Critical Deposition Velocity Research Articles

Deposition behavior of multi-particle impact in cold spraying process

In the practical cold-spraying process, a number of particles impact onto a substrate and then form a coating. To study the deformation behavior and multi-particle interactions, single-particle, two-particle, and three-particle impacts were simulated using the AN-SYS/LS-DYNA version 970. A copper coating was prepared and scanning electron microscopy (SEM) was employed to analyze the microstructures of the powders and the coating. Numerical results reveal that the critical deposition velocity is 600 m/s for a copper particle/copper substrate. The particles deform more fully due to multi-particle interactions, such as tamping, interlocking, and extrusion effects. The compression ratio increases from 40% to 70% as a result of the tamping effect. This is beneficial for achieving the cold-sprayed coating. The multi-particle morphology and compression ratio in the experiment are consistent with those of simulation results. Based on these results, the coating of high performance can be prepared through selecting appropriate parameters and suitable pre-treatment processes.

Significant influence of particle surface oxidation on deposition efficiency, interface microstructure and adhesive strength of cold-sprayed copper coatings

The critical velocity for particle deposition in cold spraying is a key parameter, which depends not only on the material type, but also the particle temperature and oxidation condition. The dependency of deposition efficiency of cold spray Cu particles on the particle temperature and surface oxidation was examined. The effect of particle surface oxide scales on the interfacial microstructure and adhesive strength of the cold-sprayed Cu coatings was investigated. The results show that the deposition efficiency significantly increases with increasing the gas temperature but decreases with augmenting the oxygen content of the starting powder. The oxide inclusions at the interfaces between the deposited particles inhibit the effective bonding of fresh metals and remarkably lower the bond strength of the deposited Cu coatings on steel.

Critical Conditions for Effective Sand-Sized Solids Transport in Horizontal and High-Angle Wells

Summary Effective removal of small, sand-sized solids is critical for successful drilling and completion operations in sand reservoirs. Recent experience in extended-reach drilling also indicates that inefficient transport of smaller cuttings is a main factor for excessive drag and torque. This study was undertaken to determine two critical conditions for efficient transport of small solids. The two conditions are represented by the critical resuspension velocity (CRV), the minimum fluid velocity necessary to initiate solids-bed erosion, and the critical deposition velocity (CDV), the minimum fluid velocity required to prevent bed formation. Experiments were conducted in a field-scale flow loop (8 × 4.5 in., 100 ft long) to determine CRV and CDV for 0.45-mm and 1.4-mm sands in different fluids over a range of bed heights and hole inclinations. The results show that, depending on sand size and fluid properties, CDV is approximately two to three times larger than CRV. Water is more effective than low-concentration polymer solutions for bed erosion. However, polymer solutions are more helpful than water in preventing bed formation. This indicates the need for different drilling fluids for cleanout and drilling operations. A mechanistic model was developed to predict CRV for a solids bed. Both experimental and theoretical results indicate the importance of interparticle forces that are incorporated into the model. The model accounts for drillpipe eccentricity in any direction in an annulus, which is consistent with experimental observations. The model predictions are in good agreement with experimental results. Existing CDV correlations developed for larger cuttings were verified by experimental data for sands. The differences are approximately 25%. Results in this study will be useful not only in drilling and completion through sand reservoirs, but also in extended-reach drilling and sand control.

Some aspects on 3D numerical modeling of high velocity impact of particles in cold spraying by explicit finite element analysis

Three-dimensional modeling of particle impacting behavior in cold spraying by using ABAQUS/Explicit was conducted for copper and other materials. Various combinations of calculation settings concerning material damage, Arbitrary Lagrangian Eulerian adaptive meshing, distortion control and contact interaction were examined. The effects of meshing size and particle size on the impact behavior were analyzed compared to the previous results. The results show that the simulations with material damage cope well with the element excessive distortion and the resultant output is more reasonable than that obtained without material damage. In addition, the meshing size has less effect on the output with the material damage than without material damage. Although particle size has little effect on the morphologies of the deformed particles, it has some effect on the failure of elements at contact interfaces. The critical velocity for particle deposition could be estimated given the appropriate material properties.

