Increase In Particle Velocity Research Articles

Numerical Simulation of Shock Wave in Gas–Water Interaction Based on Nonlinear Shock Wave Velocity Curve

In a gas–water interaction problem, the nonlinear relationship between shock wave velocity is introduced into a Hugoniot curve, and a Mie–Grüneisen Equation of state (EOS) is established by setting the Hugoiot curve as the reference state. Unlike other simple EOS based on the thermodynamics laws of gas (such as the Tait EOS), the Mie–Grüneisen EOS uses reference states to cover an adiabatic impact relationship and considers the thermodynamics law separately. However, the expression of the EOS becomes complex, and it is not adaptive to many methods. A multicomponent Mie–Grüneisen mixture model is employed in this study to conquer the difficulty of the complex form of an EOS. In this model, some coefficients in the Mie–Grüneisen EOS are regarded as variables and solved using newly constructed equations. The performance of the Mie–Grüneisen mixture model in the gas–water problem is tested by low-compression cases and high-compression cases. According to these two tests, it is found that the numerical solutions of the shock wave under the Mie–Grüneisen EOS agrees with empirical data. When compared to other simple-form EOSs, it is seen that the Mie–Grüneisen EOS has slight advantages in the low-compression case, but it plays an important role in the high-compression case. The comparison results show that the solution of the simple-form EOS clearly disagrees with the empirical data. A further study shows that the gap between the Mie–Grüneisen EOS and other simple-form EOSs becomes larger as the initial pressure and particle velocity increase. The impact effects on the pressure, density and particle velocity are studied. Moreover, the gas–water interaction in a spherical coordinate plane and a two-dimensional coordinate is a significant part of our work.

Compaction characteristics and mechanism of the ADC12 alloy powder by laser impact compaction

This paper focuses on the dynamic compaction experimental investigation of ADC12 alloy powder using laser impact, leveraging the high strain rate and controllable precision of pulsed lasers. The effects of varying laser energy (Em) and impactor thickness on the relative density, microstructure, and microhardness of the ADC12 alloy powder billets were examined. Utilizing 2D multi-particle finite element simulation (2D MPFEM), the densification mechanism of these billets was analysed with the help of coordination numbers. The simulation also provided insights into the particle velocity, equivalent plastic strain, and adiabatic temperature increase during compaction. Key findings include that a relative densification of up to 97.27% in the billets is achievable when the laser energy reaches 6J. Notably, a decrease in impactor thickness at constant laser energy leads to a more uniform microstructure and microhardness in the billet. Simulations with the 2D MPFEM demonstrate that thinner impactors allow billets to absorb more energy, thereby increasing particle velocity and plastic strain. This enhances both the relative density and mechanical properties of the billets. The simulation explores the stress distribution during compaction and captures the adiabatic temperature rise on the surface of the pressed billet that occurs in the transient, which is consistent with experimental revelations that heat softens or even locally melts the particles to produce sintering. This study offers new insights into the formation process of these billets from a microstructural standpoint, elucidating the relationship between processing conditions and the resulting material properties.

Gravity Effects on the Minimum Explosive Concentrations in 1-D Dust Explosion

ABSTRACT Theoretical predictions of dust-explosion characteristics, such as the minimum explosive concentration (MEC), can help improve the accuracy of quantitative risk assessment. This paper presents a continuum model to simulate one-dimensional dust-cloud combustion. It is found that the dilution of dust by thermal expansion reduces the propagation speed of a combustion wave through a dust cloud. At the same time, the delay in the increase of particle velocity due to relaxation time counteracts the dilution effect. Therefore, neglecting the relaxation time results in the underestimation of propagation speed. In the absence of heat loss, extinction occurs when the adiabatic combustion temperature decreases to the ignition temperature; MEC is independent of particle size in such cases. With the presence of heat loss, on the other hand, extinction occurs at a higher dust concentration; MEC increases with particle size. Accurate evaluation of ignition temperature is key to the quantitative prediction of MEC. A particular focus is given to gravity effects, reflecting recent experimental efforts to obtain fundamental insights into propagation mechanisms without being affected by gravity. In upward propagation, particles fall toward the reaction front, enhancing combustion and increasing the propagation speed. The situation in downward propagation is the opposite, and extinction occurs when the gravity level is beyond a critical value. In upward propagation, MEC can decrease with an increase in particle size, owing to the influence of gravity.

