Propagation Velocity Of Shock Wave Research Articles

Effect of polyurethane foam and carbon dioxide on the suppression of hydrogen/air explosion

This study examines the influence of polyurethane porous materials and carbon dioxide on hydrogen/air explosions within an enclosed vessel. Through analysis of peak overpressure, maximum rate of pressure rise, and shock wave propagation velocity, the suppression effects on explosions in hydrogen-air mixtures with different equivalence ratios at room temperature and atmospheric pressure are investigated. Findings indicate that porous materials with a PPI (pores per inch) of 60 significantly mitigate hydrogen/air explosions across all equivalence ratios. Conversely, a PPI below 60 exacerbates the explosions. Simultaneous presentation of PPI60 porous material and a CO2 addition level of x = 2 (carbon dioxide to oxygen ratio) reduces hydrogen explosion pressure to only 13.7 kPa at "Φ = " 1.2, representing an attenuation rate of 84% and falling well below the human safety threshold of 28 kPa. Independent effects of carbon dioxide and porous materials on hydrogen explosions across various equivalence ratios are also explored. The experimental design encompasses a broad range of equivalence ratios, covering hydrogen's explosive limits. These results contribute to the design of flame arrestors and enhance understanding of explosion suppression in hydrogen systems.

Effect of dimensionless vent ratio on the flame-shock wave evolution dynamics of blended LPG/DME gas explosion venting

To reveal the flow field-shock wave-flame coupling evolution law of LPG/DME blended gas explosion venting under different dimensionless vent ratio(KV), the numerical model for multi-blended gas explosion venting was established and research of blended gas explosion venting at KV = 0.02–0.21 was carried out based on experimental verification. The results show that, after the vent opens, the turbulence intensity increases, the velocity gradient of the flow field increases, the maximum explosion wind velocity(Vmax) of the outfield varies linearly with KV, and the flame of “mushroom shape” is elongated, and “break flame” occurs under the action of the relative motion of “primary and secondary vortex group”. When KV＞0.02, the flame propagation velocity increases locally because of the thermal-mass diffusion instability, and with increasing KV, the average flame propagation velocity decreases from 258.29 m/s to 226.58 m/s. In the process of explosion venting, a typical shock wave fluctuating pressure waveform curve is formed in the outfield. Under the combined action of the infield pressure venting effect and the outfield turbulence intensity, the maximum explosion overpressure in the outfield (Pmax) reaches maximum 423.97 kPa at KV = 0.07. Meanwhile, the larger the KV, the greater the shock wave velocity due to the lead role of the infield explosion venting shock wave and outfield flame compression shock wave on the shock wave propagation velocity.

Influence of equivalence ratio and H2 blended ratio on explosion propagation characteristics of DME/H2 blended gas in closed narrow space

To reveal the explosion risk and propagation law of dimethyl ether (DME)/hydrogen (H2) blended gas, the explosion propagation characteristics of DME/H2 blended gas under different equivalence ratio (Φ) and hydrogen blended ratio (λ) was investigated based on experimental research and theoretical analysis. The results show that the peak overpressure (Pp), the peak pressure rise rate (dP/dt)p and the peak shock wave propagation velocity (Vp) show an increasing and then decreasing trend with the increase of Φ, and reach the maximum at Φ = 1.0. The effect of a little addition of H2 on the explosion hazards of blended gas is small, but when λ > 10%, the explosion hazards increase significantly. The magnitude of increase of Pp, (dP/dt)p and Vp is different with the increase of λ. Compared with the enhancement effect on Pp and (dP/dt)p, the enhancement effect on Vp is more obvious with the continuous blend of H2. Comprehensive analysis of the thermodynamic and chemical kinetic parameters of H2, the chemical kinetic parameters of H2 play a dominant role in the explosion risk of hydrogen-blended gases.