Focused ion beam micro-dissection of cold-sprayed particles

Three different modes of cold-spray impact were compared; aluminium particles onto a piezoelectric ceramic (PZT), aluminium particles onto copper, and deep penetration of copper particles into aluminium. Adhered particles were dissected using a dual-beam scanning electron microscope/focused ion beam (SEM/FIB) for morphological and microstructural examination. It was shown that the extent of substrate deformation substantially altered the behaviour displayed during bonding of the particles. In aluminium-on-ceramic impact, no permanent deformation of the substrate was seen. Shearing of layers of metal over the ceramic left a thin coating of debris on the surface. In contrast, aluminium particles caused plastic deformation and cratering of the copper. The critical velocity for aluminium particle deposition was lower on this substrate. Copper impact onto aluminium caused adiabatic shear of the substrate, with local temperatures reaching melting point. Copper particles embedded deeply into the aluminium surface without rebounding.

Oxidation dependency of critical velocity for aluminum feedstock deposition in kinetic spraying process

In kinetic spraying process, critical velocity is an important criterion which determines the deposition of feedstock onto the substrate. It has been proven experimentally and numerically that the critical velocity is determined by physical and mechanical properties and the state of materials such as initial temperature and size. In this study, the oxidation effect on critical velocity was investigated using experimental methods. As oxygen content of feedstock increased, critical velocity significantly decreased. In order to find out reasons for difference in critical velocity with oxygen content, individual impact behavior was analyzed and interface microstructure was observed. Due to high brittleness and hardness of oxide, oxide layer on particle influences the particle deformation behavior during impact. And oxide accumulated at interface obstructs the adhesion between activated particle and substrate surface during impact.

Examination of the Critical Velocity for Deposition of Particles in Cold Spraying

The critical velocity of copper (Cu) particles for deposition in cold spraying was estimated both experimentally and theoretically. An experimental method is proposed to measure the critical velocity based on the theoretical relationship between deposition efficiency and critical velocity at different spray angles. A numerical simulation of particle impact deformation is used to estmate the critical velocity. The theoretical estimation is based on the critical velocity corresponding to the particle velocity at which impact begins to cause adiabatic shear instability. The experimental deposition was conducted using Cu particles of different particle sizes, velocities, oxygen contents, and temperatures. The dependency of the critical velocity on particle temperature was examined. Results show that the critical velocity can be reasonably measured by the proposed test method, which detects the change of critical velocity with particle temperature and oxygen content. The Cu particles of oxygen content 0.01 wt.% yielded a critical velocity of about 327 m/s. Experiments show that the oxygen content of powder significantly influences the critical velocity. Variations in oxygen content can explain the large discrepancies in critical velocity that have been reported by different investigators. Critical velocity is also found to be influenced by particle temperature as well as types of materials. High particle temperature causes a decrease in critical velocity. This effect is attributed to the thermal softening at elevated temperatures.

Production of Titanium Deposits by Cold-Gas Dynamic Spray: Numerical Modeling and Experimental Characterization

