Study of Solid−Liquid Mixing in Agitated Tanks through Computational Fluid Dynamics Modeling

Abstract

Solid-liquid mixing is one of the most important mixing operations due to its vast applications in many unit operations such as crystallization, adsorption, solid-catalyzed reaction, suspension polymerization, and activated sludge processes. In this study, a computational fluid dynamics (CFD) model was developed for solid-liquid mixing in a cylindrical tank equipped with a top-entering impeller to investigate the effect of impeller type (Lightnin A100, A200, and A310), impeller off-bottom clearance (T/6-T/2, where T is tank diameter), impeller speed (150-800 rpm), particle size (100-900 µm), and particle specific gravity (1.4-6) on the mixing quality. An Eulerian-Eulerian (EE) approach, standard k-ε model, and multiple reference frames (MRF) techniques were employed to simulate the two-phase flow, turbulent flow, and impeller rotation, respectively. The impeller torque, cloud height, and just suspended impeller speed (N js ) computed by the CFD model agreed well with the experimental data. The validated CFD model was then employed to calculate the solid concentration profiles by which the degree of homogeneity was quantified as a function of operating conditions and design parameters.

Performance evaluation of an electrochemical reactor used to reduce Cr(VI) from aqueous media applying CFD simulations

“…It was shown that the inlet position has an important effect on the reactor performance, showing that the axial velocity profiles within the reactor are specific for each inlet (footprint). Moreover, the CFD analysis has proven to be a useful tool to simulate and determine the performance in reactors and mixers (Hosseini et al, 2010), it is used to simulate a solideliquid mixing process in a cylindrical tank, evaluating the type of impeller, impeller off-bottom clearance, speed, particle size and other parameters. Predictions of the turbulence kinetic energy and the turbulence energy dissipation profiles at the impeller discharge stream using the ke 3 model gave the best results, in a standard stirred tank reactor (Gunyol and Mudde, 2009).…”

A Multiphase Model for the Numerical Simulation of Ice-Formation in Sea-Water

“…[43], for gas-solid multiphase flows, and [17,43,45], for the evaluation of the liquid-solid drag in the framework of pipeline slurry flows, fluidized bed reactors, as well as in other chemical reacting systems, see e.g. [27,22,39,46,11,37], or in numerical modelling of volcanic eruptions, see e.g. [8,9].…”

Models and Applications for Simulating Turbulent Solid–Liquid Suspensions in Stirred Tanks

“…Panneerselvam et al (2008Panneerselvam et al ( , 2009) combined the standard deviation method and cloud height criteria (i.e., the cloud height is equal to 0.9 times the liquid height) and found the latter to be determinant. Hosseini et al (2010) calculated the N js via a CFD model by using the tangent intersection method. The average solids concentration in a horizontal plane located 1 mm above the bottom of the tank was calculated, and the relationship of this parameter to the impeller speed was determined.…”

“…Fig. 2 Use of tangent intersection method to calculate just-suspended impeller speed (Hosseini et al, 2010) Ochieng and Lewis (2006a) evaluated the cloud height in a fully baffled tank with an elliptical bottom that was agitated by a hydrofoil impeller. In the CFD simulation, the cloud height was determined from the axial profile of the solid volume fraction.…”

“…The hysteresis phenomena can be well captured by the CFD models with appropriate initial guess and drag correlations. Hosseini et al (2010) compared the performance of three axial flow impellers, namely Lightnin A100, A200, and A310, at constant power input by using an E-E approach and a standard k-ε model. The A100 impeller was determined to be the most efficient for solid-liquid mixing, whereas the A200 impeller was the least effective for achieving a high degree of homogeneity.…”