In shell-and-tube heat exchangers, the thickness of typical segmental baffles (with about 25–35% cut) is generally selected to be __________ the tube wall thickness to ensure rigidity and support.

Introduction / Context:
Baffles in shell-and-tube exchangers serve multiple roles: they direct shell-side flow, enhance turbulence, and support tubes against vibration. Selecting an appropriate baffle thickness avoids warping and fretting.

Given Data / Assumptions:

• Segmental baffles with about 25–35% cut are considered.
• We compare baffle plate thickness to typical tube wall thickness.
• Mechanical integrity and manufacturability guide thickness choice.

Concept / Approach:
Baffle plates must resist flow-induced vibration and maintain geometry under differential pressure. In practice, baffles are commonly thicker than individual tube walls to provide sufficient rigidity and to securely locate tubes with drilled holes. A practical rule is choosing baffle thickness on the order of about two times the tube wall thickness for many standard designs, subject to shell diameter and span.

Step-by-Step Solution:
Step 1: Recognize that tube walls are relatively thin (for thermal performance), while baffles must be stiffer structural elements.Step 2: Adopt a conservative sizing rule: baffle thickness ≈ 2 * tube wall thickness.Step 3: Select the corresponding option.

Verification / Alternative check:
Vendor standards often specify minimum baffle thickness increasing with shell diameter; in many cases these thicknesses exceed tube wall thickness by a factor near 2 or more, consistent with the heuristic.

Why Other Options Are Wrong:
Equal to/Half/One-third: Risk inadequate stiffness and increased vibration wear.Four times: Can be overly conservative, increasing weight and cost without proportional benefit in many standard sizes.

Common Pitfalls:
Ignoring shell diameter and baffle spacing effects; larger shells or wider spans may require thicker baffles than the simple rule.

Final Answer:
twice