Over the past five years, interest in cold-gas dynamics spraying (CGDS) has increased substantially. Considerable effort has been devoted to process development and optimization for such metals as copper and aluminium. This paper describes work undertaken to expand the understanding of the deposition of titanium by cold-spray methods. CGDS deposits have been produced from commercially pure titanium using room-temperature helium gas. The effect of different powder paticle size ranges, types of substrate, substrate preparation methods, and spray parameter conditions on powder deposition have been investigated. Microhardness testing of deposits was conducted, and their microstructures have been examined by scanning electron microscopy. Samples for pull-off bond-strength tests have been prepared from a number of the more promising sets of spray parameters and adhesive strengths determined. A one-dimensional numerical model of particle acceleration, employing isentropic gas flow behavior in the nozzle, has also been used to estimate particle exit velocities. This model explicitly addresses the dependence of the drag coefficient on gas compressibility and demonstrates its significance in terms of predicted particel velocities. By linking this model with the measured particle size distributions, estimates of particle velocity distributions at the nozzle exit plane have been computed. These allow an approximate value of the critical velocity for deposition of titanium to be made. Experimental observations on the microstructure and properties of the deposits are discussed in light of powder particle size and velocity distributions and the underlying physical and mechanical properties of the powders and substrates.

Measurements of the dynamic contact angle for conditions relevant to immersion lithography

The semiconductor industry has used optical lithography to create impressively small features. However, the resolution of optical lithography is approaching limits based on light wavelength and numerical aperture. Immersion lithography is a means to extend the resolution by inserting a liquid with a high index of refraction between the lens and wafer. This enables the use of higher numerical aperture optics. Several engineering obstacles must be overcome before immersion lithography can be used on an industry-wide scale. One such challenge is the deposition of the immersion liquid onto the wafer during the scanning process; any residual liquid left on the wafer is a potential defect mechanism. The residual liquid deposition is controlled by the details of the fluid management system, and is strongly dependent on the three-phase contact line. Therefore, this work concentrates on understanding the behavior of this contact line, specifically by measuring the dynamic contact angle and the critical velocity for liquid deposition. A contact angle measurement technique is developed and verified; the technique is subsequently applied to measure the dynamic advancing and receding contact angle for a series of resist-covered surfaces under conditions that are relevant to immersion lithography.

Adiabatic shear instability based mechanism for particles/substrate bonding in the cold-gas dynamic-spray process

Particles/substrate interactions during the cold-gas dynamic-spray deposition process are studied using a dynamic axisymmetric thermo-mechanical finite element analysis. In addition, the particles/substrate bonding mechanism has been investigated using a one-dimensional thermo-mechanical model for adiabatic strain softening and the accompanying adiabatic shear localization. The results obtained show that the minimal impact particles velocity needed to produce shear localization at the particles/substrate interface correlates quite well with the critical velocity for particles deposition by the cold-gas dynamic-spray process in a number of metallic materials. This finding suggests that the onset of adiabatic shear instability in the particles/substrate interfacial region plays an important role in promoting particle/substrate adhesion and, thus, particles/substrate bonding during the cold-gas dynamic-spray process.

