Wednesday, July 25, 2012


Third Semester
Mechanical Engineering
(Common to Chemical Engineering, Production Engineering)
(Regulation 2008)
Time: Three hours Maximum: 100 Marks
Answer ALL Questions
PART A — (10 × 2 = 20 Marks)
1. State the advantages of Electric Drive.
2. Give the formula for computing power requirement for a liner movement.
3. Write down the torque equation of a DC shunt motor and give the significance of flux.
4. A 6-pole, 3-phase induction motor operating on a 50 Hz supply has rotor emf frequency as 2 Hz. Determine
(a) slip and
(b) the rotor speed.
5. Why are centrifugal switches provided on many 1-phase induction motors?
6. Draw the block diagram of soft starter for an induction motor.
7. Compare the chopper control and phase control schemes for DC motor drives.
8. State the different methods of speed control of DC series motor.
9. What is advantage of v/f speed control of Induction Motor?
10. Draw the block diagram of speed control scheme for a slip ring Induction motor.
PART B — (5 × 16 = 80 Marks)
11. (a) (i) Briefly explain the various factors that will influence the choice of an electrical drive. (Marks 8)
(ii) Explain the method of estimating equivalent continuous power rating of a motor for short time load applications. (Marks 8)
(b) (i) Explain the different classes of motor duty with the equations. (Marks 8)
(ii) The temperature rise of motor after operating for 30 minutes on full load is 20°C and after another 30 minutes it becomes 30°C on the same load. Find the final temperature rise and time constant. (Marks 8)

12. (a) (i) From electrical characteristic, derive the mechanical characteristic of DC series motor. (Marks 8)
(ii) Explain the dynamic braking of DC shunt motor with the required diagram and equations. (Marks 8)
(b) (i) Derive the Speed-Torque characteristic of 3-phase slip ring induction motor. (Marks 8)
(ii) Explain the principle operation of capacitor start and run 1-phase Induction Motor. (Marks 8)

13. (a) (i) With a neat diagram explain the operation of four point starter. Also mention the advantages of this over a three point starter. (Marks 12)
(ii) Draw the control circuit for time limit acceleration of DC shunt motor. (Marks 4)
(b) State the various starting methods of squirrel cage induction motor. Explain any two of them. (Marks 16)

14. (a) (i) Explain the operation of armature control of a DC shunt motor. (Marks 8)
(ii) Draw and explain the four quadrant speed control of DC motor using various choppers. (Marks 8)
(b) (i) With the block diagram explain the operation of armature and field control of DC motor drive using controlled rectifiers. (Marks 12)
(ii) Name the different flux control methods adopted for DC series motor. (Marks 4)

15. (a) Explain the operation of speed control techniques employed for 3-phase squirrel cage induction motor. (Marks 16)
(b) What is meant by slip power recovery scheme? Explain with the necessary diagram. (Marks 16)


Third Semester
Mechanical Engineering     
(Common to Automobile Engineering, Aeronautical Engineering and
Production Engineering)
(Regulation 2008)     
Time : Three hours Maximum : 100 marks
Any missing data can be suitably assumed.
Answer ALL questions.
PART A — (10 × 2 = 20 marks)
1. Define – compressibility and bulk modulus.
2. Mention the significance of kinematic viscosity.
3. A circular and a square pipe are of equal sectional area. For the same flow rate, determine which section will lead to a higher value of Reynolds number.
4. What do you understand by hydraulic diameter?
5. Give the Rayleigh method to determine dimensionless groups.
6. Write down the dimensionless number for pressure.
7. A pump is to discharge 0.82 m3/s at a head of 42 m when running at 300 rpm. What type of pump will be required?
8. Mention the importance of Euler turbine equation.
9. Define slip in reciprocating machines.
10. Brief on acceleration head.

