A. N. Ivanova

Nature of the concentration limits of flame propagation in hydrogen–air mixtures

A necessary condition associated with fuel caloricity and chain ignition temperature is formulated for flame propagation. The lower temperature limit of flammability as a function of mixture composition is obtained on the basis of a branched-chain mechanism corresponding to terms of the origin of a wave in a cold mixture. The rotary points of this limit that can be associated with the concentration limits of flame propagation are determined. This qualitative picture of wave formation is confirmed by numerical calculations of the structure of a wave during its propagation. Experimental data on the ignition of mixtures of different composition is compared to the calculated data on limits.

Steady-state mode of operation of the countercurrent reactor. Liquid-liquid heterogeneous system

A two-temperature model of the countercurrent plug-flow reactor for two chemically interacting liquids, the dispersion (continuous) media and dispersed phase, is developed. It is shown that there is a critical velocity of the dispersion medium that delimits two types of steady-state modes. If the velocity is greater than the critical, steady-state regimes with heating the dispersed phase near its inlet are realized. In this mode, the substance dissolved in it burns out completely. If the velocity is less than the critical value, then regimes in which the maximum heating is localized near the inlet of the dispersion medium take place, with full consumption of the reactant. It is shown that the degree of localization is higher, the greater the reaction rate. A criterion for the parameters is obtained that determines the possibility of a thermal explosion during the startup of the reactor.

Nonlinear phenomena in heterogeneous catalytic reactions with a branched-chain mechanism of formation of active centers

The branched-chain mechanism of multiplication of active centers on the surface of a catalyst results in a hysteresis temperature dependence of reaction rate. Domain structures appear because of local disturbances in the case of diffusion instability of uniform stationary states under certain conditions for transfer coefficients. Autowave transition processes are characterized by a “plateau“ of zero front velocities with the formation of standing waves.