Advanced Assessment of Biomass Materials Degradation in Pneumatic Conveying Systems: Challenges and Applications

In this study, the degradation of wood pellets and dry roasted coffee beans in a pneumatic conveyor was evaluated for high-speed impacts. The change in particle size and generation of fine particles were used as an indicating parameter for the degradation. A four-bends industrial scale conveying system was used for the degradation study in lean phase pneumatic conveying. The effects of operating parameters on the degradation were investigated, including the conveying velocity of particles and particle concentration. The experimental results showed that the degradation and the fines generation increased with an increase in particle velocity. An opposite trend was observed with an increased solid concentration in the pipeline. It was found that the two types of wood pellets traveled at different particle velocities with the same operating conditions, which resulted in significant differences in the degradation. Compared to the wood pellets, roasted coffee beans were found to travel at air velocity. In conclusion, the degradation in a pneumatic conveying system is complex and challenging to evaluate because there are many influential factors, such as the type of materials, equipment, and operation conditions. Early assessments in a laboratory will be beneficial to evaluate the degradation at all controlled operative conditions.

The influence of different preparation methods on the erosion behavior of NiP-ZrO2 nanocomposite coating

Three different deposition techniques were utilized to synthesize NiP-ZrO2 nanocomposite coatings. The structural and mechanical merits for the as-prepared coatings were compared through XRD, XRF, SEM, AFM, microhardness, and nanoindentation analysis. The pulse-electrodeposition was the most suitable technique with a hardness value of 653HV25. The erosion behavior for the different NiP-ZrO2 coatings was investigated based on erosion duration, particles velocity, and impact angle. The results shows that the erosion rate decreases linearly with increasing angle of incidence and increases with increasing particle velocity. The erosion mechanism is mainly fracturing of splats and ploughing action at low particle velocity due to the ductility merits of the different coatings. In contrast, larger craters, radial cracks, and micro cuttings were observed at higher speeds.

Аналитическая модель одномерной нестационарной динамики одиночной частицы в акустическом и электрическом полях

This paper presents the results of calculations of the dynamics of an electrically neutral and electrically charged particle in a closed channel. A mathematical model of the dynamics of a single particle in an acoustic field is presented, in which the potential of the acoustic field is given by a one-dimensional linear wave equation. The dynamics of the particle was described by a differential equation that puts the dependence of the particle velocity on the forces applied to it - the Stokes force acting from the side of the acoustic field, and the Coulomb force acting from the side of the electric field. It is revealed that the amplitude of oscillations of an electrically neutral particle is less than the amplitude of oscillations of an electrically charged particle in an electric field. It is determined that at a small amplitude of the piston oscillations, the amplitude of the change in the speed of an electrically charged particle under the action of electric field forces exceeds the amplitude of the change in the speed of an electrically neutral particle. In this paper, we analyzed the influence on the dynamics of an electrically charged particle in an acoustic field for stationary and nonstationary distributions of the electric field potential. The paper presents calculations of the dynamics of an electrically charged particle in a periodic electric field with different frequencies of electric field variation. It was found that when a particle is exposed to an alternating electric field that is in phase with the gas velocity field, the particle velocity increases, if the frequency of the alternating electric field is in antiphase with the gas velocity, then the particle velocity decreases. It is determined that if a stationary electric field acts on a particle, then the particle drifts to that part of the channel to which a potential is applied, the sign of which is opposite to the sign of the particle charge.

