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ABSTRACT
This article presents the basic theoretical concepts of the agitation-mixing unit operation. It describes the agitation-mixing operations implementing one or more phases within an agitation tank equiped with an agitator and presents all the global parameters of an agitation system. The application potential of computational fluid dynamics makes it possible to acquire local data such as velocity and turbulence fields. Examples of calculation of the various quantities of a stirring system illustrate the various theoretical concepts and show the complexity of extrapolating results obtained on a pilot unit to an industrial unit.
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Read the articleAUTHORS
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Michel ROUSTAN: INSA engineer (Toulouse National Institute of Applied Sciences) - Professor Emeritus of Process Engineering INSA Toulouse - TBI Toulouse Biotechnology Institute Bio & Chemical Engineering, CNRS, INRAe, INSA
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Alain LINÉ: Engineer INP-ENSEEIHT (Institut national polytechnique de Toulouse) - Professor of Fluid Mechanics, GP3E Department, INSA Toulouse - TBI Toulouse Biotechnology Institute Bio & Chemical Engineering, CNRS, INRAe, INSA
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Jean-Claude PHARAMOND: Contributed to the drafting of the first version of the article.
INTRODUCTION
Agitation techniques, which were long considered an art, are now based on both theoretical and experimental considerations, enabling a scientific approach to the problems posed. Enormous progress has been made, thanks in part to the accumulation of data on the operation of industrial units, and in part to the major research effort made by a number of companies and university laboratories specializing in agitation and mixing.
In very general terms, determining a stirring unit involves either selecting the right device for a new process, or extrapolating (or interpolating) the results obtained with a given device in the context of existing production.
The potential of the new experimental and numerical resources enables us to develop a local approach that complements the classic global approach to the operation of stirred tanks.
Local analysis of stirred tank operation provides access to the spatial and temporal distributions of velocity and turbulence. This information can help to understand and control mixing in the agitated tank, and may lead to optimized operation under different conditions.
In all cases, a good knowledge of the process is essential to enable the most favorable choice to be made, particularly from an economic point of view.
The aim of the article is to provide the user or designer with the basic theoretical concepts and tools needed to size or optimize a stirring system for a given mixing operation. Section 1 describes agitation-mixing operations involving one or more phases in a stirred tank equipped with an agitator. § 2 defines a stirring system, i.e. the stirrer-vessel pairing. In § 3
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KEYWORDS
mixing | Mixing | multiphase reactor | computational fluid dynamics
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