Numerical Modelling of Cuttings Transport With Foam in Horizontal Wells

Abstract In this study, a one-dimensional unsteady-state two-phase mechanistic model of cuttings transport with foam in horizontal wells has been developed. A new critical deposition velocity correlation for foam-cuttings flow is introduced. The model is solved numerically to predict cuttings bed height as a function of the drilling rate, the gas and the liquid injection rates, the rate of gas and liquid influx from the reservoir, and the borehole geometry. Results of the sensitivity analyses study are presented. Introduction The Alberta Energy and Utilities Board defines underbalanced drilling (UBD) as "when the hydrostatic head of a drilling fluid is intentionally designed to be lower than the pressure of the formation being drilled, the operation will be considered underbalanced drilling(1)." The benefits of UBD include increased productivity by reducing formation damage, increased rate of drilling bit penetration, minimization or elimination of lost circulation, improved formation evaluation while drilling, reduction or elimination of differential pipe sticking, reduced stimulation requirements, and earlier production. Foam is favourably used in UBD operations because of its variable density and good cuttings transport ability. Field application of the foamed drilling fluids is very often complicated because of the difficulties encountered in controlling their hydraulic properties. The complex flow mechanism involved in the circulation of foam makes a determination of the optimum combination of liquid and gas injection rates very difficult. Other questions also exist, such as how to predict the bottom-hole pressure and how to combine different controllable variables in order to obtain optimum cuttings transport performance and bit hydraulics. In order to simulate the hydraulics of the foam drilling realistically, factors including foam rheological properties, drag coefficient of cuttings in foam, formation fluid influx, drillpipe eccentricity, and drilling rate need to be considered in any modelling study. An example of such a modelling study is presented in this article. Okpobiri and Ikoku(2) developed a semi-empirical model for cuttings transport with air, mist, and foam in vertical wellbores. Harris et al.(3) suggested that foam-particle flow for hydraulic fracturing could be treated as a homogeneous flow. Medley and Liu(4) presented a one-dimensional steady-state foam flow model by modifying earlier models presented by Lord(5) and Sp?rker et al.(6) Drill cuttings and gas were considered as homogeneous internal phases of foam and the mixture properties were used to solve the steady-state mechanical energy balance equation. Owayed(7) developed a one-dimensional steady-state computational model for UBD by assuming a homogeneous flow of foam in a vertical well. The model included the effect of water influx into the wellbore during drilling. Valk? and Economides(8) established a method that combined the principle of volume equalization(9) with the method of constant-internal-phase(3) for foam-proppant flow. Guo et al.(10) presented an analytical model to estimate the bottom hole pressure when drilling with foam in directional wells. They recognized that the compressibility of foam could cause the cuttings concentration at a given depth to be different from the ones at the surface, rendering inappropriate calculations of the minimum required cuttings transport velocities.

Numerical investigations of liquid–solid slurry flows in a fully developed turbulent flow region

In this paper, a simplified 3D algebraic slip mixture (ASM) model is introduced to obtain the numerical solution in sand–water slurry flow. In order for the study to obtain the precise numerical solution in fully developed turbulent flow, the RNG K– ε turbulent model was used with the ASM model. An unstructured (block-structured) non-uniform grid was chosen to discretize the entire computational domain, and a control volume finite difference method was used to solve the governing equations. The mean pressure gradients from the numerical solutions were compared with the authors’ experimental data and that in the open literature. The solutions were found to be in good agreement when the slurry mean velocity is higher than the corresponding critical deposition velocity. Moreover, the numerical investigations have displayed some important slurry flow characteristics, such as volume fraction distributions, slurry density, slip velocity magnitude, slurry mean velocity distributions, and slurry mean skin friction coefficient distributions in a fully developed section, that have never been displayed in the experiments.

Particle Velocity and Deposition Efficiency in the Cold Spray Process

Copper powder was sprayed by the cold gas-dynamic method. In-flight particle velocities were measured with a laser two-focus system as a function of process parameters such as gas temperature, gas pressure, and powder feed rate. Mean particle velocities were uniform in a relatively large volume within the plume and agreed with theoretical predictions. The presence of a substrate was found to have no significant effect on in-flight particle velocities prior to impact. Cold-spray deposition efficiencies were measured on aluminum substrates as a function of particle velocity and incident angle of the plume. Deposition efficiencies of up to 95% were achieved. The critical velocity for deposition was determined to be about 640 m/s for the system studied.

Study of wear characteristics and solid distribution in constant area and erosion-resistant long-radius pipe bends for the flow of multisized particulate slurries

The wear characteristics of three types of long radius pipe bends in the flow of multisized particulate slurries have been extensively studied. Conventional long radius bend, and two types of diverging-converging bends are investigated. Measurements have been made over a range of solid concentrations and flow velocities. The results have shown that diverging-converging bend with an area ratio 2 exhibits reduced wear. and in fact can even be expected to have a longer life than a straight pipe. Further, measurement of solid distribution in the three bends has given some insight into the causes for the reduced wear in these modified bends. It has also been demonstrated taht the diverging-converging bends even with enlarged cross-sections are not prone to choking when the pipeline is operating near critical deposition velocity.

