Q. 1. The unit of thermal resistance is
A : Kelvin per Watt
B : Watt per Kelvin
C : WK
D : Watt per meter kelvin
Kelvin per Watt
Q. 2. The unit of overall coefficient of heat transfer is
A : W per square mK
B : W per square m
C : Wper mK
D : W per m
W per square mK
Q. 3. Thermal resistance in thermal circuit is analogous to which parameter in electrical
circuit?
A : Electrical resistance
B : Electric current
C : Electric potential difference
D : Electric power
Electrical resistance
Q. 4. Aluminum is used as a fin material because
A : It has higher convection heat transfer coefficient
B : It has lower convection heat transfer coefficient
C : It has lower thermal conductivity
D : It has higher thermal conductivity
It has higher thermal conductivity
Q. 5. The rate of heat transfer is proportional to the surface area exposed for heat transfer and
the temperature difference between the heat transfer surface and the flowing fluid. This is known
as
A : Fourier’s law of heat conduction
B : Stefan-Boltzmann law
C : Newton’s law of cooling
D : ohm’s law
Newton’s law of cooling
Q. 6. In radiative heat transfer, a gray surface is one
A : which appears gray to the eye
B : whose emissivity is independent of wavelength
C : which has reflectivity equal to zero
D : which appears equally bright from all directions
whose emissivity is independent of wavelength
Q. 7. The unit of thermal conductivity is
A : watt per kelvin
B : Watt per meter
C : watt per metet Kelvin
D : Wm
watt per metet Kelvin
Q. 8. The heat conduction rate per unit area normal to the direction of heat flow through unit
thickness of the body per unit temperature difference. This statement is relates to
A : Thermal conductivity
B : Thermal diffusivity
C : Thermal resitivity
D : emissivity
Thermal conductivity
Q. 9. What is the purpose of using fins in a particular heat transfer system?
A : To decrease rate of heat transfer
B : To increase rate of heat transfer
C : To maintain rate of heat transfer at a constant rate
D : Unpredictable
To increase rate of heat transfer
Q. 10. As the temperature increases, the thermal conductivity of a gas
A : Increase
B : Decrease
C : Remains same
D : First increase and then decrease
Increase
Q. 11. What is the ratio of the buoyancy force to the viscous force acting on a fluid called?
A : Prandtl number
B : Reynolds number
C : Nusselt number
D : Grashof number
Grashof number
Q. 12. Mark the system where heat transfer is given by forced convection
A : Chilling effect of cold wind on warm body
B : Fluid passing through the tubes of a condenser and other heat exchange equipment
C : Heat flow from a hot pavement to surrounding atmosphere
D : Heat exchange on the outside of cold and warm pipes
Fluid passing through the tubes of a condenser and other heat exchange equipment
Q. 13. The flow direction is immaterial in the case of heat exchange from
A : Wet or saturated steam to water
B : Water to gas
C : Oil to water
D : Oil to gas.
Wet or saturated steam to water
Q. 14. In a long fin if the convection coefficient is increased with other parameters maintained
constant.
A : The temperature drop along the length is not strongly influenced by the convection Coefficient
B : The temperature gradient depends only on heat flow rate
C : The temperature drop will be faster along the length
D : The temperature drop along the length will be at a lower rate
The temperature drop will be faster along the length
Q. 15. For evaporator and condensers LMTD for counter flow
A : Greater than parallel flow
B : Equal to parallel flow
C : Less than parallel flow
D : Very much larger than parallel flow
Equal to parallel flow
Q. 16. What is lumped heat capacity analysis?
A : The analysis of a system in which it is assumed to be at nonuniform temperature
B : The analysis of a system in which it is assumed to be at uniform temperature
C : The analysis of a system in which it is assumed to be at either uniform or nonuniform temperature
D : None
The analysis of a system in which it is assumed to be at uniform temperature
Q. 17. Thermal conductivity of solid metals with rise in temperature normally
A : Increases
B : Decreases
C : Remain constant
D : May increase or decrease depending on temperature
Decreases
Q. 18. What is the mode of heat transfer from the hot surface to the adjacent layer of fluid
which surrounds the surface?
