Question 1

In a shell and tube heat exchanger, which side is generally preferred for the fluid with the higher pressure?

Accepted Answer

The tube side is generally preferred for the fluid with the higher pressure.

Question 2

According to TEMA standards, what is a typical fouling factor (in $hr \cdot ft^2 \cdot ^\circ F/Btu$) for cooling tower treated water?

Accepted Answer

A typical fouling factor for cooling tower treated water is 0.001 $hr \cdot ft^2 \cdot ^\circ F/Btu$.

Question 3

In shell and tube exchanger design, why is the more viscous fluid typically allocated to the shell side?

Accepted Answer

The more viscous fluid is typically placed on the shell side to induce turbulence and improve the heat transfer coefficient.

Question 4

What is the rule of thumb for the overall heat transfer coefficient ($U$) in $W/(m^2 \cdot K)$ for a water-to-water heat exchanger?

Accepted Answer

The typical overall heat transfer coefficient ($U$) for a water-to-water exchanger is in the range of 1500-2500 $W/(m^2 \cdot K)$.

Question 5

A fluid that is highly corrosive or prone to fouling is typically placed on the _____ side of a shell and tube heat exchanger for easier cleaning.

Accepted Answer

tube

Question 6

In a shell and tube exchanger, why are services with small flow rates often placed on the shell side?

Accepted Answer

Placing a small flow rate on the shell side allows for a lower baffle spacing, which helps maintain velocity and improve the heat transfer coefficient.

Question 7

What is the typical range for the overall heat transfer coefficient ($U$) in $Btu/(hr \cdot ft^2 \cdot ^\circ F)$ for an exchanger cooling a light organic liquid with water?

Accepted Answer

The typical range for a light organic-to-water exchanger is 50-150 $Btu/(hr \cdot ft^2 \cdot ^\circ F)$.

Question 8

When is a floating-head type shell and tube exchanger (TEMA 'S' or 'T' type) preferred over a fixed-tubesheet type (TEMA 'L', 'M', or 'N' type)?

Accepted Answer

A floating-head type is preferred when there is a large differential thermal expansion between the shell and tubes that cannot be accommodated by an expansion joint.

Question 9

What is the primary purpose of baffles on the shell side of a shell and tube heat exchanger?

Accepted Answer

Baffles support the tubes and direct the shell-side fluid flow across the tube bundle to increase turbulence and the heat transfer coefficient.

Question 10

What is a major disadvantage of using finned tubes on the shell side of an exchanger?

Accepted Answer

Finned tubes on the shell side are much more difficult to clean mechanically than bare tubes.

Question 11

In heat exchanger design, what is the term for the deposition of undesirable material on heat transfer surfaces that adds thermal resistance?

Accepted Answer

The term is fouling, and its thermal resistance is quantified by the fouling factor.

Question 12

What is a key advantage of a U-tube heat exchanger design?

Accepted Answer

The U-tube bundle is free to expand and contract within the shell, accommodating differential thermal expansion, and the bundle can be removed for cleaning.

Question 13

In a shell-and-tube exchanger, what type of tube pitch arrangement (square or triangular) allows for easier external mechanical cleaning?

Accepted Answer

A square pitch arrangement allows for easier mechanical cleaning of the outside of the tubes.

Question 14

What is a common rule of thumb for the minimum temperature approach in a shell and tube heat exchanger design?

Accepted Answer

A minimum temperature approach of 5-10°C is a common rule of thumb, depending on the service and economics.

Question 15

A 'kettle type' reboiler is characterized by a large shell diameter relative to the tube bundle in order to provide a large _____.

Accepted Answer

vapor disengagement space

Question 16

What is a 'thermosyphon reboiler'?

Accepted Answer

A thermosyphon reboiler is a type of heat exchanger where fluid circulation is driven by the density difference between the hot two-phase mixture leaving the reboiler and the cooler liquid from the column bottom.

Question 17

What is the primary risk of having excessive superheat in the steam used as a heating medium in a reboiler?

Accepted Answer

Excessive superheat can lead to a significant reduction in the heat transfer coefficient (desuperheating is less efficient than condensing) and can cause localized overheating or fouling.

Question 18

What does a TEMA 'E' type shell signify in a shell and tube heat exchanger?

Accepted Answer

A TEMA 'E' type shell signifies a single-pass shell, the most common type.

Question 19

What does a TEMA 'J' type shell, with its divided flow, help to reduce?

Accepted Answer

A TEMA 'J' type shell helps to reduce the shell-side pressure drop for a given flow rate.

Question 20

In a shell-and-tube exchanger, why might a double-pipe (hairpin) exchanger be preferred over a multi-tube shell-and-tube unit?

Accepted Answer

A double-pipe exchanger is often more economical for small duties requiring low heat transfer area and can handle high pressures and large temperature differences effectively.

Question 21

What is the primary function of an expansion joint in a fixed tubesheet heat exchanger?

Accepted Answer

An expansion joint accommodates the differential thermal expansion between the shell and the tubes, preventing high mechanical stresses.

Question 22

What is the main advantage of a plate-and-frame heat exchanger over a shell-and-tube type for the same duty?

Accepted Answer

Plate-and-frame exchangers are more compact, have higher thermal efficiency (higher U values), and allow for easier modification of heat transfer area.

Question 23

What is a major limitation of plate-and-frame heat exchangers?

Accepted Answer

They are generally limited to lower pressures and temperatures compared to shell-and-tube exchangers, and the gaskets can be a point of failure and incompatibility with certain fluids.

Question 24

For services requiring frequent cleaning, like in food processing, which type of heat exchanger is generally preferred?

Accepted Answer

A plate-and-frame heat exchanger is generally preferred as it can be easily disassembled for cleaning and inspection.

Question 25

In the context of fluid allocation, what type of fluid is a good candidate for the shell side to take advantage of crossflow?

Accepted Answer

Gases or fluids with low heat transfer coefficients are good candidates for the shell side to benefit from the higher turbulence and improved heat transfer induced by crossflow over the baffles.

Question 26

In a shell and tube exchanger, what is 'impingement protection' and when is it required?

Accepted Answer

Impingement protection, typically a plate placed under the shell inlet nozzle, is required to prevent erosion or vibration damage to the tubes caused by high-velocity incoming fluid.

Question 27

What is the 'LMTD correction factor' (Ft) used for in heat exchanger calculations?

Accepted Answer

The LMTD correction factor is used to adjust the Log Mean Temperature Difference for multi-pass or cross-flow exchangers to account for the deviation from true counter-current or co-current flow.

Question 28

Why must the piping for a thermosyphon reboiler return line avoid inclined runs?

Accepted Answer

Inclined piping must be avoided for two-phase flow in reboiler returns to prevent flow stratification and slugging, which can cause instability and operational problems.

Shell and Tube Heat Exchangers

Overview of Shell and Tube Heat Exchangers

Fluid Allocation Strategies

TEMA Classifications and Configurations

Performance Rules of Thumb

Challenges and Mitigations

Recommended Flashcards

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Process Safety Analysis-HAZOP LOPA

Pressure Relieving Systems (PSV)