Critical velocity correlations for slurry transport with non‐Newtonian fluids

AbstractTransport properties of various uncross‐linked and cross‐linked non‐Newtonian slurries in horizontal pipes are studied. Flow data are gathered in three long, different diameter, transparent horizontal pipes. Investigated are the effects of the pipe size, polymer concentration, fluid rheological properties, cross‐linking effects, particle size and density, solids concentration, fluid density, and slurry rate on the critical deposition velocities and particle resuspension velocities. It is found that critical deposition and resuspension velocities for the non‐Newtonian carrier fluids tested are significantly lower than those for water. Both velocities depend greatly on pipe size and particle density. Higher critical velocities are required to minimize settling (1) in larger pipe sizes and (2) for pumping solids denser than sand. For less viscous fluids, critical deposition and resuspension velocities increase slightly with increasing solids concentration. They are, however, independent of solids concentration for more viscous fluids.

Hydraulic Fracturing Slurry Transport in Horizontal Pipes

Summary Horizontal-well activity has increased throughout the industry in the past few years. To design a successful hydraulic fracturing treatment for horizontal wells, accurate information on the transport properties of slurry in horizontal pipe is required. Limited information exists that can be used to estimate critical deposition and resuspension velocities when proppants are transported in horizontal wells with non-Newtonian fracturing gels. This paper presents a study of transport properties of various hydraulic fracturing slurries in horizontal pipes. Flow data are gathered in three transparent horizontal pipes with different diameters. Linear and crosslinked fracturing gels were studied, and the effects of variables—e.g., pipe size; polymer-gelling-agent concentration; fluid rheological properties; crosslinking effects; proppant size, density, and concentrations; fluid density; and slurry pump rate—on critical deposition and resuspension velocities were investigated. Also, equations to estimate the critical deposition and resuspension velocities of fracturing gels are provided.

水平輸送管路内の堆積層の厚みの算定式 堆積層を伴うスラリーの流動機構に関する理論的考察

With increasing industrial applications of the method of the transporting settling slurries, a better understanding of the mechanism of the slurry flow at lower velocities has become essential. Below the critical deposition velocity Vd of flow, the deposition of solid particles occurs on the bottom of the horizontal pipe. If the deposited particles are sufficient, the plugging of the pipeline can be induced through the large surge of flow or the sudden change of flow conditions, such as a rise in concentration or a drop in velocity V. However, some papers confirm the possibility of the stable flow configuration in pipe despite of a stationary bed.One of the main problems in the hydraulic transport for V < Vd is the assessment for bed thickness h and hydraulic gradient im. The accuracy of one of the factors is interdependent upon that of the other. Since the correlations have been basically proposed by empirical methods, the bed thickness cannot be reasonably well predicted with flow conditions.The purpose of this paper is to derive the general correlation which determine the relationships between the bed thickness and the corresponding flow condition, and to give the procedure for the pipeline design with the aid of the authors' previous results. Based on the concept of the suspension behavior introduced by Bagnold, this paper estimated the normal stress on the particle at the surface of the bed. The flow condition of initial motion of the particle, then, was considered, and thus these theoretical analyses made possible to present the general correlation of h and to simulate the slurry flow for V<Vd. Experimental values obtained were fairly well coincided with the predicted values.The results of this study may be summarized as follows:(1) For a given system and particle properties the Froude number, Fr V/√4gR, is approximately as a function of concentration alone, such as Durand's results for 0.2<hr <0.6, in which hr is the ratio of the bed thickness to the pipe diameter.(2) The predictions for the critical deposition velocity Vd agree with those by Durand for particles greater than 2mm, while for ones less than 1mm both predictions are incompatible with each other, when the equivalent thickness de/2 is substituted for the bed thickness at the initial condition of Vd.(3) The relationship between hydraulic gradient and slurry velocity, which is the im-V cure predicted, shows that the critical velocities are always less than the critical deposit velocities, and considerable care, therefore, should be exercised to determine the practical velocity in the pipeline design.