# CFD Assessment of the Hydrodynamic Performance of Two Impellers for a Baffled Stirred Reactor
## 3 Results and Discussion  
The performance of the stirring mechanism from an industrial reactor was judged from the point of view of the suspension of the entire solid phase, in a homogeneous manner, in the entire volume of the liquid phase, for as long as needed for the chemical reaction to take part. Some processes require that the particles be just suspended off the bottom, whilst, in some other processes, complete off-bottom solids suspension is necessary. To analyze the suspension of the solid phase, the distribution of the volume fraction of the solid phase was plotted on a vertical plane through the middle part of the reactor. The most relevant quantitative representation for the analysis of the performance of the stirring mechanism is represented by the histogram of the distribution of the volume fraction of the solid phase. A similar investigation of the distribution of the solid phase was presented by [PERSON] et al. [3], in order to analyze the performance of the stirring mechanism. Liquid velocities distributions also provide an insight into the mixing process occurring inside stirred reactors. The velocity components (axial, radial and tangential) are plotted on a vertical midplane and the velocity components radial distribution is presented for three sections corresponding to the impeller level (i0), above impeller (i+) and below the impeller (i-). The two cases investigated correspond to the original impeller and the new one designed by our research team. For both cases, the initial state of the flow corresponds to the homogeneous distribution of the volume fraction of the solid phase in the entire volume of liquid. This is the most favorable situation for the best operation of the reactor as it resulted from our previous research work. From analyzing Figure 4, it results that the new impeller was performing better than the original one. The volume fraction of the liquid containing no solid particles decreased from 25% to 20% as shown by the histograms. Additionally, the new impeller completely prevented the sedimentation of the solid phase on the lower part of the reactor as can be seen from the distribution of the volume fraction of the solid phase on the vertical plane and from the histogram, Figure 4b. Figure 3: Computational domain: (**a**) components of the reactor; (**b**) mesh of the computational domain. To underline the better performance of the new impeller regarding the original one, the distribution of the velocity components was analyzed. A similar representation of the velocity field, employed for analyzing the hydrodynamic performance of the impeller and also to validate the numerical results, are presented in previous research papers [3; 5; 6; 7; 8; 17]. From analyzing the distribution of the axial velocity on a vertical plane, Figure 5, and on three horizontal sections, Figure 6, it resulted that the new impeller generated a larger value for the axial component of the velocity, pointing to the bottom of the reactor. The new impeller generated, in the middle part, a downward jet below the impeller, that kept the entire volume fraction of the solid phase in suspension. Then the axial velocity was decreasing and the flow turned upwards near the walls of the reactor. The axial component of the velocity generated by the original impeller had smaller values for all the investigated sections. Moreover, in the section below the impeller (i0), Figure 6c, the value of the axial component was almost zero for the entire section and this explains the poor operation of the impeller, leading to the sedimentation of the solid phase on the bottom of the reactor. The comparison of the radial profiles of the radial velocity is shown in Figures 7 and 8. For the new impeller, in the impeller centre plane (i0), Figure 8b, the radial flow increased gradually from the wall and a maximum occurred near the impeller blade tip.