JNTU
JNTU B.Tech II FLUID MECHANICS AND HYDRAULIC MACHINERY Previous Question Paper (March - 2022 - R15)
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Main
Two coaxial cylinders 10 cm and 9.75 cm in diameter and 25 cm high have a certain liquid filled in between. Find the viscosity of the liquid which produces a torque of 0.98 Nm upon the inner cylinder when the outer one rotates at the rate of 90 rpm.
Answer
Given: Outer cylinder diameter Do = 0.1 m, Inner cylinder diameter Di = 0.0975 m, Height L = 0.25 m, Torque T = 0.98 Nm, Speed N = 90 rpm.
The radial clearance t is:
The angular velocity ω is:
The tangential velocity of the inner cylinder surface is:
The shear stress τ is given by:
The torque T is:
Substituting the values:
Discuss the influence of vapour pressure on the fluid motion.
Answer
Vapour pressure is the pressure exerted by the vapour in equilibrium with its liquid phase at a given temperature. Its influence on fluid motion is primarily observed through the phenomenon of cavitation.
- When the local pressure of a flowing fluid drops below its vapour pressure, the liquid begins to boil at the ambient temperature, forming vapour bubbles.
- These bubbles are carried by the flow to regions of higher pressure, where they collapse suddenly. This collapse generates high-frequency pressure waves and localized shock waves.
- The repeated collapse of these bubbles near solid boundaries causes pitting, material erosion, and structural damage to hydraulic machinery like pumps, turbines, and propellers.
- Cavitation also leads to a significant reduction in efficiency, increased noise, and vibrations in hydraulic systems.
- In hydraulic design, engineers must ensure that the pressure at any point in the system remains well above the vapour pressure to prevent these adverse effects.
A horizontal pipe of 7.5 cm diameter is joined by a sudden enlargement to a pipe of 15 cm diameter. Water is flowing through it at a rate of 0.0141 m3/s. If the pressure just before the junction is 6 m head, what will be the pressure head in the 15 cm pipe downstream of the junction? What will be the power loss at the junction?
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Water is flowing in an open channel at a depth of 2 m and a velocity of 3 m/s. It then flows down a chute into another channel where the depth is 1 m and the velocity is 10 m/s. Assuming frictionless flow, determine the difference in elevation of the channel floors.
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The flow of a fluid has velocity components u = 3x+y, v = 2x – 3y. Determine whether or not the flow is irrotational.
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Water is pumped from reservoir A at elevation 228 m to reservoir E at elevation 244 m through a 0.3 m pipeline. The pressure in the 0.3 m pipeline at point D at elevation 198 m is 533.3 kN/m2. The lost heads are: A to pump section B = 0.7 m; Through pump C to D = 38 V2/2g; And D to E = 40 V2/2g. Find the discharge Q and the power supplied by the pump BC.
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A pipe line 10 km long delivers a power of 50 kW at its outlet end. The pressure at the inlet end is 5000 kN/m2, and the pressure drop per km of pipeline is 50 kN/m2. Find the size of the pipe and efficiency of transmission. Take friction factor f = 0.02.
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An orifice meter with orifice diameter 15 cm is inserted in a pipe of 30 cm diameter. The water pressure on the upstream and downstream sides of the meter are 14.7 kN/cm2 and 9.81 N/cm2 respectively. Find the discharge, if the discharge coefficient, Cd = 0.6. Also find the coefficient of contraction of the jet.
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Show that the force exerted by a jet of water on an inclined fixed plate in the direction of the jet is given by
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How do you estimate hydropower potential?
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Classify the Hydroelectric power plants based on various considerations.
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A water jet 20 mm in diameter and having a velocity of 90 m/s strikes series of moving blades in a wheel. The direction of the jet makes 200 with the direction of movement of the blade. The blade angle at inlet is 350. If the jet should enter the blade without striking, what should be the blade velocity? If the outlet angle of the blade is 300, determine the force on the blade. Assume that there is no friction involved in the flow over the blade.
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With the help of velocity triangles derive expressions for power developed, hydraulic efficiency and overall efficiency of a Francis runner.
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A medium Francis runner has a diameter of 75 cm and width of 10 cm. Water leaves the guide vanes at a velocity of 16 m/s inclined at 250 with the runner periphery. The net head is 20 m. The overall and hydraulic efficiencies are 80% and 90% respectively. Assuming that 8% of the flow area is lost due to the runner vanes thickness, calculate the runner vane angle at inlet, power output, speed and specific speed of the machine.
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The diameter and width of a centrifugal pump impeller are 50 cm and 2.5 cm. The pump runs at 1200 rpm. The suction head is 6 m and the delivery head is 40 m. The frictional drop in suction is 2 m and in the delivery 8 m. The blade angle at out let is 300. The manometric efficiency is 80% and the overall efficiency is 75%. Determine the power required to drive the pump. Also calculate the pressures at the suction and delivery side of the pump.
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