Heat Transfer (HT) | Set 7

1. Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m2.°C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the

A. Higher condensing film co-efficient is desired

B. Condensate is corrosive in nature

C. Lower pressure drop through the exchanger is desired

D. Temperature of the incoming vapor is very high

Correct : B. Condensate is corrosive in nature

2. Viscosity of gases __________ with increase in temperature.

A. Increase very rapidly

B. Increase slowly

C. Decrease slowly

D. Remain unaffected

Correct : B. Increase slowly

3. In case of surface condensers, a straight line is obtained on plotting 1/U vs. __________ on an ordinary graph paper.

A. 1/V̅-0.8

B. V̅-0.8

C. V̅-2

D. 1/ V̅-2

Correct : A. 1/V̅-0.8

4. A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest?

A. Cube

B. Plate

C. Sphere

D. All will cool at the same rate

Correct : C. Sphere

5. A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the centre of the sphere reaches 350°K in 20 minutes, how long will it take for a 0.05 m radius steel sphere to reach the same temperature (at the centre) under identical conditions? Assume that the conductive heat transfer co-efficient is infinitely large.

A. 5 minutes

B. 10 minutes

C. 20 minutes

D. 40 minutes

Correct : A. 5 minutes

7. For a opaque body

A. reflectivity = 0

B. absorptivity = reflectivity = 1

C. 37,500 kg

D. absorptivity + reflectivity = 1

E. absorptivity = 0

Correct : D. absorptivity + reflectivity = 1

8. In which case the value of thermal conductivity drops with rising temperature

9. Which of the following is used as entrainer in acetic acid - water separation?

10. Which of the following provides maximum contact surface for a liquid vapour system?

12. Cork is a good insulator because

13. The value of thermal conductivity of water at room temperature is expected to be

14. The coefficient of linear expansion of a solid is L. The volume V of a cube of this solid on being heated by 1?C will change by

16. Two rods one of copper and the other of mild steel, both of diameter 20 mm and length 250 mm are coated with a uniform layer of wax all around. These rods are placed vertically in a boiling water bath with 200 mm, length of each rod projecting outside. If the melting point of wax is 10?C, then

A. equal quantity of wax will meet on the two rods

B. more wax will melt on copper rod as compared to mild steel rod

C. 37,500 kg

D. nothing can be predioted as the data is insufficient

E. more wax will melt on mild steel rod as compared to copper rod

Correct : B. more wax will melt on copper rod as compared to mild steel rod

18. Heat is transferred from an electric bulb mainly by

20. A vapour containing liquid particles to the extent of 50% by the volume is known as

21. Ice is slippery when a man walks on it for

A. There is no friction

B. Increase of pressure causes it to melt

C. It is very chill

D. Its surface is smooth

E. It has lubricating qualities

Correct : B. Increase of pressure causes it to melt

22. The total solar radiation incident on a body is 1000 kcal/min. The body reflects 400 kcal/min. If the transmissivity of the surface will be

23. The nature of flow of a fluid inside a tube i.e., whether it is turbulent or laminar, is ascertained by

24. When metallic surfaces are oxidized the emissivity

25. For which fluid combination the value of overall heat transfer coefficient will be least?

26. The rate of heat flow between a solid wall and a fluid (in contact with a solid wall) is given by

27. Radio active nuclear waste is treated in

A. Pulsed column extractor

B. Mixer settler extractor

C. Sieve plate extraction column

D. Bollman extractor

E. None of the above

Correct : A. Pulsed column extractor

28. In which case does the thermal conductivity increase from left to right?

A. Aluminium, silver, copper

B. 37,500 kg

C. Aluminium, copper, silver

D. Silver, copper, aluminium

E. Copper, silver, aluminium

Correct : C. Aluminium, copper, silver

29. If two systems are being compared on the basis of temperature and heat flux, the similarity being considered is

33. The temperature inside a furnace is generally measured by

34. At all wavelengths and temperatures the monochromatic emissivity of a white body is equal to

35. If the bubbles formed on a submerged hot surface get absorbed in the mass of liquid, the process of boiling is termed as

36. The rate of radiant energy, which is emitted by a surface at any temperature and in small wavelength is found from the known rate of energy, which under the same condition would be emitted from a black surface by multiplying with the absorptivity. Above enunciation is known as

37. A radiation shield should have

38. In heat exchanger design, one transfer unit means

A. Condition when the change in temperature of 1?C numerically equals the average driving force.

B. The equivalent length of tubes in case the heat exchange was for a temperature difference of 1?C

C. One fluid exchanging with another fluid of the same chemical composition

D. The section of heat exchanger where heat transfer surface area is one square metre

E. The section of heat exchanger which will cause temperature drop of one degree centigrade

Correct : A. Condition when the change in temperature of 1?C numerically equals the average driving force.

