Solid-liquid Slurries Research Articles

An Overview on the Process Development and the Formation of Non-Dendritic Microstructure in Semi-Solid Processing of Metallic Materials

Semi-solid metal (SSM) processing has been an attractive method for manufacturing near-net-shape components with high integrity due to its distinct advantages over conventional forming technologies. SSM processing employs a mixture of solid phase and liquid metal slurries and/or non-dendritic feedstocks as starting materials for shaping. Since the original development from 1970s, a number of SSM processes have been developed for shaping components using the unique rheological and/or thixotropic properties of metal alloys in the semi-solid state, in which the globular solid particles of primary phase are dispersed into a liquid matrix. In this paper, the progress of the development of shaping technologies and the formation of non-dendritic microstructure in association with the scientific understanding of microstructural evolution of non-dendritic phase are reviewed, in which the emphasis includes the new development in rheomoulding, rheo-mixing, rheo/thixo-extrusion and semi-solid twin roll casting, on the top of traditional rheocasting, thixoforming and thixomoulding. The advanced microstructural control technologies and processing methods for different alloys are also compared. The mechanisms to form non-dendritic microstructures are summarised from the traditional understanding of mechanical shear/bending and dendrite multiplication to the spheroidal growth of primary phase under intensively forced convection. In particular, the formation of spheroidal multiple phases in eutectic alloys is summarised and discussed. The concluding remarks focus on the current challenges and developing trends of semi-solid processing.

Real-Time Monitoring of Solid-Liquid Slurries: Optimized Synthesis of Tetrabenazine.

Solid-liquid slurries are vital and increasingly prevalent in the pharmaceutical and chemical industries. Despite the importance of these heterogeneous systems, process control and optimization are fundamentally hindered by a lack of compatible real-time analytical techniques. We present herein an online HPLC monitoring platform enabling access to real-time compositional information on slurries. We demonstrate the system by investigating the heterogeneous synthesis reaction of tetrabenazine. Furthermore, we integrated our online HPLC platform with the orthogonal monitoring techniques of a pH probe and a microscopic imaging probe to provide additional mechanistic insight. These combined insights enable the optimization of tetrabenazine synthesis in terms of reaction time, byproduct formation, and diastereomeric purity of the final product.

Extending estimation of the critical deposition velocity in solid–liquid pipe flow to ideal and non-ideal particles at low and intermediate solid volume fractions

The critical deposition velocity in horizontal pipe flow of liquid-solid slurries separates bed-forming and fully suspended flows. A compilation of critical deposition velocity data is presented using new experimental data (for particles ranging from 9 to 690 µm in diameter) along with data from the literature, and a close correlation between the particle Reynolds number and the Archimedes number (which describe the properties of the flow and the liquid and solid phases) is found. The role of solid particle packing is discussed and suggestions are made for the incorporation of solid-phase material properties – specifically particle shape and angularity, and surface forces – into an empirical parameter, the volume factor, α, to account for the deviation of particle behaviour from ideal, non-interacting, hard-sphere behaviour.

Pathways in particle assembly by ultrasound-assisted spray-drying of kaolin/SAPO-34 as a fluidized bed catalyst for methanol to light olefins

Fluidized bed reactor and continuous catalyst regeneration system was proposed to overcome the effects of exothermic methanol to light olefins (MTO) reaction and achieve longer lifetime. The proper catalysts for fluidized bed reactor were usually prepared via spray drying method. The shaping of SAPO-34 with the matrix of kaolin and alumina sol binder was selected to prepare in spray dryer and test in fixed and fluidized bed reactor. The main properties of spray dried catalysts such as attrition resistance and micro-spherical morphology are necessary as well as good catalytic performance. The effects of ultrasound power on solid-liquid slurries were examined by the consideration of structural and catalytic properties of the spray dried catalysts. Ultrasound application for the slurries prior to spray drying leads to different particle size distributions and dispersion. Various models of particles assembly were obtained and discussed by XRD, FESEM, NH3-TPD, EDX, BET-BJH and FTIR techniques. Pore volume was increased by the application of lower ultrasound power. Its detailed analysis showed that 22 and 78% of the pore volume increase comes from the micro and mesopores, respectively. Ultrasound application prior to spray drying mostly have influence on the arrangement of particles resulted in mesopore volume enhancement. Formation of spherical and symmetric shaped particles is enhanced at the lower power of 45 W but it was not acceptable for the higher power of 90 W. The catalyst which was sonicated at the optimized power demonstrates improvement in physiochemical characteristics but showed higher attrition rate (30% increase compared to non-sonicated one). The catalyst experienced ultrasound irradiation prior to spray showed lower MTO reaction life time (432 min) as it was reported to be 850 min for non sonicated catalyst. Shorter life time of KSAPO-HU (P = 45) can be attributed to its lower mechanical strength.

