Particle Impact Angle Research Articles

Sediment transport in high‐speed flows over a fixed bed: 2. Particle impacts and abrasion prediction

AbstractSingle bed load particle impacts were experimentally investigated in supercritical open channel flow over a fixed planar bed of low relative roughness height simulating high‐gradient non‐alluvial mountain streams as well as hydraulic structures. Particle impact characteristics (impact velocity, impact angle, Stokes number, restitution and dynamic friction coefficients) were determined for a wide range of hydraulic parameters and particle properties. Particle impact velocity scaled with the particle velocity, and the vertical particle impact velocity increased with excess transport stage. Particle impact and rebound angles were low and decreased with transport stage. Analysis of the particle impacts with the bed revealed almost no viscous damping effects with high normal restitution coefficients exceeding unity. The normal and resultant Stokes numbers were high and above critical thresholds for viscous damping. These results are attributed to the coherent turbulent structures near the wall region, i.e. bursting motion with ejection and sweep events responsible for turbulence generation and particle transport. The tangential restitution coefficients were slightly below unity and the dynamic friction coefficients were lower than for alluvial bed data, revealing that only a small amount of horizontal energy was transferred to the bed. The abrasion prediction model formed by Sklar and Dietrich in 2004 was revised based on the new equations on vertical impact velocity and hop length covering various bed configurations. The abrasion coefficient kv was found to be vary around kv ~ 105 for hard materials (tensile strength ft > 1 MPa), one order of magnitude lower than the value assumed so far for Sklar and Dietrich's model. Copyright © 2017 John Wiley & Sons, Ltd.

CFD simulation of multiphase flows and erosion predictions under annular flow and low liquid loading conditions

For many industrial applications dealing with gas-liquid flow, transporting gas and liquid simultaneously causes many challenges. Prediction of erosion in multiphase flow is a complex problem due to lack of accurate models for calculating particle impact velocities in multiphase flow. Computational Fluid Dynamics (CFD) studies of annular flow are being conducted to investigate annular flow behavior and particle impact characteristics. Volume of Fluid (VOF) method was employed for air-water flow simulation with high gas velocities and low liquid rates. Simulation results are compared with results obtained with Eulerian-Eulerian with Multi-Fluid VOF approach with the same flow rates. CFD simulations of annular flow were also compared and validated with experimental data previously obtained with wire-mesh sensors. The liquid film thickness in bends can significantly affect erosion, therefore the simulation results of liquid film thickness trends are also investigated based on the gas and liquid flow rates.Particle tracking along with flow simulations have been solved simultaneously, and the maximum values of mass removal calculated with current erosion models were recorded in order to calculate the maximum erosion magnitudes. Particle impact characteristics including particle impact velocities, particle impact angles as well as particle impact number distribution along the bend were studied in several cases with different superficial gas and liquid velocities. Predicted erosion ratios are compared with available experimental data and show very good agreement.

Abrasion erosion modeling in particulate flow

Solid particle erosion is of great importance to many industries including oil and gas production, drilling, process and transportation of minerals including oil sands. The particles that may cause erosion are of various sizes, shapes and hardnesses. These particles may impact the surface at various speeds and angles, and the influence of these parameters is characterized to some extent in the literature. Experimental and numerical studies have shown that when particles are transported by liquid (e.g. slurry transport in the pipe) or dense gas, the particle impact angles are very low. The impact angles in these cases are sometimes less than the smallest value that can be obtained in a direct impingement erosion test in gas. In this work, the mechanistic erosion equation developed previously is extended to near zero impact angles for sharp particles. The abrasion erosion equation is developed by introducing an initial penetration of the sharp particle in the equation of the motion. This initial penetration may be attributed to the sharp particle rotation and/or turbulent flow fluctuations of the carrier fluid near the wall. The empirical constants are obtained from submerged erosion experiments in liquid. The equation has been implemented in a commercially available Computational Fluid Dynamics (CFD) code (ANSYS FLUENT) to calculate erosion for a submerged impingement jet geometry, and the result is compared with the experiment. It is shown that by neglecting the abrasive term in the erosion equation, the specimen mass loss does not match the experimental measured mass loss. While by including the abrasive term, the total mass loss of the specimen agrees well with the experimental data. Moreover, the erosion pattern becomes closer to the experimentally measured pattern especially farther from the center of the highly eroded area where abrasive wear is expected to dominate.

