Shell-and-tube design practice: baffle spacing is generally constrained how, relative to the shell inside diameter (Ds)?

Introduction / Context:
Baffle spacing determines shell-side pressure drop, heat transfer, vibration risk, and tube support. Designers apply practical bounds tied to shell size to avoid extreme pressure drop or poor heat transfer.

Given Data / Assumptions:

• Conventional segmental baffles; single-phase shell-side service.
• Standard TEMA-style exchanger with typical materials.
• Goal is a reliable, economical design envelope.

Concept / Approach:
Very small spacing yields high pressure drop and potential erosion; very large spacing reduces crossflow and support, risking vibration. Rules of thumb keep baffle pitch S between roughly 0.2 * Ds and 1.0 * Ds. Thus, S is not greater than Ds and not less than about one-fifth of Ds.

Step-by-Step Solution:
Apply lower bound: S ≥ 0.2 * Ds for reasonable pressure drop and support.Apply upper bound: S ≤ 1.0 * Ds to maintain crossflow and tube support.Combine: S meets both constraints—answer is both (b) and (c).

Verification / Alternative check:
Thermal rating software trends and vendor datasheets reinforce these empirical limits for most duties; exceptions exist for special baffle types (e.g., helical baffles).

Why Other Options Are Wrong:
(a) exceeds the common upper bound; (e) is too small, giving excessive pressure drop and vibration risk.

Common Pitfalls:
Ignoring two-phase flow effects; using the same spacing for very large shells without vibration checks; overlooking nozzle interference with baffle cut.

Final Answer:
Both (b) and (c)