Variation and Prediction Methods of the Explosion Characteristic Parameters of Coal Dust/Gas Mixtures

In order to investigate the change law of the explosion characteristic parameters of hybrid mixture of coal dust and gas, and then establish an effective prediction method of these parameters, the maximum explosion pressure, explosion index, and lower explosion limit of coal dust and gas mixtures were measured in a standard 20 L spherical explosion system. Four different kinds of hybrid mixture were selected in this study and they are composed of coal dust with different components and gas respectively. According to the measured results, the change law of the explosion characteristic parameters of hybrid mixture of coal dust and gas was analyzed, and the prediction method of these parameters was discussed. The results show that the addition of gas to a coal dust cloud can obviously increase its maximum explosion pressure and explosion index and notably reduce its minimum explosion concentration. On increasing the gas equivalent ratio, the maximum explosion pressure of coal dust and gas mixture increases linearly and the explosion index increases quadratically, while the decrease curve of the lower explosion limit is nonlinear. Based on these change laws, the methods for predicting the maximum explosion pressure and the explosion index of hybrid mixture of coal dust and gas were established respectively. The applicability of the existing methods for predicting the lower explosion limit of hybrid mixture to coal dust and gas mixture was demonstrated.

Jet-shaped geometrically modified light curves of core-collapse supernovae

ABSTRACT We build three simple bipolar ejecta models for core-collapse supernovae (CCSNe), as expected when the explosion is driven by strong jets, and show that for an observer located in the equatorial plane of the ejecta, the light curve has a rapid luminosity decline, and even an abrupt drop. In calculating the geometrically modified photosphere we assume that the ejecta has an axisymmetrical structure composed of an equatorial ejecta and faster polar ejecta, and has a uniform effective temperature. At early times the photosphere in the polar ejecta grows faster than the equatorial one, leading to higher luminosity relative to a spherical explosion. The origin of the extra radiated energy is the jets. At later times the optical depth decreases faster in the polar ejecta, and the polar photosphere becomes hidden behind the equatorial ejecta for an observer in the equatorial plane, leading to a rapid luminosity decline. For a model where the jets inflate two low-density polar bubbles, the luminosity decline might be abrupt. This model enables us to fit the abrupt decline in the light curve of SN 2018don.

Study and Numerical Simulation on Explosion Propagation Characteristics of Lignite Dust

In order to reveal the explosion propagation law of lignite dust in 20L spherical explosion test device, the dust diffusion behavior and explosion propagation characteristics of lignite were studied by experiment and numerical simulation. The propagation process of dust explosion is studied by using high-speed camera and 20L spherical explosion test system, and the process of dust diffusion and explosion is simulated by using FLUENT software. The results show that the explosion propagation of lignite dust in the 20L spherical explosion test system has four different stages: the first explosion stage, the full explosion combustion stage, the continuous combustion stage and the combustion attenuation stage. The test results are slightly different from that of the fluent simulation of lignite dust explosion by using the high-speed camera to collect the dust explosion images. Results within the allowable error range, the experimental image of explosion combustion of lignite dust is well connected with the simulation results, which has a good display effect on the explosion propagation of lignite dust.

Modeling of the spherical explosion attenuation process using aqueous foam

The two-phase model of dry aqueous foam dynamic behavior under the strong shock wave influence is presented under assumption that the foam structure under shock loading is destroyed into a suspension of monodispersed microdrops with the formation of a gas-droplet mixture. The system of equations for the model of aqueous foam includes the laws of conservation of mass, momentum and energy for each phase in accordance with the single-pressure, two-speed, two-temperature approximations in a three-dimensional formulation, taking into account the Schiller–Naumann interfacial drag force and the Ranz–Marshall interfacial contact heat transfer. The thermodynamic properties of air and water forming a gas-droplet mixture are described by the Peng–Robinson and Mie–Grueneisen equations of state. The presence of non-uniform process in height of aqueous foam syneresis, which is due to gravitational forces, is taken into account by setting the distribution of the liquid volume fraction in the foam. An additional consideration of the syneresis process during calculating the intensity of interphase drag forces according to the Schiller–Naumann model was controlled by introducing the parameter depending on the spatial distribution of the initial liquid volume fraction of the foam. The spherical explosion is modeled in the form of the shock wave pulse whose energy coincided with the charge energy of the HE used in the experiments. The problem numerical solution is implemented using the OpenFOAM free software package based on the two-step PIMPLE computational algorithm. The numerical solution of the problem, obtained on the basis of the proposed gas-droplet mixture model, is in satisfactory agreement with the experimental data on a spherical explosion in aqueous foam. The analysis of the spherical shock wave dynamics while its propagation through aqueous foam is given. The causes of the significant decrease in the amplitude and velocity shock waves propagation in the medium under study are investigated.

Investigation of axisymmetric wave flows under interaction of a spherical impact pulse with a barrier of aqueous foam

The problem of spherical explosion in the gas region with a protective foam layer is solved in a two-dimensional axisymmetric formulation using a two-phase model of a gas-liquid mixture that includes the laws of conservation of mass, momentum and energy of the mixture and the equation for the dynamics of the volume content of phases. The numerical implementation of the model was carried out by modifying the standard solver of the compressibleMultiphaseInterFoam of the open package OpenFOAM. The results of computer modeling are visualized using the ParaView graphical platform.

Numerical Simulation and Experimental Study on Formation of High Concentration of H2 Generated by Gas Explosion

In coal mine fire rescues, if the abnormal increase of gas concentration occurs, it is the primary thing to analyze the reasons and identify sources of the abnormal forming, which is also the basis of judge the combustion state of fire area and formulate proper fire reliefs. Nowadays, related researches have recognized the methane explosion as the source of high concentration of H2 formation, but there are few studies about the conditions and reaction mechanism of gas explosion generating high concentration of H2.Therefore, this paper uses the chemical kinetic calculation software, ChemKin, and the 20L spherical explosion experimental device to simulate the generating process and formation conditions of H2 in gas explosion. The experimental results show that: the decomposition of water vapor is the main base element reaction (R84) which leads to the generation of H2.The free radical H is the key factor to influence the formation of H2 generated from gas explosion. With the gradual increase of gas explosion concentration, the explosive reaction becomes more incomplete, and then the generating quantity of H2 increases gradually. Experimental results of 20L spherical explosion are consistent with the change trend about simulation results, which verifies the accuracy of simulation analysis. The results of explosion experiments show that when gas concentration is higher than 9%, the incomplete reaction of methane explosion increases which leads to the gradual increase of H2 formation.