Mixing ideal chemical

The design equations for a chemical reactor contain several parameters that are functions of temperature. Equation (7.17) applies to a nonisothermal batch reactor and is exemplary of the physical property variations that can be important even for ideal reactors. Note that the word ideal has three uses in this chapter. In connection with reactors, ideal refers to the quality of mixing in the vessel. Ideal batch reactors and CSTRs have perfect internal mixing. Ideal PFRs are perfectly mixed in the radial direction and have no mixing in the axial direction. These ideal reactors may be nonisothermal and may have physical properties that vary with temperature, pressure, and composition. 

A knowledge of v can give an indication of the transit time of a plug of chemical or an ensemble of cells through a microfluidic channel network and thus to assess whether there is enough time for complete mixing or chemical reaction. Both Eq. (11) and Eq. (12) are strictly only valid under idealized conditions (i.e. incompressible and non-viscous fluids and steady flow), but can still be helpful for overall estimation and assessment. 

Even for systems with highly complex fluid dynamics, where the flow cannot adequately be approximated by a single chemical reactor, a network of ideal reactors may form the basis of a useful approximation. Because of the computational difficulties of handling mixing and chemical reaction in the complex flow patterns encountered in industrial applications,... 

Therefore, the analysis of the main object of this book, namely, the batch chemical reactor, can start by considering the different ideal chemical reactors. In fact, ideal reactors are strongly simplified models of real chemical reactors [10], which however capture the two major features mentioned above. These models can be classified according to the mode of operation (i.e., discontinuous vs. continuous) and to the quality of mixing (i.e., perfect mixing vs. no mixing). The three resulting ideal reactors are sketched in Fig. 2.1. 

As discussed in Sect. 2.1, physical and mathematical models of ideal chemical reactors are based on two very simplified fluid dynamic assumptions, namely perfect mixing (BR and CSTR) and perfect immiscibility (PFR). On the contrary, in real tank reactors the stirring system produces a complex motion field made out of vortices of different dimensions interacting with the reactor walls and the internal baffles, as schematically shown in Fig. 7.2(a). As a consequence, a complex field of composition and temperature is established inside the reactor. 

It may be seen that components of the model discussed thus far are generally applicable to any two phase ideal back-mixed reactor. Chemical kinetics and phase equilibrium are the two components which make the model unique. 

Droplet-based two-phase flows offer controlled picoliter or femtoliter volumes of droplets (Fig. 7a) which are almost ideal chemical reactors and therefore have been utilized in emulsification and encapsulation, microreaction, synthesis, mixing, and bioassay [7],... 

Figure 4.1. The three types of ideal chemical reactors. The ideal batch reactor (BR) is well mixed but closed to mass transfer. The ideal mixed flow reactor (MFR) is well mixed and subject to continuous mass transfer.The fluid in an ideal plug flow reactor (PFR) moves as slugs, which are closed to mass transfer with each other and therefore act as batch reactors moving through space.

The systems to be studied in some detail here involve various aspects of a continuous-flow, well-agitated vessel, with interacting variables such as flow, pressure, mixing, and chemical reaction. The study of stirred tanks is important for two reasons. First, stirred tank vessels are an important and frequent piece of process equipment, and engineers must be capable of modeling this kind of system. Second, the stirred tank concept is an important idealized lumped unit which can be used effectively by an experienced engineer to simulate the behavior of more complicated process equipment. 

In Oiapter 3 the importance of mixing in chemical reactors was indicated with the defmition of two ideal reactor types the plug flow reactor, in which no mixing takes place at all, and the perfectly mixed continuous reactor, with infinite mixing rates. The concept of mixing itself, however, was not analysed. 

Brodkey, R. S., and S. M. Kresta (1999). Turbulent mixing and chemical reactions in an ideal tubular reactor, presented at Mixing XVII, Banff, Alberta, Canada, Aug. 20-25. 

Gjd can be decomposed into terms representing the free energy of mechanical mixing and the free energy of ideal chemical mixing ... 

The second term in brackets, equation (6b), represents the contribution of ideal chemical mixing to G. Because 0 X 1,... 

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