Research on evolution of shock wave of ground explosion in pit type explosion containment vessel

In order to explore the evolution of shock wave in a confined space, a pit type explosion containment vessel is designed in this paper, in which the ground explosion experiments are carried out. Four gauge points are set on the container cover to collect shock wave signals. By observing the pressure history, it was found that the shock wave experiences multiple reflections in the vessel and then tends to be stable gradually. As well as each pressure crest increases abruptly and then decays rapidly. Meanwhile, the finite element analysis program ANSYS/AUTODYN is adopted to simulate the charge is detonated in the explosion containment vessel by the 2D axisymmetric algorithm. Observing the variation of the pressure field inside the container, it is found that the propagation velocity of shock wave in sand is obviously lower than that in air. And the intensity of the shock wave is obviously increased after reflection and interaction. As the shock wave propagates upward along the side wall of the vessel, the incidence angle of the shock wave also increases gradually. When the incidence angel reaches 47.73°, Mach reflection occurs. Through analyzing the distribution of pressure field near the cover, it is found that the center and the edge of the cover suffer the impact strength and bear the serious damage risk.

Modeling of attenuation and suppression of cellular detonation in the hydrogen-air mixture by circular obstacles

The results of numerical study of the interaction of the gaseous detonation with the regular obstacle consisting of checkered elements with circular cross section are presented. The aim of this work is to identify and generalize the parameters affected the attenuation of a cellular detonation propagating in a premixed stoichiometric hydrogen-air mixture. Studies of such problems are aimed at studying issues related to explosion and fire safety in the operation of highly efficient gaseous fuels, which are currently very widespread. As a result, the dependencies of the leading shock wave propagation velocity on the obstacle geometry are obtained. The contribution of each of the considered parameters to the detonation wave velocity deficit is estimated. Maps of detonation suppression and re-initiation modes for varying barrier parameters are obtained.

Explosion dynamics and sensitivity analysis of blended LPG/DME clean fuel promoted by H2 in a confined elongated space

The involvement of highly chemically reactive H2 greatly increases the fuel explosion risk. In order to reveal the elevated explosion risk of LPG/DME blended gas due to the participation of H2, the explosion-promoting dynamics of H2 and its sensitivity characteristics are investigated based on a combination method of numerical simulation, experimental verification and theoretical analysis. The results show that the participation of H2 increases the explosion overpressure and the shockwave propagation velocity by 147.9% and 90% respectively to the greatest extent. The explosion temperature shows five typical combustion stages, with the participation of H2, the maximum temperature rise range of the shock wave adiabatic compression heating period and the combustion period is significantly increased, the adiabatic holding time is prolonged, the peak flame temperature is increased, and the flame propagation velocity is also significantly improved. The addition of H2 causes the relative distance between the explosion shock wave and the flame front first increases, then decreases and then increases in the shape of “half-morning glory”. The number and sensitivity coefficients of the new explosion-promoting elementary reactions brought by H2 are larger than that of the new explosion-inhibiting elementary reactions, which explains and confirms the explosion-promoting nature of H2 in terms of the reaction mechanism.

Experimental study of effect of equivalence ratio and initial turbulence on the explosion characteristics of LPG/DME clean blended fuel

The effects of initial turbulence and equivalence ratio on the explosion characteristics of LPG/DME clean blended fuel were investigated experimentally. The results showed that as equivalence ratio increase, the explosion overpressure, rate of pressure rise, and propagation velocity of shock wave assume a "three-zone" structure, that is, first acceleration zone, then attenuation zone, finally stabilization zone. With the increase of initial turbulence, the explosion characteristic parameters such as the maximum explosion overpressure, the maximum pressure rise rate, and the maximum shock wave propagation velocity all showed different degrees of increase, and the reasons for these growths are not the same, which leads to the inconsistent levels of growth. However, the chain-based growth rate of these explosion characteristics parameters decreases with the increase of initial turbulence, which meant that the influence of initial turbulence on explosion intensity was weakened gradually. The maximum explosion overpressure and the maximum rate of pressure rise basically conformed to a linear relationship with the initial turbulence. The results of the paper can provide more basic but important information for the practical use of LPG/DME clean blended fuel, especially in safety protection strategies.

