JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II FLUID MECHANICS AND HEAT TRANSFER Previous Question Paper (May - 2019 - R13)
Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit.
PART - A
State Newton’s law of viscosity.
Answer
Newton's law of viscosity states that the shear stress on a fluid element is directly proportional to the rate of shear strain or velocity gradient. Mathematically, it is expressed as τ = μ(du/dy), where τ is shear stress, μ is the dynamic viscosity, and du/dy is the velocity gradient.
Differentiate between Real fluids and ideal fluids.
Answer
An ideal fluid is incompressible and has zero viscosity (inviscid), meaning it offers no resistance to shear. A real fluid possesses both viscosity and compressibility, resulting in shear stress and energy dissipation during flow.
What is Eulers’s equation of motion?
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What is stream lined body?
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Why is there a negative sign in the Fourier’s law of heat Conduction?
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Explain overall heat transfer coefficient for cylinder.
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Briefly explain Buckingham phi theorem.
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Define the Reynolds number. Why is it important?
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State the Kirchoff’ law.
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Distinguish between: A black body and gray body.
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PART - B
Differentiate between laminar and turbulent flows and rotational and irrotational flows.
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Derive the continuity equation from fundamentals.
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List all the fluid properties and explain why water rises in a small glass tube when inserted in water.
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The space between two parellel plates kept 3mm apart is filled with an oil of dynamic viscosity 0.2 Pa.s. What is the shear stress on the lower fixed plate, if the upper one is moved with a velocity of 1.50m/sec?
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Derive the Bernoulli’s equation and discuss its significance.
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A Water pipe changes in diameter from 400 mm at section A to 800 mm at section B which is 7 m above. The pressures at A and B are 100 KPa and 75 KPa respectively. The discharge is 400 litres/Sec. Find the direction of flow.
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Explain the principle of venturimeter with a neat sketch. Derive the expression for the rate of flow of fluid through it.
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Name the different forces present in a fluid flow. For the Euler’s equation of motion, which forces are taken into consideration?
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Define the following: i) Thermal conductivity ii) Convection heat transfer coefficient iii) Radiation heat transfer Coefficient and iv) Overall heat transfer coefficient.
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An immersion water heater of surface area 0.1m2 and rating 1kW is designed to operate fully submerged in water. Estimate the surface temperature of the heater when the water is at 40oC and the heat transfer coefficient is 300 W/m2K. If this heater is by mistake used in air at 40oC with h = 9 W/m2K, what will be its surface temperature?
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Derive differential equation of heat conduction in Cartesian coordinate system?
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A constant temperature difference of 166.7oC is maintained across the surfaces of slab of 3.05 cm thickness. Calculate the rate of heat transfer per unit area across the slab for each of the following cases: i) Slab is made copper of k = 380.7 W/mK. ii) Slab is made of Aluminium of k= 225 W/mK iii) Slab is made of carbon steel of k = 17.3 W/mK. iv) Slab is made of brick of k = 0.865 W/mK. v) Slab is made of asbestos of k = 0.173 W/mK.
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What is the Prandtl number? Show that it is a dimensionless quantity.
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Liquid sodium is to be heated from 120oC to 149oC at a rate of 2.3 kg/s in a 2.5cm diameter electrically heated tube (constant heat flux). Calculate the minimum length of the tube if its wall temperature is not to exceed 200oC.
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A vertical cylinder 1.5 m high and 180 mm in diameter is maintained at 100oC in an atmospheric environment of 20oC. Calculate heat loss by free convection from the surface of the cylinder. Assume properties of at mean temperature as ρ = 1.06 kg/m3, υ = 18.97×10-6 m2/s, cp = 1.004 kJ/kgoC and k = 0.1042 kJ/mhoC.
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A counter flow concentric tube heat exchanger is used to cool engine oil (c = 2130 J/kg.K) from 160 oC to 60 oC with water, available at 25 oC as the cooling medium. The flow rate of cooling water through the inner tube of 0.5 m diameter is 2 kg/s while the flow rate of oil through the outer annulus O.D = 0.7 m is also 2 kg/s. If the value of the overall heat transfer coefficient is 250 W/m2K, how long must the heat exchanger be to meet its cooling requirement?
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State and prove Kirchhoff’s law of radiation?
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Assuming the sum to be a black body at a temperature of 5700 oC. Calculate, i) The emissive power of the surface of the sun ii) Wavelength for maximum spectral intensity iii) Heat energy emitted by the sun per unit time assuming its diameter as 1.391 × 109 m.
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