Stages Of Explosion Research Articles

Early Stage of the Explosion of Thin Flat Foils in a High-Current Diode at a Current of 40–80 kA

The initial stage of the nanosecond explosion of 1–15 μm-thick flat foils in a diode with a current of 40–80 kA is studied. Projection radiography is used to take images of exploded foils at a spatial resolution of 3–4 μm using the soft X-ray radiation (E = 2.5–5 keV) of a hybrid X-pinch and at a time resolution of 0.1 ns. Foil strips 0.3–2 mm wide and 0.5–7 mm long were introduced in the return circuit of the diode in a high-current BIN generator with a current amplitude of 270 kA and a current rise time of 100 ns; the main load of the generator is an X-pinch. The experiments demonstrate that small-scale structures, the shape and the size of which depend on the foil material and the current density and distribution in a foil, are formed in a foil. Possible scenarios of the structure formation are discussed.

Investigation of the laser-induced surface damage of KDP crystal by explosion simulation.

Under nanosecond pulse irradiation, laser-induced damage of Potassium Dihydrogen Phosphate (KDP) crystal is a multi-physical coupling process which mainly includes energy absorption by precursor defects, temperature and pressure rise in the absorption center, and subsequent micro-explosion event. Till now, related research work mainly focuses on modeling the energy absorption stage and determining the temperature or pressure in the absorption center, but knowledge about the explosion stage is rather limited. In this paper, laser-induced damage of KDP crystal has been investigated through explosion simulation. According to the laser damage test results and morphologies of the damage craters, typical precursor defects inducing KDP surface damage have been determined. Based on the knowledge, equivalent explosion simulation models of the laser damage process have been established to reproduce damage crater formation and shockwave propagation. Finally, laser damage experiments, combined with time resolved techniques, have been utilized to investigate the variation of damage crater size and shockwave speed with laser fluences. Simulation results given by single core explosion models agree well with the experimental results at fluences lower than 60 J/cm2, while a multicore explosion model is needed to reliably simulate damage crater formation at higher fluences.

Analysis of the early stages of liquid-water-drop explosion by numerical simulation

The early stages of the shock-driven explosion of liquid-water microdrops are studied numerically with a high-resolution discretization of the axisymmetric Euler equations. A level-set based conservative interface-interaction method is extended to allow for phase transition. The method is applied to a configuration that has been investigated in recent experiments [Stan et al., Nat. Phys. 12, 966 (2016); Stan et al., J. Phys. Chem. Lett. 7, 2055 (2016)]. The presented results show that the numerical model predicts the initial stages of the violent liquid-drop explosion dynamics accurately. Our results indicate that the deformation of the cylindrical vapor cavity within the droplet is not induced by a torus-shaped negative-pressure wave as was implied from the experimental data. We rather find that this torus-shaped wave is a shock wave, and that the observed vapor-cavity deformation is caused by interaction with a negative-pressure region preceding the torus shock. The simulation results show deviations from experimental results at later stages when the drop deformation is dominated by off-center cavitation, i.e., by effects that require extension of the underlying model to take into account generalized nucleation and recondensation.

Characteristics of Aerosol Chemical Compositions and Size Distributions during a Long-Range Dust Transport Episode in an Urban City in the Yangtze River Delta

A long- and large-range heavy dust episode occurred from 3 to 8 May 2017 in China. To explore the impacts of this long-range dust transport episode on the chemical compositions and size distributions of urban aerosols, such instruments as an online analyzer for monitoring aerosols and gases (MARGA) and a wide-range particle spectrometer (WPS) were mainly used to monitor chemical components, such as PM2.5 and aerosol size distributions in the range of 10 nm to 10 μm, in Nanjing in this study. During the dust episode, the average concentrations of PM2.5 and PM10 and ions of Ca2+, Mg2+, Cl-, SO42−, NO3−, and NH4+ were 66.2, 233.9, and 1.1, 1.5, 1.1, 11.4, 7.8 and 4.4 μg·m−3, which were 4.4, 5.8, 3.7, 15, 1.38, 1.84, 1.66 and 1.83 times higher than the values observed before the episode and 2.2, 3.3, 5.5, 5.0, 1.57, 1.97, 1.39 and 1.69 times the levels after the episode. The dusts were demonstrated to have differential impacts on the water-soluble gases in the air. During the dust episode, the concentrations of HCl, SO2 and NH3 were comparably low, while the HNO2 and HNO3 concentrations were high. The diurnal variations in pollutants, including SO2, HNO3, Cl−, Ca2+, Mg2+, PM2.5 and PM10, were strongly impacted by the dust episode. However, those variations in NH3, NO3−, SO42− and NH4+ were only slightly influenced. Pollutants were distinctively featured in the various dust stages. The concentration of HNO2 was relatively high in the earliest stage but was substituted by those of SO2, PM10, PM2.5, Ca2+, Mg2+ HNO3 and Cl- in the explosion stage. The aerosol number concentrations exhibited unimodal distributions in the earliest and explosion stages but showed bimodal distributions in the duration and dissipation stages. Additionally, the aerosol size distributions were observed to shift to larger particle segments in different dust stages. The surface area concentrations exhibited four peaks in different dust stages and exhibited trimodal distributions in the non-dust episode. The surface area concentration of fine particles first increased during the earliest stage, while that of coarse particles first decreased during the dissipation stage.