A mechanistic model for stochastic rebound of solid particles with application to erosion predictions

Erosive wear due to solid particle impacts is a significant challenge in process industries, especially for oil and gas industries where multiphase flow with the presence of solid particles conveyed by the fluid is very common. Solid particle erosion is a complex phenomenon with multiple factors contributing to its severity. Based on available studies in the literature, mechanistic and empirical erosion models are available that are being used by investigators to predict erosion in complex geometries. The erosion models require particle impact speed and angle to be determined for predicting solid particle erosion. Thus, in many applications, Computational Fluid Dynamics (CFD) codes are used to track the trajectories of solid particles to model erosion in complex geometries. However, the problem of predicting erosion in complex geometries where rebounded particles can have a significant effect on erosion pattern has been addressed only by a few investigators in the literature. The complexity results from the fact that trajectories of rebounded particles and their resulting velocities must be determined. The current investigation uses experimental data and modelling to determine the effects of particle rebounds on erosion patterns. The experimental setup is composed of two stainless steel and aluminum specimens at a right angle to each other, and the angle between the nozzle and first specimen is 45 degrees. The second specimen is painted to determine the erosion pattern caused by rebounding particles from the first. The effects of material composition and surface roughness on the rebounding particles are presented. Additionally, a mechanistic rebound model describing the erosion pattern, erosion intensity and location of maximum erosion is presented, and the predictions are compared with experimental data. It is found that the rebound model has a great influence on erosion prediction especially where subsequent particle impacts are expected. It is also shown that the existing empirical rebound correlations in the literature are not effective for erosion calculation purposes.

Erosive smoothing of abrasive slurry-jet micro-machined channels in glass, PMMA, and sintered ceramics: Experiments and roughness model

Abrasive slurry jet micro-machining (ASJM) was used to machine channels in glass, PMMA, zirconium tin titanate, and aluminum nitride. The channel roughness was measured as a function of the ASJM process parameters particle size, dose, impact velocity, and impact angle. The steady-state roughness of the channels was reached relatively quickly for typical ASJM abrasive flow rates. The roughness of channels having depth-to-width aspect ratios up to about 0.25 could be reduced by approximately 35% compared to the roughest channel by decreasing particle impact velocity and angle. However, machining at such conditions reduced the specific erosion rate by 64% on average. It was therefore quicker to post-blast reference channels (225nm average root mean square (Rrms) roughness) using process parameters selected for peak removal. It was also found that the roughness of reference channels could be reduced by about 78% by post-blasting using 3μm diameter silicon carbide particles at 15° jet incidence. The smoothest post-blasted channels had an Rrms roughness of about 23nm in glass, PMMA, and zirconium tin titanate, and 170nm in aluminum nitride. Computational fluid dynamics was used to predict the particle impact conditions that were used in a model to predict the steady-state roughness due to ductile erosion with an average error of 12%.

Influence of Fracture Toughness and Microhardness on the Erosive Wear of Cermet Coatings Deposited by Thermal Spray

An evaluation of the relationship between the microhardness and fracture toughness with resistance to erosive wear of WC10Co4Cr, WC-12Co, and Cr3C2-25NiCr coatings was conducted. Powder and flexible cored wire feedstock materials were applied by high-velocity oxygen fuel (HVOF) and flame spray (FS), respectively. The erosive wear mechanism prevailing in the coatings was found to be brittle, which also explains the higher erosion rate for the experimental condition using the particle impact angle of 90 deg and impact velocity of 9.33 m/s. The best wear performance was for the coatings applied by HVOF that attains 1.83 mm3/kg for the 90 deg/3.61 m/s test condition. The coating obtained with the WC-10Co4Cr material using the FSFC method showed tungsten carbide decarburization, justifying its poor mechanical properties and poor performance in the erosive wear test. Flame-sprayed flexicords proved to be a promising alternative to HVOF in obtaining coatings with low porosity and acceptable mechanical properties, especially in applications where the use of the HVOF technique is inadequate because of inaccessibility or excessively high cost. Values of K c for the coatings obtained by HVOF (7.35 to 10.83 MPa.m1/2) were between two and three times greater than the values obtained for the coatings resulting from FSFC (2.39 to 3.59 MPa.m1/2), in a similar manner as with the microhardness.