Molecular dynamics study of temperature effects on shock response and plastic deformation mechanism of CoCrFeMnNi high-entropy alloys

High-entropy alloys have broad application prospects in aviation, aerospace, military and other fields due to their excellent mechanical properties. Temperature is an important external factor affecting the shock response of high-entropy alloys. In this paper, we investigate the effects of temperature on the shock response and plastic deformation mechanism of CoCrFeMnNi high-entropy alloys by using molecular dynamics method. The effects of temperature on the atomic volume and the radial distribution function of CoCrFeMnNi high-entropy alloy are studied. Then, the piston method is used to generate shock waves in the sample to study the shock response of CoCrFeMnNi high-entropy alloy. We observe the evolution of atomic-scale defects during the shock compression by the polyhedral template matching method. The results show that the shock pressure, the shock wave propagation velocity, and the rising of shock-induced temperature all decrease with the initial temperature increasing. For example, when piston velocity <i>U</i><sub>p</sub> = 1.5 km/s, the shock pressure at an initial temperature of 1000 K decreases by 6.7% in comparison with that at 1 K. Moreover, the shock Hugoniot elastic limit decreases linearly with the increase of temperature. The Hugoniot <i>U</i><sub>p</sub>-<i>U</i><sub>s</sub> curve of CoCrFeMnNi HEA in the plastic stage can be linearly fitted by the formula <i>U</i><sub>s</sub> = <i>c</i><sub>0</sub> + <i>sU</i><sub>p</sub>, where <i>c</i><sub>0</sub> decreases with temperature increasing. As the shock intensity increases, the CoCrFeMnNi high-entropy alloy undergoes complex plastic deformation, including dislocation slip, phase transformation, deformation twinning, and shock-induced amorphization. At relatively high initial temperature, disordered clusters appear inside CoCrFeMnNi HEA, which together with the BCC (body-centered cubic) structure transformed from FCC (face-centered cubic) and disordered structure are significant dislocation nucleation sources. Compared with other elements, Mn element accounts for the largest proportion (25.4%) in disordered cluster. Owing to the large atomic volume and potential energy, large lattice distortion and local stress occur around the Mn-rich element, which makes a dominant contribution to shock-induced plastic deformation. At high temperatures, the contribution of Fe element to plastic deformation is as important as that of Mn element. The research results are conducive to understanding the shock-induced plasticity and deformation mechanisms of CoCrFeMnNi high-entropy alloys in depth.

Orientation-dependent shock compression behavior of non-porous/porous NiTi shape memory alloy: An atomic scale study

Crystal orientation has a strong influence on the mechanical behavior of a material, especially at high-strain-rate impact loading. In this study, the effects of different crystallographic orientations on the non-porous/porous NiTi shape memory alloy (SMA) under high-strain-rate impact loading are studied by using molecular dynamic methods. The structural phase transformation process, energy propagation trajectory, defect dislocation evolution, and shock wavefront changes of the NiTi SMA under shock compression are comparatively analyzed. The simulation results show that for three typical crystal orientations, [100], [110], and [111], the phase transformation structures extend in the form of disordered dots, "X"-shaped meshes, and line segments, respectively. Both phase transformation and phase transformation-induced plasticity are more likely to occur in the [110] NiTi SMA; thus, more energy is dissipated, and the propagation speed of the shock wave is the lowest. In addition, the magnitude of the shock wave propagation velocity in the three crystal orientations is of the following order: [111] crystal orientation > [100] crystal orientation > [110] crystal orientation. Finally, the presence of voids affects the propagation patterns of the wavefront, and the crystal orientation directly affects the shape of the shock wavefront and the steepness of the shock wavefront for porous samples. In terms of the crystal orientation and voids, the [110] crystal orientation and voids uniformly arranged along a straight line can improve the buffer performance of the single-crystal NiTi SMA under high-strain-rate impact loading.

