Agitated tanks and baffles: under which condition is it acceptable to eliminate baffles because swirling is naturally suppressed by fluid properties?

Introduction / Context:
Baffles prevent vortex formation and tangential swirling in mechanically agitated tanks. However, the need for baffles depends on fluid rheology and operating conditions. Very viscous liquids exhibit such high damping that swirling is minimal even without baffles.

Given Data / Assumptions:

• Newtonian liquids unless otherwise noted.
• Standard radial or axial-flow impellers.
• Goal is to identify the regime where baffles can be omitted without compromising mixing objectives.

Concept / Approach:
At high viscosity, Reynolds number is very low; flow is laminar and dominated by viscous forces. Tangential circulation is weak and a stable free-surface vortex does not form easily. Designers commonly eliminate baffles above a high-viscosity threshold to reduce fabrication complexity and cleaning issues.

Step-by-Step Solution:
Relate need for baffles to Reynolds number and vortex tendency.Note that for μ ≳ 600 poise, viscous damping is so strong that baffles are unnecessary in most cases.Select the high-viscosity option.

Verification / Alternative check:
Mixing handbooks list rules of thumb: install baffles for low–moderate viscosities; omit for very high viscosities where laminar impellers (helical ribbon, anchor) are used.

Why Other Options Are Wrong:
Low viscosity: Needs baffles to prevent vortexing.Large diameter tanks: Size alone does not eliminate swirling; baffles are still beneficial.None of these: Incorrect because high viscosity is a valid case.

Common Pitfalls:
Ignoring non-Newtonian behavior; assuming high viscosity always guarantees mixing quality (power and impeller selection still matter).

Final Answer:
high viscosity liquids (> 600 poise).