MDE 8 Q3

The correct answer is:

A) To release air or gas trapped inside the heat exchanger to prevent air locking

Explanation:

In a tube-type heat exchanger, a vent cock is used to release any air or gas that may become trapped inside the heat exchanger. Trapped air can cause air locking, which reduces the efficiency of heat transfer because air has a much lower thermal conductivity compared to liquids. By venting the air or gas, the vent cock ensures that the heat exchanger operates efficiently, allowing the fluid to flow freely through the tubes and improving overall heat transfer.

The other options are incorrect because:

• B) To control the flow rate of the cooling fluid through the tubes: This is typically done with valves or flow regulators, not a vent cock.
• C) To monitor the pressure inside the heat exchanger during operation: Pressure monitoring is done with gauges or sensors, not a vent cock.
• D) To drain the fluid from the heat exchanger during maintenance procedures: Draining is usually done through a drain valve, not a vent cock. The vent cock specifically addresses the removal of trapped air or gas.

B) To facilitate easy cleaning and maintenance of the heat exchanger

Explanation:

In a tube-type heat exchanger, a sliding tube plate allows for easier access to the tubes for cleaning and maintenance. The sliding feature enables the tube plate to move, which can help in removing the tube bundle for inspection or cleaning without having to dismantle the entire heat exchanger. This design improves the practicality of maintaining the heat exchanger and ensures that the system remains efficient over time.

The other options are incorrect because:

• A) To allow for thermal expansion and contraction of the tubes: While thermal expansion is a consideration in heat exchanger design, the sliding tube plate specifically aids in maintenance, not in managing thermal expansion.
• C) To support the tubes and prevent them from moving during operation: The primary function of the sliding tube plate is not to support the tubes but to facilitate maintenance. Tube support is generally handled by other components of the heat exchanger.
• D) To improve the heat transfer efficiency by increasing turbulence: The sliding tube plate does not affect the heat transfer efficiency or turbulence; its main role is to enable easier maintenance and cleaning.

B) To direct the flow of the fluid, increasing turbulence and improving heat transfer efficiency

Explanation:

In a tube-type heat exchanger, baffle plates are used to direct the flow of the fluid inside the shell side of the heat exchanger. They help create turbulence in the fluid flow, which enhances the heat transfer between the fluid and the tubes. By forcing the fluid to follow a specific path and making it flow across the tube bundle multiple times, baffle plates improve the heat exchanger's efficiency in transferring heat.

The other options are incorrect because:

• A) To support and stabilize the tubes within the heat exchanger: While tube support and stabilization are important, baffle plates primarily affect fluid flow and heat transfer rather than supporting the tubes.
• C) To reduce the overall size and weight of the heat exchanger: Baffle plates do not specifically aim to reduce the size or weight of the heat exchanger; their main role is to enhance heat transfer.
• D) To filter out impurities from the fluid passing through the heat exchanger: Baffle plates are not designed to filter impurities; their purpose is to improve the flow and heat transfer efficiency.

The correct answer is:

B) To protect the heat exchanger from corrosion by acting as a sacrificial material

Explanation:

In a tube-type heat exchanger, anodes (typically made of zinc, aluminum, or magnesium) are used as sacrificial materials to protect the heat exchanger from corrosion. These anodes are more reactive than the metal of the heat exchanger's components, so they corrode instead of the tubes or other parts. This process, known as cathodic protection, helps extend the lifespan of the heat exchanger by preventing the corrosive effects of the fluid passing through it.

The other options are incorrect because:

• A) To provide structural support to the tubes and prevent vibration: This is not the function of anodes; structural support is usually provided by baffle plates and other components.
• C) To improve the heat transfer efficiency by increasing surface area: Anodes do not enhance heat transfer efficiency; they are specifically for corrosion protection.
• D) To monitor the fluid temperature and adjust the flow rate accordingly: Temperature monitoring and flow rate adjustment are handled by sensors and control systems, not anodes.

The correct answer is:

B) To provide a visual indication of leakage between the shell and tube sides

Explanation:

In a tube-type heat exchanger, a tell-tale ring (or tell-tale hole) is used to provide an early warning of leaks between the shell side and the tube side of the heat exchanger. If there is a leak in one of the tubes or at the tube-to-tube sheet joint, the tell-tale ring allows any fluid that escapes to be visibly detected outside the heat exchanger, preventing cross-contamination between the fluids in the shell and tube sides. This early detection helps in maintaining the integrity of the heat exchanger and preventing more serious failures.

The other options are incorrect because:

• A) To indicate the position of the baffle plates within the heat exchanger: The tell-tale ring does not relate to the position of baffle plates; its function is to detect leaks.
• C) To ensure proper alignment of the tube bundle during assembly: The tell-tale ring is not used for alignment purposes; it is a leakage detection feature.
• D) To improve the flow of fluid through the heat exchanger and enhance heat transfer: The tell-tale ring does not affect fluid flow or heat transfer; its role is to provide a visual indication of leaks.