**13. Tracer analysis in Fluent®**

Tracer simulations were developed considering an unsteady state, using as initial condition, the data obtained at the stationary state solution (*t*=0). The stirrer speed was set at 100 rpm using liquid water and tracer as materials. Initial injection positions are shown in **Figure 12**. This configuration was used in all tracer simulations. Monitors were defined as spheres with a radius of 0.8 cm and were used to track the tracer concentration in a specific region (**Figure 13**).

Each monitor registers a mass fraction of tracer every 0.55 s. Results for all simulations are presented in dimensionless concentration.

Asymptotic behavior of the tracer concentration is a criterion to define the mixing time. Tracer curves for each model are shown in **Figures 14**–**16**.

**Figure 12.** Tracer injection zones. Tracer 1 in (0, 4, 5) cm and Tracer 2 in (0, 4, 20) cm.

**Figure 13.** Spherical monitors and their spatial location.

**Figure 14.** ROT tracer evolution curves after injection in regions 1 and 2.

**Figure 15.** MRF tracer evolution curves after injection in regions 1 and 2.

**Figure 12.** Tracer injection zones. Tracer 1 in (0, 4, 5) cm and Tracer 2 in (0, 4, 20) cm.

**Figure 13.** Spherical monitors and their spatial location.

284 Modeling and Simulation in Engineering Sciences

**Figure 14.** ROT tracer evolution curves after injection in regions 1 and 2.

**Figure 16.** SM tracer evolution curves after injection in regions 1 and 2.

Mixing time of ROT simulations diverges drastically between injections. Tracer 1 curves start to become asymptotic at 80 s, while there is no clear tendency when the injection is made in region 2.

Results from **Figure 16** show a significant tracer concentration variation above 30 s. SM predicts that mixing time of all monitors is beyond 80 s.

SM tracer curves of **Figure 16** differ qualitatively and quantitatively from curves obtained in **Figures 14** and **15** (ROT and MRF). In general, the monitored tracer behavior is in agreement with the velocity field of a stirred tank.

Concentration contours are presented in **Table 5** for tracer 1 and 2. Mixing profiles are shown on a radial cross-section over the X-Y plane.

**Table 5.** Mass fraction of tracer dispersion at different times.
