Mechanical Engineering - Heat Transfer, Refrigeration and Air Conditioning

21. 

According to Prevost's theory of exchanges, every body irrespective of its temperature continuously emit heat radiations to the surrounding bodies and at the same time receives heat radiations from the surrounding bodies.

A. True
B. False

Answer: Option A

Explanation:

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22. 

In a boot-strap air evaporative cooling system, the evaporator is provided

A. between the combustion chamber and the first heat exchanger
B. between the first heat exchanger and the secondary compressor
C. between the secondary compressor and the second heat exchanger
D. between the second heat exchanger and the cooling turbine

Answer: Option D

Explanation:

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23. 

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: Option D

Explanation:

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24. 

A good refrigerant should have

A. high latent heat of vaporisation and low freezing point
B. high operating pressures and low freezing point
C. high specific volume and high latent heat of vaporisation
D. low C.O.P. and low freezing point

Answer: Option A

Explanation:

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25. 

The thermal diffusivity for gases is generally __________ those for liquids.

A. equal to
B. less than
C. greater than

Answer: Option C

Explanation:

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