Explosive Behavior Research Articles

Global land-use intensity and anthropogenic emissions exhibit symbiotic and explosive behavior

SummaryThe intensification of land use is accelerating and remains a threat to achieving environmental sustainability. Although prior literature identifies unsustainable demand for resources as crucial to ecosystem vitality, we highlight explosive behavior and indicators associated with changing global land-use intensity and emissions. We assess emission footprints, forestry, and agricultural land-use intensity across income groups. We find that long-term income growth above US$1005/capita has mitigation effects on emissions, whereas emissions stimulate the global expansion of land use for agricultural and forestry activities. Urban expansion has diminishing effects on agricultural lands in developed countries, which may alter future agricultural production and food consumption. The heterogeneous effects across countries demonstrate the need for domestic context, including cultural and historical factors, in assessing forest decline, agricultural expansion, and land-use intensity. The co-benefits of Reducing Emissions from Deforestation and Forest Degradation (REDD+) in developing economies are crucial to mitigating emissions while improving forest-dependent livelihoods.

Effect of a Perforated Polyethylene Material on Propane-Air Explosion in a Confined Space.

In this study, the effect of polyethylene barriers with different blockage ratios on the explosion behavior of a propane–air premixed gas in a confined space is investigated. The maximum explosion pressure (Pmax), the deflagration index (KG), and the flame propagation process of the propane–air premixed gas with different barrier thicknesses are examined by using a horizontal closed tube with a length of 0.5 m and a diameter of 0.1 m and a high-speed camera. The atmospheric pressure and temperature of the premixed gas were 101.3 kPa and 18 °C, respectively. Based on the Canny operator, the position of the flame front at different times and the shape of the barriers before and after the explosion are determined, and the propagation speed of the premixed flame and the deformation rate of the barriers are obtained. The results indicate that the barriers change the flow field structure of the unburned gas and increase the folding degree of the flame front. With the increase in the blockage ratio, the explosion of a premixed system becomes more rapid and violent. Under the action of Rayleigh–Taylor instability, the variation in the flame propagation speed induces a change in the tube pressure. In addition, the deformation of a barrier causes a change in the maximum explosion pressure. The greater the deformation ratio of the barrier after the explosion, the larger the maximum explosion pressure.

Explosion behavior of non-uniform methane/air mixture in an obstructed duct with different blockage ratios

An experimental investigation on explosion behavior of non-uniform methane/air explosion in obstructed duct with different blockage ratios is conducted. The methane/air mixture that the methane concentration decreases from top to bottom and from ignition end to opposite end of duct is tested. The results show that the vertical concentration gradient of methane upstream along the obstacle increases with blockage ratio. After ignition, the flame speed and overpressure increase exponentially when the flame propagates with a finger-liked shape. In the poorly mixed methane/air, the flame speed and overpressure reduce with the appearance of pronounced triple flame. The flame in duct without obstacle propagates with triple shape until it approaches the vent. In the obstructed duct, the flame speed increases again after the flame passes the obstacle and then the triple flame disappears as the flame becomes turbulent. In the more evenly mixed methane/air, the flame speed decreases with the disappearance of finger shaped flame. The flame speed decreases continuously in duct without obstacle but increases again when the flame passes the obstacle in obstructed duct, in which an incomplete mushroom-shape flame forms downstream the obstacle. Generally, both the flame speed and overpressure are larger in methane/air that mixes more fully.

On the flammable behavior of non-traditional dusts: Dimensionless numbers evaluation for nylon 6,6 short fibers

Safety parameters assessment is not sufficient to fully understand the flammable and explosive behaviour of a combustible dust and correctly manage potential risk. A correct evaluation requires the identification of flame propagation path as well as the limiting step controlling fire propagation, through evaluation of dimensionless numbers (Biot, Damköhler, Thiele, Sherwood, Thiele modulus numbers). Herein, these aspects were investigated for non-traditional dusts, made of nylon 6,6 short fibers. To this purpose, flammability parameters including minimum ignition energy (MIE), the maximum pressure of explosion and the deflagration index were assessed and combined with results of extensive physical-chemical characterization, by means of several techniques (TGA/DSC, FTIR, XRD). In particular, thermogravimetric analysis highlighted the presence of homogeneous and heterogeneous phase phenomena activated at different temperatures and heating rates. The homogeneous phase processes are controlled by the pyrolysis process strictly dependent on the dust size and its decomposition kinetics. The most flammable sample is characterized by smaller dimensions and a fast decomposition kinetics at low temperature. Heterogeneous flame propagation is controlled by the intrinsic heterogeneous reaction. The most reactive sample is characterized by the highest value of specific surface area and by intense exothermic phenomena at low temperature, as evidenced by the analysis of the solid residue. As a main conclusion, the processes involving nylon fibres that may modify the key parameters influencing the flammable/explosive behaviour are also discussed.

