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

1. 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

2. 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

3. 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

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

5. 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

6. 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

7. 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

8. Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ? = Density of substance, S = Specific heat, and k = Thermal conductivity)
A. h = k/ ?S
B. h = ?S/k
C. h = S/?k
D. h = k?/S
Answer : A

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

11. 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

12. 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

13. 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

14. A steam pipe is to be insulated by two insulating materials put over each other. For best results
A. Better insulation should be put over pipe and better one over it
B. Inferior insulation should be put over pipe and better one over it
C. Both may be put in any order
D. Whether to put inferior OIL over pipe or the better one would depend on steam temperature
Answer : A

15. 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

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. 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

18. 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

19. 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

20. Log mean temperature difference in case of counter flow compared to parallel flow will be
A. Same
B. More
C. Less
D. Depends on other factors
Answer : B

21. 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

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

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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 these
Answer : B

30. The use of heat exchangers is made in
A. Radiators in automobile
B. Condensers and boilers in steam plants
C. Condensers and evaporators in refrigeration and air conditioning units
D. All of the above
Answer : D

31. Unit of thermal conductivity in S.I. units is
A. J/m² sec
B. J/m °K sec
C. W/m °K
D. Option (B) and (C) above
Answer : D

32. Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of
A. 1 : 1
B. 2 : 1
C. 1 : 2
D. 4 : 1
Answer : C

33. 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

34. 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

35. An ordinary passenger aircraft requires a cooling system of capacity.
A. 2 TR
B. 4 TR
C. 8 TR
D. 10 TR
Answer : C

36. The time constant of a thermocouple is
A. The time taken to attain the final temperature to be measured
B. The time taken to attain 50% of the value of initial temperature difference
C. The time taken to attain 63.2% of the value of initial temperature difference
D. Determined by the time taken to reach 100°C from 0°C
Answer : C

37. 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

38. 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

39. The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is
A. Equal to one
B. Greater than one
C. Less than one
D. Equal to Nusselt number
Answer : A

40. 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

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

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

43. 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

44. 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

45. 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

46. 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

47. The heat of sun reaches to us according to
A. Conduction
B. Convection
C. Radiation
D. None of these
Answer : C

48. 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

49. 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

50. A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h?, h? and h? respectively. The average heat transfer coefficient for the cube is
A. h? + h? + h?
B. (h?.h?.h?)1/3
C. 1/h? + 1/h? + 1/h?
D. None of these
Answer : D