Random packings — A Lessing ring is created by adding a transverse partition across the centre of a Raschig ring. Approximately how much does this modification increase the available surface area (relative to the original ring)?

Introduction:
Random tower packings such as Raschig, Lessing, Berl saddles, and Pall rings aim to maximise surface area and wetting while limiting pressure drop. Understanding how design changes affect area helps predict mass-transfer performance.

Given Data / Assumptions:

• Raschig ring: simple hollow cylinder.
• Lessing ring: Raschig ring with an internal partition (web) across the diameter.
• Question asks for approximate percentage area increase.

Concept / Approach:
The partition increases internal surface exposure and improves liquid redistribution and gas–liquid contact. Typical data show a moderate area increase—significant but not extreme—on the order of a few tens of percent relative to the original Raschig ring.

Step-by-Step Solution:
Compare geometries: added web introduces two extra faces and breaks channeling.Industry references report area gains around one-third for Lessing vs. Raschig of similar size.Therefore, select ≈35% as a representative increase.

Verification / Alternative check:
Comparative performance charts list Lessing rings with improved HETP and a moderate area increase over Raschig rings, consistent with ≈35% augmentation.

Why Other Options Are Wrong:

• 5%: too small to justify design change.
• 20%: low relative to common references.
• 55%: too high for a single web; larger jumps occur with Pall rings (windows and tabs) rather than a single partition.

Common Pitfalls:
Confusing Lessing rings with Pall rings or saddle packings which can have much larger effective area gains.

Final Answer:
35 %