ONE-DIMENSIONAL HEAT FLOW. OF THESE STATEMENTS
4. One-dimensional heat flow.
Of
these
statements:
(a) 1, 2 and 3 are correct
(b) 1, 2 and 4 are correct
(c) 2, 3 and 4 are correct
(d) 1, 3 and 4 are correct
IES-3.
A plane wall is 25 cm thick with an area of 1 m
2
, and has a thermal
conductivity of 0.5 W/mK. If a temperature difference of 60°C is
imposed across it, what is the heat flow?
[IES-2005]
(a) 120W
(b) 140W
(c) 160W
(d) 180W
IES-4.
A large concrete slab 1 m thick has one dimensional temperature
distribution: [IES-2009]
T = 4 – 10x + 20x
2
+ 10x
3
Where
T is temperature and x is distance from one face towards other
face of wall. If the slab material has thermal diffusivity of 2 × 10
-3
m
2
/hr,
what is the rate of change of temperature at the other face of the wall?
(a) 0.1°C/h
(b) 0.2°C/h
(c) 0.3°C/h
(d) 0.4°C/h
IES-5.
Thermal diffusivity of a substance is:
[IES-2006]
(a) Inversely proportional to thermal conductivity
(b) Directly proportional to thermal conductivity
(c) Directly proportional to the square of thermal conductivity
(d) Inversely proportional to the square of thermal conductivity
IES-6. Which one of the following expresses the thermal diffusivity of a
substance in terms of thermal conductivity (k), mass density (ρ) and
specific heat (c)? [IES-2006]
(a)
k
2
ρc (b)
1/ρkc (c)
k/ρc (d)
ρc/k
2
Page 4 of 97
IES-7.
Match List-I and List-II and select the correct answer using the codes
given below the lists:
[IES-2001]
h
m
- mass transfer coefficient,
D - molecular diffusion coefficient,
L - characteristic length dimension,
k - thermal conductivity,
ρ - density,
C
p
- specific heat at constant pressure, µ- dynamic viscosity)
List-I
List-II
k
A. Schmidt number
1.
(p
)ρ
C D
B. Thermal diffusivity
2.
h L
m
D
μ
C. Lewis number
3.
ρ
D.
Sherwood number
4.
ρ
C
p
Codes:
A B C
D A B C D
(a)
4
3
2
1
(b)
4
3
1
2
(c)
3
4
2
1
(d)
3
4
1
2
IES-8.
Match List-I with List-II and select the correct answer using the codes
given below the lists:
[IES-1996]
A. Momentum transfer
1. Thermal diffusivity
B. Mass transfer
2. Kinematic viscosity
C. Heat transfer
3. Diffusion coefficient
Codes:
A B C A B C
(a)
2
3
1
(b)
1
3
2
(c)
3
2
1
(d)
1
2
3
IES-9.
Assertion (A): Thermal diffusivity is a dimensionless quantity.
Reason (R): In M-L-T-Q system the dimensions of thermal diffusivity
are [L
2
T
-1
] [IES-1992]
(a) Both A and R are individually true and R is the correct explanation of A
(b) Both A and R are individually true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
IES-10. A furnace is made of a red brick wall of thickness 0.5 m and
conductivity 0.7 W/mK. For the same heat loss and temperature drop,
this can be replaced by a layer of diatomite earth of conductivity 0.14
W/mK and thickness
[IES-1993]
(a) 0.05 m
(b) 0.1 m
(c) 0.2 m
(d) 0.5 m
IES-11. Temperature profiles for four cases are shown in the following
figures and are labelled A, B, C and D.
Page 5 of 97
Match the above figures with
[IES-1998]