Ignition, extinction, and thermal hysteresis of a heterogeneous exothermic reaction

Critical conditions of ignition and extinction are studied theoretically for the case of a heterogeneous exothermic reaction proceeding on the uniformly accessible surface of a channel or a pore. Particular emphasis is placed on the thermal-hysteresis effect of the reaction (an ignition temperature in excess of the extinction temperature), which ensures stability of the reaction against changes in the external conditions. A model for the process is proposed and substantiated. It permits one to analyze the main regularities of the thermal reaction regime with allowance for the distribution of heat flows from the reaction zone to the reaction medium and the channel wall. The dependence of the critical conditions of ignition and extinction on the rate constants of heat release, the reaction order, and the thermal and geometric characteristics of the system is established. A rule is proposed that permits evaluating the effect of heat losses on the critical phenomena and the thermal hysteresis of a reaction on a cooled surface in the case where the critical conditions for the reaction on an adiabatic surface are known.