1000+ Heat & Mass Transfer MCQ for LIC AAO [Solved]
Thursday 9th of March 2023
1. Joule sec is the unit of
A. Universal gas constant
B. Kinematic viscosity
C. Thermal conductivity
D. Planck's constant
Answer : D
2. The emissivity for a black body is
A. 0
B. 0.5
C. 0.75
D. 1
Answer : D
3. Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of
A. 1 : 1
B. 2 : 1
C. 1 : 2
D. 4 : 1
Answer : C
4. Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium.
A. Cold body to hot body
B. Hot body to cold body
C. Smaller body to larger body
D. Larger body to smaller body
Answer : B
5. The heat is transferred by conduction, convection and radiation in
A. Melting of ice
B. Boiler furnaces
C. Condensation of steam in condenser
D. None of these
Answer : B
6. When ? is absorptivity, ? is reflectivity and ? is transmissivity, then for a diathermanous body,
A. ? = 1, ? = 0 and ? = 0
B. ? = 0, ? = 1 and ? = 0
C. ? = 0, ? = 0 and ? = 1
D. ? + ? = 1 and ? = 0
Answer : D
7. The heat of sun reaches to us according to
A. Conduction
B. Convection
C. Radiation
D. None of these
Answer : C
8. Absorptivity of a body will be equal to its emissivity
A. At all temperatures
B. At one particular temperature
C. When system is under thermal equilibrium
D. At critical temperature
Answer : C
9. 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
Answer : D
10. The energy distribution of an ideal reflector at higher temperatures is largely in the range of
A. Shorter wavelength
B. Longer wavelength
C. Remain same at all wavelengths
D. Wavelength has nothing to do with it
Answer : A
11. The critical radius is the insulation radius at which the resistance to heat flow is
A. Maximum
B. Minimum
C. Zero
D. None of these
Answer : B
12. Depending on the radiating properties, a body will be black when
A. P = 0, x = 0 and a = 1
B. P= 1, T = 0 and a = 0
C. P = 0, x = 1 and a = 0
D. X = 0, a + p = 0 Where a = absorptivity, p = reflectivity, X = transmissivity.
Answer : A
13. In regenerator type heat exchanger, heat transfer takes place by
A. Direct mixing of hot and cold fluids
B. A complete separation between hot and cold fluids
C. Flow of hot and cold fluids alternately over a surface
D. Generation of heat again and again
Answer : C
14. The most commonly used method for the design of duct size is the
A. Velocity reduction method
B. Equal friction method
C. Static regains method
D. Dual or double method
Answer : C
15. In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by
A. Convection
B. Radiation
C. Conduction
D. Both convection and conduction
Answer : C
16. Depending on the radiating properties, a body will be opaque when
A. P = 0, x = 0 and a = 1
B. P=1, x = 0 and a = 0
C. P = 0, x = 1 and a = 0
D. X = 0, a + p = 1 Where a = absorptivity, p = reflectivity, X = transmissivity.
Answer : D
17. Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in
A. Electric heater
B. Steam condenser
C. Boiler
D. Refrigerator condenser coils
Answer : C
18. When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by
A. Conduction
B. Convection
C. Radiation
D. Conduction and convection
Answer : C
19. According to Newton's law of cooling, the heat transfer from a hot body to a cold body is
A. Directly proportional to the surface area
B. Directly proportional to the difference of temperatures between the two bodies
C. Either (A) or (B)
D. Both (A) and (B)
Answer : D
20. The critical thickness of insulation for a sphere is
A. k/h?
B. 2k/h?
C. h?/k
D. h?/2k
Answer : B
21. 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
Answer : B
22. The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as
A. Emissivity
B. Transmissivity
C. Reflectivity
D. Intensity of radiation
Answer : D
23. In counter current flow heat exchanger, the logarithmic temperature difference between the fluids is ________ as compared to parallel flow heat exchanger.
A. Same
B. Less
C. Greater
D. None of these
Answer : C
24. In case of liquids and gases, the heat transfer takes place according to
A. Conduction
B. Convection
C. Radiation
D. None of these
Answer : B
25. The heat transfer by conduction through a thick cylinder (Q) is given by (where T? = Higher temperature, T? = Lower temperature, r? = Inside radius, r? = Outside radius, l = Length of cylinder, and k = Thermal conductivity)
