Shell-and-tube hydraulics — In a heat exchanger, which design choices can be used to change the shell-side fluid velocity (at fixed flow rate)?

Introduction:
Shell-side performance depends on crossflow area, baffle configuration, and tube bundle geometry. Designers often tune shell-side velocity to improve heat-transfer coefficients while controlling pressure drop and fouling.

Given Data / Assumptions:

• Fixed shell-side volumetric flow rate.
• Conventional single-segmental baffles (concept applies more generally).
• Changes are made to tube arrangement parameters.

Concept / Approach:
Shell-side velocity is approximately flow rate divided by crossflow area. Tube layout (triangular vs. square) and tube pitch set the ligament spacing and thus the window and crossflow areas. Tighter pitches and triangular layouts reduce crossflow area and increase velocity (and heat transfer), but also raise pressure drop and potential vibration risk.

Step-by-Step Solution:
Recognise that geometry defines crossflow area.Changing tube pitch alters spacing → changes velocity.Changing layout (triangular vs square) alters flow path porosity and crossflow area → changes velocity.

Verification / Alternative check:
Comparative ratings show triangular pitch typically yields higher shell-side h and higher ΔP than square pitch at the same flow, consistent with higher velocity.

Why Other Options Are Wrong:

• (a) alone or (b) alone are incomplete; both knobs are effective.
• (d) incorrect because geometry strongly influences shell-side hydraulics.

Common Pitfalls:
Ignoring baffle cut and spacing, which also significantly impact velocity; overlooking vibration limits and erosion in services with solids.

Final Answer:
both (a) & (b)