The Role of Fluid Flow and Fluid Shear Rates in Mixing and Dispersion

Author:

James Y. Oldshue

The document discusses how fluid flow and shear rates influence mixing and dispersion within industrial mixing tanks. It explains how factors such as impeller speed, power input, and tank geometry affect shear rate distribution, circulation time, and overall mixing efficiency. The content emphasizes that proper control of these variables is essential for achieving consistent particle dispersion and predictable process performance during scale-up.

Key Learnings

• Fluid flow and shear rates directly influence mixing efficiency and particle dispersion in mixing tanks.
• Macro-scale and micro-scale shear rates operate differently, affecting particles of varying sizes.
• Maintaining constant power per unit volume or tip speed significantly alters shear rate distribution and circulation time.
• Larger tanks exhibit longer circulation and blend times compared to smaller tanks.
• Geometric similarity impacts shear rate behavior during scale-up; adjusting the D/T ratio can help achieve more consistent results.
• Turbulent flow generates higher shear rates near the impeller zone, driving dispersion and energy dissipation.
• The balance between dispersion and coalescence determines the final particle size distribution.
• Measuring and controlling shear rate, viscosity, and power input are essential for optimizing mixing performance.
• Scale-up requires compensating for reduced power levels and changes in impeller pumping capacity to maintain uniform mixing.
• Understanding shear rate distribution and residence time is crucial for achieving predictable process outcomes.