Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2019 Winter 5th Sem New 2151909 Heat Transfer Previous Question Paper
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ? V (New) EXAMINATION ? WINTER 2019
Subject Code: 2151909 Date: 25/11/2019
Subject Name: Heat Transfer
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary. Use of steam table, heat transfer
tables and charts are permitted.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a)
Distinguish between natural and forced convection heat transfer
03
(b) A double pipe counter flow heat exchanger, 10000 kg/h of an oil
having a specific heat of 2095 J/Kg K is cooled from 80 ? to 50
? by 8000 kg/h of water entering at 25 ?. Determine the heat
exchanger area for an overall heat transfer co efficient of 300
W/m
2
.K. Take Cp of water as 4180 J/Kg K.
04
(c) Assuming that a man can be represent by a cylinder of 30 cm in
diameter and 1.7 m high with a surface temperature of 30 ?,
calculate the heat he would be loss while standing in a 36 km/h
wind at 10 ?.
Use NuD = 0.027 (ReD)
0.805
(Pr
1/3
)
And physical properties of air at 20 ? are k=0.00259 W/mk
Pr=0.707, ? = 0.000015 m
2
/s
07
Q.2 (a)
Define following: 1) Nusselt number 2) Reynolds number
03
(b) Determine the heat loss from an insulated steel pipe, carrying hot
liquid, to the surrounding per meter length of the pipe, given the
following particular.
I.D. of the pipe=10 cm
Wall thickness = 1 cm
Thickness of the insulation = 3 cm
Temperature of hot liquid = 85 ?
Temperature of surroundings = 25 ?
Thermal conductivity of steel = 58 W/Mk
Thermal conductivity for insulating material = 0.2 W/Mk
Inside heat transfer coefficient = 720 W/m
2
K
Outside heat transfer coefficient = 9 W/m
2
K
04
(c)
Derive equations of temperature distribution and heat dissipation for
Fin insulated at tip.
07
OR
(c)
Derive general heat conduction equation in Cartesian coordinates
07
Q.3 (a) What is difference between conduction, convection and radiation
mode of heat transfer
03
(b) Calculate the rate of heat loss for a red brick wall of length 5 m,
height 4 m and thickness 0.25 m. the temperature of the inner
surface is 110 ? and that of outer surface is 40 ?. The thermal
conductivity of red brick, k=0.7 W/Mk. Calculate also the
temperature at an interior point of the wall, 20 cm distance from
the inner wall.
04
(c)
Using dimensional analysis, obtain a general form of equation for
forced Convective heat transfer.
07
FirstRanker.com - FirstRanker's Choice
1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ? V (New) EXAMINATION ? WINTER 2019
Subject Code: 2151909 Date: 25/11/2019
Subject Name: Heat Transfer
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary. Use of steam table, heat transfer
tables and charts are permitted.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a)
Distinguish between natural and forced convection heat transfer
03
(b) A double pipe counter flow heat exchanger, 10000 kg/h of an oil
having a specific heat of 2095 J/Kg K is cooled from 80 ? to 50
? by 8000 kg/h of water entering at 25 ?. Determine the heat
exchanger area for an overall heat transfer co efficient of 300
W/m
2
.K. Take Cp of water as 4180 J/Kg K.
04
(c) Assuming that a man can be represent by a cylinder of 30 cm in
diameter and 1.7 m high with a surface temperature of 30 ?,
calculate the heat he would be loss while standing in a 36 km/h
wind at 10 ?.
Use NuD = 0.027 (ReD)
0.805
(Pr
1/3
)
And physical properties of air at 20 ? are k=0.00259 W/mk
Pr=0.707, ? = 0.000015 m
2
/s
07
Q.2 (a)
Define following: 1) Nusselt number 2) Reynolds number
03
(b) Determine the heat loss from an insulated steel pipe, carrying hot
liquid, to the surrounding per meter length of the pipe, given the
following particular.
I.D. of the pipe=10 cm
Wall thickness = 1 cm
Thickness of the insulation = 3 cm
Temperature of hot liquid = 85 ?
Temperature of surroundings = 25 ?
Thermal conductivity of steel = 58 W/Mk
Thermal conductivity for insulating material = 0.2 W/Mk
Inside heat transfer coefficient = 720 W/m
2
K
Outside heat transfer coefficient = 9 W/m
2
K
04
(c)
Derive equations of temperature distribution and heat dissipation for
Fin insulated at tip.
07
OR
(c)
Derive general heat conduction equation in Cartesian coordinates
07
Q.3 (a) What is difference between conduction, convection and radiation
mode of heat transfer
03
(b) Calculate the rate of heat loss for a red brick wall of length 5 m,
height 4 m and thickness 0.25 m. the temperature of the inner
surface is 110 ? and that of outer surface is 40 ?. The thermal
conductivity of red brick, k=0.7 W/Mk. Calculate also the
temperature at an interior point of the wall, 20 cm distance from
the inner wall.
04
(c)
Using dimensional analysis, obtain a general form of equation for
forced Convective heat transfer.
07
2
OR
Q.3 (a) Explain in brief about thermal conductivity. 03
(b)
Define Prandtl number. What is the physical interpretation when its
value is lesser or greater than one? Show with neat sketches.
04
(c) Define Grashof number. Explain concept of thermal boundary
layer.
07
Q.4 (a) Define absorptivity, emissivity and monochromatic emissive
power.
03
(b)
?It is true that insulation is provided to reduce heat transfer rate but due
to insulation heat transfer rate is not reduced always? Justify the
statement analytically.
04
(c)
Define total emissive power (E b) and intensity of radiation (I b). Show
that E b = ??I b
07
OR
Q.4 (a) Explain shape factor for radiation. 03
(b)
State and prove Kirchoff?s law for radiation.
04
(c) A pipe carrying steam having an outside diameter of 20 cm runs
in a large room and is exposed to air at a temperature of 30 ?.
The pipe surface temperature is 400 ?. Calculate the loss of heat
to the surrounding per meter length of pipe due to thermal
radiation. The emissivity of pipe surface is 0.8.
What would be the loss of heat due to radiation if the pipe is
enclosed in a 40 cm diameter brick conduit of emissivity 0.91.
07
Q.5 (a) Justify that good absorber is also good emitter for radiation heat
transfer.
03
(b)
Explain drop wise and film wise condensation
04
(c)
Derive an expression for log mean temperature difference of parallel
flow heat exchanger.
07
OR
Q.5 (a)
Why is counter-flow Heat Exchanger more effective than a parallel
flow heat exchanger.
03
(b) Discuss the various regimes of boiling. 04
(c)
Derive equation of effectiveness for parallel flow heat exchanger
07
***********
FirstRanker.com - FirstRanker's Choice
This post was last modified on 20 February 2020