Routing high-pressure fluids in shell-and-tube exchangers: For mechanical integrity and economy, where should the higher-pressure stream be placed?

Introduction / Context:
Mechanical design strongly influences exchanger cost. The placement of the higher-pressure fluid determines required wall thicknesses, gasket stresses, and fabrication complexity. Choosing the tube side for high pressure is a common and economical practice.

Given Data / Assumptions:

• Conventional fixed or floating head shell-and-tube exchanger.
• One stream has significantly higher design pressure.
• Materials and fouling tendencies do not mandate the opposite routing.

Concept / Approach:
The tube side consists of many small-diameter tubes with relatively thick walls that can withstand high internal pressures with modest metal thickness. By contrast, designing a large-diameter shell for high pressure demands very thick walls, heavier flanges, and more expensive fabrication. Therefore, routing the high-pressure stream through the tubes reduces cost and weight.

Step-by-Step Solution:

Verification / Alternative check:
Mechanical design equations show required thickness increases roughly with diameter for a given pressure; hence smaller tubes are favorable.

Why Other Options Are Wrong:

• Shell side for pressure drop or heat transfer: routing is not primarily decided by pressure drop or U-values.
• Counter-current/co-current rule: flow arrangement is a thermal consideration, not a pressure containment rule.

Common Pitfalls:
Ignoring fouling/viscosity that might force the viscous fluid to the shell side; forgetting tube-side velocity limits for erosion or vibration.

Final Answer:
Tube side, to avoid heavy high-pressure shell construction