The effect of the micro-structures on the scorpion surface for improving the anti-erosion performance

New bionic function surface inspired from desert scorpion was developed for erosion resistance application in this research. Three elements, bump, groove-shape and curvature, were applied on the surface. Using of Stereo Microscope, the micro-structures of the scorpion (Androctonus australis) were analyzed. According to information, bionic samples were manufactured. Solid particle erosion behavior is investigated using a blasting jet machine at particle impact angle (30°) and stress of air compressor is 0.5MPa. The experimental results of bionic samples were compared with traditional smooth sample and each other, respectively. Results of erosion test and Scanning Electron Microscope (SEM) were selected as evaluation standard and explored anti-erosion mechanisms of these micro-structures which were on the bionic surface. The experimental results show that bionic samples have superior solid particle erosion resistance than traditional smooth sample, owing to the micro-structures on the surface. Referring to the analysis, both the bump and curvature can improve the anti-erosion performance by changing the relative impact angle which is compared to the surface of sample.

Numerical study of particle motion near a charged collector

The behavior of particles impacting the surface of a charged droplet involves adhesion, rebound, and submersion. In the present study, a numerical model for simulating particle impacts on charged droplets is presented that takes into account the various impact modes. With the droplet considered as a solid boundary, the criterion for rebounding is that the particle’s impact angle is <85°. The simulated trajectories of the particles are verified by comparing with experimental data for low-velocity particles to assess the reliability of the model. For impact angles >85°, particles undergo three distinct modes depending on normal impact velocities. The critical velocity of adhesion/rebound and rebound/submersion is used to identify the mode that the particles are undergoing. The criteria are also verified by comparing with analytical data. The results show that the impact angle of particles increases with increasing Coulomb number and decreases dramatically with increasing Stokes number, both of which lead to a high probability for particle rebound.

Solid particle erosion behaviour of cenosphere reinforced LM6 (Al-Si12) matrix alloy composites

Solid particle erosion of squeeze-cast LM6 (Al-Si12)/cenosphere composites was investigated at ambient temperature. Experiments were performed with different weight percentages (5%, 7.5%, 10% and 12.5%) of composites, having four velocities (48 m/s, 70 m/s, 82 m/s and 109 m/s), at impact angle (30°, 45°, 60° and 90°) and with silica sand as abrasive particle. The eroded surfaces were analysed using scanning electron microscopy (SEM). The results revealed that the particle velocity and impact angle affected the erosion behaviour of the composites. It was found that with the addition of reinforcement to the matrix, the erosion rate was increased at high particle velocities or upon increasing impact angle. The erosion mechanisms observed for the composites are micro ploughing and micro cutting at low impact angles, whereas at high impact angles the erosion of the composites is due to fracture.

パウダージェット加工における粒子衝突角度と加工現象に関する研究（ハイドロキシアパタイト膜形成による歯科治療）

Powder jet machining is one of blasting processes conducted under room temperature and atmospheric pressure. This process brings both deposition and removal process, and in this study, it refers to powder jet deposition (PJD) and abrasive jet machining (AJM). As an application of PJD, the authors have proposed an innovative dental treatment method with the hydroxyapatite (HA) fine particle. By this method, thick HA coating can be fabricated directly in the human oral cavity. In this study, the effect of the particle impact angle was investigated as a parameter that affects the machining phenomenon. The experiments showed that the machining phenomenon transited depending on the blasting angle. In the vertical blasting condition, PJD process was just observed. On the other hand, in the more acute blasting angle such as 45 deg. or 60 deg. both coating and removal process appeared at the same time and in the most acute angle of 30 deg. only removal process was detected. The TEM observations showed that the impact surface of the HA substrate deformed and the deformation depth increased as the blasting angle get more acute. The smoothed particle hydrodynamics (SPH) method was utilized for the analysis for the fracture behavior of the HA substrate. The result indicated that the decrease of the impact angle induced the increase of the strain and the temperature of the interface between the particle and the substrate. Thus it is concluded that the shear stress, which refers to the impact angle, induces the destruction of the substrate by the deformation and the brittle fracture due to the thermal stress.

