Dark zone velocity

In the dark zone, the temperature increases relatively slowly and so for the most part the temperature gradient is much less steep than that in the fizz zone. However, the temperature increases rapidly at about 50 pm from where the flame reaction starts to produce the luminous flame zone. The gas flow velocity increases with increasing distance due to the increase in temperature. The mole fractions of NO, CO, and Hj decrease and those of N2, CO2, and H2O increase with increasing distance in the dark zone. The results imply that the overall reaction in the dark zone is highly exothermic and that the order of reaction is higher than second order because of the reduction reaction involving NO. The derivative of temperature with respect to time t in the dark zone is expressed empirically by the formulal =l... 

Mechanisms of Flame Stabilization. CRITICAL BOUNDARY VELOCITY GRADIENT. A flame stabilized at the port of a Bunsen burner does not actually touch the rim. There is a dark region, called the dead space, between the rim and the flame. Heat is removed and free radicals are destroyed by the solid surface the burning velocity is reduced to zero and the flame is quenched. Even beyond the dead space, where the flame is able to exist as a luminous reaction zone, the burning velocity only gradually rises to the value achieved at a distance from solid surfaces. 

Figure 16 Schematic illustration of mechanisms for transfer of sediments, volcanics, and/or lower erustal gabbros into the mantle wedge from the subducting plate and the base of arc crust. Dark black line indicates position of the subduction zone below this line, material subducts at the convergence velocity. Above this line, material is carried downward more slowly. Any process leading to slow transport of low-melting point metasediment, metabasalt, or metagabbro into the mantle wedge would lead to partial melting of this material beneath an arc.

Figure 6.5 Top view of canopy. Circles represent cylindrical stems of diameter d. Behind each stem is a recirculation zone (black) of length yd, where y is an 0(1) function Re. The wake downstream of each recirculation zone has length (Co ) 1 (light gray). Where wakes overlap (dark gray), the velocity deficit is the linear sum of individual wake deficits. Particles 1, 2, 3 released together at x = 0 and t = 0 pass through different velocity zones and travel different longitudinal distances (x1,x2,x3) in time, t, such that the spatial variance in the velocity field produces longitudinal dispersion.

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