Mechanical Engineering - Heat Transfer, Refrigeration and Air Conditioning

36. 

A refrigerating system operating on reversed Brayton refrigeration cycle is used for maintaining 250 K. If the temperature at the end of constant pressure cooling is 300 K and rise in the temperature of air in the refrigerator is 50 K, then the net work of compression will be (assume air as working substance with cp = 1 kJ/kg)

A. 25 kJ/kg
B. 50 kJ/kg
C. l00 kJ/kg
D. 125 kJ/kg

Answer: Option B

Explanation:

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37. 

Wet bulb temperature indicates the moisture content in air.

A. Agree
B. Disagree

Answer: Option A

Explanation:

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38. 

A designer chooses the values of fluid flow rates and specific heats in such a manner that the heat capacities of the two fluids are equal. A hot fluid enters the counter flow heat exchanger at 100° C and leaves at 60° C. A cold fluid enters the heat exchanger at 40° C. The mean temperature difference between the two fluids is

A. 20°C
B. 40°C
C. 60°C
D. 66.7°C

Answer: Option A

Explanation:

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39. 

The inclined and non-uniformly spaced straight lines on a psychrometric chart indicates wet bulb temperature.

A. Agree
B. Disagree

Answer: Option A

Explanation:

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40. 

The heat transfer by conduction through a thick cylinder(Q) is given by (where T1 = Higher temperature, T2 = Lower temperature, r1 = Inside radius, r2 = Outside radius, l = Length of cylinder, and k = Thermal conductivity)

A.
B.
C.
D.

Answer: Option A

Explanation:

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