Heat transfer

1. Name of the Subject: HEAT TRANSFER
QUIZ BITS UNIT-1
S.No Question A B C D Ans
UNIT-1
1
Consider system A at uniform temperature t and system B at another
uniform temperature T
(t > T). Let the two systems be brought into contact and be thermally
insulated from their surroundings but not from each other. Energy will
flow from system A to system B because of
Temperatur
e difference
Energy
difference
Mass
difference
Volumetric
difference A
2
Unit of the rate of heat transfer is Joule Newton Pascal Watt D
3
Convective heat transfer coefficient doesn’t depend on Surface
area
Density Viscosity Orientation
of solid
surface
A
4 Thermal conductivity is maximum for which substance Silver Ice Aluminium Diamond D
5
A radiator in a domestic heating system operates at a surface
temperature of 60 degree Celsius. Calculate the heat flux at the surface
of the radiator if it behaves as a black body
697.2 W/m2 786.9
W/m2 324.7 W/m2 592.1
W/m2
A
6 Which of the following is an example of forced convection?
Chilling
effect of
cold wind
Flow of
water in
condenser
Cooling of
billets in the
Heat
exchange
on cold and
B

2. on a warm
body
tubes atmosphere warm pipes
7 Which statement is true regarding steady state condition?
There is a
variation in
temperature
in the
course of
time
Heat
exchange is
constant
It is a function
of space and
time
coordinates
Internal
energy of
the system
changes
B
8 Which of the following is an example of steady state heat transfer?
Boilers and
turbines
Cooling of
I.C engine
Chilling effect
of cold wind
on a warm
body
Electric
bulb cools
down by
the
surroundin
g
atmosphere
D
9
Heat transfer in a long, hollow cylinder which is maintained at uniform
but different temperatures on its inner and outer surfaces may be
assumed to be taking place in which direction?
Axial only
Unpredicta
ble
Radial only
No heat
transfer
takes place
C
10 Heat transfer takes place according to which law?
Zeroth law
of
thermodyna
mics
Second law
of
thermodyna
mics
Newton’s
second law of
motion
First law
of
thermodyna
mics
B
11 Heat transfer takes place in liquids and gases is essentially due to Radiation
Conduction
Convection
Conduction
as well as
convection
C
12
The appropriate rate equation for convective heat transfer between a
surface and adjacent fluid is prescribed by
Newton’s
first law
Wein’s
displaceme
nt law
Kirchhoff’s
law
Newton’s
law of
cooling
D
13 Identify the wrong statement The For heat A material Heat flow D

3. process of
heat
transfer is
an
irreversible
process
exchange, a
temperature
gradient
must exist
medium is not
necessary for
heat
transmission
doesn’t
depend on
temperature
14
During a cold winter season, a person prefers to sit near a fire. Which
of the following modes of heat transfer provides him the maximum
heat?
Conduction
from the
fire
If it is near
the fire,
convection
sounds
good
Convection
and radiation
together
Radiation
will
provide
quick
warmth
D
15 Fourier law of heat conduction is best represented by
Q = -k A d
t /d x
Q = k A d
x/d t
Q = -k A
Q = k d t/d
x
A
16
Here are some assumptions that are made for Fourier law. Identify the
wrong one
No internal
heat
generation
Steady
state heat
conduction
Non- linear
temperature
profile
Isotropic
and
homogenou
s material
C
17
Negative sign in Fourier heat conduction equation indicates
Heat
always
flow is in
the
direction of
positive
temperature
gradient
Heat
always
flow in the
direction of
negative
temperature
gradient
No heat flow
is there
Data is
insufficient
B
18 Transmission of heat i.e. molecular is smallest in case of Gases Liquids Alloys Solids A
19
Which one is not the unit of thermal conductivity?
kcal/m hr
K
KJ/m hr K W/m s K Cal/cm s K C
20 Thermal conductivity represents the amount of heat conducted across True False CANT BE NONE OF A

4. the unit area when a temperature difference of one kelvin”. DEFINED THE
ABOVE
21
Which of the following is the unit of thermal resistance? degree/kcal
hour
degree
s degree/kcal degree/W D
22
Thermal conductivity is defined as the heat flow per unit time
When the
temperature
gradient is
unity
Across the
wall with
no
temperature
Through a
unit thickness
of the wall
Across
unit area
where the
temperature
gradient is
unity
D
23
Mark the matter with least value of thermal conductivity Air Water Ash
Window
glass
A
24 Which one of the following forms of water have the highest value of
thermal conductivity?
Boiling
water
Steam Solid ice Melting ice C
25 Identify the very good insulator Saw dust Cork Asbestos sheet Glass wool D
26
Most metals are good conductor of heat because of
Transport
of energy
Free
electrons
and
frequent
collision of
atoms
Lattice defects
Capacity
to absorb
energy
B
27
Heat conduction in gases is due to
Molecular
collision
Movement
of electrons
EM Waves
Mixing of
gases
A
28 The heat energy propagation due to conduction heat transfer will be
minimum for
Lead Water Air Copper C
29
Cork is a good insulator because
It is
flexible
It can be
powdered
Low density It is porous D

