A multiphase CFD model of DAF process

Area of Science:

• Environmental Engineering
• Fluid Dynamics
• Water Treatment

Background:

• Dissolved air flotation (DAF) is a key process in water treatment for removing suspended solids.
• Accurate modeling of multiphase flow and particle dynamics is crucial for optimizing DAF tank performance.
• Previous studies often lack detailed validation of CFD models with experimental data for full-scale DAF systems.

Purpose of the Study:

• To develop and validate a computational fluid dynamics (CFD) model for simulating air/water flow and floc dynamics in a full-scale DAF tank.
• To predict particle removal efficiency, settled solid profiles, and overall flow dynamics.
• To compare CFD predictions with experimental data from flow visualization and velocity measurements.

Main Methods:

• Employed a Eulerian-Eulerian multiphase CFD model for air/water flow simulation.
• Utilized a 3D structure grid incorporating air nozzle and tank geometry.
• Tracked floc particles using a discrete Lagrangean model within the simulated air/water fluid.
• Validated the model against flow visualization and acoustic Doppler velocimetry (ADV) measurements.

Main Results:

• The CFD model successfully predicted the air/water volume fraction, influencing effective fluid density.
• Floc fate (escape, settling, breakthrough) was accurately correlated with floc size and density.
• Model predictions for general flow patterns and average fluid velocities showed good agreement with experimental observations.

Conclusions:

• The developed CFD model provides a reliable tool for predicting performance in full-scale DAF tanks.
• The model aids in understanding and optimizing floc removal and solid settling processes.
• CFD simulations, when validated, are effective for enhancing the design and operation of DAF systems.