Reacting flows, multicomponent

There are many excellent texts on combustion [153,235,380,412,424,435], all of which discuss fundamental principles but differ in their applications focus. The classic book by Bird, Stewart, and Lightfoot emphasizes the fundamental principles of transport phenomena, including multicomponent and chemically reacting flow [35]. Rosner s book [339] also develops much of the transport theory for chemically reacting flow systems. In materials processing, such as the synthesis of electronic thin films, there are fewer texts that present the details of chemically reacting flow. However, excellent presentation of the fundamentals can be found in book chapters by Kleijn [228] and Jensen [202]. 

The objective of this problem is to explore the multicomponent diffusive species transport in a chemically reacting flow. Figure 3.18 illustrates the temperature, velocity, and mole-fraction profiles within a laminar, premixed flat flame. These profiles are also represented in an accompanying spreadsheet (premixed h2. air-flame. xls). 

Expressions for the transport coefficients suitable for use in computational simulations of chemically reacting flows are usually based on the Chapman-Enskog theory. The theory has been extended to address in detail transport properties in multicomponent systems [103,178]. 

Consistent with the objective of this chapter, it is important to return to the type of flow encountered in the freeboard of the rotary kiln and address reacting flows. The freeboard flow of interest involves the reacting flow type, which is almost always multicomponent, composed of fuel, oxidizer, combustion products, particulates, and so forth. The thermodynamic and transport properties of multicomponent reacting fluids are functions, not only of temperature and pressure, but also of species concentration. The basic equations that describe the simplest case of reacting turbulent flow include conservation equations for mass, concentration, momentum, and enthalpy equations as well as the associated reaction and equations of state for the system (Zhou, 1993),... 

The application of NMR to the study of chemical reactions has been expanded to a wide range of experimental conditions, including high pressure and temperatures. In 1993, Funahashi et al. [16] reported the construction of a high pressure 3H NMR probe for stopped-flow measurements at pressures <200 MPa. In the last decade, commercial flow NMR instrumentation and probes have been developed. Currently there are commercially available NMR probes for pressures of 0.1-35 MPa and temperatures of 270-350 K (Bruker) and 0.1-3.0 MPa and 270-400 K (Varian). As reported recently, such probes can be used to perform quantitative studies of complicated reacting multicomponent mixtures [17]. 

The reaction mixture is usually composed of a multicomponent system and the reactants have to diffuse through a complex network structure of a large pore size distribution, which ranges from micropores to macropores. Actually the flow of the reaction mixture through the porous media is limited by the diffusion rates of the reacting components. 

The mathematical model, which makes it possible to consider the influence of the hydrodynamic conditions of flow on the processes of mixing and chemical transformations of reacting substances in a liquid phase, assumes that the average flow characteristics of a multicomponent system can be described by the equations of continuum mechanics and will satisfy conservation laws. 

---