Heating and Welding

11. Heat is transferred simultaneously by condition, convection and radiation

1. inside boiler furnaces
2. during melting of ice
3. through the surface of the insulted pipe carrying steam
4. from refrigerator coils to freezer of a refrigerator

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12. The process of heat transfer during the reentry of satellites and missiles, at very high speeds, into earth’s atmosphere is known as

1. ablation
2. radiation
3. viscous dissipation
4. irradiation

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13. Which of the following has the highest value of thermal conductivity?

1. Water
2. Steam
3. Solid ice
4. Melting ice

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14. Induction heating process is based on which of the following principles?

1. Thermal ion release principle
2. Nucleate heating principle
3. Resistance heating principle
4. Electro-magnetic induction principle

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15. Which of the following insulating materials was suitable for low temperature applications?

1. Asbestos paper
2. Diatomaceous earth
3. 80 percent magnesia
4. Cork

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16. A non-dimensional number generally associated with natural convection heat transfer is

1. Prandtl number
2. Grashoff number
3. Pecelet number
4. Nusselt number

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17. The temperature inside a furnace is usually measured by which of the following?

1. Optical pyrometer
2. Mercury thermometer
3. Alcohol thermometer
4. Any of the above

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18. Which of the following will happen if the thickness of refractory wall of furnace is increased?

1. Heat loss through furnace wall will increase
2. Temperature inside the furnace will fall
3. Temperature on the outer surface of furnace walls will drop
4. Energy consumption will increase

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19. The material of the heating element for a furnace should have

1. lower melting point
2. higher temperature coefficient
3. high specific resistance
4. all of the above

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20. In a resistance furnace the atmosphere is

1. oxidising
2. deoxidising
3. reducing
4. neutral

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