Assignment 1
1. The conduction mode of heat transfer takes place due to a temperature gradient
(a) in a medium
(b) in solids only
(c) only in a stationary medium
(d) in fluid medium only
2.
For a given amount of heat transfer during steady state one-dimensional heat conduction
through a plane wall with constant thermal conductivity and no internal heat generation,
higher the value of thermal conductivity of the wall, the temperature gradient within the
wall will be
(a) higher
(b) lower
(c) same
(d) dependent on ambient conditions.
3.
For steady state one-dimensional heat conduction through a plane wallwith constant
thermal conductivity and no internal heat generation, temperature distribution within the
wall will be
(a) parabolic
(b) hyperbolic
(c) linear
(d) logarithmic
4.
Heat conduction in solids is due to
(a) flow of free electrons
(b) propagation of lattice vibrational waves
(c) both flow of free electrons and propagation of lattice vibrational waves
(d) transfer of kinetic energy between the randomly moving molecules due to their
collisions
5.
A wall of thickness 0.6 m and of thermal conductivity 0.6 W/mK is having surface area
1 m2. If the inner and outer temperatures of the wall are 1840°C and 340°C, respectively,
the rate of heat transfer will be
(a) 150 W
(b) 75 W
(c) 750 W
(d) 1500 W
6.
7.
Diamond has a very high thermal conductivity as compared to pure metals. This is due to
(a) flow of free electrons
(b) propagation of lattice vibrational waves
(c) transfer of kinetic energy between the randomly moving molecules due to their
collisions
(d) very high density
A plane wall has a thermal conductivity of 1.15 W/mK. If the inner surface is at 1100°C
and the outer surface is at 350°C, then the design thickness (in meter) of the wall to
maintain a steady heat flux of 2500 W/m2 should be
(a) 0.13 to 0.15
(b) 0.28 to 0.30
(c) 0.33 to 0.35
(d) 0.43 to 0.45
8. The back surface of a plate is heated at the rate of 50 W/m 2 and the front surface is cooled
by air flow at 30 o C . It is given that the heat transfer coefficient between the air and the
plate surface is 50 W/ ( m 2 o C ) . Considering steady state heat transfer, what is the
temperature of the front surface of the plate?
(a) 21 o C (b) 31 o C (c) 41 o C (d) 51 o C
9. Thermal diffusivity of a substance physically signifies
(a) the ability of the substance to conduct heat
(b) the ability of the substance to store thermal energy
(c) the ability of the substance to conduct heat relative to its ability to store thermal energy
(d) the ratio of rate of diffusion of momentum through a substance to the diffusion of heat in
that substance.
10.
According to Fourier’s law of heat conduction, the rate of heat transfer through a body is
(a) proportionalonly to the area normal to the direction of heat flow
(b) proportional only to the temperature gradient along the direction of heat flow
(c) dependent upon the material of the body
(d) proportional to the area normal to the direction of heat flowand the temperature
gradient along the direction of heat flow, and is dependent upon the material of the body.
11.
Thermal diffisivity of a substance is
(a) directly proportional to thermal conductivity
(b) inversely proportional to thermal conductivity
(c) directlyproportional to (thermal conductivity)2
(d) inversely proportional to (thermal conductivity)2
12.
The heat conduction equation in a medium in a generic form can be written in a
rectangular Cartesian coordinate system as
(a) ρ c p
(b) 0 =
∂T ∂  ∂T  ∂  ∂T  ∂  ∂T 
=  kx
 +  kz
 +  ky
 + Q′′′
∂t ∂x  ∂x  ∂y  ∂y  ∂z  ∂z 
∂  ∂T  ∂  ∂T  ∂  ∂T 
∂p
 +  kz
 kx
 +  ky
 + Q′′′ + β T
∂x  ∂x  ∂y  ∂y  ∂z  ∂z 
∂t
(c) ρ c p
∂T ∂  ∂T  ∂  ∂T  ∂  ∂T 
∂p
=  kx
 +  kz
 +  ky
 + Q′′′ + β T
∂t ∂x  ∂x  ∂y  ∂y  ∂z  ∂z 
∂t
(d) ρ c p
∂T ∂  ∂T  ∂  ∂T  ∂  ∂T 
∂p
=  kx
 +  kz
 +  ky
 + Q′′′ + β
∂t ∂x  ∂x  ∂y  ∂y  ∂z  ∂z 
∂t
where ρ is the density, cp is the constant pressure specific heat, k is the thermal conductivity, T is
the temperature, t is the time, Q′′′ is the rate of generation of thermal energy per unit volume,
β is the volume expansion coefficient and p is the pressure.