Horizontal-tube evaporator design: identify the incorrect statement about flow arrangement, suitability, and common dimensions.

Introduction / Context:
Horizontal-tube evaporators circulate process liquor through banks of horizontal tubes while steam condenses on the opposite side. These units are common for moderate-viscosity solutions but have limitations with heavily scaling or crystallizing duties. Understanding correct flow descriptions and typical dimensions helps in screening their applicability.

Given Data / Assumptions:

• Conventional horizontal-tube, shell-and-tube style natural-circulation evaporator.
• Liquor is on one side; condensing heating steam is on the other.
• We evaluate correctness of statements concerning suitability and geometry.

Concept / Approach:
In standard practice, liquor flows inside the tubes and steam condenses on the shell side. However, describing steam as “submerging the tubes” is inaccurate. Steam does not submerge tubes; rather, the tubes may be immersed in the liquor or accommodated by baffles, and steam condenses on the tube exterior with condensate drainage. The misstatement suggests steam immersion like a liquid bath, which is not how condensing steam is typically depicted or controlled.

Step-by-Step Reasoning:

Verification / Alternative check:
Evaporator manuals describe steam condensing on the shell side with condensate removal via traps; any “submergence” discussion typically refers to liquor level, not steam immersion.

Why Other Options Are Wrong (or Right):

• (a), (b), and (c) are consistent with standard design guidelines.
• (e) is a reasonable caution; maldistribution can occur on long tube passes.

Common Pitfalls:
Confusing the roles of steam and liquor, and assuming highly scaling slurries are acceptable without specialized designs (e.g., forced circulation or falling film).

Final Answer:
Process liquor flows inside the tubes while steam outside “submerges the tubes”