Synergistic inhibition effect on the self-acceleration characteristics in the initial stage of methane/air explosion by CO2 and ultrafine water mist

Cellular instability is responsible for the self-acceleration of a flame, and such acceleration might cause considerable damage. This paper presents an experimental study on the inhibition effect of CO2 and an ultrafine water mist on the self-acceleration characteristics of a spherical flame in the initial stage of a 9.5% methane/air explosion in a constant volume combustion bomb. Results showed that insufficient water mist enhanced the self-acceleration of the spherical flame and the intensity of the explosion; nevertheless, the synergistic inhibition effect of CO2 and ultrafine water mist prevented enhancement of the explosion and significantly mitigated the self-acceleration of spherical flames, which observably delayed the appearance time of a cellular flame, and reduced the flame propagation speed, overpressure and the mean rate of pressure rise, indicating that suppression of flame self-acceleration could effectively mitigate the damage from a methane/air explosion. The reason for the synergistic effect was a result of a combination of physical suppression and chemical suppression: due to the preferential diffusion dilution effect of CO2, the initial flame speed was reduced, and the flame became thicker, which increased the evaporation time and quantity of droplets around the flame front, accordingly enhancing the cooling effect on the flame front. The increased flame thickness could withstand greater disturbance and inhibit the formation and development of a cellular flame. Meanwhile, CO2 and H2O can also reduce the concentration of active radicals (O, H and OH) and reduce the reaction rate and combustion rate of a methane/air explosion.

Investigation on probing explosive nitroaromatic compound vapors using graphyne nanosheet: a first-principle study

We studied the geometric stability of pristine graphyne nanosheet (Gpn-NS) and electronic properties for the possible use of graphyne sheet for the chemical sensor. The center of attention of the work is to probe the nitroaromatic compounds (NACs) at the earlier stage of chemical explosion using Gpn-nanosheet material. The geometric stability of pristine Gpn base material is entrenched with the formation energy and also verified with phonon band structure. The interaction of different NACs such as hexanitrostilbene, M-dinitrobenzene, picric acid, and 2,4,6-trinitrotoluene on Gpn material is studied in connection with the Bader charge transfer, average energy gap changes, adsorption energy, and band gap. Moreover, the adsorption energy of NACs on Gpn-NS varies in the order of − 0.178 to − 0.627 eV. The outcomes of the suggested work infer that Gpn-NS can be used to probe the NAC vapors.

Heterogeneous decomposition and oxidation during combustion of magnesium diboride particles

Magnesium diboride (MgB2) is a potential substitute of amorphous boron (B) as high energy density fuel. The heterogeneous decomposition and oxidation mechanisms during combustion of MgB2 were studied using a laser ignition testing system, an X-ray diffractometer, and a thermogravimetric differential scanning calorimetry combined thermal analysis system. B and magnesium (Mg) were also tested in the laser ignition experiments as control groups. The combustion process of MgB2 contained two stages: an explosion stage and a stable combustion stage. During the explosion stage, a great number of sparks were created and burst out from the sample stack. The color of combustion flame was white at first, and then turned into yellow before the stable combustion stage started. Compare with B and Mg, MgB2 had shorter ignition delay time (8 ms) and longer stable combustion stage time (891 ms), which indicated its outstanding energy release properties. Characteristic emission spectra of MgB2 showed MgO, BO2, and gaseous Mg were the major gaseous intermediate products during combustion. Moreover, decomposition and oxidation products of MgB2 were both found in the condensed combustion products. The thermal oxidation process of MgB2 contains three exothermic peaks: melt and oxidation of Mg impurity (∼650 °C), start of MgB2 decomposition (∼850 °C), and oxidation of Mg-B compounds (∼900 °C).

