Heat & Mass Transfer 1000+ MCQ with answer for SSC Stenographer

1. 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

2. According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the
A. Absolute temperature
B. Square of the absolute temperature
C. Cube of the absolute temperature
D. Fourth power of the absolute temperature
Answer : D

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

4. The value of the wave length for maximum emissive power is given by
A. Kirchhoff's law
B. Stefan's law
C. Wines law
D. Planck's law
Answer : C

5. According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to
A. Absolute temperature
B. Square of temperature
C. Fourth power of absolute temperature
D. Fourth power of temperature
Answer : C

6. The transfer of heat by molecular collision is known as
A. Conduction
B. Convection
C. Radiation
D. None of these
Answer : B

7. 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

8. Heat conducted through per unit area and unit thick face per unit time when temperature difference between opposite faces is unity, is called
A. Thermal resistance
B. Thermal coefficient
C. Temperature gradient
D. Thermal conductivity
Answer : D

9. 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

10. 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

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

12. 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

13. Free convection flow depends on
A. Density
B. Coefficient of viscosity
C. Gravitational force
D. All of these
Answer : D

14. Thermal conductivity of wood depends on
A. Moisture
B. Density
C. Temperature
D. All of the above
Answer : D

15. 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

16. 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

17. Kirchhoff's law states that
A. The total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature
B. The wave length corresponding to the maximum energy is proportional to the absolute temperature
C. 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
D. None of the above
Answer : C

18. The product of Reynolds number and Prandtl number is known as
A. Stanton number
B. Biot number
C. Peclet number
D. Grashoff number
Answer : C

19. 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

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

21. Heat transfer in liquid and gases takes place by
A. Conduction
B. Convectin
C. Radiation
D. Conduction and convection
Answer : B

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

23. Which of the following is expected to have highest thermal conductivity?
A. Steam
B. Solid ice
C. Melting ice
D. Water
Answer : B

24. Which of the following is a case of steady state heat transfer?
A. I.C. engine
B. Air preheaters
C. Heating of building in winter
D. None of the above
Answer : D

25. 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

26. Film coefficient is defined as Inside diameter of tube
A. Equivalent thickness of film
B. Thermal conductivity Equivalent thickness of film Specific heat × Viscosity
C. Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity
D. Film coefficient × Inside diameter Thermal conductivity
Answer : B

27. 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

28. 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

29. The unit of Stefan-Boltzmann constant is
A. Watt/mK
B. Watt/m²K²
C. Watt/m²K⁴
D. Watt/mK²
Answer : C

30. Pick up the wrong case. Heat flowing from one side to other depends directly on
A. Face area
B. Time
C. Thickness
D. Temperature difference
Answer : C

31. Reynolds number (RN) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ? = Density of fluid, cp = Specific heat at constant pressure, and ? = Coefficient of absolute viscosity)
A. RN = hl/k
B. RN = ? cp/k
C. RN = ? V l /?
D. RN = V²/t.cp
Answer : C

32. A perfect black body is one which
A. Is black in colour
B. Reflects all heat
C. Transmits all heat radiations
D. Absorbs heat radiations of all wave lengths falling on it
Answer : D

33. If the energy radiated per second per sq. cm. of the surface for wave lengths lying between ?, and ? + d? is represented by (e?.d?), then e? is called
A. Absorptive power
B. Emissive power
C. Emissivity
D. None of these
Answer : B

34. The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called
A. First law of thermodynamics
B. Newton's law of cooling
C. Newton's law of heating
D. Stefan's law
Answer : B

35. Upto the critical radius of insulation,
A. Added insulation will increase heat loss
B. Added insulation will decrease heat loss
C. Convective heat loss will be less than conductive heat loss
D. Heat flux will decrease
Answer : A

36. 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

37. According to Dalton's law of partial pressures, (where pb = Barometric pressure, pa = Partial pressure of dry air, and pv = Partial pressure of water vapour)
A. Pb = pa - pv
B. Pb = pa + pv
C. Pb = pa × pv
D. Pb = pa/pv
Answer : B

38. Thermal diffusivity is a
A. Function of temperature
B. Physical property of a substance
C. Dimensionless parameter
D. All of these
Answer : B

39. 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

40. Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ? = Density of substance, S = Specific heat, and k = Thermal conductivity)
A. h = k/ ?S
B. h = ?S/k
C. h = S/?k
D. h = k?/S
Answer : A

41. 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

42. In free convection heat transfer, Nusselt number is function of
A. Grashoff number and Reynold number
B. Grashoff number and Prandtl number
C. Prandtl number and Reynold number
D. Grashoff number, Prandtl number and Reynold number
Answer : B

43. 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

44. 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

45. Unit of thermal conductivity in S.I. units is
A. J/m² sec
B. J/m °K sec
C. W/m °K
D. Option (B) and (C) above
Answer : D

46. In counter flow heat exchangers
A. Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state
B. Both the fluids at inlet are in their hottest state
C. Both the fluids at exit are in their hottest state
D. One fluid is in hottest state and other in coldest state at inlet
Answer : B

47. 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

48. The radiation emitted by a black body is known as
A. Black radiation
B. Full radiation
C. Total radiation
D. All of these
Answer : D

49. 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

50. Metals are good conductors of heat because
A. Their atoms collide frequently
B. Their atoms are relatively far apart
C. They contain free electrons
D. They have high density
Answer : A