This set of Heat Transfer Operations Multiple Choice Questions & Answers (MCQs) focuses on “Extended Surface Heat Exchangers – Construction and Operation “.
1. 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
View Answer
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.
2. For using fins, the heat flow is assumed to be in _______
a) Exponentially increasing
b) Unsteady State
c) Linearly decreasing
d) Steady State
View Answer
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.
3. The fin material should be homogeneous and _________ for steady state operation.
a) Isotropic
b) Isentropic
c) Isochoric
d) Isobaric
View Answer
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.
4. The thermal conductivity of the fin should _________ with time.
a) Exponentially increasing
b) Increasing
c) Decreasing
d) Constant
View Answer
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 thermal conductivity of the fin material should stay constant. If it changes with time, then the heat transfer rate will also be affected by this change.
5. The Heat Transfer Coefficient remains constant throughout the surface of the fin.
a) True
b) False
View Answer
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 heat transfer coefficient should stay constant. If it changes with time, then the heat transfer rate will also be affected by this change.
6. Which one of the following is correct about the temperature of the fluid in contact with the fins?
a) Is at a constant temperature
b) Temperature increases along the fin length
c) Temperature decreases along the fin length
d) Depends on flow pattern
View Answer
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. As a consequence of this, the temperature of the fluid in contact with the fins should be at a constant temperature.
7. What is the correct values of X and Y in the following diagram?
H = Total heat transferred
a) X = H, Y = 0
b) X = 0, Y = H
c) X = H/2, Y = H/2
d) X = H/L, Y = H – H/L
View Answer
Explanation: It is assumed that the heat transferred across the width of the fin is negligible because of the large length of the fin which absorbs all the heat.
8. By increasing the fin density, the heat transfer coefficient associated with fins__________
a) Decreases
b) Increases
c) Remains the same
d) Increases tenfold
View Answer
Explanation: There is a limit to which we can apply fins to a surface, if the fin density crosses this threshold value, the heat transfer coefficients decreases as the liquid fails to make proper contact with the provided surface.
9. What is the flow area in the following diagram?
Inner Tube Diameter = 20mm
Outer Tube Diameter = 40mm
Fin width = 5mm
a) 743.5 sq mm
b) 740.5 sq mm
c) 742.5 sq mm
d) 741.5 sq mm
View Answer
Explanation: We have Total Area, A = π/4 (402 – 202) – 5×10×4 = 742.5 sq mm.
10. Adding fins inside the tube, that is for the tube side usually ________ the heat transfer coefficient.
a) Decreases
b) Increases
c) Tenfold
d) Does not change
View Answer
Explanation: Usually the tube side contains the cooling liquid and the heat transfer coefficient is already high there, hence adding extra heat transfer area will not be of any help rather would decrease flow rate and eventually decrease the heat transfer coefficient.
11. Which type of fin is not used in Plate-Fin Heat exchangers?
a) Louver
b) Triangular or corrugated
c) Wavy
d) Longitudinal
View Answer
Explanation: Usually the fins used for Plate Fin heat exchangers are Wavy, Louver and corrugated Fins. Longitudinal fins are not used for plate fins rather for it, needle fins are used if the above three are not available.
12. Recognize the equipment for the following fin.
a) Shell and Tube
b) Tube Fin
c) Double Pipe
d) Plate Fin
View Answer
Explanation: Usually the fins used for Plate Fin heat exchangers are Wavy, Louver and corrugated Fins. The diagram shown above is that of a Corrugated Fin.
13. Tube Fin HE can be classified to two categories which are Conventional and Specialised Tube Fins HE.
a) True
b) False
View Answer
Explanation: The statement is true because in tube fin HE, there are two possible arrangement, one is conventional where we keep the fins at the gas side and other specialised here we decide fins on the side which has lesser HT coefficient.
14. In Conventional Tube Fin HE, the fins are used on the _________ side.
a) Shell side
b) Tube side
c) Gas Side
d) Liquid side
View Answer
Explanation: In Conventional Tube Fin HE, we decide to keep the fins on the gas side. The gas to be kept is decided by the designer, which maybe the tube side or the shell side.
15. Tube fin heat exchangers can withstand high pressure drop ________
a) On the tube side
b) On the shell side
c) On the side which has fins attached
d) On the opposite side of the fins
View Answer
Explanation: The fins welded to the surface of the tube makes them mechanically very strong and capable to handle very high pressure drops on the tube side. We still should avoid pressure drops at the shell side as this may damage the fins.
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