39. A 1-2 heat exchanger means

A. Single pass on shell side and double pass on tube side

B. Single pass on tube side and double pass on shell side

C. Two tubes of hot fluid pass through one tube of cold tube

D. Single liquid cools two liwuids at different temperatures

E. Two tubes of cold fluid pass through one tube of hot fluid

Correct : A. Single pass on shell side and double pass on tube side

40. When a body is in thermal equilibrium with its surroundings, the absorptivity and the emissivity of the body are same. This Law is known as

41. The process of separation of solutes of different molecular sizes in a liquid solution by use of a sutable membrane is known as

42. The propose of using multiple pass heat exchangers is to

A. Increase pressure drop

B. Increase the rate of heat transfer

C. Neutralise viscous friction

D. Reduce pressure drop

E. Reduce fluid flow friction losses

Correct : B. Increase the rate of heat transfer

43. The range of diffusivity of gases in cm2/sec at atmospheric pressure is

44. Four identical copper cubes are painted with different paints. Now if all the cubes are heated to the same temperature and are left in vacuum, which cube will lose heat more rapidly? The colours of the cubes are

48. Which one of the following is a very good insulator?

49. A device for transferring heat from one fluid to another is known as

50. Which insulating material is suitable for low temperature applications?

51. Steady state heat transfer occurs when

A. The flow of heat is uniform

B. The flow of heat is uniformly increasing

C. The flow of heat is uniformly decreasing

D. The flow of heat is negligible

E. The flow of heat is independent of time

Correct : C. The flow of heat is uniformly decreasing

54. Thermal conductivity of liquids can be determined by

55. The temperature of sun can be measured using a

56. Any of the following could be the unit for Stefan Boltzmann constant EXCEPT

57. Which one of the following approximates to the black body condition?

59. Which of the following method is used for finding the thermal conductivity of rubber?

60. The ratio of thermal conductivity of copper to that of brass is nearly

A. 37,500 kg

B. 8

C. 4

D. 2

Correct : D. 2

61. The relation between the emissive and absorptive power of a surface is developed under

62. In air prelieater for boiler heat is least transferred by

63. The rate of heat loss through a furnace wall is 1000 kcal per hour when inside temperature is 1000?C and outside wall temperature is 500?C. What should be the wall thickness in case the thermal conductivity of wall material is 0.5 kcal/m-hr?C

65. What energy transformation takes place when ice and salt mixture is converted into water

A. Heat energy to sensible heat

B. Kinetic energy to heat energy

C. Heat energy to latent heat

D. Heat energy to potential energy

E. Heat energy to kinetic energy

Correct : C. Heat energy to latent heat

67. Pyrometer which react to all wavelengths of incident radiant energy are known as

A. Multicolour pyrometers

B. Total radiation pyrometers

C. Polarising pyrometers

D. Optical pyrometers

E. Ddisappearing filament type pyrometers

Correct : B. Total radiation pyrometers

68. A relationship between the temperature of a black body and the wavelength at which the maximum value of monochromatic emission power occurs, is established under

70. Two parallel opposed, infinite black planes are maintained at 300?C and 400?C respectively. If the temperature difference is doubled by increasing the temperature from 400?C to 500?C, the heat exchange rate will increase by a factor of about

71. The overall co-efficients of heat transfer is used in the problems of

72. Identity the correct statement

A. Only some substances emit radiation

B. A substance will emit radiation at a particular wavelength only

C. Quality and quantity of radiation depends on the properties of the material only

D. All substances emit radiation the quality and quantity depends on the absolute temperature and the properties of the material composing the radiating body

E. Bodies black in colour are known as black bodies

Correct : D. All substances emit radiation the quality and quantity depends on the absolute temperature and the properties of the material composing the radiating body