5. 30
Choose the false statement
For pure
metal
thermal
conductivit
y is more
Thermal
conductivit
y decreases
with
increase in
the density
of the
substance
Thermal
conductivity of
dry material is
lower than that
of damp
material
Heat
treatment
causes
variation in
thermal
conductivit
y
B
31 Low temperature insulation are used when the enclosure is at a
temperature lower than the ambient temperature. Which one of the
following is not a low temperature insulation?
Asbestos Cork Cattle hair Slag wool A
32 The thermal conductivity and the electrical conductivity of a metal at
absolute temperature are related as
k/σ T k/σ k σ/T k/T A
33 The unit of thermal diffusivity is m2
/hr-K kcal/m2
-hr m2
/hr m/hr-K C
34
The diffusion equations
Ɏ2
t + q g = (1/α) (d t/d r)
Governs the temperature distribution under unsteady heat flow through
a homogeneous and isotropic material. The Fourier equation follows
from this expression when
Temperatur
e doesn’t
depends on
time
There is no
internal
heat
generation
Steady state
conditions
prevail
There is no
internal
heat
generation
but
unsteady
state
condition
prevails
D
35
Chose the correct one with respect to the critical radius of insulation
There is
more heat
loss i.e.
conductive
There
occurs a
decrease in
heat flux
Heat loss
increases with
addition of
insulation
Heat loss
decreases
with
addition of
insulation
C
36 For an object i.e. spherical the value of critical radius would be 2k/3h 3k/h 2k/h k/h C

6. QUIZ BITS UNIT-2
S.N
o
A B C D ANSWE
R
1 The extended surface used for the enhancement of heat dissipation
is
Convective
coefficient
Fourier
number
Fin No finned
surface
C
2 If the fin is sufficiently thin, so heat flows pertain to
One
dimension
al heat
conduction
Two
dimension
al heat
conduction
Three
dimensional
heat
conduction
No heat
flow is
there
A
3 In order to achieve maximum heat dissipation, the fin should be
designed in such a way that has a
Maximum
lateral
surface
towards
Minimum
lateral
surface
near the
Maximum
lateral surface
at the root
Maximum
lateral
surface
near the
C
37 Maximum value of critical radius is 0.01 m 0.04 m 0.06 m 0.0001 m A
38 An electric cable of aluminum (k = 240 W/ m degree) is to be
insulated with rubber (k = 6 W/ square meter degree). If the cable is in
air (h = 6 W/square meter degree). Find the critical radius?
80 mm 160 mm 40 mm 25 mm D
39 The value of critical radius in case of a cylindrical hollow object is 2k/h 2h/k k/h h/k C
40
Heat flux is
Heat
transfer per
unit time
Heat
transfer per
unit volume
Rate of heat
transfer per
unit area
None C

7. the tip side
of fin
center line side of fin center of
fin
4 On a heat transfer surface, fins are provided to Increase
turbulence
in flow for
enhancing
heat
transfer
Increase
temperatur
e gradient
so as to
enhance
heat
transfer
Pressure drop
of the fluid
should be
minimized
Surface
area is
maximum
to promote
the rate of
heat
transfer
D
5 In the process of heat transfer through extended surfaces or fins, the
entire surface area is at
the same
constant
temperature
different
temperature
s
maximum base
temperature
minimum
temperature
B
6 Temperature at the base of the fin having uniform cross-sectional area
is
maximum minimum similar to the
heat
generation
temperature
unpredictab
le
A
7 Temperature at the end tip of the fin having uniform cross-sectional
area is
maximum minimum similar to the
heat
generation
temperature
unpredictab
le
B
8 Temperature distribution in the case of long fin B

