Turbine agitators in mixing: identify the incorrect statement about speed, flow pattern, sizing, and placement in a stirred tank.

Introduction / Context:Turbine agitators (flat- and pitched-blade) are standard impellers for blending, gas dispersion, and heat/mass transfer in chemical and bioprocess tanks. Understanding their flow patterns and typical design rules improves scale-up and process reliability.

Given Data / Assumptions:

• Pitched-blade turbines are compared to flat-blade (radial) turbines.
• Typical industrial design heuristics for diameter, placement, and speed apply.

Concept / Approach:Flat-blade (Rushton) turbines generate highly radial flow. By contrast, pitched-blade turbines are intentionally angled (usually 30–45°) to produce a significant axial flow component for top-to-bottom circulation. Hence, any statement claiming “only radial” for a pitched blade is incorrect.

Step-by-Step Solution:Check peripheral speed: 200–250 m/min is a common recommended range.Check sizing: D/T in the range 1/3 to 1/6 is typical; blade length heuristics are reasonable.Check placement: clearance ≥ impeller diameter and multiple impellers for deep liquids are standard practices.Therefore option (b) is wrong.

Verification / Alternative check:Vendor literature shows pitched-blade turbines used when axial circulation is desired.

Why Other Options Are Wrong:They reflect standard mixing design guidelines in common use.

Common Pitfalls:Assuming all turbines are purely radial; blade pitch changes the flow to mixed or axial.

Final Answer:A pitched-blade turbine produces only radial flow with no axial component at all.