JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II FLUID MECHANICS AND HYDRAULIC MACHINES Previous Question Paper (October - 2020 - R16)
Answer any five questions. All questions carry equal marks.
Main
A 25 cm diameter vertical cylinder rotates concentrically inside another cylinder of diameter 15.10 cm. Both cylinders are 25 cm high. The space between the cylinders is filled with a liquid whose viscosity is unknown. If a torque of 12.0 Nm is required to rotate the inner cylinder at 100 r.p.m., determine the viscosity of the fluid.
Answer
Given: Diameter of inner cylinder D1 = 0.151 m, Diameter of outer cylinder D2 = 0.25 m, Height L = 0.25 m, Torque T = 12.0 Nm, Speed N = 100 r.p.m.
The clearance thickness t is:
Angular velocity ω is:
Tangential velocity u at the surface of the inner cylinder is:
Shear stress τ is given by:
The shear force F is:
Torque T is:
Substituting the values:
What is differential manometer? Explain the working principle of U-tube differential manometer with a neat sketch.
Answer
A differential manometer is a device used to measure the difference of pressure between two points in a pipe or in two different pipes. It consists of a U-tube containing a heavy liquid (manometric fluid) whose two ends are connected to the points whose pressure difference is to be measured.
Working Principle: The pressure difference is determined by the difference in the levels of the manometric fluid in the two limbs of the U-tube. By applying the principle of hydrostatics—that pressure is the same at any horizontal level in a continuous static fluid—the pressure at the interface of the manometric fluid is equated for both limbs. The resulting equation accounts for the pressures exerted by the fluid columns in the pipes and the manometric fluid, allowing the calculation of the pressure head difference (P1 - P2) based on the deflection of the manometric liquid column.
Define compressibility. Prove that compressibility for a perfect gas undergoing isothermal compression is 1/p while for a perfect gas undergoing isentropic compression is 1/γp.
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The barometric pressure at sea level is 760 mm of mercury while that on a mountain top is 735 mm. If the density of air is assumed constant at 1.2 kg/m3, what is the elevation of the mountain top?
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Distinguish between (i) Compressible and incompressible flow, (ii) Steady flow and un-steady flow, (iii) Rotational and irrotational flow.
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A tank 1.5 m high stands on a trolley and is full of water. It has an orifice of diameter 0.1 m at 0.3 m from the bottom of the tank. If the orifice is suddenly opened, what will be the propelling force on the trolley? Coefficient of discharge of the orifice is 0.60.
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Derive an expression for continuity for three-dimensional flow and reduce it for steady, incompressible two-dimensional flow.
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If a bend is connected to the pipe which turns through 300 and tapers uniformly from 100 mm to 50 mm. Find the force exerted on the bend other than those due to gravity.
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Discuss (a) the concept of the boundary layer with reference to fluid motion over a flat plate; (b) phenomenon of separation for flow over curved surfaces; (c) the prevention of separation.
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What is compound pipe? What will be the loss of head when pipes are connected in series?
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A pitot-tube is inserted in a pipe of 300 mm diameter. The static pressure in pipe is 100 mm of mercury (vacuum). The stagnation pressure at the centre of the pipe, recorded by the pitot-tube is 0.981 N/cm2. Calculate the rate of flow of water through pipe, if the mean velocity of flow is 0.85 times the central velocity. Take Cv=0.98.
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Explain (i) Unit speed, (ii) Unit discharge, (iii) Unit power of a hydraulic turbine.
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A Pelton wheel has a mean bucket speed of 12 m/s and is supplied with water at a rate of 750 litres per second under a head of 35 m. If the bucket deflects the jet through an angle of 1600, find the power developed by the turbine and its hydraulic efficiency. Take the coefficient of velocity as 0.98. Neglect friction in the bucket. Also determine the overall efficiency of the turbine if its mechanical efficiency is 80%.
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With the help of a neat sketch, explain in brief the functioning of volute casing of a centrifugal pump.
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Water is to be pumped out of a deep well under a total head of 95 m. A number of identical pumps of design speed 1000 r.p.m and specific speed 900 r.p.m., with a rated capacity of 150 litres/second are available. How many pumps will be needed and how should they be connected?
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