GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER- IV (New) EXAMINATION - WINTER 2019
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Subject Code: 2140503 Date: 14/12/2019
Subject Name: Process Heat Transfer
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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Q.1 (a) Explain how does thermal conductivity of gases, liquid and solids depend upon temperature? 03
(b) Derive equation to calculate the rate of heat flow through cylinder. 04
(c) Derive equation for heat transfer through a composite wall made up of three different materials in close thermal contact with each other, with no heat loss to surrounding when temperatures of hot and cold ends are Th and Tc. 07
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Q.2 (a) Define: i) emissivity, ii) black body, iii) grey body. 03
(b) Discuss the Fourier’s law of conduction. 04
(c) Draw the temperature profiles of cold and hot fluids for true co-current and counter current flow in double pipe heat exchanger, Derive expression relating Rate of heat transfer and Log mean temperature difference. 07
OR
(c) Write a short note on significance of various dimensionless numbers in heat transfer. 07
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Q.3 (a) Write short note on Natural Convection. 03
(b) Describe Regimes of Pool Boiling. 04
(c) Determine the heat transfer-coefficient for water flowing in a tube of 16 mm diameter at a velocity-of 3 m/s. The temperature of the tube is 297 K and water enters at 353 K and leaves at 309 K. Use (i) Dittus-Boelter equation and (ii) Sieder- Tate equation 07
Properties of water at 331 K, i.e. at the arithmetic mean bulk temperature are p=984.1 kg/m3, Cp=4187 J/(kg K) , n =485 x 10-6 Pa.s, k = 0.657 W/(m K), Viscosity of water at 297 K, pw =920 x 10-6 Pa.s
OR
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Q.3 (a) Explain the significance of LMTD correction factor. 03
(b) Distinguish between filmwise and dropwise condensation. 04
(c) Derive an equation for Overall heat transfer coefficient in double pipe heat exchanger. 07
Q.4 (a) Describe different analogy between heat and mass transfer. 03
(b) Explain the terms absorptivity, emissivity, transmissivity and reflectivity for heat transfer by radiation. 04
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(c) Write short notes on Vapor recompression in evaporator. 07
OR
Q.4 (a) What are the advantages of providing optimum baffle spacing and tube pitch in case of heat exchanger tubes? 03
(b) Define heat transfer coefficient and describe its dependence of various parameters. 04
(c) With a neat sketch explain the construction and working of a fin tube heat exchangers and its application. 07
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Q.5 (a) What is the reason for increasing the number of passes in a shell & tube heat exchanger? 03
(b) Write Dittus-Boeltier equation and Sieder-Tate equation explaining each term and highlight the difference. 04
(c) Give detailed construction and working of shell and tube heat exchanger with diagram. 07
OR
Q.5 (a) Discuss Capacity and Economy of evaporators. 03
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(b) Discuss about feed forward and feed backward arrangement is multiple effect evaporator. 04
(c) An evaporator is operating at atmospheric pressure. It is desired to concentrate a feed from 5% solute to 20% solute by weight at a rate of 5000 kg/hr. Dry saturated steam at a pressure corresponding to the saturation temperature 399 K is used. The feed is at 298 K and the boiling point rise is 5 K. The overall heat transfer coefficient is 2350 w/m2. K. Calculate the economy of the evaporator and the area of the heat transfer to be provided. 07
Data: Treating solution as a pure water and neglecting the B.P.R, the latent heat of condensation of steam at 399 K is 2185 KJ/kg., Latent heat of vaporization of water at 101.325 KPa and 373 K= 2257 KJ/kg and specific heat of feed is 4.187 KJ/kg. K
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