PART B — (5 × 16 = 80 marks)
11. (a) (i) A pipeline of 175 mm diameter branches into two pipes which delivers the water at atmospheric pressure. The diameter of the branch 1 which is at 35° counter-clockwise to the pipe axis is 75mm. and the velocity at outlet is 15 m/s. The branch 2 is at 15° with the pipe centre line in the clockwise direction has a diameter of 100 mm. The outlet velocity is 15 m/s. The pipes lie in a horizontal plane. Determine the magnitude and direction of the
forces on the pipes. (8)
(ii) Derive the linear momentum equation using the control volume approach and determine the force exerted by the fluid flowing through a pipe bend. (8)
(b) (i) A jet issuing at a velocity of 25 m/s is directed at 35° to the horizontal. Calculate the height cleared by the jet at 28 m from the discharge location? Also determine the maximum height the jet will clear and the corresponding horizontal location. (8)
(ii) Derive an expression for the variation of jet radius r with distance y downwards for a jet directed downwards. The initial radius is R and the head of fluid is H. (8)
12. (a) (i) Oil with a density of 900 kg/m3 and kinematic viscosity of 6.2 × 10–4 m2/s is being discharged by a 6 mm diameter, 40 m long horizontal pipe from a storage tank open to the atmosphere. The height of the liquid level above the center of the pipe is 3 m. Neglecting the minor losses, determine the flow rate of oil through the pipe. (8)
(ii) Two water reservoirs A and B are connected to each other through a 50 m long, 2.5 cm diameter cast iron pipe with a sharp-edged entrance. The pipe also involves a swing check valve and a fully open gate valve. The water level in both reservoirs is the same, but reservoir A is pressurised by compressed air while reservoir B is open to the atmosphere. If the initial flow rate through the pipe is 1.5 l/s, determine the absolute air pressure on top of reservoir A. Take the water temperature to be 25°C. (8)
(b) (i) In a water reservoir flow is through a circular hole of diameter D at the side wall at a vertical distance H from the free surface. The flow rate through an actual hole with a sharp-edged entrance (kL = 0.5) will be considerably less than the flow rate calculated assuming frictionless flow. Obtain a relation for the equivalent diameter of the sharp-edged hole for use in frictionless flow relations. (8)
(ii) A horizontal pipe has an abrupt expansion from 10 cm to 16 cm. The water velocity in the smaller section is 12 m/s, and the flow is turbulent. The pressure in the smaller section is 300 kPa. Determine the downstream pressure, and estimate the error that would have occurred if Bernoulli’s equation had been used. (8)
13. (a) (i) The power developed by hydraulic machines is found to depend on the head h, flow rate Q, density ? , speed N, runner diameter D, and acceleration due to gravity g. Obtain suitable dimensionless parameters to correlate experimental results. (10)
(ii) The capillary rise h is found to be influenced by the tube diameter D, density ? , gravitational acceleration g and surface tension ? . Determine the dimensionless parameters for the correlation of experimental results. (6)
(b) (i) Using dimensional analysis, obtain a correlation for the frictional torque due to rotation of a disc in a viscous fluid. The parameters influencing the torque can be identified as the diameter, rotational speed, viscosity and density of the fluid. (8)
(ii) The drag force on a smooth sphere is found to be affected by the velocity of flow, u, the diameter D of the sphere and the fluid properties density ? and viscosity? . Find the dimensionless groups to correlate the parameters. (8)
14. (a) (i) A pump has to supply water which is at 70°C water at 90 m3/min and 1800 rpm. Find the type of pump needed, the power required, and the impeller diameter if the required pressure rise for one stage is 200 kPa; and 1250 kPa. (10)
(ii) A dam on a river is being sited for a hydraulic turbine. The flow rate is 1600 m3/h, the available head is 25 m, and the turbine speed is to be 460 rpm. Discuss the estimated turbine size and feasibility for a Francis turbine; and a Pelton wheel. (6)

(b) (i) A centrifugal pump with backward-curved blades has the following measured performance when tested with water at 20°C : Discharge Estimate the best efficiency point and the maximum efficiency. Also, estimate the most efficient flow rate, and the resulting head and brake power, if the diameter is doubled and the rotation speed
is increased by 50%. (10)
(ii) A Pelton turbine is to produce 18MW under a head of 450 m when running at 480 rpm. If D/d ratio is 10, determine the number of jets required. (6)
15. (a) (i) Calculate the rate of flow in and out of the air vessel on the delivery side in a single acting reciprocating pump of 220 mm bore and 330 mm stroke running at 50 rpm. Also find the angle of crank rotation at which there is no flow into or out of the air vessel. (8)
(ii) Discuss in detail about rotary positive displacement pumps. (8)
(b) (i) With a neat sketch explain the working of double acting reciprocating pump with its performance characteristics. (10)
(ii) In a single acting reciprocating pump the bore and stroke are 100 and 150 mm. respectively. The static head requirements are 4 m suction and 18 m delivery. If the pressure at the end of delivery is atmospheric calculate the operating speed. The diameter of the delivery pipe is 75 mm and the length of the delivery pipe is 24 m. Determine the acceleration head at ? =33 from the start of delivery. (6)


