Decrease In Propagation Velocity Research Articles

Effect of initial pressure on hydrogen/propane/air flames in a closed duct

To investigate the flame propagation characteristics and chemical kinetics of premixed propane/hydrogen/air mixtures at elevated pressure, a series of experiments on propane/hydrogen/air mixtures with varying initial pressures (P0 = 100–300 kPa) and equivalence ratios (φ = 0.6–1.4) at a hydrogen fraction of 0.6 and an ambient temperature of 298 K were carried out in a closed duct with an aspect ratio of 15. The chemical kinetics of the elementary reaction were analyzed numerically. The results revealed that the combustion-induced rapid phase transition (cRPT) occurred in the premixed C3H8/H2/air flames. Both the combustion pressure and flame propagation velocity increase with initial pressure except at P0 = 300 kPa, where the flame propagation velocity decreases. Moreover, the linear dependence between the laminar burning velocity and peak mole fraction [H + O + OH]max was found by the effect of initial pressure on the peak mole fraction (H, O, OH). The explosion pressure Prea and the maximum rate of production of free radical H/O show excellent correlations. The maximum rate of pressure rise can be predicted by the maximum heat release rate (HHR). These results provide essential data on elevated-pressure duct accidents and have important implications for explosion prevention.

Effect of Combustor Outlet Geometry on Operating Characteristics of Disk-Shaped Rotating Detonation Engine

A disk-shaped rotating detonation engine with H2/air mixture was tested to identify the impact of combustor outlet geometry on the engine’s operating characteristics. Three combustor outlet diameters and five outlet lengths are employed in the experiments. Results show that with the increase of combustor convergent ratio, the propagation stability of the rotating detonation wave decreases, and the propagation velocity and pressure peak decrease slightly. When the convergent ratio increases to a certain value (1.70 in this study), a “platform zone” with a lower pressure value appears before the sharp rise of the dynamic pressure curve. The propagation mode varies with the increase of mass flow rate at different convergent ratios. As the mass flow rate increases, the wave head number in the combustor increases. But the change rule of propagation mode with mass flow rate is greatly affected by convergent ratio. Increasing the convergent ratio is conducive to the formation of multi-wave modes, and the critical mass flow rate for mode transition drops sharply. When the convergent ratio increases to 1.70, the unstable asymmetric dual-wave mode is obtained. With the increase in the convergent ratio, the engine’s operating range and operating stability decrease significantly. Finally, changing the combustor outlet length has little influence on the engine’s operating characteristics and detonation-wave parameters.

Porosity-dependent wave propagation in multi-directional functionally graded nanoplate with nonlinear temperature-dependent characteristics on Kerr-type substrate

The present study investigates the wave propagation characteristics of porous, multi-directional, functionally graded (FG) nanoplates embedded in a Kerr-elastic substrate. A first-order shear deformation model (FSDM) and the nonlocal strain gradient approach (NSGA) are utilized to address this issue. The NSGA is enhanced by considering softening and hardening material effects, leading to improved accuracy in the obtained results. In accordance with the law of mixing, the material properties of the nanoplates exhibit nonlinear temperature-dependent variations along the structural axes. Both even and uneven porosity profiles are considered in this study. The nonclassical governing equations for the proposed structure are derived using Hamilton's approach. The phase velocity and wave frequency are determined through the analytical solution of an eigenvalue problem, which depends on the wave number. The dispersion properties of waves in porous FG nanoplates are examined with respect to various factors, including porosity distributions, wave numbers, nonlocal and strain gradient effects, elastic foundation coefficients, and volume fraction index. The main findings of the study indicate that increasing the volume fraction index in the thickness direction leads to a decrease in the phase velocity and frequency of wave propagation in a porous FG nanoplate for a given wave number. Additionally, regardless of the porosity pattern, an increase in the porosity coefficient results in a decrease in wave frequency and phase velocity.