INVESTIGATION OF PULSE VIBRATION OF THE PERIODICALLY WORKING INJECTOR OF THE MILKING WASHING SYSTEM

As a result of the analysis of technical and technological support of washing of milking installations it is established that the most effective are circulating systems of washing with regulated formation of a stopper mode with use of air injectors on the basis of automatic control. The consequences of periodic operation of the injector is the phenomenon of hydraulic shock, which is caused by a sudden change in the phase distribution of the flow of two-phase washing solution. This leads to a sudden change in the momentum of the two-phase washing solution, causing a pressure wave moving through the system. This pressure wave can lead to the destruction of milk deposits on the walls of the milk line, as well as to possible damage to the equipment of the milk system. The aim of the study is to increase the efficiency of the milking system flushing system by using pulsed vibration of a periodically operating injector. As a result of numerical simulation of the process of washing the milk line of the milking parlor using an injector in the software package STAR-CCM + was determined by the dynamics of changes in vacuum pressure at a distance from the injector (p (0 m), p (1 m), p (2 m), p ( 3 m), p (4 m), p (5 m)) and the dynamics of changes in the content of components of the multiphase medium (washing solution αf, air αg, milk αm) for four options: the injector is constantly closed, the injector is constantly open and the injector is periodically opened (1 s and 9 s) and closes (1 s and 9 s). It is established that the use of a periodic injector allows to reduce the milk content in the milk line faster and by a larger value, which indicates a better washing process. The addition of the physical-mathematical apparatus of the hydraulic shock phenomenon for a periodically operating air injector of the flushing system allowed to establish that the rate of pressure change depends on the velocities and concentrations of phases of two-phase washing solution, ie its flow regime and shock wave propagation velocity. Therefore, the rate of pressure change Δp / Δt is chosen as a criterion for the action of hydraulic shock.

Shock wave propagation in long laboratory sparks under negative switching impulses

A series of 1.27 m air gap discharge tests under negative switching impulses were carried out to characterize shock wave expansion behavior along leader channels. A high-speed Schlieren system was used to identify shock wave propagation characteristics near the high-voltage electrode. According to the Schlieren images, three distinct types of shock waves were recognized during the leader propagation and after the air gap breakdown: (1) spherical shock wave (SSW), (2) cylindrical shock wave (CSW), and (3) bow shock wave (BSW). To the best of our knowledge, it is the first time to recognize SSWs at the point where the space leader meets the main channel and BSWs along the leader branch after the main leader bridges the air gap. According to the proposed velocity calculation method, the propagation velocity of SSW and CSW was calculated as a function of the shock radius, as well as the shock wave head of BSW. Moreover, a transient magnetohydrodynamics model was developed to predict shock wave front propagation characteristics of both straight and bending channels after breakdown. The predicted shock wave propagation velocity and shock radius showed good agreement with Schlieren images.

Experimental study on explosion characteristics of DME-blended LPG mixtures in a closed vessel

Experiments were performed to study the explosion characteristics of DME-blended LPG mixtures with different DME contents and equivalence ratios using a closed vessel. The maximum explosion pressure (Pmax), the maximum rate of pressure rise (dP/dt)max and the propagation velocity of shock wave (v) were investigated. The results indicated that both the peak overpressure and peak rate of pressure rise were raised with increasing DME content, reaching peak values at the equivalence ratio of 1.2. Furthermore, it was found that slight incorporation of DME had a small effect on the explosion hazard, but as the ratio of DME to LPG/DME mixture exceeded 30%, the explosion hazard would increase dramatically. The propagation of the shock wave behind the obstacle was divided into three stages in this paper: initial acceleration, stable acceleration and decaying. In the propagation process, Pmax, (dP/dt)max and v first increased and then decreased along the pipeline, and the peak values often appeared in the stable acceleration stage. The peak overpressure and the maximum value of v also appeared in the same location approximately, indicating that the occurrence of maximum overpressure risk was often accompanied with the appearance of the most severe dynamic evolution.

