JNTU
JNTU B.Tech II FLUID MECHANICS AND HYDRAULIC MACHINES Previous Question Paper (November/December - 2020 - R16)
Answer any five questions. All questions carry equal marks.
Main
What is the difference between the dynamic viscosity and kinematic viscosity? State their units of measurements.
Answer
Dynamic viscosity (absolute viscosity) is a measure of a fluid's internal resistance to flow under an applied shear stress. It relates the shear stress to the velocity gradient in the fluid, defined by Newton's law of viscosity as τ = μ(du/dy). Its SI unit is Pascal-second (Pa·s) or N·s/m2 (equivalent to Poise in CGS units).
Kinematic viscosity is the ratio of dynamic viscosity to the density of the fluid, representing the momentum diffusivity of the fluid. It is defined as ν = μ/ρ. Its SI unit is m2/s (equivalent to Stokes in CGS units).
The fundamental difference is that dynamic viscosity quantifies the resistance to flow due to intermolecular forces, while kinematic viscosity quantifies the resistive flow relative to the fluid's inertia (density).
A soap bubble 51 mm in diameter has an internal pressure in excess of outside pressure of 0.00021 kg(f)/cm2. Calculate the surface tension in the soap film.
Answer
For a soap bubble, there are two surfaces (inner and outer) in contact with air, so the pressure excess Δp is given by the formula:
Given data:
- Diameter (d) = 51 mm = 5.1 cm = 0.051 m
- Excess pressure (Δp) = 0.00021 kg(f)/cm2
First, convert pressure to N/m2 (Pa):
Rearranging the formula for surface tension (σ):
The surface tension in the soap film is 0.06565 N/m.
Prove that the pressure is the same in all directions at a point in a static fluid.
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An inverted differential manometer containing an oil of specific gravity 0.9 is connected to find the difference of pressures at two points of a pipe containing water. If the manometer reading is 40 cm, find the difference of pressures.
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Define the equation of continuity. Obtain an expression for continuity equation for three dimensional flow.
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State the Bernoulli’s theorem. Mention the assumptions made. List out the Engineering applications.
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Show that in case of forced vertex flow, the rise of liquid level at the ends is equal to fall of liquid level at axis of the rotation.
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Determine the rate of flow of water through a pipe of diameter 20 cm and length of 50 m when one end of pipe is connected to a tank and other end of pipe is open to the atmosphere. The pipe is horizontal and height of water in the tank is 4 m above the centre of the pipe. Consider all minor losses and take f= 0.009.
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Find the displacement thickness, energy thickness and momentum thickness for the velocity distribution in the boundary layer given by
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What is draft tube? Describe with sketch two different types of draft tubes. Why it is used in reaction turbine.
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Explain the working principles of reciprocating pump with a neat sketch.
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A single acting reciprocating pump, running at 50 r.p.m. deliver 0.01 m3/s of the water. The diameter of the piston is 200 mm and stoke length 400 mm. Determine i) the Theoretical discharge of the pump ii) Coefficient of the discharge and iii) slip and percentage of the slip.
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