Gas-Enhanced Ultra-High Shear Mixing: A Concept and Applications

The processes of mixing, homogenizing, and deagglomeration are of paramount importance in many industries for modifying properties of liquids or liquid-based dispersions at room temperature and treatment of molten or semi-molten alloys at high temperatures, prior to their solidification. To implement treatments, a variety of technologies based on mechanical, electromagnetic, and ultrasonic principles are used commercially or tested at the laboratory scale. In a large number of techniques, especially those tailored toward metallurgical applications, the vital role is played by cavitation, generation of gas bubbles, and their interaction with the melt. This paper describes a novel concept exploring an integration of gas injection into the shear zone with ultra-high shear mixing. As revealed via experiments with a prototype of the cylindrical rotor–stator apparatus and transparent media, gases injected radially through the high-speed rotor generate highly refined bubbles of high concentration directly in the shear zone of the mixer. It is believed that an interaction of large volume of fine gas bubbles with the liquid, superimposed on ultra-high shear, will enhance mixing capabilities and cause superior refining and homogenizing of the liquids or solid–liquid slurries, thus allowing their effective property modification.

Numerical Prediction of Particle Distribution of Solid-Liquid Slurries in Straight Pipes and Bends

Turbulent solid-liquid slurry flows in pipes are encountered in many engineering fields, such as mining. In particular, the distribution of the solids is a serious concern to engineers, but its determination involves considerable technical and economic difficulties. A two-fluid model for the numerical prediction of this parameter is presented. The model is robust and numerically stable, and requires relatively short computer time to provide a converged steady-state solution. The novelty of the proposed model and its better performance compared to similar ones reside in the method of accounting for some key physical mechanisms governing these flows, namely turbulent dispersion, interphase friction, and viscous and mechanical contributions to friction. The model is first validated by comparison with many experimental data available in literature regarding the horizontal pipe case over a wide range of operating conditions: delivered solid volume fraction between 9 and 40%; slurry velocity between 1 m/s and 5.5 m/s; and pipe diameter between 50 and 160 mm. A further comparison was performed with respect to recent experiments concerning a horizontal 90° bend.

Eulerian–Lagrangian modeling of turbulent liquid–solid slurries in horizontal pipes

Computations of liquid–solid slurries in horizontal pipes are performed to investigate the complex multiphase flow dynamics associated with operating conditions above and below the critical deposition velocity. A high-fidelity large eddy simulation framework is combined with a Lagrangian particle tracking solver to account for polydispersed settling particles in a fully developed turbulent flow. The two phases are fully coupled via volume fraction and momentum exchange terms, and a two-step filtering process is employed to alleviate any dependence of the liquid-phase mesh size on the particle diameter, enabling the capture of a wide range of spatial turbulent scales. A fully conservative immersed boundary method is employed to account for the pipe geometry on a uniform Cartesian mesh. Two cases are simulated, each with a pipe geometry and particle size distribution matching an experimental study from Roco & Balakrishnam, which considers a mean volumetric solid concentration of 8.4%, corresponding to just over 16 million particles. The first case considers a Reynolds number based on the bulk flow of the liquid of 85,000, resulting in a heterogeneous suspension of particles throughout the pipe cross-section. Statistics on the concentration and velocity of the particle phase for this case show excellent agreement with experimental results. The second case considers a lower Reynolds number of 42,660, leading to the formation of a stationary bed of particles. Three distinct regions are identified in the second case, corresponding to a rigid bed at the bottom of the pipe, a highly-collisional shear flow just above the bed, and a dilute suspension of particles far from the bed. Computational results indicate segregation in particle size along the vertical direction, with the smallest particles located at the top, increasing monotonically until the bed surface, where the largest particles are located. The covariance of concentration and velocity of each phase is presented, giving further insight on the multiphase dynamics. Statistics on the individual mechanisms that contribute to the motion of each particle, namely forces due to drag, the pressure gradient and viscous stresses of the surrounding fluid, and collisions, are provided for each case. It is observed that for the majority of the pipe cross-section, the drag force dominates for each case, which is balanced by inter-particle collisions in the streamwise direction, and by gravity in the vertical direction. Simulation results are also used to investigate closures from Reynolds average modeling of multiphase flows.

