Download GTU (Gujarat Technological University Ahmedabad) B.Tech/BE (Bachelor of Technology/ Bachelor of Engineering) 2020 Winter 7th Sem 2171911 Advance Heat Transfer Previous Question Paper
Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE- SEMESTER?VII (NEW) EXAMINATION ? WINTER 2020
Subject Code:2171911 Date:19/01/2021
Subject Name:Advance Heat Transfer
Time:10:30 AM TO 12:30 PM Total Marks: 56
Instructions:
1. Attempt any FOUR questions out of EIGHT questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a) Define fin effectiveness and the fin efficiency
03
(b) Define Biot number. Discuss physical significance of Biot number.
04
(c) A diecast component has a mass of 1.2 kg and density 7150 kg/m3 with
07
surface area of 0.075 m2. The thermal conductivity of the material is 95
W/mK and the specific heat is 385 J/kg K. It comes out of the machine
at 345?C and is exposed to air at 20?C with a convective heat transfer
coefficient of 56.8 W/m2K. Determine
i.
The temperature of the part after 5 minutes.
ii.
The time required to reach 50?C.
iii.
The time constant.
iv.
The value of convective heat transfer coefficient upto which the
lumped parameter model can be used.
v.
The volume/area ratio upto which the lumped parameter model
can be used.
Q.2 (a) Define: Nusselt Number, Reynolds Number, Prandtl Number
03
(b) Differentiate nucleate boiling and film boiling.
04
(c) Derive temperature distribution and heat transfer rate expression, under
07
one dimensional steady state, uniform volumetric heat generation rate in
plane wall having same temperature at both end surface.
(Assume constant cross sectional area and constant thermal
conductivity.)
Q.3 (a) Define: Grashof number. Tell physical significance of Grashof number.
03
(b) Express conventional generalised basic equation for forced convection
04
parallel flow over a flat plate for local and average skin friction heat
transfer convection coefficient using Nusselt Number, Reynolds
Number, Prandtl Number.
(c) Derive differential equation, under one dimensional steady state heat
07
conduction in straight infinite long fin of rectangular profile for
following cases:
i.
Pure convection heat transfer through fin surface.
ii.
Pure radiation heat transfer through fin surface.
iii.
Convection and radiation heat transfer through fin surface.
(Assume constant cross sectional area and constant thermal
conductivity.)
Q.4 (a) Tell physical significance of Nusselt number and Prandtl number.
03
(b) Explain radial fins of rectangular and parabolic profiles.
04
(c) State governing equation and boundary condition for 1-D flow for
07
transient heat conduction in semi-infinite solids.
1
A steel ingot (large in size) heated uniformly to 745?C is hardened by
quenching it in an oil bath maintained at 20?C. Determine the length of
time required for the temperature to reach 595?C at the depth of 12 mm.
The ingot may be approximated as a flat plate. For steel ingot, thermal
diffusivity = 1.2 x 10-5 m2/s.
Q.5 (a) Define emissivity correction factor and pressure correction factor.
03
Express equation for gas and gas mixture which correlate both above
factor.
(b) Distinguish between natural and forced convection heat transfer.
04
(c) A long 10-cm-diameter steam pipe whose external surface temperature
07
is 110?C passes through some open area that is not protected against the
winds (Fig. 2). Determine the rate of heat loss from the pipe per unit of
its length when the air is at 1 atm pressure and 10?C and the wind is
blowing across the pipe at a velocity of 8 m/s.
Assumptions: 1 Steady operating condition exists. 2 Radiation effects
are negligible. 3 Air is an ideal gas.
The Nusselt number can be determined from
4 / 5
5 / 8
1/ 2
1/ 3
0.62 Re
Pr
Re
Nu 0 3
.
1
/
1 0.4 / Pr2 / 3 1 4
282000
The properties of air at the average film temperature of Tf = (Ts + T)/2
= (110 + 10)/2 = 60?C and 1 atm pressure are
k = 0.02808 W/m ? ?C, Pr = 0.7202, = 1.896 x 10-5 m2/s.
Q.6 (a) Define terms:
03
i.
Spectral Transmissivity
ii.
Spectral absorptivity
iii.
Spectral emissivity
(b) Differentiate film wise condensation and drop wise condensation.
04
(c) A volume of 5 cm3 is available for a circular pin fin. Determine the
07
optimum diameter. Conductivity = 200 W/mK, convection coefficient =
200 W/m2K. Assume fin end is insulated.
Q.7 (a) State types of heat loss from human body.
03
(b) Saturated steam at atmospheric pressure condenses on a 2-m-high and 3-
04
m wide vertical plate that is maintained at 80?C by circulating cooling
water through the other side. When plate is vertical, then the
condensation heat transfer coefficient is 5848 W/m2 0C. Determine the
rate of heat transfer by condensation to the plate if the plate were tilted
30? from the vertical, as shown in Figure 3.
(c) Fluid motion over a vertical flat plate is steady, laminar, two-
07
dimensional and the fluid to be Newtonian with constant properties.
Prove that governing equation for natural convection flow is
u
u
2
u
v
u
v
g T
T .
x
y
y2
Draw velocity and temperature profiles for natural convection flow over
a hot vertical plate at temperature Ts inserted in a fluid at temperature T.
2
(Hint: Apply newton's second law of motion in x direction, momentum
principle in x direction)
Q.8 (a) State assumption used in Nusselt theory, laminar film condensation over
03
vertical plate.
(b) Explain radiation effect on temperature measurements. Derive
04
expression for actual temperature of fluid.
(c) Define boiling. Explain various regimes of boiling.
07
Fig. 1, Q-4 (c)
Fig. 2, Q-5(c) Fig. 3, Q-7 (b)
3
This post was last modified on 04 March 2021