Coal particle transport behavior in a rotating drill pipe used for negative pressure pneumatic conveying

Conveying gas velocity, rotation speed, and particle diameter are all common parameters in a negative pressure pneumatic conveying system that affect the system's energy consumption and design. Herein, the effect of the above three parameters on the transport behavior of coal particles was investigated by coupling Computational Fluid Dynamics and the Discrete Element Method (CFD–DEM) approach. The numerical results indicate that increasing gas velocity increased the number of coal particles entering the drill pipe. An increase in particle velocity increased conveying efficiency. With increasing particle diameter, the number of coal particles entering the drill pipe decreased. The particle velocity decreased, resulting in a decrease in conveying efficiency. In contrast, as the rotation speed increased, the particle distribution within the drill pipe became more dispersed, and the swirling flow trajectory became more apparent. The number of coal particles and conveying efficiency were decreased, although the effect on particle velocity was negligible.

Erosion characteristics of N720/alumina oxide/oxide ceramic matrix composites in a combustion environment

The erosion behavior of N720/Alumina oxide/oxide composite was investigated under a combustion environment to better represent particle ingestion of a jet engine. The effect of particle velocity, particle size, temperature and impingement angle were investigated. In addition, room temperature studies were also conducted for comparison. Eroded sites were investigated using optical and scanning electron microscopy to understand the extent of erosion and erosion mechanisms. The results indicate that erosion rate increased with an increase in particle velocity and particle size. Also, erosion rate increased from room temperature to 815 °C and then decreased from 815 °C to 1200 °C. Brittle fracture is the predominant mode under normal impacts and as the impact angle is decreased increased ploughing/wear is evident.

Critical Velocity Prediction and Characterization of Bonding Types of High-Velocity, Air-Fuel-Sprayed Titanium Coating on Aluminum Alloys

This study established finite-element models via LS-DYNA software to predict the critical velocity of Ti spray particles under different collision velocities and preheating temperatures. Particle deformation, collision temperature, and bonding types of the Ti coating/Al substrate system were simulated. At the predicted critical velocity (650 m/s) and the corresponding preheating temperature (300 °C), the TC4 titanium coating was fabricated on a 6061 aluminum substrate by high-velocity air fuel (HVAF) spray. The coating’s microstructure and phase transition were analyzed by a scanning electron microscope (SEM) equipped with energy-dispersion X-ray spectroscopy (EDS) and transmission electron microscopy (TEM), revealing that critical velocity decreases with increasing particle velocity and preheating temperature. At 650 m/s, the coating was well-bonded to the matrix in metallurgical bonding type, and mechanical interlock and metallurgical bonding coexisted among particles. Experimental results show that the coating is characterized by the metallurgical bonding type, a fusion layer, and recrystallization, which verifies the simulated collision temperatures.

Numerical Simulation of the Effect of Particle and Substrate Preheating on Porosity Level and Residual Stress of As-sprayed Ti6Al4V Components.

Nowadays, in the aerospace industry, additive manufacturing and repairing damaged metallic components like Ti6Al4V samples have grabbed attention. Among repairing techniques, solid-state additive manufacturing processes like cold spray are promising because of their unique benefits such as high deposition rate with almost no oxidation in the deposited materials. However, its main drawback is the level of porosity of as-sprayed samples. To increase density and inter-particle bonding, deposited particles must go through more degrees of deformation by increasing particle velocity and particle temperature. In order to increase these two parameters simultaneously, high-velocity air fuel (HVAF) can be utilized. For understanding the effect of using HVAF on particle deformation, a proper elastic-plastic finite-element-based simulation is required. The obtained outcomes show that enhancing particle velocity and providing more kinetic energy will increase particle deformation and sample density. Importantly, increasing particle temperature will seize particle deformation by thermal softening effect, i.e., enhancing as-sprayed sample density, while rising substrate temperature by preheating will soften the substrate resulting in a decrease in particle deformation.

Gas-liquid mass transfer in a gas–liquid-solid three-phase moving bed

The gas–liquid mass transfer was investigated in a gas–liquid-solid three-phase moving bed based on the dissolved oxygen method, and a semi-quantitative gas–liquid boundary identification method was developed to measure the gas–liquid interfacial area. Results showed that the effects of gas velocity and liquid velocity on gas–liquid mass transfer in the three-phase moving bed were the same as those in the trickle bed. Since the gas–liquid interfacial area and its renewal speed were promoted at the low particle velocity and inhibited at the high particle velocity, the liquid-phase volumetric mass-transfer coefficient first increased and then decreased with the increasing particle velocity. Moreover, an empirical correlation for the liquid-phase volumetric mass-transfer coefficient was established based on 296 data, and the average relative deviation was 8.11%. The sensitivity analysis showed that the liquid velocity was more important to gas–liquid mass transfer than gas velocity and particle velocity.

