Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2019 Winter 7th Sem New 2170102 Theory Of Heat Transfer Previous Question Paper
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ? VII (New) EXAMINATION ? WINTER 2019
Subject Code: 2170102 Date: 26/11/2019
Subject Name: Theory of 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.
4. Tables for properties of air and water are permitted.
Q.1 (a) Explain the following terms:
(a) Thermal diffusivity
(b) Thermal Conductivity
(c) Thermal contact resistance
03
(b) Define fin effectiveness. When the use of fins is not justified 04
(c) An air stream at 0
0
C is flowing along a heated plate at 90
0
C at a speed of
75 m/s. The plate is 45 cm long and 60 cm wide. Assuming the transition
of boundary layer takes place at Recr = 5 x 10
5
. Calculate the average value
of friction coefficient and heat transfer coefficient for full length of the
plate. Also calculate the heat dissipation from the plate.
The thermo-physical properties at of air are as follows:
?= 1.113 kg/m
3
, k = 0.0276 W/m-K, Pr = 0.693, ? = 1.928 x 10
-5
kg/ms
07
Q.2 (a) What is transient heat conduction? How does transient heat conduction
differ from steady state heat conduction?
03
(b) What is the ?critical radius? of insulation? Derive an expression for the
same for cylinders.
04
(c) A steel pipe is covered with two layers of insulation, first layer being 3
cm thick and second 5 cm. The pipe is made of steel (k=58 W/m-K)
having internal diameter of 160 mm and Outside diameter of 170 mm. The
inside and outside film coefficients are 30 and 5.5 W/m
2
-K, respectively.
Calculate the heat lost per metre of pipe, if the steam temperature is 300?C
and air temperature is 50?C. The thermal conductivity of two insulating
material are 0.17 and 0.093 W/m-K, respectively.
07
OR
(c) Derive an expression for heat transfer for an adequately long of
Rectangular fin with insulated tip.
07
Q.3 (a) Differentiate:
1. Mean film temp and bulk mean temp
2. Velocity and thermal boundary layer
03
(b) Explain lumped heat capacity method of heat transfer and state its
assumptions.
04
(c) Using dimensional analysis, obtain a general form of equation for forced
Convective heat transfer.
07
OR
Q.3 (a) Distinguish between natural and forced convection heat transfer. 03
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1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ? VII (New) EXAMINATION ? WINTER 2019
Subject Code: 2170102 Date: 26/11/2019
Subject Name: Theory of 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.
4. Tables for properties of air and water are permitted.
Q.1 (a) Explain the following terms:
(a) Thermal diffusivity
(b) Thermal Conductivity
(c) Thermal contact resistance
03
(b) Define fin effectiveness. When the use of fins is not justified 04
(c) An air stream at 0
0
C is flowing along a heated plate at 90
0
C at a speed of
75 m/s. The plate is 45 cm long and 60 cm wide. Assuming the transition
of boundary layer takes place at Recr = 5 x 10
5
. Calculate the average value
of friction coefficient and heat transfer coefficient for full length of the
plate. Also calculate the heat dissipation from the plate.
The thermo-physical properties at of air are as follows:
?= 1.113 kg/m
3
, k = 0.0276 W/m-K, Pr = 0.693, ? = 1.928 x 10
-5
kg/ms
07
Q.2 (a) What is transient heat conduction? How does transient heat conduction
differ from steady state heat conduction?
03
(b) What is the ?critical radius? of insulation? Derive an expression for the
same for cylinders.
04
(c) A steel pipe is covered with two layers of insulation, first layer being 3
cm thick and second 5 cm. The pipe is made of steel (k=58 W/m-K)
having internal diameter of 160 mm and Outside diameter of 170 mm. The
inside and outside film coefficients are 30 and 5.5 W/m
2
-K, respectively.
Calculate the heat lost per metre of pipe, if the steam temperature is 300?C
and air temperature is 50?C. The thermal conductivity of two insulating
material are 0.17 and 0.093 W/m-K, respectively.
07
OR
(c) Derive an expression for heat transfer for an adequately long of
Rectangular fin with insulated tip.
07
Q.3 (a) Differentiate:
1. Mean film temp and bulk mean temp
2. Velocity and thermal boundary layer
03
(b) Explain lumped heat capacity method of heat transfer and state its
assumptions.
04
(c) Using dimensional analysis, obtain a general form of equation for forced
Convective heat transfer.
07
OR
Q.3 (a) Distinguish between natural and forced convection heat transfer. 03
2
(b) Show using momentum equation that in the case of incompressible
boundary layer flow with negligible pressure gradient, ?
3
u/?y
3
= 0 at y =
0.
04
(c) Discuss the concept of thermal boundary layer in case of flow over the
plates. How it differ from velocity boundary?
07
Q.4 (a) What is a heat exchanger and where are they used? 03
(b) Explain mechanism of nucleate boiling? 04
(c) Obtain an expression for overall heat transfer coefficient for tubular heat
exchanger, subjected to fouling on its two sides of heat transfer surface.
07
OR
Q.4 (a) Why is counter-flow Heat Exchanger more effective than a parallel flow
heat exchanger.
03
(b) What are the fouling factors? Explain their effect in Heat Exchanger
design.
04
(c) Prove that the effectiveness of parallel flow heat exchanger is given by
?? =
1?exp [??????? (1+?? )]
1+??
07
Q.5 (a) Explain Kirchhoff?s law of radiation? 03
(b) Explain dropwise and filmwise condensation. 04
(c) Derive a general relation for the radiation shape factor in case of radiation
between two surfaces. Explain Wein?s displacement law of radiation.
07
OR
Q.5 (a) What does the view factor represent? When is the view factor from a
surface to itself not zero?
03
(b) Define following:
1) Absorptivity
2) Reflectivity
3) Transmissivity
4) Total Emissivity
04
(c) Define Radiation Intensity? State & Explain the Wien Displacement Law.
Show that Eb ? will be maximum, when ?max. T = 2900 ?K
07
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This post was last modified on 20 February 2020