Evaporators — Liquid entrainment (carry-over of droplets) from an evaporator most commonly results from which condition?

Introduction:
Entrainment refers to liquid droplets being carried over with the vapor leaving an evaporator. This is undesirable because it contaminates condensate, causes product losses, and can foul downstream equipment. Understanding root causes enables better mechanical separation and operational control.

Given Data / Assumptions:

• Boiling pool or film with rising vapor flow.
• Some solutions (e.g., detergents, sugars, proteins) tend to foam.
• Mechanical separators may or may not be present.

Concept / Approach:

Foaming forms stable bubbles with liquid films that can burst and project droplets upward or be swept out intact. This dramatically increases entrainment compared to non-foaming liquors at the same boil-up rate. While high throughputs can aggravate entrainment, foaming is the primary, characteristic cause across many services.

Step-by-Step Solution:

Verification / Alternative check:

Plant experience uses antifoam agents, proper disengagement height, and demisters specifically to combat entrainment caused by foaming feeds.

Why Other Options Are Wrong:

A: High vacuum alone does not cause entrainment; it may even reduce boil-up temperature. B and D: High rates can contribute but are not the primary, characteristic cause compared to foaming. E: Demisters reduce, not cause, entrainment.

Common Pitfalls:

Confusing vapor load effects with foam stability; both matter, but foaming is the hallmark driver.

Final Answer:

foaming of the solution