Secondary reaction zone

H20 and free radicals such as. Above the primary zone is the outer cone or secondary reaction zone. In this region, cooling occurs as a result of mixing with the surrounding atmosphere. This may lead in turn to the entrainment of impurities, such as sodium compounds which will increase... 

The hot, partly combusted gases then come into contact with oxygen from the air and the final flame products are formed. This occurs in what is known as the secondary reaction zone or diffusion zone. This discussion refers to premixed gas flames with laminar (i.e. non-turbulent) flow of the gas mixture to the flame. 

Therefore, taking into account the arrangement of the wood logs, close to the inlet of the secondary reaction zone a very inhomogeneous flow field with stable streaks of combustible gases and oxygen must be assumed. For a further optimisation of the combustion process the improvement of the mixing conditions should be considered besides the other parameters such as residence time and temperatures. 

The main characteristics of the flow field within the secondary reaction zone are ... 

The flow entering the secondary reaction zone is very uniform. Due to the glow bed at the bottom, the entrance velocity is quite high,... 

A body-fitted grid with approximately 200.000 nodes. Figure 12, is used to represent the secondary reaction zone of the investigated test stove. 

On the basis of the before mentioned experimentally determined boundary conditions the homogeneous gas phase combustion within the secondary reaction zone of the investigated test stove is simulated. By means of an example the results of the numerical simulation studies during the main burning phase, about 20 - 30 min after... 

Not all OH radicals will react. Consequently, the primary reaction zone is a mixture of H, OH, H202, and H2. These products will diffuse towards the bulk electrolyte forming a secondary reaction zone (Fig. 2.10). In this zone the diffusion products can undergo oxidation and reduction reactions with the components of the electrolyte. 

The formation of H202 in the liquid phase by bombardment of H20+. This mechanism produces non-faradaic yields of H2, H202, and 02. Depending on the nature of the electrolyte, further chemical reactions may take place in the secondary reaction zone as in glow discharge electrolysis. 

The structure of the flame itself consists of two major zones, the primary reaction zone and a secondary reaction or postheating zone. The primary reaction zone, the area of the flame just above the burner surface, is the region where combustion, atomization, and excitation occurs. Some typical flame combustion products formed in this region are CO, C02, H2, N2, and H20 molecules, as well as O, H, OH-, and C- radical species. The secondary reaction zone is a much cooler region where the flame gases mix with atmospheric components that may include impurities and emission interferants. Between these two zones lies a smaller, but important, intermediate region, where little reaction occurs. In this region of the flame, the fraction of the atoms in the ith excited state, a is controlled only by the prevalent temperature and can be represented by the Boltzmann distribution ... 

Both turbulent burners and premix burners have been used for atomic fluorescence. The premix burner is usually round in shape (a modification of the Meker-type burner), since this provides better geometry for fluorescence than does a slot burner. For an optimum detection limit, the premix burner is also shielded that is, an inert gas such as argon or nitrogen is directed in a sheath around the flame. This elongates the interconal zone and lifts the secondary reaction zone above the burner, separating it from the lower part of the interconal zone where the excitation beam passes. The result is less background emission and less noise, particularly in hydrocarbon flames like air-acetylene or nitrous oxide-acetylene. The premix burner, especially when shielded, appears to offer increased sensitivity over the turbulent burner. 

The dinitrogen oxide-acetylene flame can be used for those elements which cannot be determined successfully with an air-acetylene flame. The temperature of the N20-acetylene flame is only a little lower than that of the air-acetylene flame. In addition, the air-acetylene flame is safer because of its smaller burning velocity (Table 5). A slightly rich N2O-acetylene flame consists of about 2 to 4 mm high blue-white primary reaction zone, above that about 5 to 50 mm high red reduction zone, and on the top a blue-violet secondary reaction zone where the fuel gas oxidizes. The dissociation of the sample takes place in the red reduction zone. 

Measurements of the time-invariant temperature and composition proflles by axial traversal through the flame provide the data required for a quantitative investigation of the high temperature hydrogen-oxygen reaction. Typically, thermocouples, mass spectrometers (for stable component concentrations), and various optical and ESR spectroscopic techniques (for intermediate concentrations) have provided the means for determining flame structure in both the primary and secondary reaction zones. Subatmospheric pressures, and dilute mixtures which burn to produce relatively low temperatures, have been employed to slow the overall reaction, and thus provide adequate spatial resolution for experimental measurements in the primary zone. 

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