Abrasive jet machining of glass: Experimental investigation with artificial neural network modelling and genetic algorithm optimisation

AbstractThe paper presents an experimental-based study of abrasive jet machining (AJM) considering the effect of changing process parameters. A series of drilling tests were carried out on glass workpieces using sand as the abrasive powder. The influence of each process parameter; applied air pressure, standoff distance, nozzle diameter, particle grain size and impact angle on the machining performance was determined in terms of the resultant material removal rate (MRR). The experimental results revealed that MRR was highly dependent on the kinetic energy of the abrasive particles, with the applied pressure the dominant parameter. The experimental results were compared with an erosion rate model previously published by Jafar et al. Though correct trends were predicted, there was a large discrepancy between model and measured values. An artificial neural network (ANN) was utilised to model the MRR more precisely, particularly to establish relationships between applied machining parameters and experimentall...

Abrasion prediction at Asahi sediment bypass tunnel based on Ishibashi’s formula

Abrasion in a concrete-lined sediment bypass tunnel is estimated using a Japanese state-of-the-art prediction model and validated by measured invert abrasion data at Asahi Reservoir, Japan. The model is described in detail, certain shortcomings are disclosed, and a revised version is proposed. The model consists of a kinetic energy term accounting for the impact by saltating particles, and a friction work term accounting for the grinding stress. It is found that the latter term yields concrete abrasion values being consistently a multiple compared to its kinetic term contradicting other research. Based on that, and a possible particle impact angle inconsistency, it is proposed to omit the friction work term. It is shown that the calculated abrasion is overestimated by 138% on average compared with that measured, if both terms are accounted for. However, promising results are obtained with only 30% overestimation by neglecting the friction work term.

Effects of Grit Blasting on Surface Properties of Adhesive Bonded Adherents

A mechanical treatment of an adherent before an application of adhesives is one of key factors influencing resultant strength of an adhesive bond. A grit blasting belongs among one of the most often used methods of the surface treatment. A resultant structure of blasted adherent and also parameters of the surface roughness can be changed during the blasting by a suitable choice of many parameters among which a material and a size of abrasive particles, a distance of an air jet and a blasted material, a size of the jet, an air pressure and an angle of abrasive particles impact can be ranked. This experiment describes an injector system of grit blasting using basic abrasives - corundum and glass ballotini. During grit blasting of common steel adherent it came to the change of the impact angle of the abrasive particle in a range from 75° (a perpendicular angle) to 10°. Different impact angle led to different roughness parameters and to various structure of the adherent surface which was evaluated by an electron microscopy. Subsequently, it came to experimental description of the strength of adhesive bonds which were created by adherents whose surface was grit blasted under various impact angles of abrasive particles.

Effect of nitrogen alloying on the microstructure and abrasive impact wear resistance of Fe-Cr-C-Ti-Nb hardfacing alloy

Abstract The effect of nitrogen additive on the microstructure and abrasive impact wear resistance of high chromium Fe-Cr-C-Ti-Nb hardfacing alloy, which developed by an open arc welding technique was investigated in this work. The phase structure and microstructures of the hardfacing alloys were studied by means of optical microscopy (OM), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectrometry (EDS) and transmission electron microscope (TEM). Moreover, the hardness of carbides in the hardfacing alloy was measured by nanoindentation test, and abrasive impact wear resistance was determined. Besides, the influence of variables on the wear behavior was investigated. The results show that, the high chromium Fe-Cr-C-Ti-Nb hardfacing alloys with different nitrogen additive mainly consist of primary (Cr, Fe)7C3 carbides, eutectic matrix and (Ti, Nb)(C, N) precipitates. With increase of nitrogen content in high chromium Fe-Cr-C-Ti-Nb hardfacing alloy, the primary carbides can be refined obviously. Meanwhile, the hardness of (Cr, Fe)7C3 is increased slightly from 18.7 GPa to 21.3 GPa, and that of (Ti, Nb)(C, N) is from 27.0 GPa to 27.6 GPa. Moreover, the volume loss of hardfacing alloys is decreased from 72 mm3 to 39 mm3. During abrasive impact wear test, the large primary carbides in the hardfacing alloy without nitrogen additive are fractured and spalled from the matrix, its abrasive impact wear resistance is low. While, the refined (Cr, Fe)7C3 carbides in the hardfacing alloy with nitrogen additive can be bended during the wear test, which increase its abrasive impact wear resistance. The lattice disregistry between (Ti, Nb)(C, N) and (Cr, Fe)7C3 is 6.15%, which indicates that (Ti, Nb)(C, N) can serve as heterogeneous nucleation sites for the primary (Cr, Fe)7C3 carbides. So that, the large primary (Cr, Fe)7C3 are refined and the abrasive impact wear resistance is improved. In addition, it is found that the volume loss of HC2N is increased with the increase of hardness, size, velocity and impact angle of the abrasive particles.

