Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2019 Winter 5th Sem New 2153502 Introduction To Heat Transfer Previous Question Paper
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ? V (New) EXAMINATION ? WINTER 2019
Subject Code: 2153502 Date: 04/12/2019
Subject Name: Introduction to Heat Transfer
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a) State Fourier?s law of heat conduction? Mention the significance of negative
sign in heat conduction equation.
03
(b) Differentiate Critical thickness of Insulation and Optimum thickness of
Insulation
04
(c) Describe the different kind of Boundary conditions used in heat transfer
studies
07
Q.2 (a) An electrically heated plate dissipates heat by convection at a rate of q = 8000
W/m
2
into ambient air at Tf = 25 ?C. If the surface of hot plate is at TW = 125
?C. Calculate heat transfer coefficient for convection between plate and air.
03
(b) What is lumped System analysis? Mention the importance of Biot number in
lumped system analysis.
04
(c) Develop expression for one dimensional steady state temperature distribution
T(r) in a sphere where inner surface at r = a and outer surface of r = b of
hollow sphere are maintained at temperatures of T1 and T2 respectively.
Consider that thermal conductivity (k) of sphere is constant
07
OR
(c) Atmospheric air at T ? = 400 K with a velocity u ? = 1.5 m/s flows over a flat
plate L = 2 m long maintained at uniform temperature of T W = 300K.
Calculate average value of heat transfer coefficient and average heat transfer
rate from airstream to plate over entire length of L = 2m.
07
Q.3 (a) Write the significance of following dimensionless numbers used in heat
transfer studies (i) Reynolds number (ii) Prandtl number (iii) Nusselt number
03
(b) Differentiate velocity boundary layer and thermal boundary layer 04
(c) Estimate the total heat loss by convection and radiation from an unlagged
steam pipe, 50 mm o.d. at 415 K to air at 290K (17 ?C). Emissivity e = 0.90
Film coefficient for calculation of heat loss by natural convection is given by
hC = 1.18 ( ?T/DO)
0.25
W/m
2
K
07
OR
Q.3 (a) Mention the factors governing the rate of heat transfer in forced and natural
convection.
03
(b) Define Absorptivity, Reflectivity and Transmissivity 04
(c) Calculate heat transfer area of 1 ? 2 heat exchanger from the following data.
Inlet and outlet temperatures of cold fluid are 303 K and 318 K respectively.
Overall heat transfer coefficient = 4100 W/m
2
K. Heat loss = 407 kW. LMTD
correction factor = 0.84.
07
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1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ? V (New) EXAMINATION ? WINTER 2019
Subject Code: 2153502 Date: 04/12/2019
Subject Name: Introduction to Heat Transfer
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a) State Fourier?s law of heat conduction? Mention the significance of negative
sign in heat conduction equation.
03
(b) Differentiate Critical thickness of Insulation and Optimum thickness of
Insulation
04
(c) Describe the different kind of Boundary conditions used in heat transfer
studies
07
Q.2 (a) An electrically heated plate dissipates heat by convection at a rate of q = 8000
W/m
2
into ambient air at Tf = 25 ?C. If the surface of hot plate is at TW = 125
?C. Calculate heat transfer coefficient for convection between plate and air.
03
(b) What is lumped System analysis? Mention the importance of Biot number in
lumped system analysis.
04
(c) Develop expression for one dimensional steady state temperature distribution
T(r) in a sphere where inner surface at r = a and outer surface of r = b of
hollow sphere are maintained at temperatures of T1 and T2 respectively.
Consider that thermal conductivity (k) of sphere is constant
07
OR
(c) Atmospheric air at T ? = 400 K with a velocity u ? = 1.5 m/s flows over a flat
plate L = 2 m long maintained at uniform temperature of T W = 300K.
Calculate average value of heat transfer coefficient and average heat transfer
rate from airstream to plate over entire length of L = 2m.
07
Q.3 (a) Write the significance of following dimensionless numbers used in heat
transfer studies (i) Reynolds number (ii) Prandtl number (iii) Nusselt number
03
(b) Differentiate velocity boundary layer and thermal boundary layer 04
(c) Estimate the total heat loss by convection and radiation from an unlagged
steam pipe, 50 mm o.d. at 415 K to air at 290K (17 ?C). Emissivity e = 0.90
Film coefficient for calculation of heat loss by natural convection is given by
hC = 1.18 ( ?T/DO)
0.25
W/m
2
K
07
OR
Q.3 (a) Mention the factors governing the rate of heat transfer in forced and natural
convection.
03
(b) Define Absorptivity, Reflectivity and Transmissivity 04
(c) Calculate heat transfer area of 1 ? 2 heat exchanger from the following data.
Inlet and outlet temperatures of cold fluid are 303 K and 318 K respectively.
Overall heat transfer coefficient = 4100 W/m
2
K. Heat loss = 407 kW. LMTD
correction factor = 0.84.
07
2
Q.4 (a) What is drop wise condensation? Explain why heat transfer coefficient is
lesser for film wise condensation than drop wise condensation?
03
(b) With neat diagrams explain classification of heat exchangers according to
flow arrangement.
04
(c) A heat exchanger is required to cool 20 kg/s of water from 360K to 340K by
means of 25kg/s of water entering at 300K. If the overall heat transfer
coefficient is 2000 W/m
2
K. calculate the surface area required in
a) A counter current concentric heat exchanger
b) A co-current flow concentric tube heat exchanger. (Take CP of water
= 4.187 kJ/kg K)
07
OR
Q.4 (a) Discuss the phenomena of hysteresis in a boiling curve. 03
(b) Why saturated steam is used as heating medium in industries? 04
(c) Describe the significance of ? - NTU method for heat exchange analysis. 07
Q.5 (a) What is understood by boiling point elevation in evaporators 03
(b) What is Vapor recompression? Mention different methods in which vapor
recompression can be done.
04
(c) With help of boiling curve mention different regimes in a pool boiling. 07
OR
Q.5 (a) Define the terms of Capacity & Economy in Evaporators 03
(b) Explain the different methods of feeding of multiple effect evaporators. 04
(c) An evaporator operating at atmospheric pressure is designed to concentrate
5% solute to 20 % solute by weight at a rate of 5000 kg/h. Dry saturated steam
at a pressure corresponding to saturation temperature of 399K is used. The
feed is at 298 K and boiling point rise is 5 K. Overall heat transfer coefficient
is 2350 W/m
2
K. Calculate economy of evaporator and area of heat transfer
to be provided assuming that there is no boiling point elevation for the solvent.
Data: Latent heat of Condensation of steam = 2185 kJ/kg
Latent heat of vaporization of water at 101.325 kPa and 373 K = 2257 kJ/kg
Specific heat of feed = 4.187 kJ/ kg K
07
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This post was last modified on 20 February 2020