Shockwave phenomena in an inhibited gas‐to‐liquid hydrocarbon transformer oil under lightning impulse voltages

Gas-to-liquid (GTL) transformer oil is increasingly considered as an alternative to conventional mineral oils, due to its consistent performance, high purity and essentially free of sulphur. This high interest has led to growing research attention on streamer and breakdown performance of GTL oil. A large effort has been made to characterise the streamer phenomena of GTL oil. However, the secondary effect of shockwaves, which are produced synchronously with the propagation of streamers, is not well studied. Shockwave phenomena in a GTL oil under standard lightning impulse voltages were studied using a 10 mm point-plane gap and the Schlieren photograph technology. Shockwave propagation velocity and shape were measured in order to quantitatively describe the pressure profiles inside the streamer channels.

Power determination and hydrino product characterization of ultra-low field ignition of hydrated silver shots

Hydrated silver shots comprising a source of H and HOH catalyst were ignited by passing a low voltage, high current through the shot to produce explosive plasma that emitted brilliant light predominantly in the short-wavelength 10 to 300 nm region. Based on Stark broadening, the initially optically thick essentially 100% ionized plasma expanded at sound speed or greater and thinned to emit EUV and UV light. The peak power of 20 MW was measured using absolute spectroscopy over the 22.8–647 nm region wherein the optical emission energy was 250 times the applied energy. Synchronized high-speed video and spectroscopic recording of the plasma emission and the measurement of the applied ignition power over time showed that plasma persisted even after the ignition power decayed to zero. Continuous megawatt-level power was recorded on a hydrino reactor wherein continuous brilliant plasma was maintained by HOH and H produced from water-entrained injected molten silver matrix. The molten fuel produced the same EUV spectrum as the shots, but converted to 5700 K blackbody radiation of about 1 m2 surface area with a positive feedback cycle of silver vaporization and absorption of the hydrino reaction emission with the plasma becoming increasingly optically thick. The calorimetrically measured power of a typical 80 mg, 10 microliter shot ignition released by the nascent HOH catalyzed transition of H to hydrino state H2 (1/4) was 400,000 W. Based on the shockwave propagation velocity and the corresponding pressure, the high-current ignition of water in a silver matrix was measured to produce a shock wave that was equivalent to about 10 times more moles of gunpowder. The catalysis reaction product H2(1/4) was identified by Raman spectroscopy, photoluminescence emission spectroscopy, X-ray photoelectron spectroscopy, and MAS 1H NMR.

Assessment of the Temperature Estimation Method Based on the Shock Wave Propagation Velocity

The assessment of the simple temperature estimation theory based on the shock wave propagation velocity was conducted based on the comparison with the CFD simulation of the shock wave propagation through the temperature modulated field at the region from y=0 m to y=0.018m. The temperature estimated by the theory using the shock wave propagation velocity calculated from the CFD was compared with the initial temperature distribution given in CFD. This temperature estimation theory can predict the temperature distribution within at most 30 % error, for the present temperature field. The assessment suggests that the estimation error due mainly to the two dimensional effect should be paid attention for applying the theory.

Temperature Estimation of the Discharged Field Based on the Shock Wave Velocity Measurement

In this study, the temperature estimation method in the discharged field by using the shock wave propagation velocity was investigated. By using the visualization results for the shock wave propagation velocity measurement, we conducted the temperature estimation. For the case without the discharge, the estimation temperature was almost the initial temperature (~300K). On the other hand, in the case with the discharge, the higher temperature (~1000K) was estimated. Therefore, this temperature estimation method is promising method for the future temperature measurement method with some improvement.