Explosive behaviour in networks of Winfree oscillators

We consider directed networks of Winfree oscillators with power law distributed in- and out-degree distributions. Gaussian and power law distributed intrinsic frequencies are considered, and these frequencies are positively correlated with oscillators' in-degrees. The Ott/Antonsen ansatz is used to derive degree-based mean field equations for the expected dynamics of networks, and these are numerically analysed. In a variety of cases “explosive” transitions between either two different steady states or between a steady state and a periodic solution are found, and these transitions are explained using bifurcation theory.

Explosion behavior of methane-air mixtures and Rayleigh-Taylor instability in the explosion process near the flammability limits

Methane is the main component of natural gas and biogas, and it has been applied in various fields in daily life and industrial production. A better understanding of the explosion behavior of methane mixture can contribute to the safe usage of this fuel and developing advanced explosion protection technology and devices. The main purpose of this study is to investigate the explosion behavior and the Rayleigh-Taylor (RT) instability in the explosion process of methane-air mixtures using a 20 L bomb. Overpressure trajectories and flame images using high-speed schlieren technique are recorded for each experiment. Explosion behavior of methane-air mixtures is investigated at 280 K covering wide equivalence ratios (0.61–1.42) and initial pressures (50 kPa ∼ 250 kPa). By analyzing the explosion image data, flame speed and laminar burning velocity are then calculated. Results indicate that as initial pressure rises, the maximum explosion pressure increases, while the flame speed and the laminar burning velocity decrease. The effect of initial pressure and equivalence ratio (Ф) on the spherical flame is also presented and analyzed through the combination of image data and pressure data. It is suggested that mass of reactants per unit volume and fuel composition have a strong relationship to ignition feasibility and ignition delay time. When Ф is 1.42 and the initial pressure is less than 150 kPa, the dynamic ignition process is recorded. Fores (pressure gradient, density gradient) are generated at the position of the flame front due to combustion. The density of spherical flame zone (burned zone) is lower than the unburned zone, therefore the spherical flame moves upward. The moving density stratification of the flame surface changes the structure of the flame front, which induces the RT instability. Near the flammability limits (Ф = 0.61 or 1.42), the explosion pressure is weak and flame speed is slow (∼0.4 m/s). Due to the longer duration of forces, the effect of forces on the spherical flame becomes apparent. It is found that the RT instability leads to structural instability of the flame.

Effect of N2 and CO2 on explosion behavior of H2-Liquefied petroleum gas-air mixtures in a confined space

In this study, the explosion behaviors of H2-LPG-air mixtures with 30% H2 fraction under the action of N2 and CO2 were experimentally investigated respectively under the initial conditions of 1 atm and 298 K. Furthermore, the mole fraction and the rate of production (ROP) of free radicals were analyzed with reference to the detailed USC-Mech II mechanism. The results show that the addition of N2 and CO2 reduces the maximum explosion pressure and maximum rate of pressure rise of H2-LPG-air mixtures; it also postpones the arrival of explosion peak. The minimum suppression concentrations of inert gases are 35% N2 and 25% CO2, respectively. Compared with the addition of N2, the addition of CO2 with the same volume fraction boasts a better inhibitory effect on H2-LPG-air mixture explosion. The reason is as follows: N2 mainly inhibits explosion by its physical properties. In contrast, CO2 also participates in the chemical elementary reactions R31: CO + OHCO2+H, consumes free radical H and reduces its concentration. Meanwhile, the main elementary reactions affecting the generation and consumption of free radicals H, O and OH are R1, R3 and R31. The addition of N2 and CO2 decreases the maximum ROP of free radicals H, O and OH, and CO2 with a high concentration has a significant effect on the maximum ROP of the elementary reaction R31.