Effect of salt addition on the coalescence process of droplets on fiber

Fiber coalescence is an economical and effective technology for the treatment of oily wastewater. In this paper, the microscopic coalescence process of salt droplets on the fiber is studied using a high-speed camera and PIV, and the effect of salt on hydrodynamics and morphological evolution is discussed. The results show that the increase of salt concentration leads to a decrease of double layer force, a larger liquid bridge expansion, and a higher capillary wave propagation velocity. When the salt concentration is too high, the capillary wave propagation velocity decreases. A catchment region with a high velocity is formed near the traveling region of the capillary wave, and the velocity can reach 0.03 m/s. The attenuation coefficient of the oscillation process increases with the increase of salt content. By combining fiber and salt, the rate of droplet coalescence can be increased, and the production of secondary droplets can be reduced.

Stormwater management in urban areas using dry gallery infiltration systems

The increase in the frequency of extreme precipitation events due to climate change, together with the continuous development of cities and surface sealing that hinder water infiltration into the subsoil, is accelerating the search for new facilities to manage stormwater. The Canary Islands (Spain) are taking advantage of the knowledge acquired in the construction of water mines to exploit a novel stormwater management facility, which we have defined as a dry gallery. Dry galleries are constituted by a vertical well connected to a horizontal gallery dug into highly permeable volcanic layers of the vadose zone, from where infiltration takes place. However, the lack of scientific knowledge about these facilities prevents them from being properly dimensioned and managed. In this work, we simulate for the first time the infiltration process and the wetting front propagation from dry galleries based on a 3D unsaturated flow model and provide some recommendations for the installation and sizing of these facilities. The fastest advance of the wetting front takes place during the earliest times of infiltration (<2 h), with plausible propagation velocities and infiltration rates higher than 1000 m∙d−1 and 2 m3∙s−1. As time progresses, the propagation velocity and infiltration rate decrease as a consequence of the hydraulic gradient attenuation between the gallery and the aquifer. Therefore, stormwater infiltration is a highly transient process in which a sizing underestimation of 100% may be committed if unsaturated conditions or geological configuration are neglected.

Study on the suppression mechanism of (NH4)2CO3 and SiC for polyethylene deflagration based on flame propagation and experimental analysis

The polyethylene (PE) industry is in a stage of rapid development. However, PE dust floating in the air is frequently associated with unexpected explosions. To find a proper way of preventing and mitigating the potential of PE dust explosion, a study was carried out in which (NH4)2CO3 and SiC were used for the first time to suppress PE deflagration flames. In a Hartmann tube apparatus, PE deflagration flame propagation in the presence of (NH4)2CO3 and SiC powders as the suppressant was observed. The suppression effects of these two powders at different mass fractions were compared. The results showed that flame propagation velocity and acceleration decrease with increasing mass fraction of (NH4)2CO3 and SiC. Through XRD, FIRT, TG-DSC, GC–MS and sensitivity test, explosion products and combustion reactions were characterized and the PE explosion suppression mechanisms of (NH4)2CO3 and SiC for PE were compared and investigated. PE explosion is suppressed by SiC physically by reducing temperature and pressure of explosion combustion, while the explosion combustion of PE was suppressed by physical and chemical effect of (NH4)2CO3. As a result, (NH4)2CO3 is better able to suppress explosion flames. The study provides a theoretical and practical basis for the prevention and control of explosion fire accidents in the polyethylene industry.

Thermally coupled SHS processes in (Ni + Al)/(Co + Ti)/(Ni + Al) layered system: experimental and theoretical study

