Code No: 07A40302
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JAWAHARLAL NEHRU TECHNOLOGY UNIVERSITY HYDERABAD R07 II B.Tech. II Semester Regular Exams, April/May – 2009 FLUID MECHANICS & HEAT TRANSFER (Mechatronics) Time: 3 hours Max. Marks.80 Answer any Five questions All questions carry equal marks ---
Define viscosity. Derive the equation for the viscosity. The space between two parallel plates kept 3mm apart is filled with an oil of dynamic viscosity 0.2 N- Sec / m2. What is the shear stress on the lower fixed plate if the upper one is moved with a velocity of 1.5 m /sec? [8+8]
2.a)
For a two dimensional potential flow the velocity potential is given by φ = 4x (3y-4). Determine the velocity at point (2, 3). Determine also the stream function and its value at a point (2, 3). What are the cases of flow where uniform flow, non uniform flow, steady flow and unsteady flow are present? [8+8]
3.a) b)
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What do you understand by the term boundary layer? Explain the concept of boundary layer. In a stream of oil of specific gravity 0.95 and kinematic viscosity 0.92 stoke moving at 5.75 m/sec, a plate of 50 cm length and 25cm width is placed parallel to the direction of motion. Calculate the friction drag on one side of the plate. Find also the thickness of the boundary layer and the shear stress at the trailing edge of the plate. [8+8] The population of a city is 8 × 105 and it is to be supplied with water from a reservoir 6.4 km away. Water is to be supplied at the rate of 0.14m3 per head per day and half the supply is to be delivered in 8 hours. The full supply level of the reservoir is R.L 180.00 and its lowest water level is R.L.105.00. The delivery end of the main is at R.L 22.50 and the head required there is 12m. Find the diameter of the pipe. Take f = 0.04. [16]
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Derive an expression for the thermal resistance through a hollow spherical shell of inside radius ri and outside radius ro having thermal conductivity k. It is desired to limit the heat loss through a boiler furnace wall to 200 W/m2. The wall is composed of a material having thermal conductivity of 1.125 W/mK. If the inner surface temperature is 1000C and the outer surface temperature is 3500C, find the thickness of the material to the used. [8+8] Contd…2
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Calculate the appropriate Grashot numbers. State whether the flow is laminar of turbulent for the following case. A central heating radiator, 0.6m high with a surface temperature of 750C in a room at 180C ( ρ = 1.2 kg/m3, Pr = 0.72 and µ = 1.8 x 10-5 kg/ms). An aeroplane wing is 1.2m wide and its surface is at 240C. The aeroplane is flying at 240 km/hr in air at 00C and 67 cm Hg pressure. Calculate the heat loss per metre length of the wing. [8+8]
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6.a)
State and explain Wien's law of radiation? Prove that the emissivity factor F1-2 for two concentric spheres is 1 2 ⎞ 1 ⎛ r1 ⎞ ⎛ 1 + ⎜ ⎟ ⎜ − 1⎟ E1 ⎝ r 2 ⎠ ⎝ E2 ⎠ It is given that total emissivities of the two spheres are E1 and E2 the outer radius of the inner sphere is r1 and the inside radius of the outer sphere is r2. [10+6]
8.a)
What is meant by “fouling” in heat exchangers? List the factors responsible for fouling.