Experimental and numerical study of the influence of initial temperature on explosion limits and explosion process of syngas-air mixtures

To study the effect of initial temperature of 30, 60, 90, and 120 °C on the explosion limits and the explosion process of the syngas-air mixtures, the explosion limits were tested by the explosive limit instrument, and the flame propagation process in the spherical pressure vessel was recorded by the high-speed camera. The ANSYS Fluent 3D software was used to simulate the explosion behavior of syngas-air mixtures. The results showed that with the increase of the initial temperature, the lower explosion limit of syngas decreased and the upper explosion limit increased, and the effect of initial temperature on the upper explosion limit of syngas was greater than that on the lower explosion limit. The flame development process in the simulation was consistent with that in the experiment, propagating outward spherically until it filled the entire container. Both experimental and numerical results presented the same trend of accelerating the flame propagation speed with the increase of initial temperature. In addition, the simulation also obtained multi-dimensional transient explosion parameters that were difficult to obtain in the experiment. The explosion process of syngas was analyzed by the explosion parameters such as temperature and pressure field in the explosion area. An increase in temperature decreased the maximum explosion pressure and shortened the time to reach the maximum explosion pressure.

Effects of aluminum particle size distributions on the explosion behaviors of hydrogen/aluminum dust hybrid mixtures

The effects of aluminum particle size on the explosion behaviors of hydrogen/aluminum dust hybrid explosion were studied. The results show that due to the large specific surface area of small particles, the Pex and the (dP/dt)ex increased significantly with the decrease of aluminum particle size. The maximum value of the (dP/dt)ex can reach 239 MPa/s. When the particle size of aluminum dust decreased from 56.18 μm to 5.07 μm, the flame propagation displacement changed from double peaks to a single one. The actual burn time can be fitted as a function of initial hydrogen concentration. The maximum flame propagation velocities increased significantly with the decrease of aluminum particle size. When 56.18 μm and 30.82 μm aluminum dusts were burned in hydrogen/air mixtures, the expanded porous oxide layers appeared in the residues, while there was no porous oxide layer in the explosion residues of 5.07 μm aluminum dust.

Effect of an orifice plate on the explosion behaviors of H2–N2O mixtures

The explosion characteristics of H2–N2O over a wide range of equivalence ratio (φ) at a reduced pressure were studied experimentally in a cylindrical explosion vessel. Two orifice plates with the blockage ratios of 0.4 and 0.6 were employed to characterize the influence of an obstacle on the explosion behaviors. The experimental results showed that maximum explosion pressure could be higher than the adiabatic value due to the potential of flame acceleration and deflagration to detonation transition (DDT). The maximum explosion pressure was increased by the orifice plate at the fuel-lean side due to the flame instability while decreased at the fuel-rich side. This means that the roles played by the orifice plate are different for affecting the maximum pressure. The maximum pressure rise rate ((dp/dt)max) was increased by introduction of an orifice plate due to the turbulence-generator effect. The maximum (dp/dt)max was obtained at φ = 0.6, indicating that the flame instability rather than the adiabatic explosion pressure or laminar burning velocity plays a leading role.

Bubble Behavior and Its Effect on Surface Integrity in Laser-Induced Plasma Micro-Machining Silicon Wafer

Abstract Laser-induced plasma micro-machining (LIPMM) process does well in fabricating high-quality surface microstructures of hard and brittle materials. However, the liquid medium is overheated to induce lots of bubbles to defocus the laser beam, reducing machining stability, and explosive behavior of bubbles destroys the surface quality. Thus, the static and dynamical behaviors of bubbles in LIPMM are comprehensively investigated in this article. First, a series of mechanisms including bubble generation and growth, bubble motion and explosion, and the effect of bubbles behavior on machining characteristics were explained. Second, a volume of fluid (VOF) model of bubble motions in laser-induced plasma micro-machining was established to simulate the dynamical behavior of bubbles under different depths of water layer, which reflect the growth of microbubbles, the aggregation of multiple bubbles, and the floating movement of bubbles. Then, a series of experiments were carried out to reveal bubble static behaviors, and further bubble explosion behaviors on surface integrity, surface defects, and hardness were analyzed. The increase of laser frequency leads to the increase of the maximum attached bubble size. Obstructed by bubble dynamical behaviors, a discontinuous section and the unablated area are observed in the microchannel. The elastic modulus and surface hardness of surface impacted by explosion bubbles are reduced. This research contributes to better understanding bubble behavior related to machining performances in LIPMM of single-crystal silicon.