73. Baffles are provided in heat exchangers to

A. Provide better mechanical strength

B. Reduce heat transfer rate

C. Reduce vibrations

D. Increase heat transfer rate

E. Remove dirt

Correct : D. Increase heat transfer rate

74. Heat sensitive liquids are connected

A. By using insulated vessels

B. By using low intensity heating

C. By using deoxidisers

D. By using small quantities

E. By using vacuum

Correct : E. By using vacuum

75. Which sample of concrete may be expected to have highest value of thermal conductivity

A. Dry concrete having 0.4% rein-forcement

B. Concrete having 10% moisture by volume

C. Concrete having 10% meisture by volume and 0.4% reinforcement

D. Dry concrete

E. Concrete having 10% moisture by volume and 0.6% reinforcement

Correct : E. Concrete having 10% moisture by volume and 0.6% reinforcement

77. Ditus Boelter equation is applicable in case of fluids flowing in

79. The emissive power of a body depends on

80. Floating heads are provided in heat exchangers to

A. Facilitate maintenance

B. Regulate the flow

C. Increase the pressure drop

D. Avoid deformation of tubes due to thermal expansion

E. Reduce the pressure drop

Correct : D. Avoid deformation of tubes due to thermal expansion

81. The transfer of heat in case of radiation takes place by means of

A. Heated particles of the medium

B. Electromagnetic waves

C. Thermal energy of the source

D. None of the above

E. 37,500 kg

Correct : A. Heated particles of the medium

82. In case of liquids and gases, the heat transfer takes place according to

83. Which of the following has the highest value of the thermal conductivity

84. Which of the following is wrong

A. Black surfaces are better absorbers than white ones

B. Black surfaces are better radiators than white ones

C. Rough surfaces are better radiators than smooth surfaces

D. 37,500 kg

E. Highly polished mirror like surfaces are very good radiators

Correct : E. Highly polished mirror like surfaces are very good radiators

87. All bodies above absolute zero temperature emit radiation". Above statement is based on

88. Which one of the following will radiate heat to a large extent?

89. In a cooling tower which mode of heat transfer plays insignificant role?

90. A dimensionless number which is the ratio of kinematic viscosity to thermal diffusivity is known as

91. There metal walls of same cross-sectional area having thermal conductivity in the ratio 1 : 2 : 4 transfer heat at the rate of 15000 kcal/hr. For same thickness of wall, the temperature deop will be in the ratio

A. 1 ; 2 ; 4

B. 1 :

C. 4 ; 2 ; 1

D. 1 ; 1 ; 1

Correct : B. 1 :

92. Formation of fog is due to

93. The radiation from flames consists of

A. Continuous radiation from burning soot particles of microscopic and submicroscopic dimensions

B. Radiation from suspended larger particles of coal, coke or ash contributing to flame luminosity

C. Infrared radiation from water vapour and carboundioxide

D. Non-equilibrium radiation associated with the combustion process

E. All of the above

Correct : E. All of the above

94. In a shell and tube heat exchanger, the corrosive liquid is normally passed through

95. DBA = DAB, in case of

A. Stagnet diffusion

B. Equimolar counter diffusion

C. Either of (A) and (B) above

D. None of the above

E. 2.6 cm2/sec

Correct : B. Equimolar counter diffusion

96. Unsaturated vapours

A. Do not obey gas laws

B. Fully obey gas laws

C. Obey Boyle's law but not Charle's law

D. Partly obey gas laws depending upon the degree of unsaturations

E. None of the above

Correct : A. Do not obey gas laws

98. Which dimensionless number indicates the relative strength of the buoyant to viscous forces?

99. In case the hydrodynamic and thermal boundary layers are identical for a fluid flowing over a heated plate

A. The value of Prandtl number must be 0.5

B. The plate surface must be smooth

C. The plate must be of low thermal conductivity

D. The value of Prandtl number thust be 1

E. The value of Prandtl number must be zero

Correct : D. The value of Prandtl number thust be 1

100. A high value of Prandtl number indicates

A. rapid diffusion of momentum by viscous action compared to diffusion of energy

B. relative heat transfer by conduction to convection

C. rapid heat transfer by forced convection to natural convection

D. None of the above

E. 37,500 kg

Correct : A. rapid diffusion of momentum by viscous action compared to diffusion of energy

Quiznetik

Heat Transfer (HT) | Set 7

1. Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m2.°C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the

2. Viscosity of gases __________ with increase in temperature.

3. In case of surface condensers, a straight line is obtained on plotting 1/U vs. __________ on an ordinary graph paper.

4. A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest?

6. Which of the following material has lest value of thermal diffusivity?

7. For a opaque body

8. In which case the value of thermal conductivity drops with rising temperature

9. Which of the following is used as entrainer in acetic acid - water separation?

10. Which of the following provides maximum contact surface for a liquid vapour system?

11. The lower temperature limit for mercury thermometer is

12. Cork is a good insulator because

13. The value of thermal conductivity of water at room temperature is expected to be

14. The coefficient of linear expansion of a solid is L. The volume V of a cube of this solid on being heated by 1?C will change by

