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Third Semester B.Tech. Degree Examination, November 2009 (2008 Scheme) 08.303 : FLUID MECHANICS AND MACHINES (MPU) Time : 3 Hours
Max. Marks : 100
Instruction : Answer all questions from Part – A and one full question from each Module of Part – B. PART – A 1. 2. 3. 4. 5. 6. 7.
State Newton’s law of viscosity. Define absolute viscosity of a fluid. What are the limitations of Bernoulli’s equation ? Explain the Reynold’s experiment. Describe the phenomenon of water hammer. Explain velocity of flow and velocity of whirl and state their difference. Describe a scheme of governing Pelton wheel. Explain the term specific speed as applied to hydraulic turbines. Derive the expression for specific speed. 8. Describe Rayleigh method of dimensional analysis. 9. What is manometric efficiency of a centrifugal pump ? 10. Explain the working of a jet pump. (10×4=40 Marks) PART – B MODULE – I 11. a) A rectangular metal plate of size 20 cm × 10 cm, weighing 1 kg f slides over a smooth long inclined plane of slope 15°. The slope is covered with an oil of viscosity 1.50 poise. Find the terminal velocity of the plate over the inclined plane if the thickness of the oil film below the plate is estimated to be 0.2 mm. b) Two pipes of lengths 2500 m each and diameters 80 cm and 60 cm respectively, are connected in parallel. The coefficient of friction for each pipe is 0.006. The total flow is equal to 250 litres/s. Find the rate of flow in each pipe. P.T.O.
12. a) A differential manometer is connected to pipes A and B carrying liquids of specific gravity 0.9 and 0.8 respectively. The centre of pipe B is 0.8 m below pipe A. If the mercury level in the limb connected to A is 0.2 m below the centre line of pipe A and the difference in levels of mercury surfaces in two limbs is 0.95 m, find the pressure difference between A and B. b) A venturimeter of diameter 200 mm at the inlet and 100 mm at the throat is laid with the axis horizontal and is used for measuring the velocity of an oil of specific gravity 0.8. The difference of levels of the mercury manometer read 180 mm. Direct measurements was made by collecting 11520 kg of oil in 4 minutes. Calculate the discharge coefficient for the meter. MODULE – II 13. a) Derive an expression for hydraulic efficiency of a Pelton wheel. b) A wheel having radial blades is of 0.6 m radius at the outer tip of the blades and 0.3 m at the inner tip. Water enters the blades at the outer tip with a velocity of 30 m/s at an angle of 30° to tangent and leaves the blades with a velocity of flow of 4 m/s. The blades have an angle of 40° at entrance and 35° at exit. Find the work done per Newton of water entering the wheel, the speed of wheel and the efficiency. 14. a) A Kaplan turbine runner develops 9300 kW under a net head of 7.4 m. Mechanical efficiency of the wheel is 86%, speed ratio based on outer diameter is 2.2 and the flow ratio is 0.66. Diameter of the boss is 0.35 times the external diameter of the wheel. Determine i) diameter of the runner ; ii) its synchronous speed ; iii) the specific speed of the runner. Assume mechanical efficiency equal to overall efficiency. b) An inward flow reaction turbine is required to produce a power of 280 kW at 200 RPM. The effective head on the turbine is 20 m. The inlet diameter is twice as the outlet diameter. Assume hydraulic efficiency as 82% and overall efficiency as 80%. The radial velocity is 3.5 m/s and is constant. The ratio of wheel diameter to breadth is 0.1 and 5% of the flow area is blocked by vane thickness. Determine the inlet and outlet diameters, inlet and exit vane angle and guide blade angle at the inlet. Assume radial discharge.
MODULE – III 15. a) What is an air-vessel ? Describe the function of air-vessel with the help of a neat sketch. Prove that the work saved by fitting the air-vessel to the reciprocating pump is 39.2% in case of single acting reciprocating pump. b) A centrifugal pump having outer diameter equal to two times the inner diameter and running at 1000 RPM works against a total head of 40 m. The velocity of flow through the impeller is constant and is 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 500 mm and width at outlet is 50 mm determine i) Vane angle at inlet ii) Work done by impeller on water per second, and iii) Manometric efficiency. 16. a) Prove that the manometric head of a centrifugal pump running at speed N and giving a discharge Q may be written as Hmano = AN2 + BNQ + CQ2 where A, B and C are constants. b) A double-acting reciprocating pump, running at 50 RPM is discharging 900 litres of water per minute. The pump has a stroke of 400 mm. The diameter of Piston is 250 mm. The delivery and suction heads are 25 m and 4 m respectively. Find the slip of the pump and power required to drive the pump. (20×3=60 Marks) ————————
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