Mixing correlations: in low-viscosity, baffled stirred tanks, when is the Froude number typically not used for power requirement calculations?

Introduction / Context:
Two dimensionless groups dominate stirred-tank scale-up: the Reynolds number (inertial vs viscous forces) and the Froude number (inertial vs gravitational forces). Engineers often omit the Froude number in certain configurations. This question asks under what common condition that omission is appropriate for low-viscosity liquids.

Given Data / Assumptions:

• Low-viscosity, turbulent regime is typical (high Reynolds number).
• Tanks are baffled to suppress vortex formation.
• Power correlations based on power number vs Reynolds are available.

Concept / Approach:
The Froude number becomes important when free-surface vortexing and gravity effects influence hydrodynamics, as in unbaffled tanks or at very high impeller speeds. With baffles installed, surface vortexing is damped, so gravitational effects on power draw are minor and the power number depends mainly on Reynolds, not Froude. Therefore, engineers commonly avoid Froude in such calculations.

Step-by-Step Solution:
1) Identify regime: low viscosity → high Re → turbulent mixing.2) Add baffles: vortex suppression minimizes free-surface depression.3) Conclude: power requirement correlations can neglect Froude and use Po(Re) relationships.

Verification / Alternative check:
Empirical power curves for baffled tanks show flat power number in fully turbulent range, largely independent of Froude until extreme aeration or surface effects arise.

Why Other Options Are Wrong:
Option B (Re < 300) refers to laminar regime where viscous scaling dominates; Froude omission there is not the key point of the question. Option C incorrectly combines mismatched conditions. Option D ignores the standard baffling rationale. Option E is over-generalized and inaccurate.

Common Pitfalls:
Assuming Froude is universally required; it matters mainly with free surfaces and unbaffled vortex behavior.

Final Answer:
When baffled systems are used (vortexing suppressed, gravity effects minimal)