The paper focuses on the theoretical and experimental study of the mechanisms of reaction mixture combustion in the ≪chemical oven≫ mode in a three-layer Ni–Al/Ti–Co/Ni–Al sample. Experimental studies were carried out in a reactor in an argon atmosphere at atmospheric pressure and an ambient temperature of 298 K on rectangular samples pressed from Ni–Al and Ti–Co powder mixtures in the form of a three-layer package. The Ti–Co acceptor layer was in the middle of the sample, and the Ni–Al donor layer was outside. The acceptor layer thickness was varied from 4.3 to 13 mm, while the donor layer thickness (4.7 mm) remained constant. It was found that as the acceptor layer thickness increases, the combustion wave front propagation velocity and reaction initiation temperature decrease, and the maximum temperature in the front remains constant and equal to the melting point of the final product. The time of acceptor layer heating before the reaction increases. The acceptor mixture reaction proceeds in the thermal explosion mode when the thickness of the acceptor layer exceeds that of the donor one. Maximum temperature in this case is higher than the melting point of the final product. The inner layer synthesis modes change with an increase in the acceptor layer thickness: stationary – pulsating – extinction. The mathematical model of the three-layer sample high-temperature synthesis in dimensional variables is constructed taking into account heat transfer with the environment. As a result of experimental studies and numerical calculations, the critical thickness of the inner layer was found to be 15 mm, at which the inner layer combustion becomes impossible at fixed sizes of donor layers. Critical conditions for the combustion wave propagation along the acceptor layer are weakly dependent on the external heating source. The experimental technique and mathematical model of the layered system combustion can be used to assess the critical conditions for the metal composite synthesis in the frontal combustion mode.

Study on the effect and mechanism of Ca(H2PO4)2 and CaCO3 powders on inhibiting the explosion of titanium powder

In this paper, the experiment of titanium powder explosion was carried out by using Hartmann and 20-L spherical explosion tank. The inhibition effect of different proportions of Ca(H2PO4)2 and CaCO3 powders on titanium powder explosion was studied, and the inhibition mechanism of inhibitor on titanium powder explosion was analyzed. The experimental results show that with the increase of the proportion of inhibitors, the flame brightness becomes darker, the propagation velocity and distance decrease gradually, and the Pex and (dp/dt)ex decrease gradually. When 80% Ca(H2PO4)2 and CaCO3 were added, the average flame propagation speed decreased to 0.59 m/s and 1.08 m/s, respectively, and decreased by 87.7% and 77.4%; the Pex decreased to 0.152 MPa and 0.206 MPa, respectively, and decreased by 80% and 72.9%. The results show that both Ca(H2PO4)2 and CaCO3 have certain inhibition effect on titanium powder explosion, and the inhibition effect of Ca(H2PO4)2 is better.

Spatial Dependence of Dynamic Nonlinear Rock Weakening at the Alpine Fault, New Zealand

AbstractWe perform laser ultrasonic measurements to investigate the spatial dependence of dynamic nonlinear weakening in rocks from the Alpine Fault, New Zealand. Rocks outside the damage zone display no nonlinear weakening. Within the damage zone (&lt;30 m from the fault), cataclasites present a 3% reduction in shear modulus from wave amplitudes inducing 1–2 microstrain at atmospheric pressure. This nonlinear elasticity decreases with a characteristic pressure between 1 and 2.5 MPa. We show that rock weakening is therefore strongest in the near surface. However, this significant elastic nonlinearity in cataclasites at low strains confirms that rock weakening may play an important role in earthquake processes, such as fault weakening, triggering of slip, rupture propagation, and coseismic velocity decreases.

Inertant effects and mechanism of Al(OH)3 powder on polyethylene dust explosions based on flame propagation behavior and thermal analysis

To assess the inhibitory effect and mechanism of Al(OH)3 powder on the flame propagation from a polyethylene dust explosion, tests were conducted in a vertical transparent tube. The results show that the addition of Al(OH)3 powder has a significant effect on the polyethylene dust explosion flame structure and propagation characteristics. With increasing mass ratio of Al(OH)3 powder, the polyethylene dust explosion flame brightness decreases, the flame propagation velocity decreases, and pulsation of the flame during propagation diminishes. The Al(OH)3 powder destroys the continuity of the structure of a polyethylene dust explosion flame, and retards the acceleration of flame propagation. The thermal weight loss of the polyethylene gradually decreased with increasing addition of Al(OH)3 powder. Al(OH)3 powder can retard the characteristic temperature of severe heat release from polyethylene. The cumulative heat release gradually decreases with the increasing amount of Al(OH)3 powder. Al(OH)3 powder can inhibit flame propagation of polyethylene dust explosion through physical effects such as cooling, heat insulation, and suffocation. This work is of significance for the prevention and treatment of polyethylene dust explosion accidents.

