1000+ Heat & Mass Transfer MCQ for RRB JE [Solved]

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

2. 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

3. Thermal conductivity of a material may be defined as the
A. Quantity of heat flowing in one second through one cm cube of material when opposite faces ^re maintained at a temperature difference of 1°C
B. Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C
C. Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces
D. All of the above
Answer : D

4. 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

5. 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

6. 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

7. 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

8. 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

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. Absorptivity of a body will be equal to its emissivity
A. At all temperatures
B. At one particular temperature
C. When system is under thermal equilibrium
D. At critical temperature
Answer : C

11. 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

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. 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

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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

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

25. In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the
A. Reynold's number
B. Grashoff's number
C. Reynold's number, Grashoff's number
D. Prandtl number, Grashoff's number
Answer : D

26. 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

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

28. 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

29. 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

30. 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

31. 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

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

33. The automobile radiator is a heat exchanger of
A. Parallel flow type
B. Counter flow type
C. Cross flow type
D. Regenerator type
Answer : C

34. 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

35. 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

36. 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

37. 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

38. 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

39. The critical temperature is the temperature
A. Below which a gas does not obey gas laws
B. Above which a gas may explode
C. Below which a gas is always liquefied
D. Above which a gas will never liquefied
Answer : D

40. 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

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

42. Thermal conductivity of non-metallic amorphous solids with decrease in temperature
A. Increases
B. Decreases
C. Remain constant
D. May increase or decrease depending on temperature
Answer : B

43. 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

44. 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

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

46. Depending on the radiating properties, a body will be black 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 = 0 Where a = absorptivity, p = reflectivity, X = transmissivity.
Answer : A

47. Cork is a good insulator because it has
A. Free electrons
B. Atoms colliding frequency
C. Low density
D. Porous body
Answer : D

48. The concept of overall coefficient of heat transfer is used in heat transfer problems of
A. Conduction
B. Convection
C. Radiation
D. Conduction and convection
Answer : D

49. 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

50. 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