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

1. 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

2. 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

3. 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

4. The natural convection air cooled condensers are used in
A. Domestic refrigerators
B. Water coolers
C. Room air conditioners
D. All of these
Answer : A

5. 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

6. 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

7. 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

8. The unit of Stefan-Boltzmann constant is
A. Watt/mK
B. Watt/m²K²
C. Watt/m²K⁴
D. Watt/mK²
Answer : C

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. The heat transfer by conduction through a thick cylinder (Q) is given by (where T? = Higher temperature, T? = Lower temperature, r? = Inside radius, r? = Outside radius, l = Length of cylinder, and k = Thermal conductivity)
A. Q = [2?lk (T? - T?)]/2.3 log (r?/r?)
B. Q = 2.3 log (r?/r?)/[2?lk (T? - T?)]
C. Q = [2? (T? - T?)]/2.3 lk log (r?/r?)
D. Q = = 2?lk/2.3 (T? - T?) log (r?/r?)
Answer : A

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

17. Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium.
A. Cold body to hot body
B. Hot body to cold body
C. Smaller body to larger body
D. Larger body to smaller body
Answer : B

18. 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

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

20. 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

21. 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

22. 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

23. 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

24. 40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is
A. 0.45
B. 0.55
C. 0.40
D. 0.75
Answer : A

25. Which of the following property of air does not increase with rise in temperature?
A. Thermal conductivity
B. Thermal diffusivity
C. Density
D. Dynamic viscosity
Answer : C

26. 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

27. 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

28. 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

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

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. Unit of thermal conductivity in M.K.S. units is
A. K cal/kg m² °C
B. K cal m/hr m² °C
C. K cal/hr m² °C
D. K calm/hr °C
Answer : B

32. 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

33. If the temperature of a solid surface changes from 27°C to 627°C, then its emissive power changes in the ratio of
A. 6
B. 9
C. 27
D. 81
Answer : D

34. 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

35. 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

36. 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

37. 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

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

39. 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

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

41. 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

42. When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by
A. Conduction
B. Convection
C. Radiation
D. Conduction and convection
Answer : C

43. 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

44. 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

45. 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

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. 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

48. 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

49. Conduction is a process of heat transfer
A. From one particle of the body to another without the actual motion of the particles
B. From one particle of the body to another by the actual motion of the heated particles
C. From a hot body to a cold body, in a straight line, without affecting the intervening medium
D. None of the above
Answer : A

50. 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