Distillation hydraulics: which factors primarily determine vapor entrainment from one tray to the next in a column?

Introduction / Context:
Entrainment in tray columns occurs when vapor carries liquid droplets upward to the tray above. Excessive entrainment reduces efficiency, causes contamination between sections, and increases pressure drop. Designers must control operating conditions and geometry that influence entrainment.

Given Data / Assumptions:

• A tray (sieve/valve/cap) distillation column in steady operation.
• Standard hydrocarbon or similar system without unusual foaming tendency.
• Focus on mechanical/operating variables affecting entrainment.

Concept / Approach:
Three parameters dominate entrainment. Larger plate spacing gives more disengagement height, reducing droplet carryover. Greater liquid depth (froth height) tends to increase liquid holdup and the chance for droplet formation and carryover. Higher vapor velocity increases shear at the gas–liquid interface and droplet acceleration, amplifying entrainment. Hence all listed factors are relevant together.

Step-by-Step Solution:

Verification / Alternative check:
Empirical entrainment correlations and vendor guidelines relate entrainment to F-factor (velocity–density measure), froth height, and tray spacing, confirming multi-factor control.

Why Other Options Are Wrong:

• Any single-factor answer is incomplete; entrainment is multivariate.
• “None of these” contradicts well-established tray hydraulics.

Common Pitfalls:
Operating too close to flooding; ignoring foaming tendency; using insufficient spacing that prevents disengagement.

Final Answer:
All (a), (b) and (c).