NDA - Heat & Mass Transfer 1000+ MCQ [Solved] PDF Download

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

2. 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

3. Heat is closely related with
A. Liquids
B. Energy
C. Temperature
D. Entropy
Answer : C

4. 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

5. All radiations in a black body are
A. Reflected
B. Refracted
C. Transmitted
D. Absorbed
Answer : D

6. 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

7. 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

8. 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

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. The thermal diffusivities for gases are generally
A. More than those for liquids
B. Less than those for liquids
C. More than those for solids
D. Dependent on the viscosity
Answer : A

11. 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

12. Fourier's law of heat conduction gives the heat flow for
A. Irregular surfaces
B. Nonuniform temperature surfaces
C. One dimensional cases only
D. Two dimensional cases only
Answer : C

13. 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

14. The process of heat transfer from one particle of the body to another by the actual motion of the heated particles, is called
A. Conduction
B. Convection
C. Radiation
D. None of these
Answer : B

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

16. 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

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. 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. Kirchoffs law
B. Stefan's law
C. Wien' law
D. Planck's law
Answer : A

19. 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

20. 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 hese
Answer : B

21. 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

22. 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

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

24. 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

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

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

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

28. 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

29. Moisture would find its way into insulation by vapour pressure unless it is prevented by
A. High thickness of insulation
B. High vapour pressure
C. Less thermal conductivity insulator
D. A vapour seal
Answer : D

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

31. 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

32. 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

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. 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

35. Thermal diffusivity is
A. A dimensionless parameter
B. Function of temperature
C. Used as mathematical model
D. A physical property of the material
Answer : D

36. In a heat exchanger with one fluid evaporating or condensing, the surface area required is least in
A. Parallel flow
B. Counter flow
C. Cross flow
D. All of these
Answer : D

37. Temperature of steam at around 540°C can be measured by
A. Thermometer
B. Thermistor
C. Thermocouple
D. None of these
Answer : C

38. 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

39. 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

40. 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

41. 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

42. 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

43. The heat transfer takes place according to
A. Zeroth law of thermodynamics
B. First law of thermodynamics
C. Second law of thermodynamics
D. Kirchhoff's law
Answer : C

44. 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

45. 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

46. 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

47. 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

48. 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

49. 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

50. 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