The Development of Overheat Instabilities in a Metastable Metal

The development of thermal (overheat) instabilities during the electric explosion of a conducting wire has been analyzed using the theory of small perturbations. At the initial stage of electric explosion (upon melting of the metal), the substance can occur in three phases: liquid, two-phase state (liquid + vapor), and metastable metal liquid (overheated liquid). Comparative analysis of the growth of overheat instabilities is performed as dependent on the phase in which the metal can occur. It is shown that, from the standpoint of development of overheat instability, the most unstable phase is the overheated metastable liquid.

Gasoline-air mixture Explosion in a Semi-Confined Space with a 90° Bend

In this work, experiments data from vented explosions tests using gasoline-air mixtures in a small, open square duct with a 90° bend were performed using high-speed camera. It is found that pressure history in the semi-confined space can be divided into four phases, i.e. constant volume explosion, effusive flow overpressure, disturbance explosion, vibration attenuation. The bend structure has an impact on the flame structure during the explosion. In the confined space, the flame transforms from sphere to brush-like shape. The transformation of flame shape in the pipe can be classified into six stages. When flame propagates to the bend structure, it bypasses the bend along the inner wall of the pipe. Flame velocity and flame front position can be divided into four stages: explosion initial stage, accelerated effusion stage, disturbance explosion stage, and energy attenuation stage. Both changes are consistent with changes in flame morphology.

Neutrino signals of core-collapse supernovae in underground detectors

For a suite of fourteen core-collapse models during the dynamical first second after bounce, we calculate the detailed neutrino "light" curves expected in the underground neutrino observatories Super-Kamiokande, DUNE, JUNO, and IceCube. These results are given as a function of neutrino-oscillation modality (normal or inverted hierarchy) and progenitor mass (specifically, post-bounce accretion history), and illuminate the differences between the light curves for 1D (spherical) models that don't explode with the corresponding 2D (axisymmetric) models that do. We are able to identify clear signatures of explosion (or non-explosion), the post-bounce accretion phase, and the accretion of the silicon/oxygen interface. In addition, we are able to estimate the supernova detection ranges for various physical diagnostics and the distances out to which various temporal features embedded in the light curves might be discerned. We find that the progenitor mass density profile and supernova dynamics during the dynamical explosion stage should be identifiable for a supernova throughout most of the galaxy in all the facilities studied and that detection by any one of them, but in particular more than one in concert, will speak volumes about the internal dynamics of supernovae.

Environmentally-Friendly Extraction of Cellulose Nanofibers from Steam-Explosion Pretreated Sugar Beet Pulp.

Cellulose nanofibers (CNFs) with an average diameter of 22 nm were prepared from sugar beet pulp (SBP) via an environmentally-friendly method. Steam-explosion pretreated SBP was treated with hydrogen peroxide (H2O2) bleaching, high-speed blending, and ultrasonic treatment. Thermogravimetric analysis showed that hemicellulose was partially hydrolyzed in the steam-cooking stage, pectin was removed in the explosion stage, and lignin was removed by H2O2 bleaching. The removal of non-cellulosic components was confirmed by Fourier-transform infrared (FT-IR) spectroscopy. Morphological analysis showed that steam-explosion pretreatment largely extracted the binder materials of hemicellulose and pectin. This exposed the microfibrillated cellulosic fibers, which promoted subsequent nanofibrillation. X-ray diffraction showed that the CNFs had a crystallinity index of 62.3%. The CNFs had good thermal stability, and thus have potential for use as fillers in polymer matrices. The only chemical reagent used in this green method was H2O2. Combining H2O2 bleaching with steam explosion, high-speed blending, and ultrasonic treatment reduced the overall energy consumption and increased the efficiency of the CNFs extraction. The method, therefore, has potential application in industrial processes.

Synthesis of metastable cubic tungsten carbides by electrical explosion of tungsten wire in liquid paraffin

This paper describes experiments addressing the synthesis of WC1−x (metastable cubic tungsten carbide). The experiments involved exploding tungsten wires of different diameters by passing high-current electric pulses through them. This was done while the wire was immersed in a liquid-paraffin media. The explosion was studied using a high-speed video camera and by analysis of the voltage and current signals. The different stages of the wire explosion were explained based on an analysis of the recorded signals and simple thermodynamic considerations. In most of the experiments, the wire was sublimated, and the formation of carbide particles occurred due to a chemical reaction between the explosion products and the paraffin, as well as the rapid condensation of the vapors. The synthesized powders were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA). It was found that, regardless of the experimental conditions, the WC1−x phase contained approximately 42.5 at.% carbon. If the energy injected into the wire was not sufficient to completely evaporate the tungsten, large particles consisting of WC, W2C, and W phases were formed via the liquid-state diffusion mechanism.