Solid particle erosion behavior of melt-infiltrated SiC/SiC ceramic matrix composites (CMCs) in a simulated turbine engine environment

The erosion behavior of a melt infiltrated SiC/SiC ceramic matrix composite was investigated under a more representative engine environment. A special experimental facility was setup to simulate the turbine engine conditions. The influence of the operating parameters such as particle velocity, particle size, temperature, erodent concentration and impingement angle were investigated. In addition, room temperature studies were also conducted under the same operating parameters for comparison. Eroded sites were investigated under the scanning electron microscope (SEM) to understand the erosion mechanisms. The results indicate that erosion rate increased with increase in particle velocity, size and temperature. Also, at shallow impact angles the CMC shown to exhibit ductile like mode of erosion as opposed to brittle fracture mode at normal impact angles was observed. The erosion rate decreased with increase in erodent concentration which may be related to a particle shielding effect.

The effect of rotation speed and mixer size on granular flow and mixing in bladed mixers

Bladed mixers are widely used in the industry for granular mixing. In the past decades, the mixing of particles in bladed mixers has been extensively investigated experimentally and numerically. Recently, GPU-based DEM has been employed to simulate various industrial-scale applications. This work aims to apply the GPU-based DEM to investigate the effect of rotation speed and mixer size on granular mixing in bladed mixers of different sizes. The simulation in a larger mixer revealed distinct particle flow patterns that well-describe the mixing mechanism which is difficult to observe in a smaller mixer. The Lacey’s mixing index curves revealed a delay in mixing as the mixer size increases. The mixing rate decreases as the mixer size increases and it can be improved with increasing rotation speed. The average particle velocity increase significantly with increasing rotation speed and mixer size.

Study on the Influence of Sand Erosion Process on the Wear and Damage of Heat-Treated U75V Rail Steel

Abstract Usually, rail materials are exactly affected by the erosion of windblown sand in the desert environment. For this reason, the influence of impact angle, particle velocity, and particle size on the erosion wear behavior of the U75V heat-treated rail steel, a material frequently employed in Chinese railways, were studied in this work. The results showed that, with increasing impact angle, the erosion rate increased between 15 deg and 45 deg, decreased between 45 deg and 75 deg, and then increased again between 75 deg and 90 deg. The highest erosion rate occurred at about 45 deg. When the particle velocity increased, the erosion rate increased approximately in a quadratic way. As the sand particle size increased, the erosion rate presented a decreasing trend. During the initial stage of erosion, shear craters, indentation craters, and ploughing craters were the main surface damage features. The shear craters predominated at the impact angle of 45 deg whereas the indentation craters predominated at 90 deg. During the steady-state of erosion, the rail damage was mainly composed of craters, platelets, and cracks. Both the length and depth of craters increased almost linearly with increasing particle velocity, whereas the increased rate of length was significantly higher than that of depth. The length and depth of craters increased with increasing particle size at 90 deg, whereas only the length increased with increasing particle size at 45 deg. The microstructure evolution and the formation mechanism of platelet at low impact angles were different from those at high impact angles. Platelet formation was the main erosion wear mechanism.

Numerical Simulation of Impact Behavior of Ceramic Coatings Using Smoothed Particle Hydrodynamics Method