Exploding DUCs? Identifying periods of mild explosivity in the time series behavior of drilled but uncompleted wells

Recent attention has turned to drilled but uncompleted wells (DUCs) that exploration and production (E&P) companies may manage in order to address market uncertainties. DUCs act as potential supply that bridges the gap when supply and demand are unequal and can play a key role in the operations strategies of producers. This study provides evidence of mildly explosive behavior in the time series of DUCs by applying the Right-Tailed Augmented Dickey Fuller test of Phillips, Shi, and Yu (2015) (PSY). The PSY method tests for mildly explosive behavior of a time series defined by when the volume of DUCs move beyond what would be expected given the fundamental market conditions. The sample spans from December 2013 until May 2020 and includes the major oil producing regions of the United States. The analysis date stamps periods of mild explosivity and matches surges in DUCs with major contemporaneous events including the June 2014 precipitous drop in oil price, midstream bottlenecks and resource constraints, as well as the COVID-related fall in demand for oil. The findings are discussed in the context of exploration and production firms and the use of DUCs as a tool for understanding value and optimization of production over time.

Integral Functionals for Spectrally Positive Lévy Processes

We find necessary and sufficient conditions for almost sure finiteness of integral functionals of spectrally positive Lévy processes under conditional probabilities. Via Lamperti-type transforms, these results can be applied to obtain new integral tests on extinction and explosion behaviors for a class of continuous-state nonlinear branching processes.

Drivers of crop impacts from tephra fallout

Agriculture is an economic and social pillar for the least developed countries. When these regions host volcanoes that exhibit explosive behaviour, a serious risk for agricultural production arises as crops endure various impacts from tephra fall. In order to gain new insights into the factors that govern tephra impacts on crops, we collected farmers’ perceptions of crop damage and production loss due to exposure to tephra fallout in 15 villages affected by the 1999–2014 eruptions of Tungurahua volcano, Ecuador. Crop type and developmental stage - both influenced by altitude - strongly modulate the level of tephra-induced impact. Using these observations, we illustrate how crop vulnerability fluctuates spatially and temporarily in the surveyed area. The study also highlights that fine tephra (<63μm) is more harmful to crops than coarser particles. Farmers have responded to the tephra hazard by favouring crops more resistant to tephra, a practice that has reduced crop diversity.

Polynomial Noises for Nonlinear Systems with Nonlinear Impulses and Time-Varying Delays

It is known that random noises have a significant impact on differential systems. Recently, the influences of random noises for impulsive systems have been started. Nevertheless, the existing references on this issue ignore the significant phenomena of nonlinear impulses and time-varying delays. Therefore, we see the necessity to study the influences of random noises for impulsive systems with the above two factors. Stimulated by the above, a polynomial random noise is introduced to suppress the potential explosive behavior of the nonlinear impulsive differential system with time-varying delay. Fortunately, the stochastically controlled impulsive delay differential system admits a unique global solution, is bounded, and grows at most in the polynomial form.

Influence research of electrostatic environment on dispersion and explosion characteristics of typical biomass organic dust clouds

In order to explore the explosion characteristics of dust cloud under the coupling condition of electrostatic field, flow field and particle motion field, based on the theoretical analysis of the charging mechanism of dust particles in the electrostatic field, the motion mechanism and explosion behavior of three typical biomass dust were studied by means of experiment and simulation. The research results were presented in the electrostatic field to evaluate the dispersion effect and explosion hazard of dust clouds. It was found that when the dust concentration is less than 500 g/m3, both the peak explosion overpressure and the rate of explosion overpressure rise of dust increase with the increase of dust concentration under the loading of electrostatic field. Compared with the case without electrostatic field, the maximum explosion overpressure of three typical organic dusts are increased by 2.6%, 5% and 12.1% respectively. Moreover, a multi-field coupling mathematical model of particle charge and motion was established, which not only studied the influence law of electrostatic field on particle charging and gas-dust flow characteristics, but also discussed the influence mechanism of electrostatic field on dust cloud explosion intensity from the perspectives of particle concentration distribution, particle velocity distribution and turbulence intensity parameters.

