**5. Computational fluid dynamics**

The CFD simulation was made for the purpose of understanding if the separation of microplastics could be achieved with a hydro cyclone, and in how much time this separation would happen.

**Figure 3.** *Water flow simulation in a hydro cyclone through time.*

Analysis though CFD was conducted assuming the dimensions indicated in the modeling section. Using Ansys Fluent software.

The CFD simulation was made for the purpose of understanding if the separation of microplastics could be achieved with a hydro cyclone, and in how much time the separation would happen. **Figure 3** illustrates the flow of water inside the hydro cyclone. It can be observe that both underflow and overflow collect water but that most of that exits through the overflow. Also visible is the inner vortex that forms because of the pressure difference.

**Figure 4** shows the velocity inside the centre plane of the hydro cyclone. The big red spot on the top left is the velocity at inlet. The two outlets have increased velocities because of the pressure difference. Finally the inner part of the hydro

#### **Figure 4.**

*Velocity gradient for water flow in a hydro cyclone.*

**Figure 5.** *Pressure gradient for water flow in a hydro cyclone.*

*Performance Analysis and Modeling of Microplastic Separation through Hydro Cyclones DOI: http://dx.doi.org/10.5772/intechopen.99447*

**Figure 6.** *Particle flow simulation in a hydro cyclone through time.*

cyclone is under very low velocities because that is where the inner vortex flows and the velocities at the centre of it are close to 0 m/s.

**Figure 5** shows the pressure inside the hydro cyclone and the difference that is created by the two outputs, where the pressure is negative.

Finally microplastic particles of the same physical characteristics where inserted inside a flow of water. **Figure 6** shows the result of this study where less denser plastics exit through the overflow and plastics that have greater density flow through the underflow. On average for a flow of 2 m/s a particle takes 1.5 s to reach any two of the outlets.

From CFD it can be seen that there is a lot of turbulence created near the inlet, where fluid coming inside disrupts the overflow vortex. To counteract this problem the design of the hydro cyclone would have to change to implement a sleave design for the overflow so that the inlet flow does not interact with the inner vortex.
