Heat & Mass Transfer 1000+ MCQ with answer for RRB Group D

1. A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,
A. The better insulation must be put inside
B. The better insulation must be put outside
C. One could place either insulation on either side
D. One should take into account the steam temperature before deciding as to which insulation is put where
Answer : A

2. 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

3. According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a
A. Grey body
B. Brilliant white polished body
C. Red hot body
D. Black body
Answer : D

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

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

12. 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

13. LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is
A. Higher
B. Lower
C. Same
D. Depends on the area of heat exchanger
Answer : A

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

15. 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

16. Thermal conductivity of water at 20°C is of the order of
A. 0.1
B. 0.23
C. 0.42
D. 0.51
Answer : D

17. The critical thickness of insulation for a sphere is
A. k/h?
B. 2k/h?
C. h?/k
D. h?/2k
Answer : B

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

19. Fourier's law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow, and k = Thermal conductivity of the body)
A. k. A. (dT/dx)
B. k. A. (dx/dT)
C. k. (dT/dx)
D. k. (dx/dT)
Answer : A

20. 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

21. In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by
A. Convection
B. Radiation
C. Conduction
D. Both convection and conduction
Answer : C

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

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

29. 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

30. 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

31. Which of the following has maximum value of thermal conductivity?
A. Aluminium
B. Steel
C. Brass
D. Copper
Answer : A

32. An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be
A. 25 mm
B. 40 mm
C. 160 mm
D. 800 mm
Answer : A

33. 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

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

35. 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

36. 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

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

38. 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

39. 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

40. Emissivity of a white polished body in comparison to a black body is
A. Higher
B. Lower
C. Same
D. Depends upon the shape of body
Answer : B

41. 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

42. 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