Mechanical Engineering - Heat Transfer, Refrigeration and Air Conditioning

16. 

Which of the following refrigerant has the highest freezing point.

A. Ammonia
B. Carbon dioxide
C. Sulphur dioxide
D. R-12

Answer: Option B

Explanation:

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17. 

Air conditioning means

A. cooling
B. heating
C. dehumidifying
D. all of these

Answer: Option D

Explanation:

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18. 

The emissivity for a black body is

A. 0
B. 0.5
C. 0.75
D. 1

Answer: Option D

Explanation:

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19. 

Which of the following would lead to a reduction in thermal resistance?

A. In conduction, reduction in the thickness of the material and an increase in thermal conductivity.
B. In convection, stirring of the fluid and cleaning the heating surface.
C. In radiation, increasing the temperature and reducing the emissivity.
D. all of the above

Answer: Option D

Explanation:

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20. 

The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number)n, where n is equal to

A. -1/3
B. -2/3
C. 1
D. -1

Answer: Option A

Explanation:

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