Self-Sustaining Smoldering Characteristics of Corn Straw Powder Stacks.

Biomass fuels are expected to play an important role in future energy consumption. Meanwhile, the fire and explosion of biomass are the have-to-face problems in its production, storage, and application process. This work aims to reveal the influence of stacking and ventilation parameters on the smoldering propagation process and provide guidance for the safe storage of biomass pellets. The effects of stacking density and air flux on the smoldering propagation process were studied experimentally, the variations of bed temperature with these two parameters were analyzed using the numerical simulation technique, and the conditions of self-sustaining smoldering were determined by the local energy analysis method. The results showed that the peak smoldering temperature of corn straw powder was between 500 and 520 °C, and the smoldering propagation velocity was between 10 and 30 mm/h. When the stacking density was changed from 56.89 to 99.56 kg/m3, the peak smoldering temperature change rate was about 2% and the smoldering propagation velocity decrease amplitude was up to 30%. Meanwhile, when the air flux was in the range of 0.2–0.8 m3/h, the small ones had little effect on the peak smoldering temperature, while the large ones helped the peak smoldering temperature reach 560 °C. Finally, the local energy analysis showed that the net heating rate was positive with energy accumulation in the system, the smoldering was self-sustaining, and the smoldering front propagated from the bottom to top. These results provide data support to facilitate the safe storage of biomass pellets.

Experimental and numerical investigations of the effect of charge density and scale on the heat transfer behavior of Al/CuO nano-thermite

In this paper, to study the propagation behavior and the burning rate enhancement of Al/CuO nano-thermite in confined burn tubes, modification of the component was achieved by introducing energetic binder nitrocellulose (NC). The combustion behavior of Al/CuO and Al/CuO@NC nano-thermites in burn tubes was contrastively investigated by turning the charge density and the tube diameter in the range of 0.8–1.8 g/cm3 and 0.3–2 mm, respectively. Our experiments and theoretical calculation results show that the seepage of the gas flow is an important factor affecting the heat transfer process of Al/CuO nano-thermite in burn tubes, which makes the propagation velocity decrease with the increase of the charge density. Meanwhile, by introducing a certain amount of NC into the component, the reactivity can be improved while the gas production and pressurization capacity can be increased at the same time. This can greatly improve the propagation velocity of Al/CuO nano-thermite under constraint conditions. Moreover, with the decrease of the tube diameter, it can be inferred that the significant increase of the relative heat loss is the main reason for the decrease of the propagation velocity while the dimensionless parameter θ can be used to analyze the heat loss coefficient under different charge diameters.

Experimental investigation on the crack propagation behaviors of sandstone under different loading and unloading conditions

A series of laboratory tests were conducted in order to investigate the effects on crack propagation characteristics of confining pressure, as well as the effect of the unloading rates of confining pressure. Under conventional compression conditions, with increases in confining pressure levels, decreases will occur in the initial crack volumetric strain and crack volumetric propagation strain. These decreases indicate that when a specimen is under higher confining pressure conditions, it tend to generate more cracks before failure occurs. The crack closure stress, crack initiation stress and crack damage stress of sandstone gradually increase with increasing confining pressure levels. The crack propagation velocity corresponding to peak stress of sandstone undergoing uniaxial compression is the largest. In addition, with increases in confining pressure, the crack propagation velocity decreases. At the same confining pressure level, the crack volumetric propagation velocity corresponding to peak stress is the largest, followed by the crack radial and crack axial propagation velocities. With increases in the unloading rates of the confining pressure, increases will occur in the crack volumetric propagation strain and crack propagation velocity of the sandstone. The crack propagation velocity corresponding to peak stress of sandstone is larger than it is under uniaxial and conventional triaxial compression. Therefore, the larger unloading rates may cause larger crack propagation velocities and as the burst liability increases, rock burst or coal bumps may be triggered.