Abstract In this work, the impact behavior of an alumina spherical particle on alumina coating is modeled using the smoothed particle hydrodynamics (SPH) method. The effects of impact angle (0 deg, 30 deg, and 60 deg) and velocity (100 m/s, 200 m/s, and 300 m/s) on the morphology changes of the impact pit and impacting particle, and their associated stress and energy are investigated. The results show that the combination of impact angle of 0 deg and velocity of 300 m/s produces the highest penetration depth and largest stress and deformation in the coating layer, while the combination of 100 m/s and 60 deg causes the minimum damage to the coating layer. This is because the penetration depth is determined by the vertical velocity component difference between the impacting particle and the coating layer, but irrelevant to the horizontal component. The total energy of the coating layer increases with the time, while the internal energy increases with the time after some peak values, which is due to energy transmission from the spherical particle to the coating layer and the stress shock waves. The energy transmission from impacting particle to coating layer increases with the increasing particle velocity and decreases with the increasing inclined angle. The simulated impact pit morphology is qualitatively similar to the experimental observation. This work demonstrates that the SPH method is useful to analyze the impact behavior of ceramic coatings.

Effect of thermal energy on the deposition behaviour, wear and corrosion resistance of cold sprayed Ni-WC cermet coatings

Cold spraying is emerging as one of the versatile coating techniques applicable in vast variety of applications ranging from overlay coatings to structural repairs. Though variety of metals and their alloys have been successfully deposited using this technique, deposition of cermet with high volume percentage of carbide particulates is still challenging. Existing reports reveal that the deposition of cermet coatings was obtained from blend of metal (binder) and ceramic (particulates) powders. Understanding the deposition behaviour of commercially available cemented carbide in cold spraying has technical significance since these cermets have huge industrial potential to protect components from wear and corrosion. Deposition of cermet using cold spray has a challenge since increase in particle velocity not only increases the plastic deformability of binder phase but also reduces the particulate phase in coatings since the supersonic velocity leads to fracturing and shattering of particulates. State of binder and particulate in the feedstock plays a crucial role in successful deposition. In this work, two different Ni-WC cemented carbides were deposited and comprehensively characterized for inter-splat bonding state and powder state and the same is correlated with the mechanical and corrosion performances of the coatings. The role of thermal energy in the coating formation is studied and discussed in detail. Along with a proper feedstock, engineered nozzle design to enhance the thermal energy input to the feedstock is required to obtain dense cemented carbide coatings with high particulate retainment.

Effects of liquid content and surface tension on fluidization characteristics in a liquid-containing gas–solid fluidized bed: A CFD–DEM study

The fluidization process within gas–solid fluidized bed reactor can be intensified by adding liquid, as it can enhance mass and heat transfer between gas phase and solid phase. With the help of computational fluid dynamics(CFD) and discrete element methods(DEM), fluidization characteristics are investigated at different liquid contents(V^) and surface tension(Bog). To be specific, the bed expansion ratio, particle concentration and particle velocity profiles are compared and analyzed. Numerical simulations show that Bog should be less than 5 at V^ = 0.013. At this recommended range, liquid addition makes interparticle force increase and has little effect on fluidization performance. From transient particle agglomeration behavior, the Bog increase is more likely to enhance interparticle force, resulting in obvious particle agglomerations during fluidization process. The variation of stagnation zone height can be reflected from the abrupt increase of particle velocity in annulus region. It can be found that V^ increase reduces particle velocity at critical height but Bog increase is more likely to cause larger stagnation region. By analyzing the distribution of spout, annulus and fountain regions at different V^ and Bog, the annulus region expands with V^ increase below the initial bed height while the spout region expands with Bog increase.

Sand particle velocities over a subaqueous dune slope using high‐frequency image capturing

AbstractThis work presents measurements and analysis of sand particle velocities over a subaqueous dune with median sand diameter of 0.85 mm. Time‐lapse images of the mobile bed and an automated particle image velocimetry (PIV)‐based cross‐correlation method are used to obtain mean velocity of sand particles. This technique is shown to be consistent with measurements obtained with manual tracing. The measurements indicate an increase in mean particle velocity over a dune slope. Three regions are distinguished over the dune slope: (1) region of fluctuating particle velocity, (2) region of increasing particle velocity, and (3) region of maximum particle velocity. The observations are aligned with experimental and numerical modelling studies, indicating fluctuations in flow velocity over a dune stoss slope. We furthermore show that the standard deviation of the mean particle velocity is affected by the slope location and decreases from the lower slope towards the upper slope. The particle velocity variability is discussed in the context of general onset and cessation of sediment transport, the effect of the reattachment zone, sweep‐transport events, and the existence of superimposed bedforms. With this work we bridge the gap between measurements of bedload transport at the particle‐scale and at the bedform‐scale. © 2019 John Wiley & Sons, Ltd.

