A Semi-Empirical Model to Estimate Maximum Floc Size in a Turbulent Flow

Area of Science:

• * Fluid Dynamics
• * Colloid and Surface Science
• * Particle Technology

Background:

• * Traditional models for hydrodynamic stress-induced agglomerate breakage are limited to low velocity gradients (<500 s−1).
• * Existing models often use shear rates not representative of global flocculation phenomena.
• * There is a need for a model applicable to a broad shear range, from aggregation to fragmentation.

Purpose of the Study:

• * To present a semi-empirical model for predicting mean floc size over a wide range of shear rates (60–6000 s−1).
• * To provide a mechanistic approach for modeling turbidity changes with velocity gradients.
• * To analyze shear-related floc restructuring and breakage modes.

Main Methods:

• * Development of a semi-empirical model for floc size prediction.
• * Incorporation of theoretical details for orthokinetic flocculation.
• * Analysis of floc breakage using the Kolmogorov microscale and fractal dimension.
• * Experimental validation using ultrafine kaolin in a geometrically similar reactor.

Main Results:

• * The model successfully predicts mean floc size across a broad shear rate spectrum.
• * Kinetic agglomeration (ka) and breakage (kb) indices were determined.
• * Floc breakage modes and shear-induced restructuring were characterized.
• * Experimental results validated the model's predictions for floc properties.

Conclusions:

• * The developed semi-empirical model offers a robust method for predicting floc size under diverse hydrodynamic conditions.
• * The model provides mechanistic insights into flocculation dynamics, including aggregation and breakage.
• * Validation with experimental data confirms the model's applicability to ultrafine particle systems.