Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2018 Winter 6th Sem Old 161906 Heat And Mass Transfer Previous Question Paper
1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VI (OLD) EXAMINATION ? WINTER 2018
Subject Code:161906 Date: 13/12/2018
Subject Name: Heat And Mass Transfer
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1 (a) Derive the expression for heat conduction through composite wall using
electrical analogy.
07
(b) Find the shape factor F1-1, F1-2 and F2-1 for the following geometries.
(a) A black body inside a black enclosure
(b) A tube whose section is equilateral triangle
(c) Radiation exchange between a hemisphere and a plane surface.
07
Q.2 (a) 0.5 cm thick glass (k=0.78W/m. K) is exposed to air at 25? C (inner side) with
convection heat transfer coefficient of 15 W/m
2
K. The outside air is at -15?C
with convection coefficient of 50 W/m
2
K. Determine (1) temperatures at inner
and outer glass surfaces (2) heat transfer rate.
07
(b) What is critical radius of insulation? Derive the expression for condition for
minimum resistance for maximum heat flow rate for solid cylinder under one
dimensional steady state heat conduction.
07
OR
(b) A circular shaft (k= 50W/m K) 60 mm diameter having 60? C rise in
temperature due to friction. The heat transfer coefficient is 6.5W/m
2
K.
Determine (1) the expression for temperature distribution (2) the amount of heat
dissipated through the shaft. Assume the shaft is a rod of infinite length.
07
Q.3 (a) A polished metal pipe 5 cm outside diameter and 370 K temperature at the outer
surface is exposed to ambient conditions at 295 K temperature. The emissivity
of the surface is 0.2 and the convection coefficient of heat transfer is 11.35
W/m
2
-deg. Calculate the heat transfer by radiation and natural convection per
meter length of pipe. Take thermal radiation constant ?
b = 5.67 x 10
-8
W/m
2
K
4
.
What would be the overall coefficient of heat transfer by combined mode of
convection and radiation?
07
(b) Derive an expression for LMTD for counterflow heat exchanger. 07
OR
Q.3 (a) A heat treated steel plate measures 3 m x 1 m and is initially at 30? C. it is
cooled by blowing air parallel to 1 edge at 9 kmph. If the air is at 10?C,
calculate the convective heat transfer from both sides of the plate. Take the
correlation Nu= 0.664 (Re)
0.5
(Pr)
0.33
07
(b) Derive the expression for effectiveness of parallel flow heat exchanger. 07
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1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VI (OLD) EXAMINATION ? WINTER 2018
Subject Code:161906 Date: 13/12/2018
Subject Name: Heat And Mass Transfer
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1 (a) Derive the expression for heat conduction through composite wall using
electrical analogy.
07
(b) Find the shape factor F1-1, F1-2 and F2-1 for the following geometries.
(a) A black body inside a black enclosure
(b) A tube whose section is equilateral triangle
(c) Radiation exchange between a hemisphere and a plane surface.
07
Q.2 (a) 0.5 cm thick glass (k=0.78W/m. K) is exposed to air at 25? C (inner side) with
convection heat transfer coefficient of 15 W/m
2
K. The outside air is at -15?C
with convection coefficient of 50 W/m
2
K. Determine (1) temperatures at inner
and outer glass surfaces (2) heat transfer rate.
07
(b) What is critical radius of insulation? Derive the expression for condition for
minimum resistance for maximum heat flow rate for solid cylinder under one
dimensional steady state heat conduction.
07
OR
(b) A circular shaft (k= 50W/m K) 60 mm diameter having 60? C rise in
temperature due to friction. The heat transfer coefficient is 6.5W/m
2
K.
Determine (1) the expression for temperature distribution (2) the amount of heat
dissipated through the shaft. Assume the shaft is a rod of infinite length.
07
Q.3 (a) A polished metal pipe 5 cm outside diameter and 370 K temperature at the outer
surface is exposed to ambient conditions at 295 K temperature. The emissivity
of the surface is 0.2 and the convection coefficient of heat transfer is 11.35
W/m
2
-deg. Calculate the heat transfer by radiation and natural convection per
meter length of pipe. Take thermal radiation constant ?
b = 5.67 x 10
-8
W/m
2
K
4
.
What would be the overall coefficient of heat transfer by combined mode of
convection and radiation?
07
(b) Derive an expression for LMTD for counterflow heat exchanger. 07
OR
Q.3 (a) A heat treated steel plate measures 3 m x 1 m and is initially at 30? C. it is
cooled by blowing air parallel to 1 edge at 9 kmph. If the air is at 10?C,
calculate the convective heat transfer from both sides of the plate. Take the
correlation Nu= 0.664 (Re)
0.5
(Pr)
0.33
07
(b) Derive the expression for effectiveness of parallel flow heat exchanger. 07
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2
Q.4 (a) State and explain Wien?s displacement law and define Lambert?s cosine law
of radiation
07
(b) Discuss the concept of thermal boundary layer in case of flow over the plates. How
it differs from velocity boundary?
07
OR
Q.4 (a) What is meant by a lumped capacity? What are the physical dimensions necessary
for a lumped unsteady state analysis to apply?
07
(b) State and explain Fick?s law of diffusion and compare it with Fourier?s law of
heat conduction
07
Q.5 (a) A steam condenser is transferring 250 kW of thermal energy at a condensing
temperature of 65?C. The cooling water enters the condenser at 20?C with a
flow rate of 7500kg/hr. calculate the log mean temperature difference. If the
overall heat transfer coefficient for the condenser surface is 1250 W/ m
2
-deg,
what surface area is required to handle this load?
07
(b) By dimensional analysis show that for forced convection heat transfer the Nusselt
number can be expressed as a function of Prandtl number and Reynolds number.
07
OR
Q.5 (a) A counterflow heat concentric tube heat exchanger is used to cool the
lubricating oil of a large industrial gas turbine engine. The oil flows through the
tube at 0.19 kg/s (Cp = 2.18 kJ/kg K), and the coolant water flows in the
annulus in the opposite direction at a rate of 0.15 kg/s (Cp = 4.18 kJ/kg K). The
oil enters the coolant at 425K and leaves at 345 K while the coolant enters at
285 K. How long must the tube be made to perform this duty if the heat transfer
coefficient from oil to tube surface is 2250 W/m
2
K and form tube surface to
water is 5650W/m
2
? The tube has a mean diameter of 12.5 mm and its wall
presents negligible resistance to heat transfer
07
(b) Define pool boiling. Draw pool boiling curve for water and explain various
regimes of the curve.
07
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This post was last modified on 20 February 2020