Shell-and-tube heat exchanger design: For a shell inside diameter D, what is the usual range of baffle spacing selected by designers (include the standard minimum spacing in millimetres/inches and the common upper bound as a fraction of D)?

Introduction / Context:
Proper selection of baffle spacing in a shell-and-tube heat exchanger controls shell-side heat transfer, pressure drop, vibration risk, and flow-induced tube erosion. Designers typically tie baffle spacing to the shell inside diameter (D) and enforce a practical minimum distance to accommodate construction and cleaning.

Given Data / Assumptions:

• Baffles are single- or double-segmental on the shell side.
• Inside shell diameter is D.
• Common industry rules-of-thumb are used for initial sizing before detailed rating.
• A practical minimum spacing (often near 2 inches ≈ 50 mm) is observed for fabrication and bundle robustness.

Concept / Approach:
Baffle spacing governs crossflow velocity and hence the shell-side heat transfer coefficient and pressure drop. Too small a spacing increases pressure drop and vibration risk; too large a spacing reduces crossflow, lowering heat transfer and allowing flow maldistribution. A widely used preliminary range is from about D/5 up to about D, with a hard floor around 2 inches.

Step-by-Step Solution:

Verification / Alternative check:
Preliminary TEMA-style guidance and vendor practices consistently recommend a first-cut spacing between 0.2D and 1.0D, subject to vibration checks and allowable pressure drop limits.

Why Other Options Are Wrong:

• D/2 or minimum 2″ to 5D: the 5D upper bound is excessively large and not standard.
• D/5 or minimum 2″ to 5D: again, the 5D limit is not typical.
• None of these: incorrect because D/5 or minimum 2″ to D is the accepted range.

Common Pitfalls:
Using very tight spacing that creates high pressure drop; ignoring tube vibration checks at high crossflow velocity; failing to consider cleaning requirements for fouling services.

Final Answer:
D/5 or minimum 2″ to D