Weather, mobility and the evolution of the Covid-19 pandemic

PurposeThe authors investigate the effect of weather and mobility on the spread of the Covid-19 pandemic.Design/methodology/approachThe authors first estimate the effective reproduction number (Rt) as a proxy of the spread of the Covid-19 pandemic and then study the relationship between the latter and weather and mobility in a panel data framework. The authors use US daily infections data between February and September of 2020 at the county level.FindingsThe authors find that lower temperatures are associated with a higher Rt, and this effect is greater at temperatures below 0°C. In addition, mobility reductions related to certain types of locations (retail and recreation, transit stations and workplaces) are effective at reducing Rt, but it is an increase in the time spent in parks that most helps reduce the spread of the pandemic.Originality/valueThe estimates imply that a 20°C fall in temperature from summer to winter would increase Rt by +0.35, which can be the difference between a well-controlled evolution and explosive behavior of the spread of the virus. Applying these coefficients estimated with US county data to aggregate series from other countries helps explain the resurgence of the pandemic in the Northern Hemisphere during the winter of 2020. The results show that mobility reduction and social distance are best policies to cope with the Covid-19 outbreak. This strong policy lesson will help facing similar outbreaks in the future.

Comparative Analysis of Critical Factors for Nozzle Consideration in Dust Explosion Testing

Despite extensive research and efforts in handling and mitigation of dust explosion, accidents involving dust explosion take place. The mention of dust explosion in the literature dates to 1785, but industry professionals from oil and gas are unaware of this hazard. An incident is reported leading to the demise of two workers while attempting to unload barite powders. The process industry is highly dependent on powdered chemicals, which are used as an additive in drilling fluid and cements, such as barite, bentonite, calcium carbonate, lead sulphides, NaOH, etc. The explosive behaviour of these dusts can be determined with the help of the Kst values. The Kst value is dependent on the confinement, dispersion of particles, size of the dust particle, the source of ignition, and presence of free oxygen. Usually, an experimental setup of 20L sphere with two different types of nozzles i.e., perforated annular nozzle or rebound nozzles are majorly used to calculate the value of Kst. While the setup is being prepared at our end, this work presents a comparison of the performance of these nozzles using Computational Fluid Dynamics (CFD) as a tool, to understand the different parameters of dispersion, and the impact they have on the dust explosion.

Tunable acetylene sorption by flexible catenated metal-organic frameworks.

The safe storage of flammable gases, such as acetylene, is essential for current industrial purposes. However, the narrow pressure (P) and temperature range required for the industrial use of pure acetylene (100 < P < 200 kPa at 298 K) and its explosive behaviour at higher pressures make its storage and release challenging. Flexible metal-organic frameworks that exhibit a gated adsorption/desorption behaviour-in which guest uptake and release occur above threshold pressures, usually accompanied by framework deformations-have shown promise as storage adsorbents. Herein, the pressures for gas uptake and release of a series of zinc-based mixed-ligand catenated metal-organic frameworks were controlled by decorating its ligands with two different functional groups and changing their ratio. This affects the deformation energy of the framework, which in turn controls the gated behaviour. The materials offer good performances for acetylene storage with a usable capacity of ~90 v/v (77% of the overall amount) at 298 K and under a practical pressure range (100-150 kPa).

Explosion behavior investigation and safety assessment of large-format lithium-ion pouch cells

Large-format lithium-ion (Li-ion) batteries with high energy density for electric vehicles are prone to thermal runaway (or even explosion) under abusive conditions. In this study, overcharge induced explosion behaviors of large-format Li-ion pouch cells with Li[Ni0.8Co0.1Mn0.1]O2 cathode at different current rates (C-rates) (0.5C, 1C, 2C) were investigated. The explosion characteristics of the cells were elucidated by discussing the evolution of the cell voltage, the surface temperature and the shock wave pressure. Generally, the whole overcharge process could be divided into four stages according to the evolution of several key parameters and the overcharge behaviors; the overcharge C-rate has a great influence on cells’ thermal behaviors. The experimental results showed that the thermal runaway process of Li-ion cells caused by overcharging consisted of two kinds of explosions, physical explosion and chemical explosion. The existence of observable negative pressure zone in the pressure curves indicated that the Li-ion cells are not a self-supplying oxygen system during the explosion. Further, the explosion dynamics parameters were matched. An explosion TNT-equivalent conversion strategy that depended on the pressure of the shock wave was utilized to evaluate the released energy and its hazards. In addition, with respect to the overcharge of Li-ion pouch cells, a safety assessment method and a safety management method were proposed based on the explosion behaviors. From the perspective of battery safety, this study is of great significance for the safety design of Li-ion cells and can provide guidance for engineers to optimize the safety function of battery packs.