S.E. (Chemical) (Second Semester) EXAMINATION, 2012 HEAT TRANSFER (2008 PATTERN) Time : Three Hours Maximum Marks : 100

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Total No. of Questions 12] [Total No. of Printed Pages 7 Seat No. [4162]-187 S.E. (Chemical) (Second Semester) EXAMINATION, 2012 HEAT TRANSFER (2008 PATTERN) Time : Three Hours Maximum Marks : 100 N.

1 Total No. of Questions 12] [Total No. of Printed Pages 7 Seat No. [4162]-187 S.E. (Chemical) (Second Semester) EXAMINATION, 2012 HEAT TRANSFER (2008 PATTERN) Time : Three Hours Maximum Marks : 100 N.B. : Answer three questions from Section I and three questions from Section II. (ii) Answers to the two Sections should be written in separate answer-books. (iii) (iv) Neat diagrams must be drawn wherever necessary. Use of logarithmic table slide rule, Millier charts, electronic pocket calculator and steam tables is allowed. (v) Assume suitable data, if necessary. SECTION I 1. (a) Give significance of Reynolds number and Nusselt Number. [4] Explain Rayleigh s method of dimensional analysis. [6] By dimensional analysis derive the following relationship for free convection heat transfer process Nu = C[Gr a Pr b ] P.T.O.

2 where Nu = Nusselt number Gr = Grashoff number Pr = Prandtl number a, b and c are numerical constants. [8] 2. (a) State and explain : Fourier law of heat conduction (ii) Newton s law of cooling (iii) Stefan-Boltzmann s law of radiation. [9] Explain Buckingham s π theorem for dimensional analysis. [6] Explain in detail Modes of heat transfer. [3] 3. (a) Derive the relation for steady state conduction through composite (concentric) cylinder bounded by fluids at different temperatures. [8] Calculate the critical radius of insulation for asbestos (K = 0.17 W/m K) surroundings a pipe and exposed to room air at 20 C with h = 3.0 W/m 2 k. Calculate to heat loss from a 200 C, 5.0 cm diameter pipe when covered with the critical radius of insulation. [8] [4162]-187 2

3 4. (a) An aluminium rod 25 mm in diameter and 100 mm long protrudes from a wall which is maintained at 250 C into the environment maintained at 15 C. Estimate the heat loss by rod assuming that the rod end is insulated. Data : k for aluminium = 200 W/(m k) h between rod surface and environment = 15 W/m 2 K. [8] What are fins? Draw neat diagrams of four different types of fins? [5] What is thermal conductivity? Discuss the mechanism of thermal conduction in gases and solids? [3] 5. Write short notes : (ii) (iii) Heat transfer in agitated vessels Variable thermal conductivity Pool boiling (iv) Individual and overall heat transfer coefficient. [16] 6. (a) A tube of outside diameter 7.6 cm and thickness 2.6 mm covered with an insulation material of thickness 1.8 cm. A hot gas [4162] P.T.O.

4 at temperature 320 C with a heat transfer coefficient 100 W/m 2 K flows inside the tube. The outer surface of insulation is exposed to air at 20 C with heat transfer coefficient of 30 W/m 2 K. Thermal conductivity of insulating material is 0.2 W/mK. Calculate : The rate of heat loss per meter of pipe to air (ii) The temperature of the interface between metal wall and the insulation. [8] Derive expression for temperature profile and heat flow for straight rectangular fin of uniform cross-section. [8] SECTION II 7. (a) Explain Weins Displacement Law. [4] State and explain Kirchhoffs Law. [4] Two very large parallel planes with emissivities 0.8 and 0.7 exchange the heat. Estimate the percent reduction in heat transfer when a polished aluminium radiation shield with emissivity 0.03, is placed between them. [8] 8. (a) Explain specular and diffuse reflection. [4] Write short notes on : Emissive power and emissivity (ii) Shape factor. [4] [4162]-187 4

5 Calculate the heat flux emitted due to thermal radiation from a black surface at 5700 C. At what wavelength is the monochromatic emissive power maximum? [σ = W/m 2 K 4 ] [6] (d) Explain concept of an artificial black body. [2] 9. (a) Explain tripple effect evaporator with forward feed arrangement. [6] A shell and tube heat exchanger is to be provided with tubes 4 m long, 3.1 cm O.D. and 2.7 cm I.D. the heat exchanger is required for heating water from 22 C to 45 C with the help of condensing steam at 100 C on the outside of tubes. Calculate the number of tubes required if the water flow rate through tubes is 10 kg/s and heat transfer coefficients on vapour and water sides are 5500 and 850 W/m 2 K respectively. Neglect all other resistances. Assume C p water = 4186 J/kgK. Also, calculate the rate of steam consumption if latent heat is 2200 kj/kg. [10] Draw shell and tube heat exchanges and show different parts. [2] [4162] P.T.O.

6 10. (a) 20 kg/s of water at 360 K entering a heat exchanger is to be cooled at 340 K by using cold water at 300 K, flowing at a rate of 25 kg/s. If the overall heat transfer coefficient is 1500 W/m 2 K. Calculate the heat transfer area required in : Co-current flow concentric pipe heat exchanger and (ii) Counter-current flow concentric pipe heat exchanger. [10] Derive equation for log mean temperature difference for cocurrent flow double pipe heat exchanger. [6] Draw neat sketch of double pipe heat exchanger and show different parts. [2] 11. (a) An evaporator is to be fed with 5000 kg/hr. of solution containing 10% solute by weight. The feed at 40 C is concentrated to a solution containing 40% by weight of solute under atmospheric pressure. Steam is available at an absolute pressure 3 atmosphere. (The saturation temperature of 134 C). The heat transfer coefficient is 1500 kcal/hr.m 2 C. Calculate : [8] The heat transfer area that should be provided (ii) The steam requirement. [4162]-187 6

7 Treat the solution as per pure water for enthalpy calculators. Data : Temperature ( C) Enthalpy Vapour (kcal/kg) Liquid Explain with diagram Calendria type evaporator. [8] 12. Write short notes : (a) Applications of heat exchanger in dairy industry Vapour recompression in evaporators Radiosity (d) NTU-effectiveness method for heat exchanger. [16] [4162] P.T.O.

S.E. (Chemical) (Second Semester) EXAMINATION, 2011 HEAT TRANSFER (2008 PATTERN) Time : Three Hours Maximum Marks : 100

Total No. of Questions 12] [Total No. of Printed Pages 7 [4062]-186 S.E. (Chemical) (Second Semester) EXAMINATION, 2011 HEAT TRANSFER (2008 PATTERN) Time : Three Hours Maximum Marks : 100 N.B. : (i) Answers