On the particle–particle contact effects on the hole cleaning process via a CFD–DEM model

ABSTRACT

The accurate and precise computational models in order to predict the hole cleaning process is one of the helpful assets in drilling industries. Besides the bulk properties such as the flow velocity, particles average size, cleaning fluid properties, etc., that will affect the cleaning process, there is an unanswered question about the microscopic properties of the particles, particularly those which determines the contact characteristics: Do those play a major role or not? The rudimentary answer is not. The first purpose of the present work is to answer this question via a developed computational fluid dynamics coupled with discrete element method (CFD–DEM) in which the six unknown rolling and sliding friction coefficients of particle–particle contact, particle–wall contact, and particle–drill contact are considered as the main microscopic properties of the contacts. The second purpose is to search for optimum values of these coefficients in order to calibrate the CFD–DEM model with the experimental data for a near horizontal well cleaning available in the literature. The verification of the calibrated CFD–DEM model is checked by simulation of the hole cleaning process for different inclination angles of the deviated well. The results indicate the pivotal role of the microscopic properties of the particles on the characteristics of the particle transport mechanism.     

The effect of internal particle heat conduction on heat transfer analysis of turbulent gas–particle flow in a dilute state

In many cases the conduction mechanism inside a particle can not be ignored (large particles, low thermal conductivity and high porosity) during turbulent gas–particle flows. However, the accurate solution might be difficult to apply. Therefore, we first develop here the ability to conduct accurate solution and then we define the criterion for which the internal conductivity might be ignored. A combination between commercial C.F.D. code and user defined programs was developed to predict numerically the gas–particle velocity and temperature profiles. The selected criterion (defined at the outlet of the pipe’s cross-section), referred to the relation between the computational desirable average temperature difference without ignoring internal heat conductivity and the average particles temperature by ignoring internal heat conductivity, determines whether to consider the heat conduction mechanism in numerical simulations or to ignore it. It was found that the average particles temperature for T _p =  f(r) is lower than the case when T _p =  constant. Also, it was found that the non-dimensional temperature difference criterion is a continuous function of [Bi ×  (d _p/D)] for a specific geometry, various pipe and particle diameters, various particles’ thermal conductivities, constant heat flux and Re number. The numerical code enables to extend the classical criterion for Bi number of solids to various gas–particle systems and different operational conditions.     

γ′ particle coarsening and yield in Alloy 800

The age strengthening of Alloy 800 by ordered particles of-Ni₃(Al, Ti) phase has been studied by using both transmission electron microscopy and room-temperature tensile tests on aged specimens. The samples have been aged in the temperature range 525 to 650° C up to a maximum time of 10⁴ h. Two groups of samples with different Ti/Al ratios have been investigated in order to obtain more reliable information on the role played by these alloying elements on the age-hardening behaviour. The linear dimension increases with time,t, ast ^1/3 and an activation energy of 70.0 kcal mol^–1 was derived from the temperature dependence of the coarsening rate. The particle volume-fraction, as measured by electron microscopy, has been found to remain constant on ageing in the temperature range 525 to 600° C. The increase in the critical shear stress due to the particles is found to agree quantitatively with the equations of Brown and Ham which describe hardening by ordered particles. Antiphase boundary energies of 227 and 279 mJ m^–2 have been measured, respectively, for the two groups of samples investigated.     

Optimal heat exchanger network synthesis using particle swarm optimization

Heat exchanger network (HEN) synthesis has been a well-studied subject over the past decades. Many studies and methodologies were proposed to make possible the energy recovery, minimizing the utilities consumption and the number of heat transfer equipment.     

