Chernenco A. The role of thermal radiation and the Stefan flow during high heat and mass transfer of particles from gas

The topic of the thesis is scientific analysis of the role of thermal radiation, Stefan flow and parallel chemical reactions in the processes of ignition, high tempera-ture oxidation and spontaneous extinction of spherical particles in a nitrogen-oxygen mixtures, at phase and chemical transformations happening on the surface of parti-cles. It is established and experimentally confirmed that the heat loss by radiation leads to appearance of the upper limit of the area of ignition diameters for nitrogen-oxygen mixtures at room-level temperature; the condition of existence of such area was produced analytically. It is shown that the dependence of regime parameters (temperature of the gas, concentration of the oxidizer, diameter of the particle) on the stationary temperature is used for analytical determination of the critical value of ini-tial temperature. The possibility of use of condition of the time derivative of particle temperature to be equal to zero at the initial moment of time is justified, in order to estimate the conditions of ignition of metallic particles coated with condensed oxide. An influence of initial conditions (temperature and diameter of a particle) on characteristics of its high temperature heat and mass exchange and spontaneous ex-tinction is analyzed. A method to produce monodisperse carbon particles from the pre-made polydisperse ones is proposed. The important role of Stefan flow at analy-sis of characteristics of high temperature heat and mass exchange and spontaneous extinction of carbon and metallic particles (in contrast to the critical conditions of ig-nition) is specially noted. Approximate formulas for the rates of oxidation and evapo-ration of a volatile metal are produced at consideration of the Stefan flow, that allows to analyze the interaction of these processes. Two limits of self-ignition of the particle in a heated gas as well as conditions to observe them at the presence of heat loss by radiation to the cold walls of the reaction chamber are determined in analytical form.