# CFD Simulation of Solid Suspension for a Liquid-Solid Industrial Stirred Reactor
## 1 Introduction
Taking into consideration the results of the previous studies, we decided to use the RNG \(k\)-\(\varepsilon\) turbulence model, which allows sufficient accuracy of the turbulent quantities within a reasonable calculation time. There are several research studies that recommend the employment of the VOF model for the numerical simulation of a multiphase flow. [PERSON] et al. [28] implemented a volume of fluid (VOF) method to analyze the two-phase flow within a porous medium that takes into account the dynamic contact angle and its hysteresis with the help of Open-source Field Operation and Manipulation (OpenFOAM). The numerical results were compared with the experimental results, and a good agreement was determined. [PERSON] and [PERSON] [29] performed a numerical simulation with Ansys CFX 18.1, employing a three-phase VOF model to analyze the movement and formation of deposits of solid particles from a separator used in the brewing industry. The numerical results were compared to the experimental results and proved that the model employed is suitable for the analyzed phenomena and provides accurate and reliable results for the flow and the sedimentation process. [PERSON] et al. [30] presented a numerical method for the symmetric draining of capillary liquids in simple corners, employing the software interFoam and the VOF model. By comparing the numerical results with the experimental results, the good accuracy of the numerical results was underlined. [PERSON] et al. [31] employed OpenFOAM and ANSYS Fluent to study microscale gas-liquid flow. The aim of the study was to assess the capability of both software to predict the flow field by employing different models for the multiphase flow: VOF and piecewise linear interface calculation (PLIC) in ANSYS Fluent and MULES/isoAdvector in OpenFOAM. The conclusion of the research, after validating the results obtained with experimental data, is that ANSYS Fluent provides more accurate results for this type of flow. [PERSON] et al. [32] presented the results of employing an improved VOF discrete element model (DEM) for studying the soil-water interaction. All the experimental observations were accurately depicted by the numerical model. For the numerical simulation of the solid suspension from a stirred reactor, in the literature, there are also two models mentioned: the Eulerian multiphase model and the Eulerian mixture model. In the Eulerian multiphase model, continuity and momentum balance equations are solved for each phase. The Eulerian mixture model is a simplified version of the previous model, and it is recommended to be employed for thin mixtures and small-sized particles. For this model, continuity and momentum balance equations are solved for one mixture phase, the hydrodynamic parameters of which are computed from the mass-averaged properties of each phase. Only one equation for the transport of volume fraction is added and solved for the dispersed phase from the continuous phase. This term consists of four different interphase forces: lift force, Basset force, virtual mass force and drag force. Only the drag force can be considered in the interphase momentum exchange term because of the small influence on the entire process of the lift force, Basset and virtual mass forces. In the literature, results obtained from using these two models are available, and these results show that the Eulerian multiphase model [10; 11; 12; 13; 14] provides much more accurate results than the Eulerian mixture model when working with particles with a diameter greater than 100 \(\upmu\)m and a solid fraction ranging between 0.2 and 16%. The Eulerian mixture model is better adapted for small dimensions of solid particles and lower concentrations. Taking all the previous research results into consideration, for our numerical study, the Eulerian multiphase model was best suited.