Shell-and-tube exchangers: what is the primary purpose of straight tie rods installed through the baffle stack?

Introduction / Context:
In shell-and-tube heat exchangers, a series of transverse baffles guides shell-side flow across the tube bundle to enhance heat transfer and support the tubes. Straight tie rods run the length of the baffle stack, threading and clamping the baffles together in their designed sequence and spacing.

Given Data / Assumptions:

• Conventional TEMA-style exchanger with drilled baffles and tie rods.
• Tubes are fixed into tubesheets via rolling and/or welding (a separate function).
• Normal thermal expansion is accommodated by expansion joints or floating-head designs.

Concept / Approach:
Tie rods do not fix tubes to tubesheets or absorb shell expansion. Instead, they maintain the mechanical integrity of the baffle stack so that the intended flow pattern (crossflow, window flow) and tube support spacing are preserved during assembly, operation, and handling of the bundle.

Step-by-Step Solution:

Verification / Alternative check:
Standard exchanger drawings show multiple tie rods spaced circumferentially to balance loads; spacers or sleeves may be used to set exact gaps between baffles.

Why Other Options Are Wrong:

• Fixing tubes in position is the tubesheet’s job.
• Thermal expansion is handled by design features like floating heads or expansion joints.
• Changing fluid properties is unrelated to tie rods.

Common Pitfalls:
Insufficient tie-rod tension or number leading to baffle flutter; misalignment causing tube wear.

Final Answer:
Hold the baffles in position and maintain spacing