# Heat Transfer Operations Questions and Answers – Packed Beds – Bed Temperature Profiles

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This set of Tough Heat Transfer Operations Questions and Answers focuses on “Packed Beds – Bed Temperature Profiles”.

1. Which one of the following is the correct Temperature profile for a Packed Bed Heat transfer Equipment?
a)
b)
c)
d)

Explanation: The temperature profile is not completely Laminar but the packed bed offers a little less temperature gradient at the axis, hence the flat region.

2. Which one of the following setup would have the following Temperature Profile?

a) Shell and tube with hot fluid in shell and packed bed in tube
b) Shell and tube with cold fluid in shell and packed bed in tube
c) Shell and tube with hot fluid in tube and packed bed in shell
d) Shell and tube with cold fluid in tube and packed bed in shell

Explanation: The temperature profile is not completely Laminar but the packed bed offers a little less temperature gradient at the axis, hence the flat region. The temperature increases to maximum at the centre, hence the inner fluid is hot and shell fluid is cold.

3. The particles are usually _______ packed near the wall of the tube.
a) Tightly
b) Loosely
c) Very tightly
d) Negligibly

Explanation: Particles at the centre form hexagonal or octagonal close packed structure which sort of ends near the walls, hence they are loosely packed near the walls.
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4. What is the heat transfer area for the following setup?

a) 0.357m2
b) 0.4m2
c) 0.377m2
d) 0.3m2

Explanation: There are 4 tubes, hence the area is multiplied with 4. The single tube heat transfer area is, A = πDL = 3.14×0.03×1 = 0.0942. Hence the total Area = 4×0.0942 =0.377m2.

5. When is the following equipment used?

a) Exothermic Reaction
b) Endothermic Reaction
c) Heating operation
d) Cooling operation

Explanation: The operation shown in the figure has a tube passing through a shell with cold fluid but still the temperature of the fluid remains the same. This is possible only when the fluid we are considering undergoes an exothermic reaction.

6. Which one of the following is the correct velocity profile of a packed bed setup?
a)
b)
c)
d)

Explanation: The velocity profile is parabolic near the walls of the column because the packing is loose around this region and is somewhat flat or inverted parabolic at the centre. Hence the given figure is correct.

7. The presence of particles makes the inside heat transfer coefficient higher than empty tube because the superficial velocity is _______ the actual velocity.
a) Little higher than
b) Very higher than
c) Very less than
d) Little less than

Explanation: The Superficial velocity given by the relation Vs = ∅Va, where ∅ is the porosity, hence as ∅<<1, Vs>>Va.

8. The heat transfer coefficient ________ with increasing flow rate.
a) Increases
b) Decreases
c) Remains the same
d) Drops drastically

Explanation: As the heat transfer coefficient is hwall Dp/Kg=1.94 Re0.5 Pr0.33 and the Reynolds number is directly proportional to Vs, hence a power of 0.5 decreases h with increasing Re.

9. In the expression given below, what is the expression Di? This given ratio defines voidage which is controlled to obtain maximum heat transfer coefficient.
∈ = Dp/Di
a) Internal diameter of Pellets
b) Internal diameter of Tube
c) Internal diameter of Bed
d) Internal diameter of Pellets

Explanation: This ratio is used to signify the porosity of the bed without explicitly calculating the porosity. This ratio helps us to know the temperature profiles and guess the efficiency of the packed bed.

10. The value of dp/di in the range _______ gives maximum heat transfer coefficient.
a) 0.15-0.2
b) 2-3
c) 0.6-0.9
d) 0.001-0.002

Explanation: The value of dp/di in 0.15-0.2 or di/dp = 5-10 is best suited for heat transfer operations in the packed bed as this ratio perfectly fits the turbulence and mixing required.

11. For very low dp/di, the temperature pattern is similar to that of complete mixing and turbulent flow.
a) True
b) False

Explanation: When we have very low Dp/Di, which means the pellet size is very small, the flow becomes completely laminar inside the bed as the void spaces come very close to one another.

12. For very high dp/di, the mixing is very large and the heat transfer coefficient is ______
a) Low
b) Very low
c) High
d) Very high

Explanation: The heat transfer coefficient increases because there is now rapid mixing of the Fluid passing through the voids.

13. Which one is the correct temperature profile for high dp/di Packed bed setup?
a) Laminar temperature profile
b) Turbulent Temperature profile
c) Laminar near the walls and turbulent at the centre
d) Turbulent near the walls and laminar at the centre

Explanation: When we have a high Dp/Di, which means the pellet size is large, the flow becomes completely laminar near the walls and turbulent at the bed as the void spaces are more near the walls.

14. Which one is the correct temperature profile for very low dp/di packed bed setup?
a) Laminar temperature profile
b) Turbulent Temperature profile
c) Laminar near the walls and turbulent at the centre
d) Turbulent near the walls and laminar at the centre

Explanation: When we have very low Dp/Di, which means the pellet size is very small, the flow becomes completely laminar inside the bed as the void spaces come very close to one another.

15. The renowned equation used to calculate the pressure drop in a non-ideal packed bed is known as______________
a) Sieder Tate Equation
b) Kozeny Carman Equation
c) Ergun Equation
d) Arrhenius Equation

Explanation: The Ergun equation expresses the friction factor as the Reynolds number and is commonly used to calculate the pressure drop in packed beds having non laminar flow regime.

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