Flow Modeling For Reactor Engineering

Basic tasks of reaction and reactor engineering are discussed in the first chapter. A general methodology for applying computational flow modeling tools to reactor engineering is also briefly discussed in Section 1.3. Basic information about the elements of computational flow modeling (CFM) is given in Section 1.2 and Chapters 2-8. Applications of CFM to reactor engineering are now discussed here in detail.

A variety of chemical reactors are being used in industrial practice: some typical reactors are shown in Fig. 1.2. Pertinent design issues for each of these reactor types are different and are impossible to discuss in a single chapter. A general methodology can, however, be discussed without going into details of each reactor type. Before we proceed, it should be noted that most industrial chemical reactors present severe challenges to the mathematical modeler. A reactor engineer needs to be familiar with the basic concepts of the mathematical modeling of physical processes (see, for example, Denn, 1986; Aris, 1978; Polya, 1962). The relative importance and roles of governing equations, constitutive equations, boundary conditions and input data need to be clearly understood while interpreting results and drawing engineering conclusions based on simulation results.

Adequate mathematical representation of any complex physical process may require many different mathematical models, perhaps a continuum of models, each having different capabilities, appropriate to its specific objectives. Reactor engineers must recognize the possibility of employing a hierarchy of models to develop the necessary understanding and to obtain the required information to achieve complex reactor engineering objectives. Perhaps an analogy with the variety of vehicles available for transport may make the point clear. Various alternative vehicles, from a bicycle, scooter, car and helicopter to aircraft are available for a person who wants to travel. Each of these vehicles has unique features and a corresponding range of applications. Availability of powerful alternatives for transport has not made other less powerful modes obsolete. More often than not, the best way to travel the desired distance is based on using different vehicles for different parts of the journey. Similarly, there will be a hierarchy of mathematical models, each having some unique features and corresponding range of application, which may be used to construct as complete a picture of the physical process as possible. Computational flow modeling is certainly a very powerful tool and in principle, a self-consistent, comprehensive mathematical model can be constructed to simulate the behavior of industrial reactors within a CFM framework. However, it would be inefficient to use such a complex model to obtain information which might be obtained by relatively simple models. The reactor engineer has, therefore, to match the available modeling tools and reactor engineering objectives at hand. It is often difficult to develop a mathematical model which addresses the practical reactor engineering problem directly. Instead, it is necessary to use different models to develop the required understanding and information, and combining this with engineering judgement to propose an appropriate reactor engineering solution. CFM certainly enhances the capability of a reactor engineer to make deeper journeys into the underlying physics for a better understanding. It should, however, be used along with other models with different capabilities to construct an overall picture. The necessity of using a hierarchy of modeling tools and establishing a clear relationship between the reactor engineering objectives and computational flow modeling, is illustrated here with the help of some examples.

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