Isolation and characterization of cellulosic fibers from kenaf bast using steam explosion and Fenton oxidation treatment

Degumming is the dominant method to isolate cellulosic fibers in the textile industry. High content of lignin is the principle obstacle in bast-fibers degumming. In order to remove lignin efficiently, the treatment using steam explosion coupled with Fenton oxidation was conducted on kenaf bast in this study. The influence and mechanism of the combined treatment of steam explosion and Fenton oxidation were studied. Fiber microstructure, composition proportion and distribution, cellulose Segal crystallinity and polymerization as well as residual lignin structure were analyzed. The results showed that the pretreatment of steam explosion could sufficiently extract most of the hemicellulose from kenaf bast. Also, the Fenton oxidation followed by alkaline boiling could effectively remove the lignin from the fiber, especially from the fiber surface. The refined dry fibers produced only remained 8.82% of hemicellulose and 9.36% of lignin. And the whole treatment process didn’t change the cellulose crystalline structure but could gradually degrade hemicellulose, lignin and other amorphous gummy matter as well as disordered areas in cellulose, leading to the increase of fiber Segal crystallinity from 62.02 to 70.12%. Part of cellulose was damaged with the increase of degumming intensity, resulting in the decrease of the polymerization degree of cellulose. Meanwhile, the structure of residual lignin changed during the degumming stages of steam explosion, Fenton oxidation and alkaline boiling. All the results revealed that the treatment of combined steam explosion and Fenton oxidation is significantly effectual for isolating bast-fibers.

Thermal Explosions of Polymer-Bonded Explosives with High Time and Space Resolution

It has always been difficult to observe thermally induced explosions, because the onset is unpredictable. By use of ultrasound to induce intense, localized frictional heating at the surface of crystals embedded in a flexible polymer, we have created a new method for the initiation of microexplosions under conditions where temporal and spatially resolved observations can be made. Specifically, we report the use of ultrasound to flash-heat polymer-embedded 10 000 K/s. By using this extremely rapid heating on small samples, we were able to confine the explosion to narrow regions in time and space. The explosion was measured using dual thermal imagers providing temporal and spatial resolutions of 1 μs and 15 μm. Surprisingly, the explosions always occurred in two stages, an initial 0.1 ms stage and a subsequent 100 ms stage. The first stage of RDX explosion (2500 K lasting 140 μs) was less violent than that for HMX (4400 K lasting 70 μs), which is c...

An Interactive Model among Potential Human Risk Factors: 331 Cases of Coal Mine Roof Accidents in China.

In order to explore optimal strategies for managing potential human risk factors, this paper developed an interactive model among potential human risk factors based on the development processes of accidents. This model was divided into four stages, i.e., risk latency stage, risk accumulation stage, risk explosion stage and risk residue stage. Based on this model, this paper analyzed risk management procedures and relevant personal’s responsibility in each stage, and then probed into the interactive mechanism among human risk factors in three aspects, i.e., knowledge, information and communication. The validity and feasibility of the model was validated by analyzing a coal mine roof accident in China. In addition, the contribution of different functional levels’ personnel in risk evolution was discussed. It showed that this model can effectively reveal the interactive mechanism of potential human risk factors, and can thus give significant insights into the development of risk management theories and practices. It also proves that the contribution of different functional levels’ personnel in the model is different. This can further help practitioners design enhanced Behavioral-Based Safety (BBS) intervention approaches which can have a more sustainable and persistent impact on corporate personnel’s safety behavior. Specific recommendations and suggestions are provided fundamentally for future BBS practices in the coal mine industry.

Direct numerical simulation study of hydrogen/air auto-ignition in turbulent mixing layer at elevated pressures

Auto-ignition of turbulent stratified mixing layer between hydrogen and hot air under elevated pressures p = 1–30 atm is studied using direct numerical simulations (DNS) in this work. Homogeneous isotropic turbulence is superimposed on the field. Detailed chemical mechanism and multicomponent diffusion model are employed. Other than turbulent mixing ignition (TMI), homogeneous mixing ignition (HMI) and laminar mixing ignition (LMI) are also investigated for comparison. For both laminar and turbulent cases, the onset of auto-ignition always happens at the same most reactive mixture fraction isosurfaces. Most reactive mixture fractions in diffusion auto-ignition are inconsistent with HMI calculations and shift to the rich side owing to diffusion for all pressures. At elevated pressures, auto-ignition chemistry is different from low pressures. The importance of H2O2 and HO2 is highlighted as radical sinks during the ignition process, and can also be used as an indicator for locating the ignition spots. Moreover, OH radicals can be used as a marker variable for the transition of auto-ignition to flame propagation under high pressures. Two stages are involved in the diffusion ignition process: radical explosion and thermal runaway. According to our study, under elevated pressures, turbulence has little influence on the radical explosion stage. The role of turbulence is to accelerate the thermal runaway stage in the kernels to make the ignition delay time (IDT) shorter than laminar cases.