A : conduction mode of heat transfer
B : radiation mode of heat transfer
C : convection mode of heat transfer
D : None
convection mode of heat transfer
Q. 19. With rise in temperature , thermal conductivity of solid metals
A : decreases
B : increases
C : remains the same
D : first increases and then decreases
decreases
Q. 20. If the body is at thermal equilibrium, then the
A : Emissivity = absorptivity
B : Emissivity ˃ absorptivity
C : Emissivity Ë‚ absorptivity
D : None of the above
Emissivity = absorptivity
Q. 21. Which of the following is a wrong statement according to the shape factor is equal to
one?
A : For any surface completely enclosed by another surface
B : For infinite parallel planes radiating only to each other
C : For a flat or convex surface with respect to itself
D : Inside cylinder to outer cylinder of a long co-axial cylinder
For a flat or convex surface with respect to itself
Q. 22. The Grashof number in natural convection plays same role as
A : Prandtl number in forced convection
B : Reynolds number in forced convection
C : Nusselt number in forced convection
D : None
Reynolds number in forced convection
Q. 23. Log mean temperature difference in case of counter flow compared to parallel flow will
be
A : Same
B : More
C : Less
D : Depends on other factors
More
Q. 24. If the surfaces forms a close loop and the radiation emitted are absorbed by all surfaces
collectively. Then the sum of shape factors of a body wrt surrounding all bodies is always equal to
one. This statement called as,
A : Reciprocity of View Factors
B : Superposition of View Factors
C : Hottel’s Crossed String Rule of View Factors
D : Summation rule of view factors
Summation rule of view factors
Q. 25. For a cylindrical rod with uniformly distributed heat sources, the thermal gradient at
half the radius location will be
A : Four times
B : Twice
C : One fourth
D : One half
One half
Q. 26. Suppose a hot water is placed inside a closed metal vessel of thickness 5 mm. There is
atmospheric air outside the vessel at temperature lower than the temperature of hot water. The
heat is transferred from the hot water to atmospheric air. What is the mode of heat transfer in
this condition?
A : conduction then convection
B : convection then conduction
C : conduction then convection then conduction
D : convection then conduction then convection
convection then conduction then convection
Q. 27. Suppose that a hot metal ball is suddenly immersed in cold water. What is the condition
for the ball to maintain it at a uniform temperature?
A : The conduction resistance in a ball should be very large compared to the convection resistance for
heat transfer from surface of ball to water
B : The conduction resistance in a ball should be very small compared to the convection resistance for
heat transfer from surface of ball to water
C : The conduction resistance in a ball should be equal to the convection resistance for heat transfer
from surface of ball to water
D : Cannot say
The conduction resistance in a ball should be very small compared to the convection resistance for heat transfer from surface of ball to water