Influence of heat treatment and particle shape on mechanical properties of infiltrated Al2O3 particle reinforced Al–2 wt-% Cu

Abstract

Carbon dioxide (CO₂) generation by ultraviolet irradiation of poly(ethyleneterephthalate) (PET) films in oxygen was monitored by in situ Fourier transform infrared spectroscopy. Typically, the CO₂ absorbance increased by ～100 × 10^?4 in 180 min, with no evidence of hindrance by restricted diffusion of O₂ into, or CO₂ out of, the films. It was concluded that Fourier transform infrared spectrometry monitoring of CO₂ conveniently, reliably and rapidly measures PET films photostability.

Quantitative analysis of the CO₂ evolved from progressively thinner films from successive stages of the biaxial film drawing process indicated that CO₂ was generated within a few microns of the film surface and that the same amounts were generated from the irradiated surface of 540 μm cast, 150 μm uniaxially drawn and 85 μm biaxially drawn films. Although drawing increased film crystallinity, photoreactivity appeared to be unchanged. However, total CO₂ formation followed the pattern PET cast相似文献   

The influences of particle–particle interaction and viscosity of carrier fluid on characteristics of silica and calcium carbonate suspensions-coated Twaron® composite

The effects of particle–particle interaction and viscosity of carrier fluid on steady and dynamic rheological responses and quasi-static penetration resistance of Twaron® fabrics treated with shear thickening and shear thinning suspensions have been investigated. The suspensions have been made by mechanically dispersing 60 nm silica (SiO₂) and calcium carbonate (CaCO₃) nanoparticles in poly ethylene glycol (PEG) with molecular weights of 200 and 400 g/mol. The CaCO₃ suspensions display shear thinning behaviour along with the total dominance of the elastic state over the viscous state while the SiO₂ suspensions exhibit shear thickening behaviour with the emergence of both the elastic and viscous states. With the increase of molecular weight of PEG, viscosity, viscoelastic modules and instability of the suspensions increase and critical shear rate and frequency of transition to elastic state diminish. The PEG200 and PEG400-contained SiO₂ suspensions-treated Twaron® composites at 35 wt.% have quasi-static penetration resistances which are nearly 2.63 and 2.48 times and maximum absorbed energies which are about 1.54 and 1.55 times higher, respectively, than those of the corresponding CaCO₃ ones. However, the influence of increasing the PEG's molecular weight is not as considerable as the effect of particle–particle interaction on the enhancement of penetration resistance performance.     

Development of a procedure for spherical alginate–boehmite particle preparation

Herein we describe a versatile new strategy for producing spherical solid particles with 2 mm in size using integrated gelling process. The method involves the formation of spherical droplets by using a peristatic pump device and shaping the droplets in a liquid calcium chloride solution. The shape and size of these calcium alginate macroparticles depend strongly on the calcium solution concentration. The shaping mechanism of the macroparticles and the impact of the experimental conditions on particle shape and size are investigated. This method has the following features: (1) A new level of control over the shapes of the particles is offered. (2) The procedure can be scaled up to produce large numbers of particles. (3) The final porous structure of the developed particle can be designed for a specific application (adsorption, catalysis).     

Control of particle interfaces — the critical issue in nanoparticle technology

In the field of particle technology, processes cannot yet be designedfroma basic molecular understanding. Nanotechnology, however, begins to bridge this gap between molecules and particles, and may thus not only open new ways for the production and handling of particulate matter, but also for the engineered design of advanced material properties. The visions and applications in nanoparticle technology cover a broad range, e.g. quantum dots in information technology, refractory particles for advanced ceramics, highly active substances in pharmacy, catalysts and micro- and mesoporous adsorbents to name only a few applications. Starting from the concept of product engineering we investigate the basic preconditions for tailoring nanoparticulate properties, i.e. the control of the particle interactions. This concept is then applied to precipitation as an example for particle synthesis and to particulate thin film formation as an example for structure formation.     