Third Semester
Mechanical Engineering
(Regulation 2008)
(Common to Aeronautical Engineering, Automobile Engineering and
Production Engineering)
Time: Three hours Maximum: 100 Marks
Answer ALL Questions
PART A — (10 × 2 = 20 Marks)
1. A soap bubble is formed when the inside pressure is 5 N/m2 above the atmospheric pressure. If surface tension in the soap bubble is 0.0125 N/m, find the diameter of the bubble formed.
2. The converging pipe with inlet and outlet diameters of 200 mm and 150 mm carries the oil whose specific gravity is 0.8. The velocity of oil at the entry is 2.5 m/s, find the velocity at the exit of the pipe and oil flow rate in kg/sec.
3. Define boundary layer and give its significance.
4. Find the loss of head when a pipe of diameter 200 mm is suddenly enlarged to a diameter of 400 mm. Rate of flow of water through the pipe is 250 litres/s.
5. A centrifugal pump delivers 20 litres/s of water against a head of 850 mm at 900 rpm. Find the specific speed of pump.
6. What do you understand by fundamental units and derived units?
7. The mean velocity of the buckets of the Pelton wheel is 10 m/s. The jet supplies water at 0.7 m3/s at a head of 30 m. The jet is deflected through an angle of 160° by the bucket. Find the hydraulic efficiency. Take CV = 0.98.
8. The following data refer to a centrifugal pump which is designed to run at 1500 rpm. D1 = 100 mm, D2 = 300 mm, B1 = 50 mm, B2 = 20 mm, Vf1 = 3 m/s, 2 ß = 60°. Find the velocity of flow at outlet.
9. Define slip of reciprocating pump.
10. Mention the working principle of an Air-vessel.
PART B — (5 × 16 = 80 Marks)
11. (a) A drainage pipe is tapered in a section running with full of water. The pipe diameters at the inlet and exit are 1000 mm and 500 mm respectively. The water surface is 2 m above the centre of the inlet and exit is 3 m above the free surface of the water. The pressure at the exit is 250 mm of Hg vacuum. The friction loss between the inlet and exit of the pipe is 1/10 of the velocity head at the exit. Determine the discharge through the pipe.
(b) A pipe of 300 mm diameter inclined at 30° to the horizontal is carrying gasoline (specific gravity = 0.82). A venturimeter is fitted in the pipe to find out the flow rate whose throat diameter is 150 mm. The throat is 1.2 m from the entrance along its length. The pressure gauges fitted to the venturimeter read 140 kN/m2 and 80 kN/m2 respectively. Find out the coefficient of discharge of venturimeter if the flow is 0.20 m3/s.

12. (a) For a turbulent flow in a pipe of diameter 300 mm, find the discharge when the centre-line velocity is 2.0 m/s and the velocity at a point 100 mm from the centre as measured by pitot-tube is 1.6 m/s.
(b) For a town water supply, a main pipe line of diameter 0.4 m is required. As pipes more than 0.35m diameter are not readily available, two parallel pipes of same diameter are used for water supply. If the total discharge in the parallel pipes is same as in the single main pipe, find the diameter of parallel pipe. Assume coefficient of discharge to be the same for all the pipes.

13. (a) Using Buckingham's ? theorem, show that the velocity through a circular orifice in a pipe is given by v = 2gH f {d/H,µ /? vH} where v is the velocity through orifice of diameter d and H is the head causing the flow and ? and µ are the density and dynamic viscosity of the fluid passing through the orifice and g is acceleration due to gravity.
(b) The efficiency (? ) of a fan depends on ? (density), µ (viscosity) of the fluid, ? (angular velocity), d (diameter of rotor) and Q (discharge). Express ? in terms of non-dimensional parameters. Use Buckingham's ? theorem.

14. (a) In an inward radial flow turbine, water enters at an angle of 22° to the wheel tangent to the outer rim and leaves at 3 m/s. The flow velocity is constant through the runner. The inner and outer diameters are 300 mm and 600 mm respectively. The speed of the runner is 300 rpm. The discharge through the runner is radial. Find the
(i) Inlet and outlet blade angles
(ii) Taking inlet width as 150 mm and neglecting the thickness of the blades, find the power developed by the turbine.

(b) A Kaplan turbine working under a head of 20 m develops 15 MW brake power. The hub diameter and runner diameter of the turbine are 1.5 m and 4 m respectively. The guide blade angle at the inlet is 30°. = 0.9 n ? and 0.8 0 ? = . The discharge is radial. Find the runner vane angles and turbine speed.

15. (a) The diameter and stroke of a single acting reciprocating pump are 120 mm and 300 mm respectively. The water is lifted by a pump through a total head of 25 m. The diameter and length of delivery pipe are 100 mm and 20 m respectively. Find out:
(i) Theoretical discharge and theoretical power required to run the pump if its speed is 60 rpm,
(ii) Percentage slip, if the actual discharge is 2.95 l/s and
(iii) The acceleration head at the beginning and middle of the delivery stroke.
(b) Explain the working of the following pumps with the help of neat sketches and mention two applications of each.
(i) External gear pump
(ii) Lobe pump
(iii) Vane pump
(iv) Screw pump.