Investigation into stress wave propagation in metal foams

The aim of this study is to investigate stress wave propagation in metal foams under high-speed impact loading. Three-dimensional Voronoi model is established to represent real closed-cell foam. Based on the one-dimensional stress wave theory and Voronoi model, a numerical model is developed to calculate the velocity of elastic wave and shock wave in metal foam. The effects of impact velocity and relative density of metal foam on the stress wave propagation in metal foams are explored respectively. The results show that both elastic wave and shock wave propagate faster in metal foams with larger relative density; with increasing the impact velocity, the shock wave propagation velocity increase, but the elastic wave propagation is not sensitive to the impact velocity.

Experimental response of an optical sensor used to determine the moment of blast by sensing the flash of the explosion

The Council for Scientific and Industrial Research (CSIR) conducts research into the effect of underwater explosions on maritime structures and equipment. One of the parameters that are required to be measured to a large degree of accuracy is the shock wave velocity in close proximity (10-120 charge radii) of the explosion, without having to revert to the streak photography method. This distance is in the region where the near field crosses over to the far field, and it would be expected that the distance-time curve would not be linear. The streak photography method produces accuracy in the very near field of the explosion, but is not recommended for accurate measurements at distances beyond 20 charge radii. We investigated the response of an optical sensor constructed to measure the light flash of an underwater blast to determine the moment of explosion. By measurement of the time taken between this moment and the time when the shock wave reaches the pressure sensors, accurate measurements of the distance-time history (and hence shock wave velocity) could be calculated. Twelve general purpose phototransistors were used in a parallel configuration to enhance the sensitivity of the sensor. These transistors were connected directly to a conditioning amplifier which formed the interface between the transistors and the data acquisition equipment. The results that were obtained confirmed that the light intensity of the flash of the explosion increased to a maximum within several microseconds. Measurements of the average velocity of the shock wave propagation, based on the flash measurement as a marker, correlated to within 0.1%, meaning that this method of marking the moment of explosion to within several microseconds had been successful. This method can therefore be used in similar underwater blast measurement applications when a measurement marker of the moment of explosion is required. : underwater explosions, underwater blast, optical sensor, light sensor, shock wave propagation velocity measure- ment, distance-time measurements ,

Shock wave propagation in neutral and ionized gases

Preliminary measurements on a recently built shock tube are presented. Planar shock waves are excited by the spark discharge of a capacitor, and launched into the neutral argon or nitrogen gas as well as its ionized glow discharge in the pressure region 1–17 Torr. For the shock wave propagation in the neutral argon at fixed capacitor charging voltage, the shock wave velocity is found to increase nonlinearly at the lower pressures, reach a maximum at an intermediate pressure, and then decrease almost linearly at the higher pressures, whereas the shock wave strength continues to increase at a nonlinear rate over the entire range of pressure. However, at fixed gas pressure the shock wave velocity increases almost monotonically as the capacitor charging voltage is increased. For the shock wave propagation in the ionized argon glow, the shock wave is found to be most influenced by the glow discharge plasma current. As the plasma current is increased, both the shock wave propagation velocity and the dispersion width are observed to increase nonlinearly.

The critical reduced electric fields in SF6 at high gas temperatures

In this paper, the critical reduced electric fields (E/N)cr in SF6 are determined over a temperature range 298–2300 K. These fields are derived from the quasi-stationary burning voltages of a self-sustained volume discharge in SF6 irradiated by a CO2-laser through a slit diaphragm. Visualization of the shock-wave disturbances generated by the temperature jump at the boundary between the laser-heated and cold gas and measurements of the discontinuity surface propagation velocities are performed. A purpose-developed VSh method allowing determination of the gas temperature T by the shock wave propagation velocity has been proposed to evaluate the temperatures exceeding 1500 K. The (E/N)cr-values obtained at T > 2000 K are compared with those measured under the conditions of the complete thermodynamic equilibrium. The difference found is treated in terms of the authors' concept of the dielectric strength of strongly heated electronegative polyatomic gases. A number of fundamentally new physical effects are shown to arise at the discontinuity surfaces in a shock-wave-disturbed SF6 after voltage application. Some aspects of relevance to these effects are qualitatively discussed. Special attention is given to the dynamic barrier effect.