The Effect of Impeller Type on Floc Size and Structure during Shear-Induced Flocculation

Area of Science:

• Colloid and Surface Science
• Fluid Dynamics
• Particle Technology

Background:

• Shear-induced flocculation is crucial in industrial processes.
• Understanding floc evolution impacts process efficiency and product quality.
• Polystyrene-aluminum sulfate systems offer a model for studying flocculation dynamics.

Purpose of the Study:

• To investigate the impact of impeller type and shear rate on floc size and structure.
• To analyze floc evolution during shear-induced flocculation.
• To characterize floc structure using fractal geometry.

Main Methods:

• Image analysis was employed to study floc evolution.
• Radial and axial flow impeller configurations were tested.
• Fractal geometry concepts were applied to quantify floc structure.

Main Results:

• Steady-state floc size is dependent on impeller recirculation frequency and velocity gradient.
• The two-dimensional floc fractal dimension (Dpf) increased during growth, indicating more open structures.
• Shear rate did not significantly affect the steady-state Dpf.

Conclusions:

• Impeller design significantly influences floc size and evolution dynamics.
• Floc structure becomes more open during growth and stabilizes over time.
• The study provides insights into controlling floc properties in agitated systems.