b)
Water flows through a copper pipe (k=380 w/m-K) of 18mm diameter. It is surrounded by another steel pipe of 21mm and oil flow through the annular passage between copper and steel pipe. On the water side, the film coefficient is 4500 w /m2-K and the fouling factor of 0.00032 m2-K/W. The corresponding values for the soil side are 1250 W/m2-K and 0.00082 m2-K/W. Find the overall heat transfer coefficient between water and oil. [6+10]
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Code No: 07A40302
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Define fluid density, specific weight and specific gravity. What is the relation among them? A mass of liquid weighs 500 N when exposed to standard earth's gravity g is 9.806 m /s2. What is its mass? What will be its weight in a planet with acceleration due to gravity of 3.5m/s2? [8+8] The velocity components in a flow field are given by u = 2xy and v = a2 + x2- y2, show that the flow is possible. Obtain the relevant stream function. Verify whether the following functions are valid potential functions: φ = A xy i) ii) φ = m log x iii) φ = A(x3- y3) and iv) φ = A cos x [16]
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JAWAHARLAL NEHRU TECHNOLOGY UNIVERSITY HYDERABAD R07 II B.Tech. II Semester Regular Exams, April/May – 2009 FLUID MECHANICS & HEAT TRANSFER (Mechatronics) Time: 3 hours Max. Marks.80 Answer any Five questions All questions carry equal marks ---
State and prove Bernoulli’s theorem. Mention its limitations. An oil of specific gravity 0.84 flows through a uniform diameter pipe at the rate of 375 lit/sec. The energy head losses are 25 N-m per km length of the pipe. Find the slope of the hydraulic grade and total energy lines and the power lost per km of pipe. [8+8]
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What are the losses that occur when a fluid flows through a pipe? Give the formulae for calculating minor losses. Derive an expression for the energy loss at sudden expansion. [16] The thermal conductivity of a certain material varies according to the following relation. K = a + bT + cT2 where a, b and c are constants. Derive an equation for computing the heat loss per linear metre for a hollow cylinder made of this material. Assume that inner and outer radii are r1 and r2 respectively and the cylinder ends are perfectly insulated. [16]
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Explain the mechanism of heat flow by natural convection. Calculate the rate of free convection heat loss from 30 cm diameter sphere maintained at 1000C and exposed to atmospheric air at 200C. [8+8]
7.a)
What is the geometrical factor of radiation? Explain.
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6.a) b)
Estimate the heat loss by radiation from a high pressure steam pipe at a temperature of 1270C situated in a large room whose walls are at 270C. Assume emissivity of pipe surface to be 0.8. [8+8]
8.a)
Obtain an expression for the overall heat transfer coefficient of a shell and tube exchanger taking into consideration scale formation on the inside surface and film coefficients on the inside and outside surface of the tube. A steam condenser works at a temperature of 600C transferring 250 kW of energy. The cooling water enters the condenser at 200C with a flow rate of 2kg/sec.Find the logarithmic mean temperature difference. [8+8]
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Code No: 07A40302
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JAWAHARLAL NEHRU TECHNOLOGY UNIVERSITY HYDERABAD R07 II B.Tech. II Semester Regular Exams, April/May – 2009 FLUID MECHANICS & HEAT TRANSFER (Mechatronics) Time: 3 hours Max. Marks.80 Answer any Five questions All questions carry equal marks ---
Define fluid surface tension property. What are its examples? The velocity distribution in a viscous flow over a plate is given by u = 4y - y2 where u is velocity at distance y from the plate. If the coefficient of dynamic viscosity is 1.5 Pa.sec, determine the shear stress at y=0 and at y=2. [10+6]
2.a) b)
Define stream function. What is its significance in the analysis of fluid flow? A certain flow pattern has a velocity potential φ = 12x2 (3y-4). Determine the stream function and the velocity at (4, 5). [8+8]
3.a) b)
Explain momentum thickness, energy thickness and displacement thickness. Find the frictional drag on one side of the plate 20cm wide and 50cm long placed longitudinally in a steam of crude oil (specific gravity 0.925, kinematic viscosity 0.9 stoke) flowing with undisturbed velocity of 5 m/sec. Also find the thickness of boundary layer and the shear stress of the trailing edge of the plate. [8+8]
4.
