Vol 53, No 6 (2017)

This paper describes the mathematical simulation of an industrial membrane reactor for propane dehydrogenation in the thermodynamic coupling with hydrogen combustion (oxidation). Due to the effective removal of hydrogen through a membrane and the heat release as a result of an exothermic reaction, the temperature of the reaction stream at the input could be reduced to 500◦C. The fact that the process is carried out on an industrial-level membrane reactor makes it possible to reach a propane conversion of 75% with a propylene selectivity of 97%, which exceeds the figures obtained per pass in existing industrial devices at higher temperatures.

A solution is obtained to the problem of determining the conditions of hydrodynamic stability in the presence of flow of gaseous combustion products over the propellant gasification surface. The cross-flow has a small gradient along the direction of motion. Analysis of the obtained dispersion equation shows that hydrodynamic instability with oscillations develops. The transfer coefficients of natural turbulence are represented as the sum of two terms: the first is responsible for the transfer in the absence of cross-flow, and the second takes into account the enhancement of transport processes in the case of cross-flow. Their dependence on the initial temperature of solid propellant combustion predicts a reduction in the negative erosion effect in accordance with experimental data. Accounting for the relaxation time of the evaporation process has a stabilizing effect. In the limit of strong relaxation, this leads to oscillatory stability (in the absence of crossflow) where the perturbations neither grow nor decay. However, arbitrarily weak cross-flow leads to instability.

The combustion of a highly exothermic mixture of calcium chromate with aluminum and boron has been studied. It has been shown that these mixtures are able to burn in a wide range of reactant ratios. The autowave chemical transformation is accompanied by decomposition of calcium chromate, the chemical reaction of the decomposition products with aluminum and boron, the formation of a two-phase melt of the combustion products with its subsequent gravity separation, and crystallization of the layers. The results of the study may be useful for obtaining chromium borides.

This paper presents an experimental study of heat and mass transfer and phase transformations in the suppression of flaming combustion and thermal decomposition of model ground, crown, and mixed forest fires due to local exposure to water. The experiments were carried out with typical combustible forest materials (mixture of leaves, needles, and twigs) and models of trunks and branches of trees. The conditions and characteristics of suppression of the flaming combustion and thermal decomposition of combustible forest materials were determined. It is shown that in the case of crown and mixed fires, local short-term (a few seconds) action of a liquid projectile does not suppress the thermal decomposition of the material (but can only lead to localization of flaming combustion). In the case of ground forest fires, this approach can be efficient with an appropriate choice of the water-irrigated area of the combustion zone and the rate and time of water spraying.

Interaction of an expanding shock wave with a layer of particles having a rough surface is considered within the framework of the collisional model of a gas suspension. The influence of roughness on the shape of the contact boundaries in the gas phase and on the boundaries of the cloud of particles is analyzed. The development of the Richtmyer–Meshkov instability is demonstrated. Factors of particle dispersion are determined. Instability evolution is found to increase the amplitude of surface disturbances, and the development of collision dynamics favors smearing of finger-type structures. If the particle motion is essentially random, the pattern of cloud spreading is similar to that observed in experiments.

A method is proposed for determining the energy release in a combustible mixture, which is based on processing the trajectory of the expanding wave from the viewpoint of the strong explosion model. The wave trajectory in the case of critical initiation of multifront detonation in a combustible mixture is compared with the trajectory of a blast wave generated by the same initiator in an inert mixture whose gas-dynamic parameters are equivalent to those of the combustible mixture. The energy release is defined as the difference between the joint energy release of the initiator and combustible mixture in the case of critical initiation and the energy release of the initiator in the case of blast wave excitation in the inert mixture. Results of experimental validation of the method by an example of a stoichiometric acetylene–oxygen mixture are presented. Noticeable deviations of the experimental profile of energy release from available model concepts are observed.

The formation of a deposit from mixtures of PETN with fine aluminum under the action of neodymium laser radiation in a free generation mode is studied. This paper also describes the efficiency of a deposit as a means to reduce the energy of laser initiation of mixtures as a function of fineness of PETN, aluminum content in initiated mixtures and deposit, mixture density, and diameter of the laser action region on the explosive. The compositions of mixtures for preparing deposits optimal in composition, which reduce the initiation energy of mixtures of PETN and aluminum down to 3.75 times, are determined. The functioning mechanism of a deposit during laser initiation of mixtures of PETN and aluminum is under discussion.

This paper presents the results of investigation of the detonation velocity of an emulsion explosive sensitized with Expancel polymer microballoons in a wide range of initial density of 0.14–1.33 g/cm³. It is shown that at a density of the emulsion explosive less than 0.4 g/cm³, detonation with an unstable front characteristic of liquid explosives is possible.