Applications of Ultrasound to the Synthesis of Nanostructured Materials

Recent advances in nanostructured materials have been led by the development of new synthetic methods that provide control over size, morphology, and nano/microstructure. The utilization of high intensity ultrasound offers a facile, versatile synthetic tool for nanostructured materials that are often unavailable by conventional methods. The primary physical phenomena associated with ultrasound that are relevant to materials synthesis are cavitation and nebulization. Acoustic cavitation (the formation, growth, and implosive collapse of bubbles in a liquid) creates extreme conditions inside the collapsing bubble and serves as the origin of most sonochemical phenomena in liquids or liquid-solid slurries. Nebulization (the creation of mist from ultrasound passing through a liquid and impinging on a liquid-gas interface) is the basis for ultrasonic spray pyrolysis (USP) with subsequent reactions occurring in the heated droplets of the mist. In both cases, we have examples of phase-separated attoliter microreactors: for sonochemistry, it is a hot gas inside bubbles isolated from one another in a liquid, while for USP it is hot droplets isolated from one another in a gas. Cavitation-induced sonochemistry provides a unique interaction between energy and matter, with hot spots inside the bubbles of approximately 5000 K, pressures of approximately 1000 bar, heating and cooling rates of >10(10) K s(-1); these extraordinary conditions permit access to a range of chemical reaction space normally not accessible, which allows for the synthesis of a wide variety of unusual nanostructured materials. Complementary to cavitational chemistry, the microdroplet reactors created by USP facilitate the formation of a wide range of nanocomposites. In this review, we summarize the fundamental principles of both synthetic methods and recent development in the applications of ultrasound in nanostructured materials synthesis.

Erosion–corrosion performance of high-Cr cast iron alloys in flowing liquid–solid slurries

In many slurry transportation systems, such as in FGD (Flue Gas Desulphurization) and chemical processing applications, corrosion and erosion are the two main mechanisms of material degradation of the pump wet-end components including pump casing, impeller and liners. The performance of a selected material is mostly dependent upon its relative corrosion and erosion resistance to the service environment. In these cases erosion, corrosion and the related synergistic effects can be very complicated since they are affected by numerous factors including solid and slurry properties, chemical contents, hydraulic conditions and temperatures. In this experimental study, sliding Coriolis erosion testing has been performed with various corrosion factors such as pH value, chlorides content and temperature to evaluate the erosion–corrosion resistance of some high-alloyed white cast irons containing different levels of chromium and other elements. Optical microscope and SEM-EDS have also been used to examine microstructure and surface conditions of tested materials. Results indicated that material loss due to corrosion factors increased as acidity-chlorides and temperature increased. At relatively high corrosion intensity, the white cast irons with higher alloy content (especially chromium) clearly showed improved corrosion resistance and combined erosion–corrosion resistance over those with lower alloy content. Under certain corrosion and hydraulic conditions, particle size is perhaps the single most influential factor on erosion–corrosion rate of the high-Cr cast iron alloys. Relatively large particles are much more effective than small ones at removing both the corroded surface layer and the fresh material, causing substantially higher rate of material loss. Some other related factors have also been addressed.

Sensitivity analysis of the influence of slurry characteristics and pipe size on Wasp model's accuracy

Sensitivity analysis of Wasp model for pressure gradient in solid–liquid slurries was conducted. The experimental work was carried out in 22-mm ID and 45-mm ID pipelines utilizing slurries composed of spherical glass beads having particle size distribution (PSD) following the Rosin–Rammler distribution and mean size of 50 μm. The spreads of the distribution were 1.7 and 7, corresponding to wide and narrow distributions, respectively. The slurries examined in this study had concentrations ranging from 5% to 25% by volume. Statistical tests for equivalence of means and variances provided some evidence that Wasp model is more accurate in predicting pressure gradients for the slurries of narrower PSD and at higher solid concentrations. Although the model was designed specifically for relatively large pipes, it was found more accurate in predicting pressure gradients in the 22-mm ID pipeline than in the 45-mm pipeline. Experimental results obtained in the same flow loop diameter indicated that the slurry of the narrower distribution produced higher-pressure gradients than those for the slurry of wider distribution. Pressure gradient increased markedly with increasing slurry concentration regardless of the pipe diameter and slurry PSD. However, the pipe diameter was found to have more significant influence on the pressure gradient than the slurry concentration does.

