Shell-and-tube heat exchangers: what is the recommended minimum baffle spacing relative to shell inside diameter (Ds)?

Introduction / Context:
Baffles in shell-and-tube exchangers control crossflow and support tubes. Baffle spacing strongly affects shell-side pressure drop, heat-transfer coefficient, vibration risk, and mechanical support. A practical lower bound prevents excessive pressure drop and flow maldistribution.

Given Data / Assumptions:

• Single-phase shell-side service with conventional segmental baffles.
• Standard TEMA construction and allowable pressure-drop guidelines.
• Goal: avoid vibration and keep reasonable pressure drop while maintaining heat transfer.

Concept / Approach:
Too small a baffle spacing increases the number of crossflow windows, driving up pressure drop and potential erosion while offering diminishing returns on heat transfer. Too large a spacing lowers heat transfer and can permit flow-induced vibration. A widely used rule of thumb sets minimum baffle spacing at about 0.4 * Ds (often bounded also by an absolute minimum such as 50 mm).

Step-by-Step Solution:
Normalize spacing to shell ID: S_min ≈ 0.4 * Ds.Check pressure-drop and vibration constraints; increase spacing if pressure drop is too high, decrease if heat transfer is insufficient within mechanical limits.Confirm against project specs or TEMA-derived practices.

Verification / Alternative check:
Thermal rating tools show steep pressure-drop penalties as spacing drops below ~0.4 Ds, with modest gains in h, supporting the rule.

Why Other Options Are Wrong:
(a) and (c) are fixed values and not scalable; (d) is excessively large and defeats baffling purpose; (e) would cause extreme pressure drops and risk tube damage.

Common Pitfalls:
Ignoring two-phase shell-side behavior; misapplying the rule to helical or no-tubes-in-window designs; neglecting tube support criteria in vibration-sensitive services.

Final Answer:
Approximately 40% of the shell inside diameter