Himičeskaâ fizika

An experimental study of oxidative conversion of ethanol to syngas in a filtration combustion moving bed reactor was conducted. The dependence of the composition of gaseous products on the flow rate of gaseous oxidizer at a constant excess air coefficient was investigated. The nonuniformity of the gas composition over the reactor cross-section was detected. A richer mixture flows in the central part of the reactor — the excess air coefficient values were 20–30% lower than the average value, and a leaner mixture flows in the near-wall region (15–20% higher than the average value). Numerical modeling of the part of the reactor where ethanol oxidation occurs qualitatively confirmed the presence of nonuniformity reactant concentration field and gas flow rates.

The results of numerical simulation of the damping of an air shock wave from an emergency methane explosion in a mine are presented. The results of an analysis of the effectiveness of using water barriers to reduce the intensity of air shock wave, depending on their length, are presented. The effect of the gradual deposition of water droplets from the water barrier onto the walls of the mine on the intensity of the shock wave passing through the barrier has been determined. The rate of precipitation of water droplets from the gas-droplet mixture formed by the interaction of the shock wave with the water barrier has little effect on the intensity of the shock wave passing through the barrier.

The review presents the available information on the process of flameless combustion of energy materials in ballasted systems. The methods of its organization, the results of studies of the process itself and the properties of the resulting composite materials, as well as its application for obtaining new functional materials are demonstrated.

A high-speed turbulent reacting flow in a channel with a sudden expansion in the form of two symmetrically located steps is numerically investigated. Various combustion phases are described: initial phase with low combustion completeness and intensive one with high combustion completeness. In the intensive phase, depending on the heat release power, a pulsating (self-oscillating) combustion mode can be realized with periodic movement of the intensive heat release zone upstream and downstream and also a mode with thermal choking, in which the shock formed in the thermal throat, spreading upstream, enters the narrow injector channel part and blocks the flow. The transition to subsonic flow occurs if the heat release exceeds the total heat flux at the inlet by one and a half times or more. The pulsating mode, in which the velocity in the flow core remains supersonic, is realized if the total heat release power is approximately equal to the heat flux at the channel entrance. An analysis of the stages of the pulsating nonpremixed hydrogen-air combustion showed that the flame flashback accompanied by an increase in heat release, is caused by the boundary layer separation and the formation of a hot wall jet directed toward the step, i.e. against the core flow. After the heat source has stabilized at the beginning of the channel, the heat source power decreases due to the complete burnout of the oxidizer, as a result of which the thermal throat expands and fresh reagents enter the channel. At the end of the channel straight section, a new heat source is formed, which starts moving upstream, and the whole process is repeated periodically.

High attention is now devoted to a fire safety of objects with a presence of hydrogen due to a rapid development of a hydrogen energetics. An evaluation of a risk for the objects of hydrogen energetics is one of the key tasks for a such development. A decision of this task requires an information on a radiation intensity of hydrogen flames. But this information published in literature is often non-complete and sometimes contradictive. Therefore, this study is aimed on a review of literature sources published in Russian and international journals. The main value required for the fire risk evaluation is a surface radiation intensity of hydrogen flames. In this study four types of the flames were considered: gaseous jet flame; jet flame of liquid hydrogen; pool fire of liquid hydrogen; fireball. It was noted that surface thermal radiation intensity of the hydrogen flames is remarkably lower in comparison with hydrocarbon flames. The surface thermal radiation intensity Ef of a hydrogen gaseous jet flame cfn be accepted to be equal 33 kW/m² in the fire risk calculations. The Ef value for the hydrogen fireball can be accepted to be equal 330 kW/m². The surface thermal radiation intensity for combustion of liquid hydrogen (both for the jet flame and the pool fire) can be accepted to be equal 80 kW/m².