A comprehensive computational fluid dynamics CFD model was developed in the present study to gain insight into the solid suspension in a stirred slurry reactor. The preliminary simulations highlighted the need for the correct modeling of the interphase drag force. A two-dimensional model problem was then developed using CFD to understand the influence of free stream turbulence on the particle drag coefficient. The proposed correlation was then incorporated in a two-fluid model (Euler-Euler) along with the standard k-turbulence model with mixture properties to simulate the turbulent solid-liquid flow in a stirred reactor. A multiple reference frame approach was used to simulate the impeller rotation in a fully baffled reactor. A computational model was mapped on to a commercial CFD solver FLUENT6.2 (of Fluent Inc., USA). The model predictions were compared with the published experimental data of Yamazaki et al. [Powder Technol. 1986, 48, 205] and Godfrey and Zhu [AIChE Symp. Ser. 1994, 299, 181]. The predicted results show reasonably good agreement with the experimental data. The computational model and results discussed in this work would be useful for extending the applications of CFD models for simulating large stirred slurry reactors.
REVIEW In carrying out the physical mass transfer processes and chemical reactions in the gas-liquid-solid systems, in which liquid is the continuous phase and where the solid and gas phase are the discontinuous phases, there is often a need to suspend the solid particles in the presence of gas. Stirred tanks are often employed for this purpose as slurry reactors, especially for discontinuous/batch operations and for smaller production levels. The main task of the stirrer in an aerated suspension system is to suspend the solids particles completely so as to expose their total surface area for the reaction and/or for mass transfer, to disperse the gas uniformly throughout the vessel and to provide liquid mixing patterns for an intimate contact between the phases. Thus, mechanically agitated reactors are extensively used in the industry to handle the three-phase systems and fi nd application in a wide range of processes such as catalyzed oxidation and hydrogenation reactions, polymerization, evaporative crystallization, aerobic fermentation, froth fl oatation, microbial coal desulphurization, gold leaching, and bacterial sulphide oxidations. In all these applications, simultaneous dispersion of gas and the suspension of the solids by the impellers are of vital importance. Review on Mixing Characteristics in SolidReview on Mixing Characteristics in SolidLiquid and Solid-Liquid-Gas Reactor VesselsGopal R. Kasat and Aniruddha B. Pandit* Chemical Engineering Division, University Institute of Chemical Technology (UICT), University of Mumbai, Matunga, Mumbai 400-019, IndiaFor a reliable design of a three-phase stirred tank reactor, it is important to know the complex hydrodynamic problems (i.e. phase-phase interactions) associated with the demands of simultaneous gas dispersion and solids suspension with a single or multiple impellers. One of the most important parameters for the assessment of the performance of the impellers for solid suspension (both in the absence and in the presence of gas), is the minimum impeller speed required for the complete offbottom suspension of the solids in the vessel. (Zwietering, 1958;Wiedmann et al., 1980;Chapman et al., 1981 Chapman et al., , 1983Frijlink et al., 1990;Rewatkar et al., 1991a; Mechanically agitated reactors with single and multiple impeller systems are used in the industry for the various three-phase mixing processes such as crystallization, fermentation, and hydrogenation, etc. The paper reviews the experimental work reported in the literature along with different techniques used for the measurement of the specifi c quantities such as minimum or critical impeller speed for solid suspension. The work critically surveys the literature and makes specifi c recommendations for the use of appropriate correlations and conditions to be used for the success of such equipment. This assessment will put all the relevant literature on a common footing and will help to validate work reported earlier.Les réacteurs agités mécaniquement munis d'une seule turbine et de turbines mult...
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