8. 9 Rate of Heat transfer in the case of long fin
10 Temperature distribution for the fin with insulated end. C
11 Efficiency of very long fin B
12 fin Efficiency when fin tip is insulated A
13 Which analysis is the easiest among the three cases of the fins
Infinite
length fin
Finite
length fin
with tip
insulated
A fin of finite
length None
A
14 In which case the efficiency of the fin will be maximum
Infinite
length fin
Fin of finite
length with
tip insulated
Finite length
fin
None
C
15 Aluminum is used as a fin material because it has
higher
convection
it has
higher
thermal
it has lower
convection
heat transfer
it has lower
thermal
conductivit
B

9. heat
transfer
coefficient
conductivit
y
coefficient y
16 Temperature distribution in case of a fin of infinite length is
linear Parabolic Exponential None
C
17 What is the effect of thermal conductivity k on fin effectiveness? fin is
effective
for smaller
value of
thermal
conductivit
y k
fin is
effective
for larger
value of
thermal
conductivit
y k
thermal
conductivity k
does not affect
the fin
effectiveness
cannot say
B
18 What is the effect of convective heat transfer coefficient h on fin
effectiveness?
fin is
effective if
the value of
convective
heat
transfer
coefficient
h is small
fin is
effective if
the value of
convective
heat
transfer
coefficient
h is large
fin
effectiveness
does not
affected by the
value of
convective
heat transfer
coefficient h
none of the
above
A
19 For effective working of fins, the thickness of the fines should be
Large Small
thickness of
fin does not
affect the fin
effectiveness
d.
unpredictab
le
B
20
Transient condition means
Conductio
n when
temperatur
e at a
point
varies
Very little
heat
transfer
Heat transfer
with a very
little
temperature
difference
Heat
transfer
for a short
time
A

10. with time
21
Transient conduction is also known as
Steady
state heat
conductio
n
Unsteady
state heat
conductio
n
Both A & B None B
22
The quantity having the dimension of time is often called the time
constant for lumped heat system hA/ρCV hV/ρCA ρCV/hA ρCA/hV C
23
The curve for unsteady state cooling or heating of bodies is
Hyperbolic
curve
asymptotic
both to
time and
temperature
axis
Exponentia
l curve
asymptotic
both to
time and
temperature
axis
Parabolic
curve
asymptotic to
time axis
Exponentia
l curve
asymptotic
to time axis
D
24
Biot Number is the ratio of
Convection
to the
conduction
Conduction
resistance
to the
convective
resistance
Bothe A &B none C
25
Biot number is defined as
k/hL kL/h hL/k h/kL C
26
For lumped heat transfer analysis Biot Number Bi is 0.01 0.1 1 10 B
27
If body is having high thermal conductivity, K value, then
Temperatur
e variations
are more in
the body
Temperatur
e variations
are
negligible
in the body
Bothe A &B None

11. 28
Characteristic length Lc is the ratio of
surface
area to
Volume
(As/V)
Volume to
surface area
(V/As)
Volume to
cross sectional
area (V/Ac)
None B
29 Characteristic length Lc in the case of plane wall of thickness 2L 4L 3L 2L L D
30 Characteristic length Lc in the case of plane wall of thickness 10cm 20 cm 10 cm 5 cm 2.5 cm C
31 Characteristic length Lc in the case of cylinder of radius R and length
L
2R R R/2 R/L C
32 Characteristic length Lc in the case of cylinder of 30 cm R and length
100 cm
30 cm 20 cm 15 cm 7,5 cm D
33 Characteristic length Lc in the case of Sphere of diameter D D/2 D/4 D/6 None C
34 Characteristic length Lc in the case of Sphere of diameter 60 mm 60 mm 30 mm 15 mm 10 mm D
35
Fourier number indicates
faster
propagation
of heat
through a
body.
heat
Conveted
from the
body to
surroundin
g fluid.
Both A & B None A
36
Heisler's chart shows the temperature time history of a solid in
transient heat conduction as a function of
Fourier &
Biot
number
Reciprocal
of Fourier
number &
Biot
number
Fourier
number &
reciprocal of
Biot number
Reciprocal
of Fourier
number &
reciprocal
of Biot
number
C
37
In transient heat conduction, the two significant dimensionless
parameters are
Reynolds
number
and
Fourier
Reynolds
number
and Biot
Reynolds
number and
Prandtl
Biot
number
and
Fourier
D

12. number number number number
38 What is the criterion for the applicability of lump system
analysis?
Mean
length
Normal
length
Characteristic
s length Mass no C
39 According to lumped system analysis, solid possesses thermal
conductivity that is
Infinitely
large
Infinitely
small
Moderate 50% small A
40 Which of the following dimensionless number gives an
indication of the ratio of internal (conduction) resistance to the
surface (convective) resistance?
Biot
number
Fourier
number
Stanton
number
Nusselt
number
A