Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech II FLUID MECHANICS AND HEAT TRANSFER Previous Question Paper (July/August - 2021 - R16)
Answer any five questions. All questions carry equal marks.
Main
Differentiate between simple manometers and differential manometers.
Answer
A simple manometer is a device used to measure the pressure of a fluid at a single point in a pipe or container. It typically consists of a glass tube bent in a U-shape, with one end connected to the point where pressure is to be measured and the other end open to the atmosphere. It measures gauge pressure relative to atmospheric pressure.
A differential manometer is used to measure the difference in pressure between two points in a pipe or between two different pipes. It consists of a U-tube containing a heavy liquid, where both ends are connected to the two points whose pressure difference is required. It does not measure absolute or gauge pressure directly but provides the pressure drop or difference between the two connected locations.
If the velocity distribution over a plate is 1.2 m long and 0.75 m wide is given by
- Shear stress on the plate surface
- Shear stress at 50 mm above the plate
Assume viscosity as 0.9 N-s/m2.
Answer
Given: Velocity distribution u = 2y - y2, Viscosity μ = 0.9 N-s/m2.
The velocity gradient is du/dy = d/dy(2y - y2) = 2 - 2y.
According to Newton's law of viscosity, shear stress τ = μ(du/dy).
- At the plate surface (y = 0):
du/dy = 2 - 2(0) = 2 s-1.
τ = 0.9 × 2 = 1.8 N/m2. - At 50 mm above the plate (y = 0.05 m):
du/dy = 2 - 2(0.05) = 2 - 0.1 = 1.9 s-1.
τ = 0.9 × 1.9 = 1.71 N/m2.
State Newton’s Law of viscosity and also derive the Coefficient of viscosity.
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In a flow field the velocity components as defined as below
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State the assumptions made in the derivation of Bernoulli’s equation. Derive the expression for the discharge through a venturimeter.
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Find the velocity of the flow of oil through a pipe, when the difference of mercury level in a differential u-tube manometer connected to the two tapping of the pitot tube is 100 mm. Take coefficient of pitot tube is 0.98 and sp.gr. of oil=0.8.
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Consider one-dimensional heat conduction through a cylindrical rod of diameter D and length L. What is the heat transfer area of the rod if:
- the lateral surfaces of the rod are insulated
- the top and bottom of the rod are insulated
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An aluminum fin of 7 mm thick and 50 mm long protrudes from a wall, which is maintained at 120°C. The ambient air temperature is 22°C. The heat transfer coefficient and conductivity of the fin material are 140 W/m2K and 55 W/mK respectively. Determine:
- Temperature at the end of the fin
- Temperature at the middle of the fin
- Total heat dissipated by the fin
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Explain the development of hydrodynamic and thermal boundary layers with suitable figures and explain the following. If a straight tube of 50 mm diameter, water is flowing at 15 m/s. The tube surface temperature is maintained at 60°C and the flowing water is heated from the inlet temperature 15°C to an outlet temperature of 45°C. Calculate the heat transfer coefficient from the tube surface to the water and the length of the tube.
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What is drag? What causes it? Why do we usually minimize it?
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Assuming that a man can be represented by a cylinder of 30 cm diameter and 1.7 m high with a surface temperature of 30°C, calculate the heat he would lose while standing in a 36 mph wind at 10°C.
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What is shape factor? How does it influence the radiation?
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Two black square plates of size 2 × 2 meters are placed parallel to each other at a distance of 0.5 m. One plate is maintained at a temperature of 1000°C and the other at 500°C. Find the heat exchange between the plates.
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Derive the expression for the estimation of heat transfer coefficient in a counter flow heat exchanger.
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What is the influence of fouling factors in the heat exchangers? Explain.
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