Agitator design — role of baffles:\nInstalling baffles in a mixing tank primarily helps to minimise which undesirable hydrodynamic tendencies?

Introduction / Context:
Unbaffled, cylindrical tanks often develop strong swirling flow and a central vortex under top-entry agitation, which reduces mixing efficiency and can entrain air. Baffles are vertical strips fixed to the wall to disrupt swirling and promote top-to-bottom circulation and turbulence where appropriate.

Given Data / Assumptions:

• Standard baffled tank with 4 radial baffles is considered.
• Newtonian liquids without yield stress.

Concept / Approach:
Baffles break tangential flow, converting rotational motion into radial and axial components, suppressing global swirl and the formation of a deep vortex. This improves power transfer from the impeller to the bulk liquid and enhances mixing, gas dispersion (when present), and heat transfer. Thus, they minimise both swirling and vortexing simultaneously.

Step-by-Step Solution:

Verification / Alternative check:
Mixing correlations (power number, blend time) are specified for baffled tanks; unbaffled tanks show distinct, less efficient hydrodynamics with vortex formation.

Why Other Options Are Wrong:

• Picking only one neglects the coupled nature of swirl and vortex.
• “Neither” contradicts the primary purpose of baffles.
• Cavitation relates to local pressure drops at impellers and is not the main reason for wall baffles.

Common Pitfalls:
Undersized or mispositioned baffles will not adequately suppress vortexing; typical width is about 1/12 of tank diameter.

Final Answer:
Both (a) and (b)