1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6.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.
7. 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.
8. In assumption for using fins, the heat flow and temperature distribution throughout the fins is _______ time.
a) Directly Proportional to
b) Independent of
c) Inversely Proportional to
d) Square proportional to
Explanation: When we are required to use fins, for steady state operation and calculations to be correct we assume that the heat flow and temperature distribution is independent of time, that is it should not change with time else the equations derived would be invalid.
9. For using fins, the heat flow is assumed to be in _______
a) Exponentially increasing
b) Unsteady State
c) Linearly decreasing
d) Steady State
Explanation: The first and the prime assumption we make while deriving equations for Fins is that we assume the heat flow to be in steady state.
10. The fin material should be homogeneous and _________ for steady state operation.
a) Isotropic
b) Isentropic
c) Isochoric
d) Isobaric
Explanation: The first and the prime assumption we make while deriving equations for Fins is that we assume the heat flow to be in steady state. For the heat flow to be in steady state, the material of the fin should be isotropic, which means its properties should be the same when measured in any direction.