Q. 28. Critical thickness of insulation for sphere is given by
A : 2 times thermal conductivity per convective heat transfer coefficient
B : 2 times Convective heat transfer coefficient per thermal conductivity
C : 2 times thermal conductivity per convective heat transfer coefficient
D : 2 times thermal conductivity per thermal diffusivity
2 times thermal conductivity per convective heat transfer coefficient
Q. 29. Fourier law of heat conduction is best represented by
A : Q = minus k A d T by d x
B : Q = k A d x by d t
C : Q = minus k A
D : Q = k d T by d x
Q = minus k A d T by d x
Q. 30. The value of thermal conductivity depends upon
A : the material through which the heat is transferred
B : The area which is parallel to the heat transfer
C : The intensity of heat energy which is being transferred
D : Surrounding envirnment of the material
the material through which the heat is transferred
Q. 31. The transfer of heat by molecular collision is smallest in
A : Solids
B : Liquids
C : Gases
D : None of these
Gases
Q. 32. The temperature profile for heat conduction through a wall of constant thermal
conductivity in the presence of a heat source is
A : A straight line
B : Parabolic
C : logarithmic
D : Hyperbolic
Parabolic
Q. 33. What happens when the thickness of insulation on a pipe exceeds the critical value?
A : Heat transfer rate increases
B : Heat transfer rate decreases
C : Heat transfer rate remain constant
D : Unpredictable
Heat transfer rate decreases
Q. 34. Condensation refers to a change from the
A : Solid to a liquid phase
B : Vapor to a liquid phase
C : Liquid to a solid phase
D : Liquid to a vapor phase
Vapor to a liquid phase
Q. 35. For steady state and a constant value of thermal conductivity, the temperature
distribution associated with radial convection through a cylinder is
A : Linear
B : Parabolic
C : Logarithmic
D : Exponential
Logarithmic
Q. 36. The ratio of Nusselt number and the product of Reynold’s number and Prandtl number
is equal to
A : Stanton number
B : Biot number
C : Peclet number
D : Grashoff number
Stanton number
Q. 37. In free convection heat transfer transition from laminar to turbulent flow is governed
by the critical value of the
A : Reynold’s number
B : Grashoff’s number
C : Reynold’s number, Grashoff’s number
D : Prandtl number, Grashoff’s number
Prandtl number, Grashoff’s number
Q. 38. In the process of heat transfer through extended surfaces or fins, the entire surface area
is at
A : The same constant temperature
B : Different temperatures
C : Maximum base temperature
D : Minimum temperature
Different temperatures
Q. 39. The ratio of the emissive power and absorptive power of all bodies is the same and is
equal to the emissive power of a perfectly black body. This statement is known as
A : Wien’s law
B : Stefan’s law
C : Kirchhoff’s law
D : Planck’s law
Kirchhoff’s law
Q. 40. Two insulting materials of thermal conductivity K and 2K are available for lagging a
pipe carrying a hot fluid. If the radial thickness of each material is same
A : Material with higher thermal conductivity is used for inner layer and one with lower thermal
Conductivity for outer one
B : Material with lower thermal conductivity is used for inner layer and one with higher thermal
Conductivity for outer one
C : It is Immaterial in which sequence the insulating Material is used
D : It is impossible to judge
Material with lower thermal conductivity is used for inner layer and one with higher thermal Conductivity for outer one
Q. 41. In parallel flow heat exchangers,
A : the exit temperature of hot fluid is always equal to the exit temperature of cold fluid
B : the exit temperature of hot fluid is always less than the exit temperature of cold fluid
C : the exit temperature of hot fluid is always more than the exit temperature of cold fluid
D : we cannot predict comparison between exit temperatures of hot fluid and cold fluid
the exit temperature of hot fluid is always more than the exit temperature of cold fluid
Q. 42. Heat is generated in a solid sphere of 10 cm diameter of the rate of 600 W per cubic m.
Surface heat transfer coefficient is 10 W per sq. m-K and surrounding air temperature is 30
degree Celsius. Conductivity of material is 0.2 W per mK. The maximum temperature in the
sphere is,
A : 30degree Celsius
B : 32degree Celsius
C : 34degree Celsius
D : 36degree Celsius
32degree Celsius
Q. 43. The temperature distribution associated with radial conduction through a sphere is
represented by
A : Parabola
B : Hyperbola
C : Linear
D : Ellipse
Hyperbola
Q. 44. A plane brick wall 25cm thick, is faced with 15cm thick concrete layer. If the
temperature of exposed brick face is 700 K and that of the concrete is 250 K, through a wall of
15m by 10m. Thermal Conductivity of brick and concrete are 0.7 W per mK and 0.95 W per m-K
respectively. What is the total thermal resistance of the system in kelvin per watt.
A : 2.8
B : 3
C : 3.4
D : 3.8
3.4
Q. 45. A spherical vessel of 0.5 m outside diameter is insulated with 0.2 m thickness of
insulation of thermal conductivity 0.04 W/m-K. The surface temperature of the vessel is minus
195 degree Celsius and outside insulation surface is at 10 degree Celsius. Determine heat flow.
A : minus 37 W
B : minus 47 W
C : minus 57 W
D : minus 67 W
minus 57 W
Q. 46. Water flows at the rate of 0.1 Kg per sec through a thin metallic tube of 1 cm diameter
and 3 m length. It enters the tube at 25 degree Celsius. The outer surface of the tube maintained
at a constant temperature of 100 degree Celsius. The hydraulic diameter of the system is,
A : 0.001 m
B : 0.01 m
C : 0.1 m
D : 1 m
0.01 m
Q. 47. A fin has 5 mm diameter and 100 mm long thermal conductivity of fin material is 400
Wper mk one end of fin is maintained at 130 deg C and its other face is exposed to air at 30 deg C
