Solid–Liquid Suspensions in Top-Covered Unbaffled Vessels: Influence of Particle Size, Liquid Viscosity, Impeller Size, and Clearance

Optimized Design of Solid-Liquid Dual-Impeller Mixing Systems for Enhanced Efficiency

Flow interferences occur in the dual-impeller stirred tank between paddles as well as between paddles and baffles and the tank wall, leading to inefficient utilization of the stirring energy. To address this issue, this study investigates the flow characteristics within the mixing tank using Euler-Euler numerical simulation and the particle image velocimetry (PIV) experimental method. The three-dimensional nonconstant flow characteristics are analyzed to optimize the critical stirrer geometry. By employing the Sobol method, an approximate model is established for sensitivity analysis to identify key parameters affecting the solid-liquid dual-impeller stirred tank's performance. Numerical simulations demonstrate that the optimized stirred tank exhibits a significantly improved solid-liquid suspension capacity and considerably reduces flow losses near the wall and baffle areas. Under the designated conditions, the cloud height is increased by 8.7%, and power consumption is reduced by 15.6% compared to the prototype. PIV tests performed on the stirred tank before and after optimization confirmed the reliability of the obtained optimization results. The primary objective of this study is to enhance mixing efficiency and homogeneity in solid-liquid mixing tanks while concurrently minimizing energy consumption and cost. These results validate the feasibility of employing a multiobjective optimal design approach that combines the RBF agent model with the Sobol method. The findings offer valuable insights for the design of similar mixing tanks.

Just Suspended Speed Simulation in Torus Reactor Using Multiple Non-Linear Regression Model

In the chemical and water treatment industries, it is necessary to achieve maximum contact between the solid and liquid phase, thus promoting the mass and heat transfer, to obtain a homogeneous solution. Increasing stirring speed is the most recommended solution in different types of reactors: stirred tank, column, and tubular. However, this inadvertently increases the energy consumption of the industry. Determination of the minimum speed, labeled the just suspended speed (Njs) and crucial to attaining homogeneity, has been widely investigated. Numerous studies have been carried out to assess formulas for determining the solid particle speed in various reactor types. Given the limitations of the existing formulations based on a generalization of a unique equation for computing Njs for all soil classifications, it appears that most formulas can only approximate complex phenomena that depend on several parameters. A novel formula was developed, and the results given in this paper demonstrate the effectiveness of generating significant uncertainties for the estimation of Njs. The purpose of this study was the elaboration of experiment-based data-driven formulas to calculate Njs for different particle size classes. Nonlinear multiple regression (MNLR) models were used to generate the new formulas. The gradient descent optimization algorithm was employed to solve the hyperparameters of each novel equation, utilizing supervised learning. A comparison of the data indicated that the unique formulas presented in this study outperformed empirical formulas and provide a useful means for lowering energy consumption, while increasing the heat and mass transfer in torus type reactors.

A General Review of the Current Development of Mechanically Agitated Vessels

The mixing process in a mechanically agitated vessel is a widespread phenomenon which plays an important role among industrial processes. In that process, one of the crucial parameters, the mixing efficiency, depends on a large number of geometrical factors, as well as process parameters and complex interactions between the phases which are still not well understood. In the last decade, large progress has been made in optimisation, construction and numerical and experimental analysis of mechanically agitated vessels. In this review, the current state in this field has been presented. It shows that advanced computational fluid dynamic techniques for multiphase flow analysis with reactions and modern experimental techniques can be used with success to analyse in detail mixing features in liquid-liquid, gas-liquid, solid-liquid and in more than two-phase flows. The objective is to show the most important research recently carried out.

Critical review of different aspects of liquid-solid mixing operations

Mechanically stirred slurry tanks are utilized in several industries to perform various unit operations such as crystallization, adsorption, ion-exchange, suspensions polymerization, dispersion of solid particles, leaching and dissolution, and activated sludge processes. The major goal of this review paper is to critically and thoroughly analyse the different aspects of previous research works reported in the literature in the field of liquid-solid mixing. This paper sheds light on the advantages and limitations of various particle concentration measurement methods employed to assess the suspension quality and the extent of solid suspensions in slurry reactors. Attempts are being made to identify and compare various mathematical models and methods to quantify particle dispersion and distribution in slurry reactors. It has been shown that various factors such as geometric configurations, agitation conditions, and physical characteristics of liquid and solid have pronounced influence on local suspension quality and power consumption. Computational fluid dynamics (CFD) modeling can be extremely useful in assessing the suspension of solid particles in slurry tanks. A critical review of different scale-up procedures employed for solid suspension and distribution in liquid-solid systems is presented as well. The findings of this review paper can be useful for future research works in liquid-solid mixing.