15. The unit of thermal conductivity in S.I. units is

16. Two rods one of copper and the other of mild steel, both of diameter 20 mm and length 250 mm are coated with a uniform layer of wax all around. These rods are placed vertically in a boiling water bath with 200 mm, length of each rod projecting outside. If the melting point of wax is 10?C, then

17. Oxygen boils at -183?C, this temperature is

18. Heat is transferred from an electric bulb mainly by

19. The average value of thermal conductivity for air at 20?C is about

20. A vapour containing liquid particles to the extent of 50% by the volume is known as

21. Ice is slippery when a man walks on it for

22. The total solar radiation incident on a body is 1000 kcal/min. The body reflects 400 kcal/min. If the transmissivity of the surface will be

23. The nature of flow of a fluid inside a tube i.e., whether it is turbulent or laminar, is ascertained by

24. When metallic surfaces are oxidized the emissivity

25. For which fluid combination the value of overall heat transfer coefficient will be least?

26. The rate of heat flow between a solid wall and a fluid (in contact with a solid wall) is given by

27. Radio active nuclear waste is treated in

28. In which case does the thermal conductivity increase from left to right?

29. If two systems are being compared on the basis of temperature and heat flux, the similarity being considered is

30. Thermal conductivity of air at room temperature in kcal/m-hr-?C is nearly

31. Steam traps are used to

32. ?40?C is equivalent to

33. The temperature inside a furnace is generally measured by

34. At all wavelengths and temperatures the monochromatic emissivity of a white body is equal to

35. If the bubbles formed on a submerged hot surface get absorbed in the mass of liquid, the process of boiling is termed as

36. The rate of radiant energy, which is emitted by a surface at any temperature and in small wavelength is found from the known rate of energy, which under the same condition would be emitted from a black surface by multiplying with the absorptivity. Above enunciation is known as

37. A radiation shield should have

38. In heat exchanger design, one transfer unit means

39. A 1-2 heat exchanger means

40. When a body is in thermal equilibrium with its surroundings, the absorptivity and the emissivity of the body are same. This Law is known as

41. The process of separation of solutes of different molecular sizes in a liquid solution by use of a sutable membrane is known as

42. The propose of using multiple pass heat exchangers is to

43. The range of diffusivity of gases in cm2/sec at atmospheric pressure is

44. Four identical copper cubes are painted with different paints. Now if all the cubes are heated to the same temperature and are left in vacuum, which cube will lose heat more rapidly? The colours of the cubes are

45. In case of ideal mono-atomic gas, the ratio of specific heats would be

46. Thermal conductivity of glass wool depends on

47. The average value of thermal conductivity for water at 20?C is about

48. Which one of the following is a very good insulator?

49. A device for transferring heat from one fluid to another is known as

50. Which insulating material is suitable for low temperature applications?

51. Steady state heat transfer occurs when

52. Which of the following material has thermal conductivity closest to silver?

53. A constant gas thermometer is based on

54. Thermal conductivity of liquids can be determined by

55. The temperature of sun can be measured using a

56. Any of the following could be the unit for Stefan Boltzmann constant EXCEPT

57. Which one of the following approximates to the black body condition?

58. Heat is shown to be closely related to

59. Which of the following method is used for finding the thermal conductivity of rubber?

60. The ratio of thermal conductivity of copper to that of brass is nearly

61. The relation between the emissive and absorptive power of a surface is developed under

62. In air prelieater for boiler heat is least transferred by

63. The rate of heat loss through a furnace wall is 1000 kcal per hour when inside temperature is 1000?C and outside wall temperature is 500?C. What should be the wall thickness in case the thermal conductivity of wall material is 0.5 kcal/m-hr?C

64. Non-isotropic conductivity is exhibited in case of

65. What energy transformation takes place when ice and salt mixture is converted into water

66. The rate of energy stored in the wall will be

67. Pyrometer which react to all wavelengths of incident radiant energy are known as

68. A relationship between the temperature of a black body and the wavelength at which the maximum value of monochromatic emission power occurs, is established under

69. In case of white body, absorptivity is

70. Two parallel opposed, infinite black planes are maintained at 300?C and 400?C respectively. If the temperature difference is doubled by increasing the temperature from 400?C to 500?C, the heat exchange rate will increase by a factor of about

71. The overall co-efficients of heat transfer is used in the problems of

72. Identity the correct statement

73. Baffles are provided in heat exchangers to

74. Heat sensitive liquids are connected

75. Which sample of concrete may be expected to have highest value of thermal conductivity

76. Which rays have the least wavelength?

77. Ditus Boelter equation is applicable in case of fluids flowing in

78. Transmission of heat by molecular collision is

79. The emissive power of a body depends on