Advanced Heat And Mass Transfer 2b5n5b

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Code No: D9101 JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD M.Tech II SEMESTER EXAMINATIONS APRIL/MAY-2013 ADVANCED HEAT AND MASS TRANSFER (HEATING VENTILATION AND AIR CONDITIONING) Time: 3hours Max.Marks:60 Answer any five questions All questions carry equal marks --1a) Explain how the three thermal boundary conditions be reproduced in laboratory. Explain the physical significance of boundary condition of the third kind. b) A steel plate of thickness of 5 cm and thermal conductivity K = 20 W/m K is subjected to a uniform heat flux of 600 W/m2 on one of its surface and dissipates heat by convection with a heat transfer coefficient of 80 W/m2 0C from the other surface into the ambient air at 280C. What is the temperature of the surface dissipating heat by convection?

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Q6 Q6 Q6 3.a) When areQ6 extended surfaces used to transfer heat?

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b) A thermometer well mounted through the wall of steam pipe is a steel tube with a 0.10 cm wall thickness, 1.25 cm OD, 5 cm length and K = 26 W/m2 K. The steam flow produces and average heat transfer coefficient of 100 W/m2 K on the thermometer well. If the thermo meter reads 1490C and the temperature of the steam pipe is 650C, estimate the average steam temperature. Derive the relevant equation used.

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2.a) Derive the expression for temperature distribution through a plane slab of thickness, L subjected to uniform heat generation at the rate of q(x) = q x2. One boundary at x = 0 is insulated and other boundary is kept at zero temperature. b) A 2 cm stainless steel ball is uniformly heated to 8000C. It is to be hardened by dropping into an oil bath with ambient temperature of 500C. How long the ball be kept in oil bath to reach a temperature of 1000C, if the heat transfer coefficient for oil is 300 W/m2K.

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Engine oil at 200C enters a 3 mm diameter, 15 m long tube with a flow rate of 0.01 kg/s. The tube wall is maintained at 1000C by condensing steam outside the tube surface. Determine. (i) Hydrodynamic entry length (ii) Thermal entry length (iii) Heat transfer coefficient and outlet temperature of the fluid.

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5.a) Show the temperature and velocity profiles under free convection from a vertical plate b) Calculate the total heat loss by convection and radiation from unlagged horizontal steam pipe, 6 cm outside diameter at 1150C to air at 250C. Assume the emissivity of the surface to be ε = 0.9.

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Contd…2

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::2:: 6.a) What are the assumptions made by Nusselt in his theory of condensation over a vertical plate? b) What at saturation temperature and atmospheric pressure is boiled with an electrically heated horizontal platinum wire pf diameter, 2 mm. boiling takes place with an excess temperature of 4540C. Obtain the boiling heat transfer coefficient assuming the emissivity of the heater surface as 1.

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7.a) What are Q6 radiation shields?Q6 Give their applications Q6 Q6 Q6 Q6 b) Dry air at 30 C flows aver a flat plate at 30 C which is covered with a water film.

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The velocity of flow of air is 6m/s. the plate is 1 m long. Determine the average convective mass transfer coefficient and also the mass of water evaporated per second. Given diffusion coefficient, DAB = 2.6 X10-6 m2/s, Sc = 0.615, density of water vapor at 300C is ρw = 0.03 kg/m3

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a) Von Karman integral analysis for laminar flow over a flat plate. b) Regimes of pool boiling

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