# Heat Transfer Operations Questions and Answers – Extended Surface Heat Exchangers – Design

This set of Heat Transfer Operations Multiple Choice Questions & Answers (MCQs) focuses on “Extended Surface Heat Exchangers – Design”.

1. What are the three parts of Extended Surface heat exchangers when it is classified based on flow pattern?
a) Compound flow, Plate Fin and Cross Counter Flow
b) Compound flow, Tube Fin and Cross Counter Flow
c) Compound flow, Tube Fin and Plate Fin
d) Compound flow, Cross Parallel and Cross Counter Flow

Explanation: When classified based on flow pattern, they can be divided to 3 parts, they are – Compound flow, Cross Parallel and Cross Counter Flow and when classified based on construction can be divided to 2 parts, they are – Plate Fin and Tube Fin.

2. Extended Surface heat exchangers are a subset of the broader category of _____ flow type Heat Exchangers.
a) Multi Pass
b) Single Pass
c) Compound
d) Split

Explanation: An extended surface HE is a subset of the multipass flow arrangement. When classified based on flow pattern under multipass flow, they can be divided to 3 parts, they are – Compound flow, Cross Parallel and Cross Counter Flow.

3. Compound flow Extended surface heat exchangers are superior to Counter flow operation.
a) True
b) False

Explanation: An extended surface HE is always superior to a normal HE. When classified based on flow pattern can be divided to 3 parts, they are – Compound flow, Cross Parallel and Cross Counter Flow.

4. In case of Classification based on construction, extended surface heat exchangers can be classified into _________
a) Plate Fin and Tube Fin
b) Cross Parallel and Plate Fin
c) Tube Fin and Cross Parallel
d) Compound flow and Tube Fin

Explanation: An extended surface HE when classified based on construction can be divided to 2 parts, they are – Plate Fin and Tube Fin.

5. Plate type Extended Fins HE is a classification based on the _____ of the heat exchanger.
a) Construction
b) Flow pattern
c) Phase pattern
d) Heat transfer mechanism

Explanation: An extended surface HE when classified based on construction can be divided to 2 parts, they are – Plate Fin and Tube Fin. Plate type Extended Fins HE is a classification based on the construction of the heat exchanger.
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6. Compound flow Fins extended surface heat exchangers are classification based on______
a) Construction
b) Flow pattern
c) Phase pattern
d) Heat transfer mechanism

Explanation: An extended surface HE when classified based on flow pattern can be divided to 3 parts, they are – Compound flow, Cross Parallel and Cross Counter Flow.

7. Fins primarily increase the ______
a) Turbulence
b) Heat transfer area
c) Heat transfer rate
d) Heat transfer coefficient

Explanation: Fins are primarily used to increase the heat transfer area, the rest of the factors given are consequences of this change.

8. Which of the following are not affected by adding Fins?
a) Net Heat Transfer
b) Heat transfer coefficient
c) Heat transfer rate
d) Turbulence

Explanation: The net heat transfer in a particular operation should remain the same, fins are used to decrease the area and time for that process.

9. Fins can be added only to one side of a heat exchanger.
a) True
b) False

Explanation: Fins can be added to any side of the surface if necessary but it should be checked that the side it is attached to has fluid with low U.

10. Fins are not usually attached to the main body of the heat exchanger by ______
a) Welding
b) Glue
c) Brazing
d) Groove fitting

Explanation: Fins are attached to the surface by brazing, soldering, welding, gluing and integrally built with the tubes. Fins are not usually attached to the main body of the heat exchanger by Groove fitting.

11. To which side given below should we add fins?
a) Gas Side
b) Liquid side
c) Solid side
d) Any side possible

Explanation: We add fins to that side which has low heat transfer coefficient so as to increase area at that side to facilitate heat transfer. Hence adding it to gas side is beat suited as gases have low heat transfer coefficient.

12. On which of the following parts fins are usually not attached?
a) Baffles
b) Outer Tube
c) Shell
d) Inner surface of tube

Explanation: Fins can only be attached where heat transfer is taking place, hence the wrong option is baffles as no heat transfer takes place across it.

13. The equivalent diameter on the shell side _____ on adding fins.
a) Increases
b) Decreases
c) Remains the same
d) Very large change beyond measure

Explanation: Adding Fins to the surface, the interaction of the fluid with the wall increases, the wall now occupies a larger portion of the flow area hence its wetted perimeter increases with a decrease in flow area. As De = 4A/P, A decreases and P increases implies De too decreases.

14. The wetted perimeter ______ on adding fins hence the flow area _____
a) Increases, Decreases
b) Decreases, Increases
c) Increases, Increases
d) Decreases, Decreases

Explanation: Adding Fins to the surface, the interaction of the fluid with the wall increases, the wall now occupies a larger portion of the flow area hence its wetted perimeter increases with a decrease in flow area.

15. The Fanning friction factor ________ on adding Fins.
a) Increases
b) Decreases
c) Remains the same
d) Very large change beyond measure

Explanation: On adding Fins to the surface, the interaction of the fluid with the wall increases and hence the resistance to its flow increases. This implies that the flow now experiences greater hindrance hence it has greater friction factor.

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