Packed tower efficiency: which packing shape generally provides the highest mass-transfer performance among the choices given?

Introduction / Context:
Random packings provide interfacial area and promote contact between gas and liquid in absorption, stripping, and distillation operations. Their geometry affects surface area per volume, wetting characteristics, pressure drop, and mass-transfer coefficients. Comparing classic shapes helps understand performance trends.

Given Data / Assumptions:

• Random packings of similar nominal size under comparable service conditions.
• Focus on classic ceramic/metal forms: Raschig, Lessing, and cross-partition rings.
• Performance judged by effective interfacial area and mass-transfer rate at similar pressure drop.

Concept / Approach:
Raschig rings are simple cylinders; they offer moderate area but can suffer from channeling. Lessing rings introduce internal partitions and improved geometry to increase surface area and liquid redistribution, thereby increasing effective area and mass transfer. Cross-partition rings improve over plain Raschig rings but typically provide less performance than well-designed Lessing rings of the same size.

Step-by-Step Solution:

Verification / Alternative check:
Empirical tower tests often show capacity-efficiency curves where Lessing rings outperform Raschig rings of equal size, with cross-partition rings in between.

Why Other Options Are Wrong:

• Raschig rings: baseline geometry, generally lower a_eff.
• Cross-partition rings: improved but typically not as high-performing as Lessing rings.
• “All the same” is incorrect; geometry matters markedly.

Common Pitfalls:
Ignoring material/size effects; comparing at different pressure drops; not accounting for fouling or liquid distribution quality in real columns.

Final Answer:
Lessing rings