Erosion Behaviour of API X100 Pipeline Steel at Various Impact Angles and Particle Speeds

Erosion is the gradual removal of material due to solid particle impingement and results in a failure of pipeline materials. In this study, a series of erosion tests were carried out to investigate the influence of particle speed and impact angle on the erosion mechanism of API X100 pipeline steel. A dry erosion machine was used as the test equipment, while the particle speed ranged from 20 to 80 m/s and impact angles of 30° and 90° were used as test parameters. The eroded API X100 steel surface was characterized using scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The weight loss and erosion rate were also investigated. The results showed that at a 90° impact angle, a ploughing mechanism was occurring on the tested specimens, while material removal through low-angle cutting was the dominant mechanism at lower impact angles. Embedment of alumina particles on the target steel surface, micro-cutting, and low-angle cutting were observed at low impact angles. Therefore, the scratches, cuttings, and severe ploughings observed on some failed oil and gas pipelines could be attributed to the erosion mechanism.

Absorbed shear energy during solid particle impact on ductile surface

The shearing action of solid particle during its oblique impact on ductile target material is known to be one of the most dominant mechanisms of material removal in erosion. In this work, the shear energy, which absorbed in the target material, was analyzed using numerical model of rigid ellipsoid particles impact at ductile fully-plastic target. The effect of particle shape, impingement angle, angular velocity and orientation on the extent of the shear energy per unit area was examined. It was noticed that backward rotating particles with a long shape produce very high shear energy at low impingement angles (typically under 30°). The high shear energy is due to scooping mechanism, i.e. the particles rotate backward during the impact and detach with their leading tip facing upwards. This enables larger contact surface, which slides on the eroded face of the target material and thus increase the shear energy. It was noticed that for particles with no initial rotation or initial forward rotation, the scooping mechanism does not take place. Also, particles which are more spherical have less tendency to scoop due to lower moment which is exerted on them during the impact. These findings agree with experimental data, which shows higher erosion rate for backward rotating particles, and offer a reasonable mechanistic cause to this observation. Moreover, the ascent in the shear energy with the particle sharpness and their higher tendency for scooping, present additional explanation for the well-known phenomena of sharp particle which erode more severely than spherical particles.

Reducing bend erosion with a twisted tape insert

Due to the ongoing problem related to erosion caused by the impingement of solid particles in many engineering fields, parts such elbows, for instance, are particularly prone to erosion issues. In this work, the insertion of a twisted tape at different positions upstream of a bend is investigated numerically with the intent of reducing the elbow erosion. To ensure the reliability of the numerical calculations, experimental data were used to validate the CFD model for the standard elbow. Subsequently, simulations considering one, two and four-way coupling were evaluated for both the standard and the twisted tape-equipped elbows. Simulations were run to evaluate the average particle impact angle, impact frequency and impact velocity and the penetration ratio for each geometry. It was found that the swirling motion imparted to the particles by the twisted tape reduces the maximum penetration ratio in the bend. Another important finding is that the farther the insert is placed upstream of the elbow, the lower the erosion in the elbow, although the tape itself becomes more prone to erosion. In general, it was noticed that the fluid-particle and particle-particle interactions are very important and cannot be neglected. Consequently, depending on the mass loading and geometry configuration, elbow erosion can be dramatically reduced.

