Shell-and-tube heat exchanger practice: which routing rule below is WRONG? (Assume comparable duties and materials; decide where to place each stream for safe, efficient operation.)

Introduction / Context:
In chemical process design, choosing which stream goes tube-side versus shell-side in a shell-and-tube heat exchanger has big implications for safety, operability, and lifecycle cost. Rules of thumb help engineers make sound decisions quickly. This question asks you to identify the incorrect (WRONG) routing rule from commonly accepted practice.

Given Data / Assumptions:

• Conventional shell-and-tube exchanger with removable tube bundle possible.
• Comparable allowable velocities and heat transfer coefficients assumed unless noted.
• Goal is safe containment of hazards and reasonable pressure drop.

Concept / Approach:
Typical heuristics are: (1) Corrosive or fouling streams go tube-side so tubes can be cleaned/replaced and to minimize expensive corrosion allowances in large shells. (2) Highly viscous streams often go shell-side because the shell side can accommodate higher crossflow areas and different baffle arrangements to reduce pressure drop and improve heat transfer. (3) Very high-pressure streams nearly always go tube-side: small-diameter tubes withstand high pressures with thinner walls and provide safer containment than a big shell.

Step-by-Step Solution:
Evaluate (a): Corrosive/fouling → tube-side for maintainability and containment — this is correct.Evaluate (b): Viscous → shell-side to lower pressure drop and improve crossflow — this is correct.Evaluate (c): Lower flow rate → often tube-side to maintain velocity and heat transfer; routing it shell-side risks too low velocity — statement as written is dubious, but not as definitively unsafe as (d).Evaluate (d): High-pressure stream → should be tube-side, not shell-side — this statement is WRONG.

Verification / Alternative check:
Design texts and vendor guides emphasize placing the high-pressure or hazardous fluid inside tubes to reduce inventory and wall thickness for a given design pressure, improving both safety and economy.

Why Other Options Are Wrong (or Right):
(a) Right: aligns with maintenance and corrosion strategies.(b) Right: shell-side suits viscous service with proper baffles.(c) Often considered less preferred; many designers route low-flow stream tube-side to preserve velocity, but it is not as categorically incorrect as (d).

Common Pitfalls:
Assuming pressure routing is arbitrary; underestimating how tube diameter dominates pressure design; ignoring cleanability of corrosive services.

Final Answer:
Higher pressure fluid stream should be routed through the shell side.