Heat & Mass Transfer 1000+ MCQ with answer for SBI Clerk

1. 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
Answer : C

2. The rate of heat flow through a body is Q = [kA (T? - T?)]/x. The term x/kA is known as
A. Thermal coefficient
B. Thermal resistance
C. Thermal conductivity
D. None of these
Answer : B

3. A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h?, h? and h? respectively. The average heat transfer coefficient for the cube is
A. h? + h? + h?
B. (h?.h?.h?)1/3
C. 1/h? + 1/h? + 1/h?
D. None of these
Answer : D

4. The highest thermal diffusivity is of
A. Iron
B. Lead
C. Concrete
D. Wood
Answer : B

5. A steam pipe is to be insulated by two insulating materials put over each other. For best results
A. Better insulation should be put over pipe and better one over it
B. Inferior insulation should be put over pipe and better one over it
C. Both may be put in any order
D. Whether to put inferior OIL over pipe or the better one would depend on steam temperature
Answer : A

6. Thermal conductivity of water in general with rise in temperature
A. Increases
B. Decreases
C. Remain constant
D. May increase or decrease depending on temperature
Answer : D

7. According of Kirchhoff's law
A. Radiant heat is proportional to fourth power of absolute temperature
B. Emissive power depends on temperature
C. Emissive power and absorptivity are constant for all bodies
D. Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body.
Answer : D

8. Fouling factor is used
A. In heat exchanger design as a safety factor
B. In case of Newtonian fluids
C. When a liquid exchanges heat with a gas
D. None of the above
Answer : A

9. Joule sec is the unit of
A. Universal gas constant
B. Kinematic viscosity
C. Thermal conductivity
D. Planck's constant
Answer : D

10. A non-dimensional number generally associated with natural convection heat transfer is
A. Grashoff number
B. Nusselt number
C. Weber number
D. Prandtl number
Answer : A

11. Heat transfer by radiation mainly depends upon
A. Its temperature
B. Nature of the body
C. Kind and extent of its surface
D. All of the above
Answer : D

12. LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is
A. Higher
B. Lower
C. Same
D. Depends on the area of heat exchanger
Answer : A

13. Emissivity of a white polished body in comparison to a black body is
A. Higher
B. Lower
C. Same
D. Depends upon the shape of body
Answer : B

14. The amount of heat flow through a body by conduction is
A. Directly proportional to the surface area of the body
B. Directly proportional to the temperature difference on the two faces of the body
C. Dependent upon the material of the body
D. All of the above
Answer : D

15. 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

16. In a shell and tube heat exchanger, baffles are provided on the shell side to
A. Improve heat transfer
B. Provide support for tubes
C. Prevent stagnation of shell side fluid
D. All of these
Answer : D

17. The heat transfer by conduction through a thick sphere is given by
A. Q = 2?kr₁ r₂ (T₁ - T₂)/ (r₂ - r₁)
B. Q = 4?kr₁ r₂ (T₁ - T₂)/ (r₂ - r₁)
C. Q = 6?kr₁ r₂ (T₁ - T₂)/ (r₂ - r₁)
D. Q = 8?kr₁ r₂ (T₁ - T₂)/ (r₂ - r₁)
Answer : B

18. The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.
A. Equal to
B. Directly proportional to
C. Inversely proportional to
D. None of these
Answer : B

19. 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

20. 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

21. 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

22. The unit of overall coefficient of heat transfer is
A. kcal/m²
B. kcal/hr °C
C. kcal/m² hr °C
D. kcal/m hr °C
Answer : C

23. Stefan Boltzmann law is applicable for heat transfer by
A. Conduction
B. Convection
C. Radiation
D. Conduction and radiation combined
Answer : C

24. In heat exchangers, degree of approach is defined as the difference between temperatures of
A. Cold water inlet and outlet
B. Hot medium inlet and outlet
C. Hot medium outlet and cold water inlet
D. Hot medium outlet and cold water outlet
Answer : D

25. The amount of radiation mainly depends on
A. Nature of body
B. Temperature of body
C. Type of surface of body
D. All of the above
Answer : D

