Computational fluid dynamics stirred tank flow

Measurements have been made of turbulence structure by a number of workers using laser-Doppler methods and using hot-film anemometry Application of computational fluid dynamics to turbulent flow in stirred tanks is developing rapidly and involves using assumptions inherent in Kolmogoroff s theory and turbulence measurements to supply boundary conditions. 

Computational fluid dynamics (CFD) is rapidly becoming a standard tool for the analysis of chemically reacting flows. For single-phase reactors, such as stirred tanks and empty tubes, it is already well-established. For multiphase reactors such as fixed beds, bubble columns, trickle beds and fluidized beds, its use is relatively new, and methods are still under development. The aim of this chapter is to present the application of CFD to the simulation of three-dimensional interstitial flow in packed tubes, with and without catalytic reaction. Although the use of... 

ASME CFSTR CFD CFM DIERS exp IR HA/AN HAZOP MM MMM American Society of Mechanical Engineers Continuous flow stirred tank reactor Computational fluid dynamics Computational fluid mixing Design Institute for Emergency Relief Systems exponential Infrared (spectroscopy) Hazard analysis Hazard and operability studies Michaelis-Menten Maximum-mixedness model... 

Currently a wide range of calculation methods and powerful computers are available. In the EU, 13 research groups have joined forces to tackle the numerical and experimental investigation of flow conditions in stirred tanks [122]. Both commercially obtainable CFD codes and those further developed in the universities are available (CFD - Computational Fluid Dynamics). Simple k-s and advanced turbulence models are utilized and compared with one another k - kinetic energy per mass s - stirrer power per mass). The flow produced by the stirrer is described by approximate calculations of the 3-dimensional (3D), non-steady state circulation of the stirrer paddles. 

Mixing properties and flow fields in stirred tanks are usually studied on a laboratory scale. Practical scale-up of a stirred tank cannot be performed requiring that every individual mixing and fluid mechanical parameters in the small scale tank should be maintained in the larger one. Therefore, scale-up procedures for different types of processes have been determined through experience, testing and computational fluid dynamics simulations. 

Accurate CFD (computational fluid dynamic) simulation of the flow in stirred tanks requires correct specification of both the geometry and the physical conditions of the flow. While specification of the geometry, the gridding, and the solution algorithm is relatively straightforward, some other issues remain difficult. The most challenging problem is definition of a physically accurate, computationally tractable impeller or impeller model which incorporates the effect of the tank geometry. This... 

This chapter deals with basic fundamentals of novel reactor technology and some of green reactor design softwares and their applications. Basic understanding of flow pattern in stirred-tank reactor by computational fluid dynamics and simulation of CSTR model by using ASPEN Plus were mainly presented in this chapter. 

Computational Fluid Dynamic (CFD) and mechanistic models of gas-liquid flow and mass transfer at turbulent conditions are useful for studying local inhomogeneities and operation conditions of gas-liquid stirred tanks. They are applicable also as scale-up and design tools of gas-liquid stirred tank reactors and other gas-liquid contacting devices with greater confidence compared to purely heuristic design methods. Experiments are needed for the development and the verification of these models. 

Two basic approaches are often used for fluidized bed reactor modeling. One approach is based on computational fluid dynamics developed on the basis of the mass, momentum, and energy balance or the first principle coupled with reaction kinetics (see Chapter 9). Another approach is based on phenomenological models that capture the main features of the flow with simplifications by assumption. The flow patterns of plug flow, CSTR (continuous-stirred tank reactor). 

Zalc, J. M. (2000). Computational fluid dynamic tools for investigating flow and mixing in industrial systems the koch-GUtsch SMX static mixer and a three Rushton turbine stirred tank, Ph.D. dissertation, RutgCTs, The State University of New Jersey. 

In spite of the success of CFD simulations for the multiphase turbulent fluid flow in stirred-tank bioreactors (see Section 3.4), their application to coupled material balance equations in case of more complicated reaction networks is still limited by the required computing power. Even in case of successful approaches for model reduction, the number of compounds necessary for reliable portrayal of cellular dynamics in response to spatial variation of extracellular compounds may be still too large. An interesting method to overcome these numerical difficulties is the general hybrid multizonal/CFD [27-36], which gave momentum to the application of CFD modeling for bioreactors. 

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