Erosion–corrosion behaviour of WC-based MMCs in liquid–solid slurries

In the oilsands industry erosive wear and erosion–corrosion can cause high rates of material loss, particularly in the hydrotransport system where corrosive slurries are encountered. Metal Matrix Composites (MMCs), comprising a ductile binder with a reinforcing hard phase, are seeing greater applications as coatings and hardfacing for critical components, where there is a requirement for high durability. In this paper the erosion–corrosion performance of WC-MMCs applied by the PTA process is evaluated. Four MMCs, with varying WC-size range, all with a Ni–Cr–Si–B matrix, have been considered. The erosion–corrosion behaviour of the MMCs is compared to UNS S31603 austenitic stainless steel. The material degradation is assessed as a function of sand particle size and sand loading. The materials were eroded by two sizes of silica sand with stream velocities of 10 and 17 m/s at 65 °C. The solid loading (wt.%) was varied from 1%, 5%, 10%, 15% and 20% with most tests being conducted at 1% and 5%. With the smaller sand size the MMCs showed considerably reduced damage due to erosion–corrosion compared to UNS S31603. Using the coarse sand, the MMCs show inferior resistance to erosion–corrosion compared to UNS S31603; the finding are explained by careful consideration of the material degradation mechanisms.

Investigations of Particle Velocities in a Slurry Pump Using PIV: Part 1, The Tongue and Adjacent Channel Flow

Transport of solid-liquid slurries in pipeline transport over short and medium distances is very important in many industries, including mining related processes. The particle image velocimetry technique was successfully utilized to investigate the velocities and kinetic energy fluctuations of slurry particles at the tongue region of an optically-clear centrifugal pump. The experiments were conducted using 500 micron glass beads at volumetric concentrations of 2.5% and 5% and at pump speeds of 725 rpm and 1000 rpm. The fluctuation kinetic energy increased approximately 200% to 500% as the pump speed was increased from 725 rpm to 1000 rpm. The directional impingement mechanism is more significant at the pressure side of the blade, tongue and the casing. This mechanism becomes more important as the speed increases. This suggests that the impeller, tongue and the casing of the slurry pump can wear out quickly, especially with an increase in speed. In this paper the emphasis is on the tongue region. The random impingement mechanism caused by the fluctuation kinetic energy of the solids can play an important role on the erosion of the tongue area.

Comparing the performance of HIPed and Cast Stellite 6 alloy in liquid–solid slurries

In this paper, results from erosion–corrosion tests performed under liquid–solid erosion conditions in 3.5% NaCl liquid medium are reported. The focus of the paper is to compare the behaviour of Cast and Hot Isostatically Pressed (HIPed) Stellite 6 alloy in terms of their electrochemical corrosion characteristics, their resistance to mechanical degradation and relationship between microstructure and degradation mechanisms. It has been shown that HIPed Stellite 6 possesses better erosion and erosion corrosion resistance than that of Cast Stellite 6 and two stainless steels (UNS S32760 and UNS S31603) under the same solid loading (200 and 500 mg/l), and same temperature (20 and 50 °C). The material removal mechanisms have been identified by using atomic force microscopy (AFM) and shown preferential removal of the Co-rich matrix to be less extensive on the HIPed material.

Mechanisms of wear on a Co-base alloy in liquid–solid slurries

The efficient performance of drilling tools in aqueous environments requires materials to be used, which can effectively resist excessive material loss due to the combined effects of erosion and corrosion. In this paper, the interactions between electrochemical corrosion and mechanical erosion have been assessed in liquid–solid slurries on a Co-base material (Stellite X40), which is currently used in the manufacture of oil tools. The material degradation is assessed as a function of aqueous environment and sand loading. Corrosion has been shown to represent an important factor in the degradation of this material even though it essentially exhibits passivity in static saline conditions. The relative importance of corrosion and its synergistic effect when combined with erosion are quantified and the implications in terms of material performance and of potential methods of reducing oil tool degradation are discussed.

