B.E./B.Tech. DEGREE EXAMINATION, APRIL/MAY 2010

Third Semester

Mechanical Engineering

ME2204 — FLUID MECHANICS AND MACHINERY

(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)

Third Semester

Mechanical Engineering

ME2204 — FLUID MECHANICS AND MACHINERY

(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.

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.

Or

(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.

Or

(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.

Or

(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.

Or

(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.

Or

(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.

Or

(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.