Heat Transfer Mcqs

Q:

Consider the above problem, find the steam condensation rate

A) 52.22 kg/hr B) 42.22 kg/hr
C) 32.22 kg/hr D) 22.22 kg/hr
 
Answer & Explanation Answer: D) 22.22 kg/hr

Explanation: Not available for this question

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16
Q:

In a surface condenser, the water flowing through a series of tubes at the rate of 200 kg/hr is heated from 15 degree Celsius to 75 degree Celsius. The steam condenses on the outside surface of tubes at atmospheric pressure and the overall heat transfer coefficient is estimated at 860 k J/m2 hr degree. Find the number of transfer units of the heat exchanger. At the condensing pressure, stream has saturation temperature 0f 100 degree Celsius and the latent heat of vaporization is 2160 k J/kg. Further, the steam is initially just saturated and the condensate leaves the exchanger without sub-cooling i.e. only latent heat of condensing steam is transferred to water. Take specific heat of water as 4 k J/kg K

A) 3.224 B) 2.224
C) 1.224 D) 0.224
 
Answer & Explanation Answer: C) 1.224

Explanation: Effectiveness = 1 – exponential [- NTU].

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25
Q:

E – NTU method is particularly useful in thermal design of heat exchangers when

A) Inlet temperature of the fluid streams are not known as a priori B) The outlet temperatures of the hot fluid streams is known but that of cold fluid stream is not known as a priori
C) The outlet temperatures of the fluid streams is known as a priori D) The outlet temperatures of the fluid streams are not known as a priori
 
Answer & Explanation Answer: D) The outlet temperatures of the fluid streams are not known as a priori

Explanation: It is useful when outlet temperatures of the fluid streams are not known as a priori.

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28
Q:

After expansion from a gas turbine, the hot exhaust gases are used to heat the compressed air from a compressor with the help of a cross flow heat exchanger of 0.8 effectiveness. What is the number of transfer units of the heat exchanger?

A) 2 B) 4
C) 8 D) 16
 
Answer & Explanation Answer: B) 4

Explanation: Effectiveness = NTU/NTU – 1 = 0.5.

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20
Q:

A cross flow type air heater has an area of 50 cm². The overall heat transfer coefficient is 100 W/m² K and heat capacity of both hot and cold stream is 1000 W/m K. The value of NTU is

A) 1000 B) 500
C) 5 D) 0.2
 
Answer & Explanation Answer: B) 500

Explanation: Not available for this question

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17
Q:

Pick the odd one out

A) Open feed water heaters B) Jet condensers
C) De-super heaters D) Surface condensers
 
Answer & Explanation Answer: D) Surface condensers

Explanation: In surface condenser, the heat transfer occurs between the fluid streams without mixing or physical contact with each other.

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13
Q:

Consider the above problem, find the capacity ratio of the heat exchanger

A) 0.555 B) 0.444
C) 0.333 D) 0.222
 
Answer & Explanation Answer: C) 0.333

Explanation: Capacity ratio = 10/30 = 0.333.

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12
Q:

For evaporators and condensers, for the given conditions, the logarithmic mean temperature difference for parallel flow is

A) Does not depend on counter flow B) Smaller than counter flow
C) Greater than counter flow D) Equal to counter flow
 
Answer & Explanation Answer: D) Equal to counter flow

Explanation: The temperature of one of the fluid remains constant during the flow passage.

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