Plate impact investigation of the dynamic response of commercial tungsten carbide under shock-induced compression and combined compression-and-shear loading

This article presents results from a series of plate-impact experiments designed to study dynamic response of commercial purity (99.6%) tungsten carbide (WC) under shock-induced normal compression and simultaneous compression-and-shear stress wave loading. The normal shock compression experiments utilize a heated WC flyer plate which impacts a WC target at room temperature, enabling inelastic response of the WC target plate as well as the elevated temperature shock-impedance of the heated WC flyer plate to be probed simultaneously. The measured normal particle velocity profiles at the free surface of the WC target plate exhibit an elastic precursor, which corresponds to a longitudinal stress of ∼5.9–6.2 GPa, and decreasing particle velocity levels in the shocked state with increasing temperature of the WC flyer. The shock impedance of the heated WC flyer is estimated to decrease from 1.05 × 108 to 8.23 × 107 kg/m2s over the temperature range 23–600°C. The simultaneous compression-and-shear loading experiments are conducted using a symmetric oblique plate-impact experimental configuration with progressively increasing angles of inclination (5°, 10°, and 22°), resulting in increasing shear to longitudinal stress ratios upon impact in the WC flyer and target plates. The measured longitudinal and transverse components of the free surface particle velocity in experiments with inclination angles of up to 10° and impact velocities ∼100 m/s (corresponding to shear and longitudinal stress levels of 0.5 GPa and 4.5 GPa, respectively), coincide well with their corresponding elastic particle-velocity predictions. However, the free-surface normal particle velocity profiles for experiments conducted at an oblique impact angle of 22° (corresponding to shear stresses ∼1.3 GPa and longitudinal stress of ∼4.9 GPa) are remarkably different and exhibit a sudden increase in particle velocity from their plateau levels reminiscent of failure waves observed by other investigators in soda lime glass and silicon carbide (SIC-B). The new normal particle velocity level, after the arrival of the recompression/re-acceleration signal, exceeds the magnitude of the impact velocity, suggesting failure of the WC target plate during the stress wave loading process. The relatively large undulations present in the measured free-surface transverse particle velocity profiles provide further evidence for the heterogeneous brittle failure processes in WC under the resulting simple-shear state of stress, and is used to provide estimates for the critical range of simple-shear loading that can initiate catastrophic failure (fracture) in pure WC.

Measurement of Aerodynamic Particle Size Distribution of Orally Inhaled Products by Cascade Impactor: How to Let the Product Specification Drive the Quality Requirements of the Cascade Impactor.

The multi-stage inertial cascade impactor is used to determine the mass-weighted aerodynamic particle size distribution (APSD) as a critical quality attribute for orally inhaled products (OIPs). These apparatuses progressively size-fractionate the aerosol passing through a series of stages containing one or more nozzles, by increasing particle velocity. Nozzle sizes for a given multi-nozzle stage can be described collectively by effective diameter ([Formula: see text]), related to the cut-point size, providing the link to aerodynamic diameter. Users undertake stage mensuration periodically to assure that each stage [Formula: see text] remains within the manufacturer's tolerance, but there is no guidance on how frequently such checks should be made. We examine the philosophy that particle size-related specifications of the OIP should determine when an impactor is mensurated. Taking an example of a dry powder inhaler-generated aerosol sampled via a Next Generation Impactor with pre-separator, we find that there are only three critical stages that could have a material effect on the measured APSD specified as four groupings of stages following current regulatory practice. Furthermore, [Formula: see text] for the most critical stage having the smallest nozzle sizes could be relaxed by a factor of four or more before risking an inability to measure the mass fraction of API in the group containing the finest particles to a specification within ± 10% of nominal. We therefore conclude that users should consider letting the specification for APSD performance of an OIP in terms of accepted stage groupings drive the impactor quality requirements and frequency that stage mensuration is undertaken.