JU – 744

*JU744*

Third Semester B.E. (Civil) Engg. Degree Examination, Jan./Feb. 2014 (2K6 Scheme) CE 303 : FLUID MECHANICS AND HYDRAULIC MACHINERY Time : 3 Hours

Max. Marks : 100

Instruction : Answer question no. 1 and five from the remaining choosing at least one question from each Part. PART – A 1. Explain the following :

(10×2=20)

a) Real fluids and ideal fluids b) Viscosity and capillary rise c) Cohesion and Adhesion d) Hydrostatic law e) Vortex flow f) Hydraulic grade line and Total energy line g) Velocity of approach h) Aeration holes in weir i) Nappe and Crest j) Reynold’s number and Froude’s number. PART – B 2. a) Obtain an expression for capillary rise of a liquid with neat figure.

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b) Two large fixed parallel planes are 12 mm apart. The space between the surfaces is filled with oil of viscosity 0.972 Ns/m2. A flat thin plate 0.25 m2 area moves through the oil at a velocity of 0.3 m/s. Calculate the drag force : i) When the plate is equidistant from both the planes, and ii) When the thin plate is at a distance of 4 mm from one of the plane surfaces. 10 P.T.O.

JU – 744

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*JU744*

3. a) With a neat schematic diagram, explain Atmospheric pressure, Gauge pressure, Vacuum pressure and Absolute pressure.

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b) A differential mercury manometer is connected at a two points of a pipe. The vertical distance between these points is 3 m. The liquid flowing through the pipe is oil of specific gravity 0.80. If the pressure at these points are 100 kN/m2 and 180 kN/m2, find out the difference in mercury level in the manometer.

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c) With a neat figure obtain an expression for total pressure and centre of pressure over an inclined immersed plane surface.

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4. a) Define velocity potential and stream function. Show that the streamlines and equipotential lines are orthogonal to each other.

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b) A 6m × 2m rectangular gate is hinged at the base and is inclined at an angle of 60° with the horizontal. The upper end of the gates is kept in position by a weight of 60 kN acting at angle of 90°. Neglecting the weight of the gate find the level of water when the gate begins to fall. 10 PART – C 5. a) With neat figure obtain Bernoulli’s equation by deriving Euler’s equation.

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b) The following data relate to an inclined venturimeter : Diameter of the pipeline = 400 mm Inclination of the pipeline with the horizontal = 30° Throat diameter = 200 mm The distance between the mouth and throat of the meter = 600 mm Sp gravity of oil flowing through the pipeline = 0.7 Sp gravity of heavy liquid (U tube) = 13.6 Reading of the differential manometer = 50 mm The coefficient of the meter = 0.98 Determine the rate of flow in the pipe line.

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JU – 744

6. a) Obtain an expression for the discharge over a triangular weir.

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b) Define the hydraulic coefficients Cd, Cv and Cc.

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c) A tank has two identical orifices one vertically above the other and 3 m apart in one of its vertical sides. The water surface is 4 m above the upper orifice. It is found that the jets issuing from the two orifices intersect each other at a horizontal distance of 8.7 m from the vena-contracta. Determine the value of Cv of orifices.

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7. a) Show that the efficiency of a free jet striking normally on a series of flat plate mounted on the periphery of a wheel never exceeds 50%.

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b) A jet of water 75 mm diameter and with velocity of 20 m/s flows tangentially on to a stationary vane, which deflects the water through 120°. What is the magnitude and direction of the resultant force on the vane ? If the jet flows on to a series of vanes moving in the direction of jet with velocity 12 m/.s, find the force on the system of vanes in the direction of motion, the work done per second, and the efficiency.

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8. a) With a neat sketch explain the working of a double acting-reciprocating pump.

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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 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 : • Vane angle at inlet, • Work done by impeller on water per second and • Manometric efficiency.

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9. a) State Buckingham’s π theorem. Why this theorem is considered superior over the Rayleigh’s method for dimensional analysis ?

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b) Prove using Buckingham’s π theorem ΔP ρV

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=

L ⎡ ρV D K ⎤ φ , ⎥ D ⎢⎣ μ D⎦

ΔP − Pressure difference, D – Diameter of pipe, ρ − Density, μ − Viscosity,

V – velocity, K – Roughness factor, L – length of pipe. ———————

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