Preparation and properties of cast aluminium alloy–sillimanite particle composite

An attempt has been made to explore the possibility of using natural mineral namely sillimanite for synthesizing aluminium alloy composite through a solidification technique. The sillimanite particles were characterized in terms of X-ray, differential thermal analysis in order to examine their suitability for preparing the composite. An aluminium alloy (BS:LM6) was used as the matrix alloy. The sillimanite particles of mean size 140 μm (major axis) were used as reinforcement. The sillimanite particles were added into the matrix melt by creating a vortex with the help of a mechanical stirrer and the melt temperature was maintained between 750 and 800°C. The cast composite was characterized in terms of microstructural, mechanical and abrasive wear properties. It was noted that the sillimanite particles were reasonably uniformly distributed within the matrix and exhibited good mechanical bonding with the matrix. The strength of the composite was noted to be marginally lower than that of the base alloy but the hardness and the wear resistance of the composite were found to be significantly higher than those of the base alloy.     

Detailed analysis of particle–substrate interaction based on a centrifugal method

The interaction between particles and inclined substrates in a centrifuge was investigated theoretically and experimentally. First, the balance of the force acting on a particle adhering to the substrate, with an inclination angle from 0 to 90° to the horizontal, was formulated separately in the normal and tangential directions. The adhesion force was then derived based on the point-mass model as a function of the angular velocity. Next, the balance of the moments of the forces acting on a particle adhering to the substrate was formulated; theoretical equations for the adhesion force and the effective contact radius were then derived from the angular velocities, obtained at any two inclination angles, based on the rigid-body model. Finally, the removal fraction curves of spherical/nonspherical particles with median diameters of less than 10 µm were experimentally obtained by increasing the angular velocity at each inclination angle. The experimentally obtained angular velocities were substituted into the theoretical equations to compare the point-mass and rigid-body models. The effects of the particle shape on the adhesion force and effective contact radius and that of the inclination angle on the removal fraction curves based on the theoretical equation were also investigated.     

Effects of higher wall roughness on dense particle–laden dispersion behaviors

To analyze the effects of higher wall roughness on dense particle–laden dispersion behaviors under reduced gravity environments, a dense gas–particle two-phase second-order-moment turbulent model are developed. In this model, the wall roughness function and the kinetic theory of granular flows are coupled and closed. Anisotropy of gas–solid two-phase stresses and the interaction between gas–particle are fully considered using two-phase Reynolds stress model and the two-phase correlation transport equation. Numerical simulation test is validated by Sommerfeld and Kussin (2003) experiments data with higher wall roughness 8.32 μm. Predicted results showed that the particle concentration distribution, particle fluctuation velocity, particle temperature and particle collision frequency are greatly affected by higher wall roughness, as well as particle Reynolds stress and interactions between gas and particle turbulent flows are redistributed. Under microgravity conditions, particle temperature and collision frequency are greatly less than those of earth and lunar gravity.     

CFD–DEM investigation of particle separations using a sinusoidal jigging profile

This paper presents a numerical investigation of solid separation in jigging device. Jigging is a gravity separation method commonly used by the minerals industry to separate coal, iron ore, diamonds and other minerals on the basis of particle size and/or density. Separation is recognised as being heavily dependent on fluid motion in the jig. This study explores the effects of the inlet time dependent velocity profile in relation to a wide criterion on jigging performance. Modelling of the liquid–solid system is performed through a combination of computational fluid dynamics (CFD) to simulate liquid flow and discrete element method (DEM) to resolve particle motion. The initial packing conditions consist of a binary-density particle system of 1130 particles each 1 cm in diameter. A range of jigging profiles have been implemented in mineral processing. In this study the sinusoidal pulsation profile is selected adopting variations in both amplitude and frequency. The performance of profile variants are compared in terms of solid flow patterns, separation kinetics, energy, and mean particle position. These quantitative comparisons demonstrate significant differences in the segregation rate, energy, and solid phenomena, helping find an alternative optimum operating setting for the system. In addition, boundaries of operation are found in terms of frequency and amplitude limits and the concentration mechanics are investigated in these regions.     

