Paddle agitator characteristics:\nWhich statement best describes the typical operating domain of a paddle agitator?

Introduction / Context:
Paddle agitators are simple, flat-blade impellers used in tanks for blending and maintaining uniformity. Recognising their strengths and limitations helps select the right impeller for viscosity, shear sensitivity, and mixing objectives (blending, suspension, or gas dispersion).

Given Data / Assumptions:

• Flat or slightly pitched paddles mounted on a central shaft.
• Baffled tank for effective mixing.
• Service: blending and mild heat transfer in low-viscosity liquids.

Concept / Approach:
Paddle agitators run at moderate speeds and generate predominantly radial and tangential flow patterns in laminar to transitional regimes. They are best for low-viscosity blending and maintaining homogeneity, not for strong axial pumping, deep-circulation solids suspension, or gas dispersion. High-shear applications require rotor–stator or Rushton-type impellers; axial-flow pitched-blade or hydrofoils are chosen when strong top-to-bottom circulation is needed.

Step-by-Step Solution:

Verification / Alternative check:
Mixing guides specify paddles for blending at Re ranges where laminar/transitional correlations apply; axial-flow impellers are specified when bulk circulation is required.

Why Other Options Are Wrong:

• (b) Axial flow is characteristic of pitched/hydrofoil impellers.
• (c) Paddles do not run at very high tip speeds nor produce intense shear.
• (e) Gas–liquid dispersion uses Rushton or high-shear designs, not simple paddles.

Common Pitfalls:
Using paddles in high-viscosity service without close-clearance anchors or helical ribbons; choose geometry appropriate to viscosity.

Final Answer:
It is suitable for mixing low-viscosity liquids (laminar to transitional flow).