Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2019 Summer 6th Sem Old 161906 Heat And Mass Transfer Previous Question Paper
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VI(OLD) ? EXAMINATION ? SUMMER 2019
Subject Code:161906 Date:31/05/2019
Subject Name: Heat And Mass 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.
Q.1 (a) Derive general heat conduction equation in Cylindrical coordinates with general
notations
07
(b) A metal plate of 4 mm thickness with thermal conductivity 95.5W/m
0
C is
exposed to vapour at 100
0
C on one side and cooling water at 25
0
C on the
opposite side. The heat transfer coefficients on vapour side and water side are
14500 W/m
2 0
C and 2250 W/m
2 0
C respectively. Determine
i) The rate of heat transfer
ii) The overall heat transfer coefficient and
iii) Temperature drop at each side of heat transfer
07
Q.2 (a) Write a short note on critical thickness of insulation 07
(b) Derive an expression for heat dissipation in rectangular fin of uniform cross-
section which is insulated at tip.
07
OR
(b) An egg with mean diameter of 4 cm and initially at 25
0
C is placed in a boiling
water pan for 4 minutes and found to be boiled. For how long should a similar
egg be boiled when taken from a refrigerator at 5
0
C?
07
Q.3 (a) Define Reynolds number, Nusselt number and Prandtl number. Explain their
importance in convection heat transfer.
07
(b) Air at atmospheric pressure and 200
0
C flows over a plate with a velocity of 5
m/s. The plate is 15 mm wide and is maintained at a temperature of 120
0
C.
Calculate the thicknesses of hydrodynamic and thermal boundary layers and the
local heat transfer coefficient at a distance of 0.5 m from the leading edge.
Assume that flow is on one side of the plate. Density of air is 0.815 kg/m
3
,
dynamic viscosity is 24.5*10
-6
Ns /m
2 0
C, Prandtl number is 0.7 and thermal
conductivity is 0.0364 W/m
0
C
OR
Q.3 (a) Obtain a general form of equation for forced Convective heat transfer using
dimensional analysis
07
(b) A horizontal fluorescent tube which is 3.8 cm in diameter and 120 cm long
stands in still air at 1 bar and 20
0
C. if the surface temperature is 40
0
C and
radiation is neglected, what is heat transfer rate by convection.
Use equation Nu = 0.53 (Gr.Pr)
0.25
. Kinematic viscosity is 15.6*10
-6
m
2
/s,
Prandtl number is 0.701 and thermal conductivity is 2.673 *10
-2
W/m
K.
07
Q.4 (a) Describe briefly the factors considered for the selection criteria for heat
exchanger.
07
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Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VI(OLD) ? EXAMINATION ? SUMMER 2019
Subject Code:161906 Date:31/05/2019
Subject Name: Heat And Mass 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.
Q.1 (a) Derive general heat conduction equation in Cylindrical coordinates with general
notations
07
(b) A metal plate of 4 mm thickness with thermal conductivity 95.5W/m
0
C is
exposed to vapour at 100
0
C on one side and cooling water at 25
0
C on the
opposite side. The heat transfer coefficients on vapour side and water side are
14500 W/m
2 0
C and 2250 W/m
2 0
C respectively. Determine
i) The rate of heat transfer
ii) The overall heat transfer coefficient and
iii) Temperature drop at each side of heat transfer
07
Q.2 (a) Write a short note on critical thickness of insulation 07
(b) Derive an expression for heat dissipation in rectangular fin of uniform cross-
section which is insulated at tip.
07
OR
(b) An egg with mean diameter of 4 cm and initially at 25
0
C is placed in a boiling
water pan for 4 minutes and found to be boiled. For how long should a similar
egg be boiled when taken from a refrigerator at 5
0
C?
07
Q.3 (a) Define Reynolds number, Nusselt number and Prandtl number. Explain their
importance in convection heat transfer.
07
(b) Air at atmospheric pressure and 200
0
C flows over a plate with a velocity of 5
m/s. The plate is 15 mm wide and is maintained at a temperature of 120
0
C.
Calculate the thicknesses of hydrodynamic and thermal boundary layers and the
local heat transfer coefficient at a distance of 0.5 m from the leading edge.
Assume that flow is on one side of the plate. Density of air is 0.815 kg/m
3
,
dynamic viscosity is 24.5*10
-6
Ns /m
2 0
C, Prandtl number is 0.7 and thermal
conductivity is 0.0364 W/m
0
C
OR
Q.3 (a) Obtain a general form of equation for forced Convective heat transfer using
dimensional analysis
07
(b) A horizontal fluorescent tube which is 3.8 cm in diameter and 120 cm long
stands in still air at 1 bar and 20
0
C. if the surface temperature is 40
0
C and
radiation is neglected, what is heat transfer rate by convection.
Use equation Nu = 0.53 (Gr.Pr)
0.25
. Kinematic viscosity is 15.6*10
-6
m
2
/s,
Prandtl number is 0.701 and thermal conductivity is 2.673 *10
-2
W/m
K.
07
Q.4 (a) Describe briefly the factors considered for the selection criteria for heat
exchanger.
07
2
(b) In a certain double pipe heat exchanger hot water flows at a rate of 5000kg/h
and gets cooled from 95
0
C to 65
0
C. At the same time 50000kg/h of cooling
water at 30
0
C enters the heat exchanger. The flow conditions are such that
overall heat transfer coefficient remains constant at 2270 W/m
2
K. Determine
the heat transfer area required and the effectiveness, assuming two streams are
in parallel flow. For the both the streams , assume specific heat at constant
pressure to be 4.2 kJ/kg K.
07
OR
Q.4 (a) Explain the typical boiling curve for water at 1 atm pressure with a neat sketch. 07
(b) Write short notes:
i. Film condensation
ii. Dropwise condensation
07
Q.5 (a) State the following laws for radiation heat transfer
i) Plank?s law
ii) Wien?s law
iii) Stefan Boltzmann law
iv) Kirchhoff?s law
v) Lambert cosine law
07
(b) A furnace emits radiation at 2000 K treating it as a black body radiation, calculate the
following:
i) Monochromatic radiant flux density at 1 ? wavelength.
ii) Wavelength at which emission is maximum and corresponding radiant flux
density.
iii) Total emissive power.
07
OR
Q.5 (a) State and explain Fick?s law of diffusion. Express Fick?s law in terms of partial
pressures of gases
07
(b) A 30 mm deep pan is filled with water to a level of 15 mm and is exposed to
dry air at 40
0
C. Assuming the mass diffusivity as 0.25*10
-4
m
2
/s, calculate the
time required for all the water to evaporate.
07
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This post was last modified on 20 February 2020