Рост перегревных неустойчивостей в метастабильном металле

AbstractThe development of thermal (overheat) instabilities during the electric explosion of a conducting wire has been analyzed using the theory of small perturbations. At the initial stage of electric explosion (upon melting of the metal), the substance can occur in three phases: liquid, two-phase state (liquid + vapor), and metastable metal liquid (overheated liquid). Comparative analysis of the growth of overheat instabilities is performed as dependent on the phase in which the metal can occur. It is shown that, from the standpoint of development of overheat instability, the most unstable phase is the overheated metastable liquid.

A non-equilibrium multiphase model for pressure escalation in fuel coolant interaction during explosion

A non-equilibrium model is used to simulate the multiphase interactions of molten fuel and coolant at explosion stage. In the current model, fluids are liquid coolant, vapor, molten drop and molten fragment. According to the non-equilibrium concept, an energy balance is built at vapor film surrounding the melt. Heat transferred from the melt to the vapor film interface directly participates to evaporate the liquid coolant, without heating the bulk liquid. Mass transfer between molten drop and molten fragment are dominated by thermal and hydrodynamic fragmentation mechanisms. The conservation equations are solved by the modified MCBA-SIMPLE method, with a semi-implicit iteration. Shock tube tests in two-phase medium and two simulations of the KROTOS experiments are used to validate the model. Simulations of KROTOS42 are performed for sensitivity study on fragmentation model, melt diameter, void fraction and melt temperature. Results reveal that the non-equilibrium multiphase model can give reasonable predictions on pressure generation and escalation in fuel coolant interaction. Fragmentation model analysis reveals that thermal fragmentation at trigger stage has unobvious effect on hydrodynamic fragmentation and hydrodynamic fragmentation is the major factor on pressure escalation. With the escalation of pressure, hydrodynamic fragmentation based on stripping mechanism results in a weaker pressurization against Rayleigh–Taylor mechanism. It is suggested that Rayleigh Taylor instability will be more preponderant at higher relative velocity in vapor explosion. Besides, the sensitivity study indicates that the steam generation and quenching process during the premixing have significant effect on explosion. Further, the model is preliminarily applied to a reactor simulation and integrity of the cavity wall is evaluated.

Centimeter-wide worm-like fossils from the lowest Cambrian of South China

The trace fossil record implies that large worm-like animals were in place along with the skeletonizing organisms during the initial stage of the Cambrian explosion. Body fossils of large worms, however, have so far not been found. Here, we describe a large, soft-bodied, worm-like organism, Vittatusivermis annularius gen. et sp. nov. from the lowest Cambrian of South China, which is constrained to the Fortunian Age (541–529 Ma) of the Cambrian Period. The elongate body of Vittatusivermis was large enough to have supported organ systems and a fluid skeleton that facilitated peristaltic locomotion, thus allowing for more complex patterns of movement than those of flatworms. Its occurrence on the same bedding surface as trace fossils suggests that Vittatusivermis might have produced epichnial trails and shallow burrows on and within sediments. Therefore, Vittatusivermis is likely to have been one of the long expected producers of trace fossils in the earliest Cambrian.

Detailed Numerical Simulation of Cathode Spots in Vacuum Arcs—I

A model of cathode spots in high-current vacuum arcs is developed, with account of the plasma cloud left over from a previously existing spot, all mechanisms of current transfer to the cathode surface, including the contribution of the plasma produced by ionization of the metal vapor emitted in the spot, and the Joule heat generation in the cathode body. The simulation results allow one to clearly identify the different phases of life of an individual spot: the ignition, the expansion over the cathode surface, and the thermal explosion. The expansion phase is associated with a nearly constant maximum temperature of the cathode, which occurs at the surface and is approximately 4700–4800 K. Thermal explosion is a result of thermal instability (runaway), which develops below the cathode surface when the Joule heating comes into play. The development of the spot is interrupted if the plasma cloud has been extinguished: the spot is destroyed by heat removal into the bulk of the cathode due to thermal conduction. Therefore, different scenarios are possible depending on the time of action of the cloud: the spot may be quenched before having been formed or during the expansion phase, or even at the initial stage of thermal explosion.