if h= 40 W per m2K heat loss in watt from fin is
A : 08
B : 5
C : 7
D : 7.8
5
Q. 48. What is critical heat flux in boiling heat transfer process?
A : the heat flux which reaches at a certain constant value at a particular excess temperature
B : the heat flux which reaches at the minimum value at a particular excess temperature
C : the heat flux which reaches at the maximum value at a particular excess temperature
D : none of the above
the heat flux which reaches at the maximum value at a particular excess temperature
Q. 49. The rate of heat transfer per unit area through a copper plate of 4.5 cm thick, whose one
face is maintained at 450 K and the other face at 150 K. Take thermal conductivity of copper as
370 W per mK.
A : 1.5 W per sq. meter
B : 2.0 W/sq. meter
C : 2.5 W per sq. meter
D : 3.0 W per sq. meter
2.5 W per sq. meter
Q. 50. What is the effect of convective heat transfer coefficient h on fin effectiveness?
A : Fin is effective if the value of convective heat transfer coefficient h is small
B : fin is effective if the value of convective heat transfer coefficient h is large
C : fin effectiveness does not affected by the value of convective heat transfer coefficient h
D : None
Fin is effective if the value of convective heat transfer coefficient h is small
Q. 51. Which one of the following is correct? The effectiveness of a fin will be maximum in an
environment with
A : free convection
B : forced convection
C : radiation
D : convection and radiation
free convection
Q. 52. The parameters of a infinitely long fin are given below, Diameter of the fin is 2 cm,
Thermal conductivity is 200 W per m-K, Convective heat transfer coefficient is 12 Wper sq. m-K,
Base temperature of the fin is 500 degree Celsius and surrounding air temperature 50 degree
Celsius. The rate of heat transfer will be,
A : 85 W
B : 87 W
C : 95 W
D : 97 W
97 W
Q. 53. A steel rod (k is 30 W per m degree) 1 cm in diameter and 5 cm long protrudes from a
wall which is maintained at 10 degree Celsius. The rod is insulated at its tip and is exposed to an
environment with h = 50 W per m2 degree and ambient 30 degree Celsius. Calculate the rate of
heat dissipation
A : 2.658 W
B : 3.658 W
C : 4.658 W
D : 5.658 W
3.658 W
Q. 54. Assume a natural convection heat transfer on a vertical flat plate surrounded by a fluid.
Where will be the fully developed turbulent layer of fluid established, if the plate is hotter than
the fluid?
A : At the bottom of the plate
B : At the middle of the plate
C : At the top of the plate
D : nowhere on the surface
At the top of the plate
Q. 55. A steel plate of thermal conductivity 50 W/mK and thickness 10 cm passes a heat flux by
conduction of 25 kWper square meter. If the temperature of the hot surface of the plate is 100
degree celcius, then what is the temperature of the cooler side of the plate?
A : 30 degree celcius
B : 40 degree celcius
C : 50 degree celcius
D : 60 degree celcius
50 degree celcius
Q. 56. A steel rod (k is 30 Wper mK) 1 cm in diameter and 5 cm long protrudes from a wall
which is maintained at 10 degree Celsius. The rod is insulated at its tip and is exposed to an
environment with convective coefficient of 50 W per sq. mK and surrounding air at 30 degree
Celsius. Calculate the fin efficiency
A : 46.5 percent
B : 56.5 percent
C : 66.5 percent
D : 76.5 percent
66.5 percent
Q. 57. The inner and outer surfaces of a 5m by 6 m brick wall of thickness 30 cm and thermal
conductivity 0.69 W per mK are maintained at temperatures of 20 degree celcius and 5 degree
celcius respectively. determine the rate of heat transfer through the wall in W
A : 135
B : 10.35
C : 103.5
D : 1035
1035
Q. 58. If heat dissipation for one fin is given by 377.45 k J per hour, then what is the heat
dissipation for 12 fins in kJ per hour ?
A : 7529.4
B : 6529.4
C : 5529.4
D : 4529.4
4529.4
Q. 59. If the temperature of the sun is doubled. The rate of energy received on the earth will be
increased by a factor of
A : 2
B : 4
C : 8
D : 16
16
Q. 60. A wall of thickness 0.6 m width has a normal area 1.5 square meter and is made up of
material of thermal conductivity 0.4 W per mK. The temperature difference on the two sides are
800 degree celcius. What is the thermal resistance of the wall?
A : 1Wper K
B : 1.8 Wper K
C : 1 K per W
D : 1.8 Kper W
1 K per W