pump has an outer diameter of 250 mm and an effective
area of the 0.0l7 m2. The blades are bent backward so that the
direction of outlet relative velocity makes an angle of l48 deg. with the
tangent drawn in the direction of impeller rotation. The diameters of suction
and delivery pipes are l50 mm and l00 mm respectively. The pump delivers 0.03l m3/s
at l450 rpm when suction and delivery lifts are 4.6 m and l8 m respectively.
The head losses in the suction and delivery pipes are 2 m and 2.9 m
respectively. The motor driving the pump delivers l0 kW. Assuming that water
enters the pump without shock and whirl, determine (i) Manometric efficiency
and (ii) The overall Efficiency of the pump. [10 marks]
(OR)
Q. 8. a)
Discuss the significance of the effect of outlet blade angle on performance of centrifugal
pump. [7 marks]
Q. 8. b) Three
stage centrifugal pump has impellers 40 cm diameter and 2 cm wide at outlet.
The vanes are curved back at the outlet at 45 deg. and reduce the
circumferential area by l0%. Its Manometric efficiency is 90% and overall
efficiency is 80%. Determine the head generated by the pump when running at
l000 rpm delivering 50 LPS. What should be the shaft power and specific speed? [6 marks]
Q. 8. c)
Tests on a pump model indicate a Thomas cavitation factor is 0.l. A homologous
unit is installed at a location where atmospheric pressure is 0.9l bar and
vapour pressure as 0.035 bar (abs) and is to pump water against a head of 25 m.
What is the maximum permissible suction lift / head? Neglect frictional losses
in the suction pipe. [3 marks]
May 2018
Q. 7. a) What
do you mean by cavitation? What are its effects? How we can overcome the
cavitation effect in centrifugal pump. Derive relation for maximum suction lift
of a centrifugal pump. [8 marks]
Q. 7. b)
The outer diameter of an impeller of a Centrifugal pump is 400 mm and outlet
width is 50 mm. The pump is running at 800 rpm and is working against a total
head of l5 m. The vanes angle at outlet is 40° and manometric efficiency is
75%. Determine: [10 marks]
i)
Velocity of flow at outlet,
ii)
Velocity of water leaving the vane,
iii)
Angle made by the absolute velocity at outlet with the direction of motion at
outlet,
iv)
Discharge
(OR)
Q. 8. a)
Show that rise in pressure in impeller of a centrifugal pump is expressed as:
Where,
all symbols have their usual meanings. [6
marks]
Q. 8. b) A
centrifugal pump impeller has an external diameter of 450 mm and discharge area
of 0.ll m2. The vanes are bent backwards at an angle of 35° at
outlet. The diameter of the suction and delivery pipes is 300 mm and 230 mm
respectively. Pressure gauge at points on suction and delivery pipes close to
the pump and each gauge l.50 m above the level of supply sump showed gauge
pressure head of 3.70 m below and l9 m above atmospheric head respectively.
When the pump was delivering 200 lit/sec of water at 800 rpm. It requires 70 kW
to drive the pump. Find the loss of head in the suction pipe, manometric
efficiency and overall efficiency of the pump. [12 marks]
December 2018
Q. 7. a)
Define maximum suction lift. State the expression to calculate it. What factors
affect its values? [6 marks]
Q. 7. b)
The effective inlet and outlet radial area of flow of a centrifugal pump are
respectively 645 cm2 and 580 cm2, the water entering with
the radial velocity of 5.50 m/s. The impeller vanes are set back at an angle of
45º to the tangent at outlet. The outer peripheral velocity is 27.50 m/s and
manometric efficiency is 80%. Assuming the losses of head due to friction are
i) between suction flange and impeller inlet = 3.05 m, ii) Through impeller =
4.80 m, iii) between guide vanes and delivery flange = 1.52 m and that at the
outlet velocity from the guides is two-fifths of the inlet velocity to them.
Find: 1) The loss of head due to friction in guides vanes. 2) The guide vane
efficiency. [12 marks]
(OR)
Q. 8. a)
What is cavitation? Explain the phenomenon of cavitation. State some methods of
eliminating or reducing cavitation. [6
marks]
Q. 8. b) Show
that rise in the pressure in the impeller of a centrifugal pump is given by:
A
centrifugal pump has an impeller of internal diameter 125 mm and exit diameter
250 mm and rotates at 1800 rpm. The absolute velocity of water at inlet is
radial and the vanes are bent back at an angle of 30º to the tangent at
discharge. The breadth of the impeller at inlet and outlet are 12.5 mm and 6.25
mm respectively. Determine the rise in pressure head as water passes through
the impeller neglecting losses. The discharge of the pump is 8.5 lit/sec. [12 marks]
May 2019
Q. 7. a)
Explain the effect of blade angle (outlet) on discharge in centrifugal pump. [4 marks]
Q. 7. b)
Explain NPSH and cavitation with respect to centrifugal pump. [4 marks]
Q. 7. c)
A three stage centrifugal pump has impeller diameter at outlet 400 mm and 20 mm
wide. The vane angle at outlet is 45o and the area occupied by the
thickness of vane is 8% of total area. Inner diameter of impeller is half of
outer diameter and inlet width is twice as that of outlet. The pump discharges
3.6 m3 per minute and runs at 920 rpm. Flow velocity is constant
from inlet to outlet. Find:
i)
Power output of pump in kW,
ii)
Total manometric head,
iii)
Specific speed,
iv)
Shaft Power,
v)
Vane angle at outlet.
Take
mechanical efficiency = 88%, Manometric efficiency = 77%. [10 marks]
(OR)
Q. 8. a)
A centrifugal pump at 900 rpm has an impeller diameter of 500 mm and eye
diameter of 300 mm. The blade angle at outlet is 35o with tangent.
Determine assuming zero whirl at inlet, the inlet blade angle, absolute
velocity at outlet and its direction and the manometric head. The velocity of
flow is constant throughout and is 3 m/sec. [10 marks]
Q. 8. b) What
is the significance of specific speed? Derive the relation for the same for
centrifugal pump. [4 marks]
Q. 8. c)
Explain different types of casing used in centrifugal pumps. [4 marks]
(Next Paper will be Dec. 2019)
