Heat Transfer

91. Which of the following is the case of heat transfer by radiation

1. blast furnace
2. heating of building
3. cooling of parts in furnace
4. heat received by a person from fireplace
5. all of the above.

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92. wo 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

1. 1 :1
2. 2: 1
3. 1 : 2
4. 4 : 1
5. 1 : 4.

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93. wo plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by

1. convection
2. free convection
3. forced convection
4. radiation
5. radiation and convection.

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