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

1. 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

2. 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

3. Thermal conductivity of water ________ with rise in temperature.
A. Remain same
B. Decreases
C. Increases
D. May increase or decrease depending upon temperature
Answer : D

4. The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to
A. Stanton number
B. Biot number
C. Peclet number
D. Grashoff number
Answer : A

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

6. 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

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

8. The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number) n, where n is equal to
A. -1/3
B. -2/3
C. 1
D. -1
Answer : A

9. 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

10. 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

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

12. 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

13. Which of the following statement is correct?
A. A grey body is one which absorbs all radiations incident on it.
B. At thermal equilibrium, the emissivity and absorptivity are same.
C. The energy absorbed by a body to the total energy falling on it, is called emissivity.
D. A perfect body is one which is black in colour.
Answer : B

14. The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit
A. Temperature
B. Thickness
C. Area
D. Time
Answer : D

15. 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

16. 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

17. Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be
A. One
B. Two
C. Three
D. Four
Answer : C

18. 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

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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

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

27. 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

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

29. The rate of energy transferred by convection to that by conduction is called
A. Stanton number
B. Nusselt number
C. Biot number
D. Peclet number
Answer : B

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

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

32. 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

33. 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

34. Thermal conductivity of glass wool varies from sample to sample because of variation in
A. Composition
B. Density
C. Porosity
D. All of the above
Answer : D

35. 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

36. 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

37. 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

38. According to Wien's law, the wavelength corresponding to maximum energy is proportion to
A. Absolute temperature (T)
B. I²
C. F
D. T
Answer : A

39. 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

40. 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

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

42. 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

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

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

45. 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

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

47. 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

48. 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

49. 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

50. 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