Effects of Shot Peening on Fatigue Life of Ground Component of 7075-T6 Aluminum Alloy

The aircraft corroded components can continue to be used after removing the corroded portion by grinding and strengthening the ground area by shot peening. The finite element analysis model of the ground specimen with complex shape surface was established based on ABAQUS software. The residual stress distributions under three conditions of without shot peening, ground surface shot peening and three surfaces shot peening were analysed. On this basis, the cyclic alternating load was introduced into the shot peening model, and the fatigue analysis was carried out based on MSC. Fatigue software. The result shows that the position of the maximum tensile stress moves from the surface to the subsurface of the ground specimen after shot peening; shot peening conditions will affect the location of the crack sources, the propagation direction of the crack; with the increasing of the numbers of peened surface, the location of stress danger point shifts from ground surface to side surface or sub-surface, and the crack propagation velocity decreases. All of these increases the fatigue life. The experimental results conform well to the simulation one.

Two-dimensional numerical study of two-phase rotating detonation wave with different injections

Two-dimensional numerical simulations on the two-phase rotating detonation wave of a stoichiometric ratio of the air-octane mixture by the discrete phase model are performed. The propagation process and stable flow field of the rotating detonation wave under nonpremixed and nonuniform injection conditions are analyzed. The effects of air injection total temperature and fuel injection inhomogeneity on the gas-liquid two-phase rotating detonation wave are investigated. The results show that under the same conditions, with the increase in the total temperature of air injection, the peak temperature, height, and propagation velocity of the detonation wave increase, but the peak pressure of the detonation wave decreases. The larger the jet spacing, the more pronounced the detonation wave is disturbed by the fuel jet. As the fuel jet spacing increases, the detonation wave propagation velocity decreases, but the peak temperature and peak pressure of the detonation wave increase. For the case of a jet spacing of 10 mm, the detonation wave cannot propagate when the air total temperature is 300 K, but the detonation wave can be stably propagated when the air total temperature is increased to 600 K. The stable propagation boundary of the rotating detonation wave with the combined action of the air total temperature and the jet spacing is obtained.

Transverse Vibration and Wave Propagation of Functionally Graded Nanobeams with Axial Motion

Based on the nonlocal elasticity theory, the vibration behavior and wave propagation of functionally graded Euler nanobeams with axial motion are investigated. Assuming that the axial velocity of nanobeams is a constant and the graded material parameters vary along the thickness direction in terms of power index, we apply the hypothesis of neutral plane to derive the axial displacement of geometry surface caused by non-uniformity of graded materials. Effects of graded index, axial velocity and nonlocal scale parameter on natural frequencies are analyzed through numerical examples. Also, the relationship between wave propagation frequency, wave velocity and wave number is revealed. The complex mode method is utilized to solve the governing equation, and the natural frequencies and wave velocity are obtained accordingly. To solve the derived transcendental equations, the Newton iteration method is used and a detailed solution flowchart is provided. For vibration, with the increase of non-dimensional axial velocity, non-dimensional nonlocal parameter and gradient index, natural frequencies decrease. For wave propagation, with the increase of wave number, frequency of wave propagation increases. However, with the increase of wave number, velocity of wave propagation decreases. Moreover, increasing the gradient index causes a decrease in frequency and velocity of wave propagation, increasing the axial velocity causes an increase in frequency and velocity of wave propagation, and increasing the nonlocal parameter causes a decrease in frequency and velocity of wave propagation.

The influence of the rheological parameters on the dispersion of the flexural waves in a viscoelastic bi-layered hollow cylinder

The paper investigates the influence of the rheological parameters which characterize the creep time, the long-term values of the mechanical properties of viscoelastic materials and a form of the creep function around the initial state of a deformation of the materials of the hollow bi-layered cylinder on the dispersion of the flexural waves propagated in this cylinder. Constitutive relations for the cylinder\'s materials are given through the fractional exponential operators by Rabotnov. The dispersive attenuation case is considered and numerical results related to the dispersion curves are presented and discussed for the first and second modes under the first harmonic in the circumferential direction. According to these results, it is established that the viscosity of the materials of the constituents causes a decrease in the flexural wave propagation velocity in the bi-layered cylinder under consideration. At the same time, the character of the influence of the rheological parameters, as well as other problem parameters such as the thickness-radius ratio and the elastic modulus ratio of the layers\' materials on the dispersion curves, are established.