A. Q = [2?lk (T? - T?)]/2.3 log (r?/r?)
B. Q = 2.3 log (r?/r?)/[2?lk (T? - T?)]
C. Q = [2? (T? - T?)]/2.3 lk log (r?/r?)
D. Q = = 2?lk/2.3 (T? - T?) log (r?/r?)
Answer : A
26. Film coefficient is defined as the ratio of
A. Thermal conductivity to the equivalent thickness of the film of fluid
B. Temperature drop through the films of fluids to the thickness of film of fluids
C. Thickness of film of fluid to the thermal conductivity
D. Thickness of film of fluid to the temperature drop through the films of fluids
Answer : A
27. All radiations in a black body are
A. Reflected
B. Refracted
C. Transmitted
D. Absorbed
Answer : D
28. The emissive power of a body depends upon its
A. Temperature
B. Wave length
C. Physical nature
D. All of the above
Answer : D
29. The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body
A. Move actually
B. Do not move actually
C. Affect the intervening medium
D. Does not affect the intervening medium
Answer : B
30. Wiens law states that the wave length corresponding to ________ is proportional to the absolute temperature.
A. Minimum energy
B. Maximum energy
C. Both (A) and (B)
D. None of these
Answer : B
31. Conduction is a process of heat transfer
A. From one particle of the body to another without the actual motion of the particles
B. From one particle of the body to another by the actual motion of the heated particles
C. From a hot body to a cold body, in a straight line, without affecting the intervening medium
D. None of the above
Answer : A
32. According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a
A. Grey body
B. Brilliant white polished body
C. Red hot body
D. Black body
Answer : D
33. Sensible heat factor is given by (where S.H. = Sensible heat, and L.H. = Latent heat)
A. S.H/(S.H + L.H)
B. (S.H + L.H) /S.H
C. (L.H - S.H)/S.H
D. S.H/(L.H - S.H)
Answer : A
34. Thermal conductivity of non-metallic amorphous solids with decrease in temperature
A. Increases
B. Decreases
C. Remain constant
D. May increase or decrease depending on temperature
Answer : B
35. Which of the following property of air does not increase with rise in temperature?
A. Thermal conductivity
B. Thermal diffusivity
C. Density
D. Dynamic viscosity
Answer : C
36. In heat transfer, conductance equals conductivity (kcal/hr/sq.m/ °C/cm) divided by
A. Hr (time)
B. Sq. m (area)
C. °C (temperature)
D. K.cal (heat)
Answer : D
37. The highest thermal diffusivity is of
A. Iron
B. Lead
C. Concrete
D. Wood
Answer : B
38. A composite slab has two layers of different materials with thermal conductivities k? and k?. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be
A. k? k?
B. (k? + k?)
C. (k? + k?)/ k? k?
D. 2 k? k?/ (k? + k?)
Answer : D
39. When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred to as heat transfer by
A. Conduction
B. Convection
C. Radiation
D. Conduction and convection
Answer : A
40. The ratio of the energy absorbed by the body to total energy falling on it is called
A. Absorptive power
B. Emissive power
C. Absorptivity
D. Emissivity
Answer : A
41. The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles caused by some mechanical means, is known as
A. Conduction
B. Free convection
C. Forced convection
D. Radiation
Answer : C
42. The thermal diffusivities for solids are generally
A. Less than those for gases
B. Less than those for liquids
C.D. More or less same as for liquids and gases
Answer : C
43. The expression Q = ? AT4 is called
A. Fourier equation
B. Stefan-Boltzmann equation
C. Newton Reichmann equation
D. Joseph-Stefan equation
Answer : B
44. Unit of thermal diffusivity is
A. m²/hr
B. m²/hr °C
C. kcal/m² hr
D. kcal/m. hr °C
Answer : A
45. Depending on the radiating properties, a body will be white when
A. P = 0, x = 0 and a = 1
B. P=1, T = 0 and a = 0
C. P = 0, x = 1 and a = 0
D. X = 0, a + p = 1 Where a = absorptivity, p = reflectivity, x = transmissivity
Answer : B
46. The ratio of surface convection resistance to the internal conduction resistance is known as
A. Grashoff number
B. Biot number
C. Stanton number
D. Prandtl number
Answer : B
47. Heat transfer takes place as per
A. Zeroth law of thermodynamics
B. First law of thermodynamic
C. Second law of the thermodynamics
D. Kirchoff's law
Answer : C
48. The amount of radiation mainly depends upon the
A. Nature of the body
B. Temperature of the body
C. Type of surface of the body
D. All of these
Answer : D
49. The time constant of a thermocouple is
A. The time taken to attain the final temperature to be measured
B. The time taken to attain 50% of the value of initial temperature difference
C. The time taken to attain 63.2% of the value of initial temperature difference
D. Determined by the time taken to reach 100°C from 0°C
Answer : C
50. The concept of overall coefficient of heat transfer is used in heat transfer problems of
A. Conduction
B. Convection
C. Radiation
D. Conduction and convection
Answer : D