For mixing very high viscosity liquids (greater than 50,000 cP), which agitator design—characterised by a large blade area and slow rotational speed—is preferred?

Introduction / Context:
Agitation of high-viscosity fluids challenges conventional impellers due to laminar flow regimes and poor bulk circulation. Correct impeller choice prevents dead zones and excessive power draw.

Given Data / Assumptions:

• Viscosity > 50,000 cP (laminar regime).
• Goal: tank-wide circulation and surface renewal.
• Impeller needs high swept area at low rpm.

Concept / Approach:
Helical screw or anchor agitators sweep close to the vessel wall, minimising bypass and creating axial movement even in laminar flow. Propellers and turbines are efficient in low-to-moderate viscosities where turbulent flow and strong shear are achievable but are ineffective in extremely viscous systems.

Step-by-Step Solution:
Identify the mixing regime (laminar) from viscosity.Select agitator with large blade area and wall-sweeping action.Choose helical screw (anchor) agitator.

Verification / Alternative check:
Mixing handbooks recommend anchors/helixes for polymer melts, resins, and high-solids slurries at very high viscosities.

Why Other Options Are Wrong:
Propeller/Turbines: rely on turbulent pumping; performance collapses in viscous laminar flow.

Common Pitfalls:
Attempting to compensate with high rpm, which only increases power without improving macromixing in laminar regimes.

Final Answer:
Helical screw (anchor) agitator