What is meant by hydraulic gradient line and what is meant by total energy line? Also draw both these lines for a horizontal pipe as well as an inclined pipe. Describe the Reynolds experiment. [16]
5.a) b)
Explain Fourier heat conduction equation. Derive the general conduction equation in cylindrical coordinates by considering the infinitesimal volume. [6+10]
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Explain the physical significance of: i) Reynolds number ii) Prandtl number. A horizontal pipe 30.5 cm in diameter is maintained at a temperature of 2500C in a room where the ambient air temperature is 200C. Calculate the free convection heat loss per metre length of the pipe per hour. [6+10]
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Is the absorptivity of a substance always equals to its emissivity? If so, does this mean that energy absorbed is always equal to its emissivity? Does it also mean that the net gain of radiation energy is always equal to zero? Two equal parallel black discs, 0.5 m diameter are located 0.25 m apart and directly opposite to each other. If the temperature of the discs are 2000C and 500C, calculate the net radiant heat transfer per square meter of surface area. [8+8]
Derive an expression for logarithmic mean temperature difference for the case of parallel flow of heat exchanger. A hot fluid enters a heat exchanger at a temperature of 2000C at a flow rate of 2.8 Kg/Sec (sp.heat 2.0 kJ/kg-K) it is cooled by another fluid with a mass flow rate of 0.7 kg/sec (Sp.heat 0.4 kJ/kg-K). The overall heat transfer coefficient based on outside area of 20m2 is 250 W m2-K. Calculate the exit temperature of hot fluid when fluids are in parallel flow. [8+8]
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Code No: 07A40302
SET-4
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JAWAHARLAL NEHRU TECHNOLOGY UNIVERSITY HYDERABAD R07 II B.Tech. II Semester Regular Exams, April/May – 2009 FLUID MECHANICS & HEAT TRANSFER (Mechatronics) Time: 3 hours Max. Marks.80 Answer any Five questions All questions carry equal marks ---
What are the different types of pressure gauges? Two discs of 20 cm diameter are placed 1mm apart and the gap is filled with an oil of viscosity 2 Pa-sec. Determine the power required to rotate the upper disc at 600 rpm while holding the lower one stationary. [6+10]
2.a) b)
Will the stream line, path line and streak line coincide ? If so when will they coincide? What is the irrotational velocity field associated with the velocity potential function φ = 3x2 -3 x + 3y2+ 16t2 + 12zt. Does the flow field satisfy the continuity equation? [8+8]
3.a) b)
What is a orifice meter? Derive an expression for the discharge through a orifice meter. A vertical venturimeter has its inlet and throat diameters as 25 cm and 12.5 cm respectively. A differential mercury manometer connected to the inlet and throat points gives a reading of 25cm. Find the rate of flow. Take Cd=0.98. The liquid flowing through the meter is water. [8+8]
4.
A pipe 50 mm dia is 6 m long and the velocity of flow of water in the pipe is 2.4 m/s. What loss of head and the corresponding power would be saved if the central 2m length of pipe was replaced by 75mm dia pipe, the change of section being sudden? Take f= 0.04 for the pipes of both diameter. Consider the minor losses also. [16]
5.a) b)
What is the basic difference between conduction and radiation heat transfer processes? Identify the modes of heat transfer in the following examples: i) A car disc brake during braking ii) A domestic boiler iii) Heating a room using an electric fan heater iv) Soldering an electric circuit board v) Gas welding two sheets of steel plate. [6+10]
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What are the factors affecting convective heat transfer? Calculate Reynolds number for the following data: D = 15 cm; V = 3 m/sec; ρ = 14,400 kg/m3 and µ = 0.0372 kg/m-sec. A flat plate 10 cm wide and 18 cm high kept at 2500C is placed vertically in air at 1 atm and 200C. Determine the total heat loss from the two sides of the plate. [4+6+6]
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When a body is said to be black what is the range of wave lengths it absorbs? Compute the radiant energy loss from 1 cm diameter opening in a thin walled furnace located in a large enclosure, if the temperature with in the furnace is 9000C and the surroundings is at 200C. [6+10]
8.
Steam is condensed in a single pass condenser at a pressure of 0.5 bar. The condenser consists of 100 thin walled tubes of 2.5 cm nominal diameter and 2m length. The cooling water enters and leaves at a temperature of 100C and 500C with a mean velocity of 2 m/Sec. The condensing heat transfer coefficient is 5 KW/m2-K. Find: a) Overall heat transfer coefficient for heat exchanger b) Condensation rate of steam c) Mean temperature of metal at the center of condenser length. [16]
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