Main and interaction effects of matrix particle size,reinforcement particle size and volume fraction on wear characteristics of Al–SiCp composites using central composite design

The aim of this study was to investigate the effects of matrix particle size, reinforcement particle size, volume fraction, and their interactions on the wear characteristics of Al–SiC_p composites. Central composite design method was used to perform a series of experiments. The statistical analysis of experimental results showed that both main effect and interaction effect of factors investigated were effective on the wear behavior of Al–SiC_p composites. Wear loss decreased as volume fraction increased; however, beyond volume fraction of 17.5%, it increased due to reinforcement particle clustering depending on volume fraction and matrix particle size to reinforcement particle size ratio. With decreasing of matrix particle size and increasing of reinforcement particle size, wear loss also decreased. However, after a certain volume fraction, large sized reinforcement particles had a negative effect on the wear resistance.     

Penetration behaviour of individual hydrophilic particle at a gas–liquid interface

The penetration behaviour of a hydrophilic particle impacting on a gas–liquid interface was studied both experimentally and mathematically. The aim of this study was to determine the critical impact velocity below which a falling hydrophilic particle would remain on a horizontal liquid surface. A model to predict the critical velocity has been developed based on energy balance of both the particle and liquid volume in the vicinity of the impact zone. The model also includes the effect of hydrophobicitiy (contact angle) of the particle as well as the change in potential energy of the impacted liquid. Experiments were performed using spherical glass beads of diameter 0.97–1.66 mm, and using liquids with varying density (1000–1182 kg/m³), viscosity (1.002–4.796 mPa s) and surface tension (50.31–87.42 mN/m). High speed video camera was used to obtain the particle impact velocity, cavity profile and velocity of the three-phase contact line (TPCL) at the critical conditions. The TPCL line velocity and cavity profile were used as inputs for the model. The fitted advancing contact angle was employed in the model. It was found that the model was in good agreement with the experimental observations, and the fitted advancing contact angle agreed with the combined molecular-hydrodynamic model well.     

纳米材料（nano material）与纳米粒子（nano particle）

纳米级结构材料简称为纳米材料（nano material），是指其结构单元的尺寸介于1nm～100nm范围之间。由于它的尺寸已经接近电子的相干长度，它的性质因为强相干所带来的自组织使得性质发生很大变化。并且，其尺度已接近光的波长，加上其具有大表面的特殊效应，因此其所表现的特性，例如熔点、磁性、光学、导热、导电特性等等，往往不同于该物质在整体状态时所表现的性质。     

Compressive properties of closed cell Al alloy–fly ash particle composite foams

Abstract

The closed cell aluminium alloy–fly ash particle composite (Al/FA) foams containing 1·5 wt-% fly ash were manufactured by molten body transitional foaming process. The quasi-static compressive properties of Al/FA have been investigated. Results show the compressive stress–strain curves of Al/FA foams exhibit three regions, i.e. the elastic region, the plastic plateau region and the densification region. A linear relationship between the densification strain and the relative density was obtained. The relation between the plastic collapse stress and the relative density can be described with Gibson and Ashby’s model. The energy absorption capacities of the Al/FA foams gradually increase with increasing strain and relative density.     

Double global optimum genetic algorithm–particle swarm optimization-based welding robot path planning

Spot-welding robots have a wide range of applications in manufacturing industries. There are usually many weld joints in a welding task, and a reasonable welding path to traverse these weld joints has a significant impact on welding efficiency. Traditional manual path planning techniques can handle a few weld joints effectively, but when the number of weld joints is large, it is difficult to obtain the optimal path. The traditional manual path planning method is also time consuming and inefficient, and cannot guarantee optimality. Double global optimum genetic algorithm–particle swarm optimization (GA-PSO) based on the GA and PSO algorithms is proposed to solve the welding robot path planning problem, where the shortest collision-free paths are used as the criteria to optimize the welding path. Besides algorithm effectiveness analysis and verification, the simulation results indicate that the algorithm has strong searching ability and practicality, and is suitable for welding robot path planning.