FLAME PROPAGATION IN LIQUID FUEL DROPLETS SPRAY

Taking into account the significant volumes of liquid fuels consumption in the world fuel balance, one of the most urgent tasks of our time is to reduce the anthropogenic impact on the biosphere by completely or partially replacing mineral fuels with their renewable plant origin analogues. In this paper we present the experimental studies results of the flame propagation process in a one-dimensional set of ethanol droplets with water addition up to 50% by volume. In contrast to studies of processes accompanying the combustion of a single liquid fuel droplet, the combustion of their aggregate, in the form of a jet, has been studied to a lesser extent. The proposed scheme of a jet generator with a vibrating needle makes it possible to obtain a chain of monodisperse fuel droplets with a diameter d=490±5 μm, which is sufficiently stable over time (within 10 min), with the possibility of varying the inter-drop distance. As control parameters for changing this distance, the vibration frequency of the membrane and the value of constant pressure on the reservoir with liquid were used. Using the developed experimental procedure, dependences of the relative distance between the droplets, on the value of constant pressure on the reservoir with liquid fuel, at different monodisperse aerosol generator needle oscillation frequencies were obtained.The whole process of the flame front propagation along the monodisperse aerosol chain was recorded with a frequency of 300 fps. The video capturing results analysis of the flame propagation process made it possible to determine the dependence of flame propagation velocity on the distance between the droplets. A qualitative picture process analysis showed the flame propagation velocity decrease along the inter-droplet distance increase. The critical distance between droplets that is an order of magnitude greater than the droplet size under experimental conditions, at which the flame propagation stopped, was determined experimentally. The obtained results are explained with a sufficient degree of reliability within the framework of the proposed relay flame propagation mechanism within a one-dimensional monodisperse aerosol system.

Noninvasive Magnetogastrography Detects Erythromycin-Induced Effects on the Gastric Slow Wave

The prokinetic action of erythromycin is clinically useful under conditions associated with gastrointestinal hypomotility. Although erythromycin is known to affect the electrogastrogram, no studies have examined the effects that erythromycin has on gastric slow wave magnetic fields. In this study, gastric slow wave activity was assessed simultaneously using noninvasive magnetogastrogram (MGG), electrogastrogram, and mucosal electromyogram recordings. Recordings were obtained for 30 min prior to and 60 min after intravenous administration of erythromycin at dosages of 3 and 6 mg/kg. MGG recordings showed significant changes in the percentage power distribution of gastric signal after infusion of both 3 and 6 mg/kg erythromycin at t = 1-5 min that persisted for t = 30-40 min after infusion. These changes agree with the changes observed in the electromyogram. We did not observe any statistically significant difference in MGG amplitude before or after injection of either 3 or 6 mg/kg erythromycin. Both 3 and 6 mg/kg erythromycin infusion showed retrograde propagation with a statistically significant decrease in slow wave propagation velocity 11-20 min after infusion. Propagation velocity started returning toward baseline values after approximately 21-30 min for the 3 mg/kg dosage and after 31-40 min for a dosage of 6 mg/kg. Our results showed that the magnetic signatures were sensitive to disruptions in normal slow wave activity induced by pharmacological and prokinetic agents such as erythromycin. This study shows that repeatable noninvasive bio-electro-magnetic techniques can objectively characterize gastric dysrhythmias and may quantify treatment efficacy in patients with functional gastric disorders.

Ultrasonic detection of decrease in propagation velocity of contraction response due to myocardial ischemia in swine heart wall

Ultrasonic detection of decrease in propagation velocity of contraction response due to myocardial ischemia in swine heart wall