Agitation and baffling: angled baffles help control swirling at ~200 poise. Above what liquid viscosity may baffles be completely omitted because swirling is inherently suppressed?

Introduction / Context:
Baffles are installed in stirred tanks to suppress vortex formation and promote top-to-bottom mixing. However, in extremely viscous liquids, bulk swirling and vortexing are naturally damped by high viscous resistance, and baffles can sometimes be omitted to avoid excessive power draw and stagnant zones.

Given Data / Assumptions:

• Newtonian liquid behavior at high viscosity.
• Radial or helical impellers used as appropriate.
• Focus on the rule-of-thumb viscosity above which baffles may be omitted.

Concept / Approach:
For moderate viscosities (order 100–200 poise), angled baffles help break rotational flow. As viscosity climbs, Reynolds number falls drastically, vortexing becomes negligible, and the flow tends toward laminar circulation dominated by shear. Above a threshold (often cited about 600 poise), the benefit of baffles diminishes; their presence can even hinder circulation by creating dead zones. Engineers may switch to helical ribbon, anchor, or screw impellers and operate without baffles.

Step-by-Step Solution:
Identify the operating regime: high-viscosity mixing with very low Re.Recognize that tangential flow and vortexing are minimal at very high viscosity.Apply the handbook threshold: baffles can be omitted at ≥ about 600 poise.Therefore, select 600 poise as the viscosity beyond which baffles may be eliminated.

Verification / Alternative check:
Mixing practice guides show baffles are common for water-like to moderately viscous fluids. Beyond several hundred poise, laminar impellers and unbaffled configurations are used to encourage axial circulation and avoid stagnant pockets behind baffles.

Why Other Options Are Wrong:
300 poise: still beneficial to have baffles with suitable impeller selection.1000 or 1500 poise: also high, but standard threshold for “may omit” is typically cited lower, near 600 poise.

Common Pitfalls:
Using turbine impellers without baffles in moderate viscosity; adding baffles indiscriminately in extreme viscosity, increasing power without mixing improvement.

Final Answer:
600 poise