1000+ Heat & Mass Transfer Multiple Choice Question Answer [Solved]

1. 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

2. Depending on the radiating properties, body will be transparent when
A. P = 0, x = 0 and a = 1
B. P=1, x = 0, and a = 0
C. P = 0, T= 1, and a = 0
D. X = 0, a + p = 1
Answer : C

3. 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

4. The transfer of heat by molecular collision is smallest in
A. Solids
B. Liquids
C. Gases
D. None of these
Answer : C

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

6. 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

7. 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

8. 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

9. 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

10. Total emissivity of polished silver compared to black body is
A. Same
B. Higher
C. More or less same
D. Very much lower
Answer : D

11. 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

12. 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

13. 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

14. 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

15. 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

16. Fourier's law of heat conduction is valid for
A. One dimensional cases only
B. Two dimensional cases only
C. Three dimensional cases only
D. Regular surfaces having non-uniform temperature gradients
Answer : A

17. According to Stefan's law, the total radiation from a black body per second per unit area is proportional to
A. Absolute temperature
B. T²
C. T?
D. T
Answer : D

18. A heat exchanger with heat transfer surface area A and overall heat transfer coefficient U handles two fluids of heat capacities Cmax and Cmin. The number of transfer units (NTU) used in the analysis of heat exchanger is specified as
A. A.C_min/U
B. U/A.C_min
C. A.U.C_min
D. A.U/C_min
Answer : D

19. 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

20. The thermal diffusivities for solids are generally
A. Less than those for gases
B. Less than those for liquids
C. More than those for liquids and gases
D. More or less same as for liquids and gases
Answer : C

21. Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of
A. 0.002
B. 0.02
C. 0.01
D. 0.1
Answer : B

22. 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

23. The logarithmic mean temperature difference (t_m) is given by (where ?t₁ and ?t₂ are temperature differences between the hot and cold fluids at entrance and exit)
A. t_m = (?t₁ - ?t₂)/ log_e (?t₁/?t₂)
B. t_m = log_e (?t₁/?t₂)/ (?t₁ - ?t₂)
C. t_m = t_m = (?t₁ - ?t₂) log_e (?t₁/?t₂)
D. t_m = log_e (?t₁ - ?t₂)/ ?t₁/?t₂
Answer : A

24. Which of the following would lead to a reduction in thermal resistance?
A. In conduction, reduction in the thickness of the material and an increase in thermal conductivity.
B. In convection, stirring of the fluid and cleaning the heating surface.
C. In radiation, increasing the temperature and reducing the emissivity.
D. All of the above
Answer : D

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

26. 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

27. 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

28. 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

29. The insulation ability of an insulator with the presence of moisture would
A. Increase
B. Decrease
C. Remain unaffected
D. May increase/decrease depending on temperature and thickness of insulation
Answer : B

30. When absorptivity (?) = 1, reflectivity (?) = 0 and transmissivity (?) = 0, then the body is said to be a
A. Black body
B. Grey body
C. Opaque body
D. White body
Answer : A

31. The unit of overall coefficient of heat transfer is
A. W/m²K
B. W/m²
C. W/mK
D. W/m
Answer : A

32. 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

33. 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

34. The emissivity for a black body is
A. 0
B. 0.5
C. 0.75
D. 1
Answer : D

35. 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

36. 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
Answer : B

37. 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

38. 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

39. 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

40. 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

41. The critical radius is the insulationradius at which the resistance to heat flow is
A. Maximum
B. Minimum
C. Zero
D. None of these
Answer : B

42. 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

43. 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

44. 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

45. 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

46. The heat of sun reaches to us according to
A. Conduction
B. Convection
C. Radiation
D. None of these
Answer : C

47. Reynolds number is the ratio of
A. Energy transferred by convection to that by conduction
B. Kinematic viscosity to thermal diffusivity
C. Inertia force to viscous force
D. None of the above
Answer : C

48. 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

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

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