Calibrated CFD erosion modeling of abrasive slurry jet micro-machining of channels in ductile materials

Abrasive slurry jet micro-machining (ASJM) uses a relatively high-speed jet of fine abrasive slurry to precisely machine controlled-depth micro-features such as channels. Existing surface evolution models, developed for air-driven erosion processes, cannot account for the effect of slurry flow on the channel sidewall erosion that leads to the progressive channel widening observed in the ASJM of ductile materials. This paper presents a novel numerical–empirical model to predict the profiles of micro-channels in ductile materials (i.e. polymethylmethacrylate (PMMA), 6061-T6 aluminum alloy, 316L stainless steel and Ti–6Al–4V titanium alloy) using ASJM. The specific erosion rates of these materials were measured as a function of jet angle using a 10μm nominal diameter aluminum oxide slurry. The erosion rate-impact angle relations were corrected using computational fluid dynamic (CFD) models to account for the local impact angles and velocities of the particles. The erosion rate-impact angle relations were then used in three-dimensional CFD models to obtain the particle trajectories, impact angles, and velocities on a shallow eroded profile, and thus predict the erosion for deeper profiles. The model was verified by comparison with experiments which showed the previously-observed widening of the machined channels as the depth increased due to secondary erosion by particles impacting the channel sidewalls. The widening effect was found to be substantial in the PMMA but less important in Ti–6Al–4V titanium alloy due to its greater erosion resistance. The numerical–empirical approach could accurately estimate the widening and predicted the channel cross-sections up to an aspect ratio of approximately 1 with a maximum error of less than 5%.

Numerical Prediction of Erosion in Coal Burner of 210 MW Boiler Through Computational Fluid Dynamics Modeling

The splitter plates of coal burners in Indian thermal plants are subjected to severe erosion and erosioncorrosion conditions owing to the combined effect of abrasive nature of coal and elevated service temperature environment. During service, tilting of splitter plates is adopted to achieve the desired final steam outlet temperature which shifts the fireball location and heat release area in the combustion zone. The tilt condition gives rise to a change in the incidence angle of the coal particle as well as the change in flow profile. The erosion life of these plates is predominantly affected by the coal particle velocity, impact angle, particle size and steady state metal temperature during service. The sensitivity of burner tilt angle on the erosion life requires an understanding of primary air with coal particle flow phenomenon within the burners. The effect of burner tilt angle on the erosion of presently used SS310 grade splitter material was studied through computational fluid dynamics. The erosion sensitive velocity exponent was calculated based on the laboratory simulated erosion tests at elevated temperatures upto 700°C. The life of the splitter plates was calculated based on the predicted erosion rate intensity.

Numerical and experimental study on ultrasonic vibration-assisted micro-channelling of glasses using an abrasive slurry jet

The ultrasonic-vibration assisted micro-channelling process on glasses by an abrasive slurry jet (ASJ) is presented and discussed both numerically and experimentally. A numerical investigation using the dynamic meshing technique in Computational Fluid Dynamics (CFD) is carried out first to model the ASJ flow and explore the effect of ultrasonic vibration on the stagnation zone, particle impact velocity and impact angle, and viscous flow induced erosion process. It has been found that the static pressure in the stagnation zone, particle impact velocity and impact angle are varied periodically with an assistance of the ultrasonic vibration on the workpiece which in turn could affect the material removal process in ASJ micro-channelling of glasses. It is also found from simulation that the ultrasonic vibration is beneficial to the viscous flow induced erosion during the low pressure ASJ micro-machining process. Then, a set of ultrasonic vibration-assisted micro-channelling experiments are conducted on glasses using an ASJ to evaluate its effect on the major micro-channelling performance. It is found that ultrasonic vibration-assisted ASJ micro-channelling increases the material removal rate, channel depth and top channel width, while decreases the channel wall inclination angle, as compared to the traditional ASJ micro-channelling process at the same experimental condition. However, the surface quality on the bottom of the channel seems to be not significantly affected by the ultrasonic vibration. These findings from the experiment are in a reasonably good agreement with the corresponding simulated results.