99/03031 Preparation and transportation of solid-liquid coal slurries

99/03031 Preparation and transportation of solid-liquid coal slurries

Sonochemistry

Ultrasound causes high-energy chemistry. It does so through the process of acoustic cavitation: the formation, growth and implosive collapse of bubbles in a liquid. During cavitational collapse, intense heating of the bubbles occurs. These localized hot spots have temperatures of roughly 5000 degrees C, pressures of about 500 atmospheres, and lifetimes of a few microseconds. Shock waves from cavitation in liquid-solid slurries produce high-velocity interparticle collisions, the impact of which is sufficient to melt most metals. Applications to chemical reactions exist in both homogeneous liquids and in liquid-solid systems. Of special synthetic use is the ability of ultrasound to create clean, highly reactive surfaces on metals. Ultrasound has also found important uses for initiation or enhancement of catalytic reactions, in both homogeneous and heterogeneous cases.

Interparticle Collisions Driven by Ultrasound

Ultrasound has become an important synthetic tool in liquid-solid chemical reactions, but the origins of the observed enhancements remained unknown. The effects of high-intensity ultrasound on solid-liquid slurries were examined. Turbulent flow and shock waves produced by acoustic cavitation were found to drive metal particles together at sufficiently high velocities to induce melting upon collision. A series of transition-metal powders were used to probe the maximum temperatures and speeds reached during such interparticle collisions. Metal particles that were irradiated in hydrocarbon liquids with ultrasound underwent collisions at roughly half the speed of sound and generated localized effective temperatures between 2600 degrees C and 3400 degrees C at the point of impact for particles with an average diameter of approximately 10 microns.

Power Consumption in Solid-Liquid Slurries

Power Consumption in Solid-Liquid Slurries

Sand Movement in Horizontal Fractures

Abstract This study extends our information on solid-liquid slurries to the flow of sand in horizontal fractures. Inasmuch as this is basically an unsteady-state process. a comprehensive photographic study was undertaken in a 10- ft windowed cell to determine if the basic flow regimes described for steady-state flow in pipes applied to the subject process. Since the number of potential variables far exceeds the capacity of a single study, emphasis has been placed on the effects of sand concentration, oil viscosity and oil flow rate. The extensive photographic evidence obtained has proven very valuable in gaining an insight into the basic flow mechanisms. Being able to follow visually the flow characteristics that accompany the quantitative data is valuable in the application of the results. Although the use of dimensionless parameters was carefully investigated, it was found that the data obtained could be more easily, and as accurately, correlated by judicious use of the dimensional variables investigated. However, a study into the feasibility of scaling slurry flow was made in the event this technique is justified in future investigations. The data presented show that the pressure behavior observed in solids transport in pipes basically applies to slurry flow in horizontal fractures. The roles of the parameters are altered but a basic equivalence exists. The most significant correlating parameter was the oil viscosity (mu) and the bulk velocity of the slurry (vB), expressed as "muv" product. The most significant correlation expresses the rate of advance of the sand as a function of the variables investigated. There are many practical ramifications of this phase of the investigation that should aid in better treatment design. Evaluation of sand advance rates provides a means of estimating sand placement efficiencies during a treatment and the resulting sand distribution in the fracture. The results show that sand placement efficiencies are low under typical treatment conditions. A brief description of the effects of overflushing is also included. Introduction The flow of sand-oil slurries in fractures is an area in which little basic knowledge is available. This stems to some degree from the fact that it is impossible to duplicate fractures at the surface. They occur in various shapes and sizes with an infinite combination of irregularities. Unfortunately, we can never "see" these fractures except in cores and by indirect means of measurement. In spite of this inherent difficulty, it is desirable to develop some basic concepts that will provide a better understanding of the sand transport mechanism. An insight into the problem is provided by investigations of fluid flow in rectangular conduits. Several studies on the flow of liquids in non-circular conduits show that a Reynolds number-Fanning friction factor relationship can be written if the hydraulic diameter is substituted for the regular diameter in a circular pipe. This hydraulic, or equivalent, diameter is taken as four times the cross-sectional area occupied by the flowing fluid divided by the wetted perimeter. Eq. expresses an extension of this same work when applied to infinite parallel planes b distance apart.(1)