Stability diffusive regime

Laminar flame speed is one of the fundamental properties characterizing the global combustion rate of a fuel/ oxidizer mixture. Therefore, it frequently serves as the reference quantity in the study of the phenomena involving premixed flames, such as flammability limits, flame stabilization, blowoff, blowout, extinction, and turbulent combustion. Furthermore, it contains the information on the reaction mechanism in the high-temperature regime, in the presence of diffusive transport. Hence, at the global level, laminar flame-speed data have been widely used to validate a proposed chemical reaction mechanism. 

A link between laminar and turbulent lifted flames has been demonstrated based on the observation of a continuous transition from laminar to turbulent lifted flames, as shown in Figure 4.3.13 [56]. The flame attached to the nozzle lifted off in the laminar regime, experienced the transition by the jet breakup characteristics, and became turbulent lifted flames as the nozzle flow became turbulent. Subsequently, the liftoff height increased linearly and finally blowout (BO) occurred. This continuous transition suggested that tribrachial flames observed in laminar lifted flames could play an important role in the stabilization of turbulent lifted flames. Recent measurements supported the existence of tribrachial structure at turbulent lifted edges [57], with the OH zone indicating that the diffusion reaction zone is surrounded by the rich and lean reaction zones. 

Barkey, Tobias and Muller formulated the stability analysis for deposition from well-supported solution in the Tafel regime at constant current [48], They used dilute-solution theory to solve the transport equations in a Nernst diffusion layer of thickness S. The concentration and electrostatic potential are given in this approximation... 

Influence of Sample Thickness and 02 Diffusion. As shown above, the overall conversion of thermal degradation can depend of the sample thickness in the diffusion-controlled regime. Thus, stability comparisons are only valid for samples of comparable thickness. Let us now compare two polymers of glass transition temperatures Tgl and Tg2, oxidized at a temperature T, such that Tgl < T < Tg2. Even if the intrinsic oxidation rates are equal, polymer 1 will appear more unstable than polymer 2 because oxygen diffusion is faster above than below Tg. The thickness of the oxidized layer will be higher for polymer 1 than for polymer 2. 

In the present case, the flame front is stabilized by the CRZ (1) but the heat release magnitude is reduced in the evaporation zone because of both effects (2) and (3). To determine the flame regime (premixed and/or diffusion), the Takeno index T = VYjp.VYq and an indexed reaction rate... 

Most of the electrochemical phenomena occur in size regimes that are very small. The effects of size on diffusion kinetics, electrical double layer at the interface, elementary act of charge transfer and phase formation have recently been reviewed by Petrri and Tsirlina [12]. Mulvaney has given an excellent account of the double layers, optical and electrochemical properties associated with metal colloids [11]. Special emphasis has been given to the stability and charge transfer phenomenon in metal colloid systems. Willner has reviewed the area of nanoparticle-based functionalization of surfaces and their applications [6-8]. This chapter is devoted to electrochemistry with nanoparticles. One of the essential requirements for electrochemical studies is that the material should exhibit good conductivity. 

A summary picture is presented in Fig. 5.43. The catalytic process can be carried out in the kinetic and in the diffusion-limited regime. In the figure the former case is represented by the smooth Pt data. The catalyst potential stabilizes at a rather high value ( 1 V) — at lower values the alcohol oxidation would not be able to keep up with the 02-reduction rate. At this potential the Pt surface is covered to an appreciable extent with Oad species (that are not involved in the... 

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