Species temperature and

Because many practical flames are turbulent (spark ignited engine flames, nil field flares), an understanding of the interaction between the complex fluid dynamics of turbulence and the combustion processes is necessary to develop predictive computer models. Once these predictive models are developed, they arc repeatedly compared with measurements of species, temperatures, and flow in actual flames for iterative refinement. If the model is deficient, it is changed and again compared with experiment. The process is repeated until a satisfactory predictive model is obtained. 

Figures 4.6—4.8 are the results for the stoichiometric propane-air flame. Figure 4.6 reports the variance of the major species, temperature, and heat release Figure 4.7 reports the major stable propane fragment distribution due to the proceeding reactions and Figure 4.8 shows the radical and formaldehyde distributions—all as a function of a spatial distance through the flame wave. As stated, the total wave thickness is chosen from the point at which one of the reactant mole fractions begins to decay to the point at which the heat release rate begins to taper off sharply. Since the point of initial reactant decay corresponds closely to the initial perceptive rise in temperature, the initial thermoneutral period is quite short. The heat release rate curve would ordinarily drop to zero sharply except that the recombination of the radicals in the burned gas zone contribute some energy. The choice of the position that separates the preheat zone and the reaction zone has been made to account for the slight exothermicity of the fuel attack reactions by radicals which have diffused into...

Tunable diode-laser sensors offer considerable promise for combustion research and development and also for process sensing and control applications. These devices are rugged and relatively easy to operate and they have been demonstrated to yield simple and quantitative measurements of species, temperature, and velocity, where line-of-sight measurements are useful or preferred. These techniques will grow in use as costs of laser sources and fiber-optic components decrease and access to more wavelength regions improves. 

Species, Temperature, and Current Distribution Mapping in Polymer Electrolyte Membrane Fuel Cells... 

Chapters 4-6 address specific diagnostic methods in PEFCs. Martin et al. provide a detailed review of methods for distributed diagnostics of species, temperature, and current in PEFCs in Chapter 4. In Chapter 5, Hussey and Jacobson describe the operational principles of neutron radiography for in-situ visualization of liquid water distribution, and also outline issues related to temporal and spatial resolution. Tsushima and Hirai describe both magnetic resonance imaging (MRI) technique for visualization of water in PEFCs and tunable diode laser absorption spectroscopy (TDLAS) for measurement of water vapor concentration in Chapter 6. 

For the 1-D gas channel model, the specie, temperature, and velocity distributions inside the gas channels are assumed to be varying only in the direction of gas flow. The control volume employed, shown in Figure 5.5, encompasses the whole... 

FORTRAN computer program that predicts the species, temperature, and velocity profiles in two-dimensional (planar or axisymmetric) channels. The model uses the boundary layer approximations for the fluid flow equations, coupled to gas-phase and surface species continuity equations. The program runs in conjunction with CHEMKIN preprocessors (CHEMKIN, SURFACE CHEMKIN, and TRAN-FIT) for the gas-phase and surface chemical reaction mechanisms and transport properties. The finite difference representation of the defining equations forms a set of differential algebraic equations which are solved using the computer program DASSL (dassal.f, L. R. Petzold, Sandia National Laboratories Report, SAND 82-8637, 1982). 

The number of adsorbed species, temperature, and pressure or solute concentration will determine the position of the equilibrium, i.e., how much solute is adsorbed relative to how much remains in solution. Adsorption will increase with solute concentration and decreasing temperature. Figure 1 shows plots of the... 

Let us assume that the microenulsion contains spherical globules of a single size. For given numbers of molecules of each species, temperature and external pressure, we consider an ensemble of systems in which the radii and volume fractions of the globules can take arbitrary values. Because the equilibrium state of the system is completely determined by the number of molecules of each species, the temperature and external pressure, the actual values of the radius and volume fraction will result from the condition that the free energy of the system be a mlnlnum. 

All these factors are functions of the concentration of the chemical species, temperature and pressure of the system. At constant diffu-sionai resistance, the increase in the rate of chemical reaction decreases the effectiveness factor while al a constant intrinsic rate of reaction, the increase of the diffusional resistances decreases the effectiveness factor. Elnashaie et al. (1989a) showed that the effect of the diffusional resistances and the intrinsic rate of reactions are not sufficient to explain the behaviour of the effectiveness factor for reversible reactions and that the effect of the equilibrium constant should be introduced. They found that the effectiveness factor increases with the increase of the equilibrium constants and hence the behaviour of the effectiveness factor should be explained by the interaction of the effective diffusivities, intrinsic rates of reaction as well as the equilibrium constants. The equations of the dusty gas model for the steam reforming of methane in the porous catalyst pellet, are solved accurately using the global orthogonal collocation technique given in Appendix B. Kinetics and other physico-chemical parameters for the steam reforming case are summarized in Appendix A. 

In the case of methanol adsorption and oxidation, which has been thoroughly studied since several years, and which was taken as a typical example, apart fiom the poisoning CO species, which are always present at the electrode surface, particularly for high methanol concentration ( 0.1 M), there are many other adsorbed species at the electrode surface, which behave as reactive intermediates, namely methyl, formyl, formate radicals, and even methyl formate. The surface distribution of the different adsorbed species was shown to depend strongly on the electrode structure, electrode potential, concentration of the electroreactive species, temperature and pH of the electrolytic solution. 

Understanding. As electrochemical reactors with gradients of species, temperature, and potential in all dimensions and over a broad range of scales from nanometers to meters, fuel cells are complex devices. Changing a single parameter (e.g., the gas humidity in a PEMFC) can result in effects on the scale of reaction kinetics and other parameters, all the way to temperature distribution in a fuel ceU stack. This multitude of effects, as well as their consequences as felt in important parameters such as efficiency or power density, is difficult or impossible to comprehend without modeling approaches. 

---