Shell-and-tube heat exchanger internals: the center-to-center spacing between successive baffles is called the baffle pitch (baffle spacing). Which of the following is NOT a function of baffles?

Introduction / Context:
Baffles are key internals in shell-and-tube heat exchangers. Their geometry and spacing (baffle pitch) strongly influence shell-side flow pattern, pressure drop, heat transfer, and mechanical stability. Knowing what baffles do—and do not do—prevents design misunderstandings.

Given Data / Assumptions:

• Baffles mounted on the shell side (segmental, double-segmental, or various designs).
• Tube bundle supported by baffles and tie rods.
• Tube-side flow is confined within tubes and unaffected directly by baffles.

Concept / Approach:
Baffles primarily act on the shell-side fluid: they create crossflow over tubes, increase shell-side turbulence and heat-transfer coefficient, control leakage and bypass streams, and support the tubes to mitigate vibration. They do not act directly on the tube-side flow; tube-side coefficients are governed by tube flow velocity, tube roughness, and fluid properties, not by shell baffles.

Step-by-Step Solution:

Verification / Alternative check:
TEMA and exchanger design references list baffle objectives specifically for shell-side performance and structural support.

Why Other Options Are Wrong:

• Residence time increase on shell side: a consequence of longer flow path via crossflow/zig-zag.
• Support to tube bundle: a primary mechanical function.
• Vibration reduction: achieved by limiting tube unsupported span and altering flow-induced excitation.
• Directing crossflow on shell side: central to enhancing shell-side heat transfer.

Common Pitfalls:
Assuming baffles affect tube-side performance; overlooking pressure-drop penalties from too-tight baffle spacing.

Final Answer:
To increase the tube-side heat-transfer coefficient by inducing turbulence