26. A designer chooses the values of fluid flow rates and specific heats in such a manner that the heat capacities of the two fluids are equal. A hot fluid enters the counter flow heat exchanger at 100° C and leaves at 60° C. A cold fluid enters the heat exchanger at 40° C. The mean temperature difference between the two fluids is
A. 20°C
B. 40°C
C. 60°C
D. 66.7°C
Answer : A

27. Planck's law holds good for
A. Black bodies
B. Polished bodies
C. All coloured bodies
D. All of the above
Answer : A

28. Which of the following has least value of conductivity?
A. Glass
B. Water
C. Plastic
D. Air
Answer : D

29. Thermal diffusivity of a substance is
A. Directly proportional to thermal conductivity
B. Inversely proportional to density of substance
C. Inversely proportional to specific heat
D. All of the above
Answer : D

30. The expression Q = ? AT⁴ is called
A. Fourier equation
B. Stefan-Boltzmann equation
C. Newton Reichmann equation
D. Joseph-Stefan equation
Answer : B

31. A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,
A. The better insulation must be put inside
B. The better insulation must be put outside
C. One could place either insulation on either side
D. One should take into account the steam temperature before deciding as to which insulation is put where
Answer : A

32. According to Prevost theory of heat exchange
A. It is impossible to transfer heat from low temperature source to t high temperature source
B. Heat transfer by radiation requires no medium
C. All bodies above absolute zero emit radiation
D. Heat transfer in most of the cases takes place by combination of conduction, convection and radiation
Answer : C

33. The natural convection air cooled condensers are used in
A. Domestic refrigerators
B. Water coolers
C. Room air conditioners
D. All of these
Answer : A

34. The value of Prandtl number for air is about
A. 0.1
B. 0.3
C. 0.7
D. 1.7
Answer : C

35. The unit of Stefan Boltzmann constant is
A. Watt/cm² °K
B. Watt/cm4 °K
C. Watt²/cm °K?
D. Watt/cm² °K?
Answer : D

36. The emissive power of a body depends upon its
A. Temperature
B. Wave length
C. Physical nature
D. All of the above
Answer : D

37. 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

38. A grey body is one whose absorptivity
A. Varies with temperature
B. Varies with wavelength of the incident ray
C. Is equal to its emissivity
D. Does not vary with temperature and. wavelength of the incident ray
Answer : C

39. Heat flows from one body to other when they have
A. Different heat contents
B. Different specific heat
C. Different atomic structure
D. Different temperatures
Answer : D

40. Unit of thermal diffusivity is
A. m²/hr
B. m²/hr °C
C. kcal/m² hr
D. kcal/m. hr °C
Answer : A

41. An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be
A. 25 mm
B. 40 mm
C. 160 mm
D. 800 mm
Answer : A

42. Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by
A. Convection
B. Radiation
C. Forced convection
D. Free convection
Answer : B

43. 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

44. Sensible heat is the heat required to
A. Change vapour into liquid
B. Change liquid into vapour
C. Increase the temperature of a liquid of vapour
D. Convert water into steam and superheat it
Answer : C

45. Which of the following is the case of heat transfer by radiation?
A. Blast furnace
B. Heating of building
C. Cooling of parts in furnace
D. Heat received by a person from fireplace
Answer : D

46. A grey body is one whose absorptivity
A. Varies with temperature
B. Varies with the wave length of incident ray
C. Varies with both
D. Does not vary with temperature and wave length of the incident ray
Answer : D

47. The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles due to difference of density caused by temperature of the particle is known as
A. Conduction
B. Free convection
C. Forced convection
D. Radiation
Answer : B

48. Which of the following statement is wrong?
A. The heat transfer in liquid and gases takes place according to convection.
B. The amount of heat flow through a body is dependent upon the material of the body.
C. The thermal conductivity of solid metals increases with rise in temperature
D. Logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference.
Answer : C

49. When heat is transferred by molecular collision, it is referred to as heat transfer by
A. Conduction
B. Convection
C. Radiation
D. Scattering
Answer : B

50. 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