A batch electrocoagulators CFD simulation is very important for the water treatment industry. Batch electrocoagulators are special tanks that clean polluted water using electricity. The key to making them work well is good mixing. A batch electrocoagulators Fluent analysis helps engineers see exactly how the water moves inside the tank. Good mixing helps spread the cleaning chemicals evenly, which makes the water cleaner, faster. A simulation is the only way to see this process clearly.

This report shows how a electrocoagulators fluent simulation was done using a special method called MRF (Multiple Reference Frame). This method is perfect for simulating things that spin, like the stirrer inside the tank. The MRF model helps us see how the spinning stirrer creates the mixing patterns that clean the water. The simulation also uses a VOF (Volume of Fluid) model because the cleaning process creates tiny gas bubbles. These bubbles are also important for the cleaning process. This CFD study gives engineers the information they need to design better, more efficient electrocoagulators that use less energy and do a better job of cleaning our water.

• Reference [1]: Ardhan, Natthaphon, et al. “Comparison of performance of continuous-flow and batch electrocoagulators: A case study for eliminating reactive blue 21 using iron electrodes.” Separation and Purification Technology146 (2015): 75-84.

Simulation Process: Fluent MRF & VOF Model Setup, Building the Virtual Reactor

The simulation process for this batch electrocoagulators CFD study started with building a detailed 3D computer model of the reactor. This model included the main tank, the electrodes that do the cleaning, and the small stirrer at the bottom that mixes the water. After the model was built, the space inside was filled with a computational mesh. The mesh was made of 1,213,196 mostly  hexagonal cells, which are like small, six-sided bricks. Hexagonal cells are a very good choice for this shape of tank because they give very accurate results and help the computer solve the problem faster. The mesh was made much denser with smaller cells in the most important areas, especially around the spinning stirrer and near the electrodes on the walls.

Inside ANSYS Fluent, the physics of the cleaning process was carefully set up. The most important part was the MRF (Multiple Reference Frame) model. This model was used to simulate the stirrer spinning at 500 RPM. The MRF method creates a small spinning zone around the stirrer and a large still zone for the rest of the tank, and it correctly calculates how the spinning motion affects the still water. The simulation also used the VOF (Volume of Fluid) multiphase model. This was needed to track the tiny hydrogen and oxygen gas bubbles that are created at the electrodes during the cleaning process. The model even included special settings for wall adhesion to correctly show how these bubbles stick to and move along the walls. This complete setup created a very realistic virtual model of the real-life electrocoagulator.

Figure 1: 3D geometry and the computational mesh used for the batch electrocoagulator CFD simulation. The mesh has 1,213,196 hexagonal cells.

Post-processing: An Engineering Investigation into Mixing Performance

The simulation results give us a complete picture of what is happening inside the tank. We will now investigate these results to understand the quality of the mixing, which is the most important factor for good water treatment. First, we need to understand the overall pattern of the flow. The flow streamlines in Figure 3 and the velocity contour in Figure 4 give us a clear view of the mixing structure. The streamlines are like maps that show the path of the water. They show that the small stirrer at the bottom creates a large, powerful, three-dimensional circulation pattern throughout the entire tank. The water is pulled down towards the center, then shot outwards by the spinning stirrer, and then flows up along the walls.

The velocity contour in Figure 4 supports this story. The red and orange colors show the fastest moving water (up to 1.27 m/s) is right around the stirrer, which is the engine of the mixing. The green and yellow colors show that this motion spreads out into the middle of the tank. Most importantly, the slow-moving blue areas are only found in the very corners and right next to the walls. This means the stirrer is doing an excellent job of mixing the entire volume of water. The design successfully eliminates “dead zones”—areas where water could get stuck and not be cleaned properly. This complete mixing is a very important achievement.

Now that we know the mixing pattern is good, we need to measure how strong it is. The velocity plot in Figure 2 gives us the exact numbers we need. This plot measures the speed of the water along a straight line up the center of the tank.

• In the main body of the tank (from 0.0m to 0.14m), the velocity is quite low, around 0.0 to 0.2 m/s. This is actually very good. This calm zone is where the electrodes are, and this slow movement gives the electrical cleaning process enough time to work properly.
• Then, as we get closer to the stirrer, we see a very sharp and powerful peak in velocity, reaching a maximum of 1.35 m/s. This high-speed jet of water is the proof of intense mixing. This is where the chemicals created by the electrodes are grabbed and powerfully mixed and distributed throughout the entire tank.

This plot shows that the design has a perfect balance. It has calm zones for the cleaning reactions to happen and a zone of high-intensity mixing to make sure everything is distributed evenly. The simulation proves that a stirrer speed of 500 RPM provides excellent mixing for this design.

Figure 2: Water velocity distribution plot along centerline from batch electrocoagulators CFD simulation using MRF

Figure 3: Flow streamlines visualization from batch electrocoagulator CFD simulation in ANSYS Fluent displaying three-dimensional rotational flow patterns

Figure 4: Velocity magnitude contour in horizontal cross-section of batch electrocoagulator from CFD simulation

This batch electrocoagulators CFD simulation provides clear and valuable information for the people who design and build these water treatment systems:

1. It Proves the Design Works: The simulation shows that this simple stirrer design is very effective. It creates a complete mixing pattern that cleans the entire tank. This gives the manufacturer confidence that their product will perform well for their customers.
2. It Helps Choose the Right Motor: The simulation shows that 500 RPM is a good speed. It is fast enough for intense mixing but not so fast that it wastes a lot of energy. This helps designers choose the most efficient motor, saving electricity costs for the final user.
3. It Allows for Future Improvements: Now that they have a trusted computer model, engineers can test new ideas easily. They can try different stirrer shapes or change the position of the electrodes on the computer. This allows them to develop better, more efficient water treatment systems much faster and cheaper than by building and testing many physical prototypes.