Mechanical Engineering - Heat Transfer, Refrigeration and Air Conditioning

21. 

In counter-current flow heat exchanger, the logarithmic temperature difference between the fluids is __________ as compared to parallel flow heat exchanger.

A. same
B. less
C. greater

Answer: Option C

Explanation:

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22. 

Environmental protection agencies advice against the use of chloro-fluoro-carbon refrigerants since

A. these react with water vapour and cause acid rain
B. these react with plants and cause green-house effect
C. these react with oxygen and cause its depletion
D. these react with ozone layer

Answer: Option D

Explanation:

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23. 

When the lower temperature of a refrigerating machine is fixed, then the coefficient of performance can be improved by

A. operating the machine at higher speeds
B. operating the machine at lower speeds
C. raising the higher temperature
D. lowering the higher temperature

Answer: Option D

Explanation:

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24. 

The refrigerant carbon dioxide is not widely used because of its __________ power require ments per tonne of refrigeration and high operating pressures.

A. low
B. high

Answer: Option B

Explanation:

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25. 

The by-pass factor of a cooling coil decreases with

A. decrease in fin spacing and increase in number of rows
B. increase in fin spacing and increase in number of rows
C. increase in fin spacing and decrease in number of rows
D. decrease in fin spacing and decrease in number of rows

Answer: Option A

Explanation:

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