This set of Heat Transfer Operations Multiple Choice Questions & Answers (MCQs) focuses on “Indirect Contact Condensers”.
1. Which one of the following is not a shell and tube condenser?
a) Baffled
b) Cross-flow
c) Tube-side
d) Sparge pipe
View Answer
Explanation: The Sparge pipe condenser supplies the vapour gas into a pool of coolant liquid with the help of a perforated tube and hence is a direct contact condenser, whereas the other condensers are indirect contact ones.
2. Which one of the following condenser matches the given description – ‘The condenser has a shell containing tubes within which the coolant liquid usually flows. The flow on the shell-side is so designed that the vapour gas mainly flows in the cross-flow direction with respect to the tubes’?
a) Cross-flow
b) Counter flow
c) Co-current Flow
d) Mixed flow
View Answer
Explanation: The cross-flow condenser is the only one that is described by the statement and the sentence – The shell-side flow is such that the vapour flows mainly in the cross-flow direction to the tubes, confirms the answer.
3. The__________ condenser is generally used for low-pressure applications, where there is a large volume of vapour flow and a low-pressure drop is desired.
a) Co-current Flow
b) Counter flow
c) Cross-flow
d) Mixed flow
View Answer
Explanation: The cross flow condenser has a shell containing tubes within which the coolant liquid usually flows. The flow on the shell-side is so designed that the vapour gas mainly flows in the cross-flow direction with respect to the tubes and is thus well suited for low pressure applications.
4. _______________ baffles may be specified to achieve reduced pressure drop.
a) Double segmental
b) Single segmental
c) Triple segmental
d) Quadruple segmental
View Answer
Explanation: The more the number of segments, the more the pressure drop but the only exception is the double segmental which has significantly less pressure drop than the single segmental ones.
5. The space between the baffles is not determined by considerations such as _____________
a) The tubes need to be supported to avoid tube vibration
b) Pressure drop depends on vapour velocity which itself depends on baffle spacing
c) The resistance to heat transfer because of non-condensing gases is inversely proportional to the vapour velocity
d) Low vapour velocities can reduce resistance to heat transfer
View Answer
Explanation: High vapour velocities can reduce resistance to heat transfer by the shear forces it applies on the condensate film whereas the statement – “Low vapour velocities can reduce resistance to heat transfer” given is wrong.
6. _______________ can reduce resistance to heat transfer through the shear effect on the condensate film.
a) Low vapour velocity
b) Fluctuating vapour velocity
c) High vapour velocities
d) Oscillating vapour velocity
View Answer
Explanation: High vapour velocities can reduce resistance to heat transfer by the shear forces it applies on the condensate film, removing the film continuously so that the vapour is always in contact with the cool surface.
7. The size of the baffle cut is generally chosen such that the vapour velocity in the tube is _________ that in the overlap area between the baffle discs.
a) More than
b) Equal to
c) Less than
d) Very less than
View Answer
Explanation: The size of the baffle cut is chosen such that the vapour velocity in the tube is more or less equal to that in the overlap area between the baffle plates so that the pressure drop is lesser and lesser loss of condensate from the feed gas.
8. A possible configuration for low pressure drop is the ______________
a) K-shell with double segmental baffles
b) J-shell with double segmental baffles
c) M-shell with double segmental baffles
d) N-shell with double segmental baffles
View Answer
Explanation: The J-shell given by TEMA is the best suited configuration for low pressure drop applications. The TEMA stands for – Tubular Exchanger Manufacturers Association is an association of fabricators of shell and tube type heat exchangers.
9. Condensation on the ____________ is preferred when the coolant is a gas.
a) Shell side
b) Tube side
c) Front side
d) Back side
View Answer
Explanation: When the coolant is a gas, it should be kept on the side that has the ability to handle high pressure drops, which is generally the tube side, hence the condensation occurs at the shell side.
10. Tube-side condenser is preferred when the coolant is a gas, such as air.
a) True
b) False
View Answer
Explanation: When the coolant is a gas, it should be kept on the side that has the ability to handle high pressure drops, which is generally the tube-side, hence the condensation occurs at the shell side. The tube walls are thick and strong to handle this whereas the shell side large pressure drops can cause large damage to the setup, to the baffles and to the tubes.
11. __________ condensers are preferred if the condensing fluid is at a higher pressure than the coolant.
a) Shell side
b) Tube side
c) Front side
d) Back side
View Answer
Explanation: Designers usually prefer to keep the component which will probably show higher pressure to be on the tube side as tube walls are thick and strong to handle this whereas the shell side large pressure drops can cause large damage to the setup, to the baffles and to the tubes. Hence when the coolant is a gas or a liquid, it is on the tube side.
12. A condenser has coolant in counter-current flow with the vapour flowing upward and itself flowing downward, then it is commonly known as the _______________
a) Packed column
b) Reflux condenser
c) Sparge tube condenser
d) Tray type condenser
View Answer
Explanation: The reflux condenser is a special type of condenser which is designed such that vapour velocity is less than the flooding velocity hence it protects the setup from any unforeseen damage that can be caused in future.
13. The reflux condenser must be designed such that vapour velocity is ________ the flooding velocity.
a) Less than
b) More than
c) Equal to
d) Oscillating with
View Answer
Explanation: A condenser has coolant in counter-current flow with the vapour flowing upward and itself flowing downward, and is such designed that vapour velocity is less than the flooding velocity. Hence it protects the setup from any unforeseen damage that can be caused in future.
Sanfoundry Global Education & Learning Series – Heat Transfer Operations.
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