Shell-and-tube heat exchangers: to accommodate differential thermal expansion between shell and tube passes in a multipass design, which construction is commonly used?

Introduction / Context:
Thermal expansion can differ significantly between the shell side and tube side of a shell-and-tube heat exchanger, particularly in multipass arrangements where tubes can be long and temperature gradients large. Proper mechanical design must allow relative movement so that tubes are not overstressed, tubesheets are not distorted, and leakage does not occur at joints.

Given Data / Assumptions:

• Multipass shell-and-tube exchanger operating with appreciable temperature difference between fluids.
• Normal industrial construction standards (e.g., TEMA-style components).
• Goal is to mitigate differential thermal expansion stresses.

Concept / Approach:
Two classic construction choices address expansion: (1) U-tube bundles, in which each tube is bent into a U-shape so free expansion occurs without stressing a fixed second tubesheet; and (2) floating-head designs, where one tubesheet is allowed to “float” axially within the shell to relieve expansion, while the other end is fixed. Both achieve the same objective using different mechanical means and are widely specified depending on service, cleanability, and cost considerations.

Step-by-Step Solution:

Verification / Alternative check:
Equipment catalogs and design handbooks list U-tube (TEMA K-type) and floating-head (TEMA P, S, T) as standard expansion accommodations for large temperature differences.

Why Other Options Are Wrong:

• “Neither” ignores well-established designs.
• Shell bellows are sometimes used for small shells but are not a universal substitute across baffle windows.

Common Pitfalls:
Choosing U-tubes where mechanical cleaning of the bend side is required; ignoring bundle removal and gasket selection for floating heads.

Final Answer:
Either (a) or (b)