Glass Beads In Water Research Articles

Numerical Investigation of Slurry Pressure Drop at Different Pipe Roughness in a Straight Pipe Using CFD

Slurry flow (water–glass beads) through a horizontal pipe of diameter, 0.0549 m and length, 3.8 m with two particle sizes, i.e., 125- and 440-micron, has been numerically modeled and investigated based on the kinetic theory of slurry transportation. The effect of particles interaction on the pipe flow characteristics such as velocity profile, wall shear stress, vector regime, granular pressure and temperature has been evaluated at different solid concentration and flow velocity range. It is well established that the pressure drop is the key parameter for the design of efficient slurry pipeline system, which is influenced by factors such as flow velocity, slurry viscosity, solid concentration, pipe material and pipe geometry. However, to best of our knowledge, the estimation of pressure drop at different pipe roughness height and a concentration range of 40–60% is not yet established. Therefore, in the present work, the numerical simulation is carried out for slurry flow through a horizontal pipeline at different roughness heights (Rh = 10–50 micron) and Prandtl numbers, i.e., 1.34, 2.14, 3.42 and 5.83. The kinetic parameters are calculated at a flow velocity (Vm) of 1–5 ms−1 and solid concentration (Cw) range of 40–60%. The results and procedure of the current simulation are validated against the available experimental results in the literature. The outcomes of the present work reveals that pressure drop increases with increase in pipe roughness height for the chosen velocity and solid concentration range. In addition, the larger particle is found to have more influence on the pressure, velocity, temperature distribution for the entire range of flow velocity and solid concentration. Furthermore, settling velocity and specific energy consumption are also predicted and discussed through the slurry pipeline. The findings show that the settling velocity of particle increases with increase in particle size at different Prandtl number. The energy efficiency for solid transportation through pipeline at different Prandtl numbers and particle size are also evaluated. Based on the results, it is concluded that specific energy efficiency varies with solid concentration and particle size, i.e., higher concentration and larger particle size demonstrates higher energy consumption. Furthermore, fluid at low Prandtl number exhibits higher energy consumptions. In order to design the efficient slurry pipeline system, it is recommended that the slurry must be transported at low velocity and high Prandtl number.

A first-order segregation phenomenon in fluid-immersed granular systems

A vast majority of widely accepted granular segregation mechanisms are attributed to dynamic phenomena such as percolation, kinetic sieving, convection-induced segregation, condensation, inertia and granular temperature gradients. We distinguish the ballistics of the particles from such dynamic and material properties and show that the former is a dominant mechanism in the segregation of particles sedimented in a container. We first perform granular sedimentation experiments with glass beads in water that exhibit size-segregation of bidisperse grains. We then show through simulations using a simple, first-order model that the ballistics of the particles alone is sufficient to qualitatively predict this segregation.

Gas dispersion and solid suspension in a three-phase stirred tank with triple impellers

The hydrodynamics is still not fully understood in the three-phase stirred tank equipped with multi-impeller due to the intensive interaction between phases. In this work, the solid critical suspension speed ( N JSG ), relative power demand (RPD) and overall gas holdup ( ε G ) were measured in an air–water–glass beads stirred tank equipped with multi-impeller, which consists of a parabolic blade disk turbine below two down-pumping hydrofoils. Results show that either the N JSG or the specific power consumption increases when increasing the volumetric solid concentration or superficial gas velocity. RPD changes less than 10% when solid volumetric concentration ranges from 0 to 15%. ε G decreases with the increase of solid concentration, and increases with the increase of both superficial gas velocity and the total specific power consumption. The quantitative correlations of N JSG , RPD and ε G were regressed as the function of superficial gas velocity, specific power consumption, Froude number and gas flow number, in order to provide the reference in the design of such three-phase stirred tank with similar multi-impellers. • Just-suspension speed, RPD and gas holdup with triple impeller were measured. • Superficial gas velocity significantly affects the suspension speed. • Overall gas holdup is evidently affected by the solid.

Sand Transport in Slightly Upward Inclined Multiphase Flow

In order to assess the critical sand deposition condition, a unique 4-in ID test facility was designed and constructed, which enables the pipe to be inclined 1.5 deg upward. Experiments were conducted with air–water-glass beads at low sand concentrations (< 10,000 ppm), and the air and water flow rates were selected to ensure stratified flow regime along the pipe. At constant superficial liquid velocity, the gas velocity was reduced to find the critical sand deposition velocity. Six sand flow regimes are identified, namely, fully dispersed solid flow, dilute solids at the wall, concentrated solids at the wall, moving dunes, stationary dunes, and stationary bed. The experimental results reveal that sand flow regimes under air–water stratified flow are strong functions of phase velocities, particle size, and particle concentration. Also, the results show that air–water flow regime plays an important role in particle transport; slug flow has high capability to transport particles at the pipe bottom, while the stratified flow has high risk of sand deposition. As long as the sand dunes are observed at the pipe bottom, the critical sand deposition velocities slightly increase with concentrations, while for stationary bed, the critical velocity increases exponentially with concentration.

Relating Nanoparticle Shape and Adhesiveness to Performance as Flotation Collectors

Cationic polystyrene-core-poly(n-butyl methacrylate)-shell (PS–PB) nanoparticles perform as flotation collectors as they spontaneously adsorb onto 43 μm glass beads in water, promoting glass bead attachment to air bubbles. Under our flotation conditions at room temperature, polystyrene is a hard plastic, whereas, with glass transition near room temperature, poly(n-butyl methacrylate) is a soft polymer. Colloidal probe atomic force microscopy measurements revealed that the pull-off forces and the work of adhesion of PS–PB nanoparticles to glass were significantly higher than observed with harder PS particles. Glass bead recovery in laboratory flotation experiments increased significantly with thickness of the soft PB shells on the PB–PS core/shell nanoparticles. Ninety-two nm Janus particles consisting of one PS and one PB lobe were also very effective collectors. We propose that high nanoparticle/glass bead adhesion minimizes nanoparticle removal by bead/bead collisions (nanoscale ball milling) during mix...

Polymer-Based Wireless Resonant Magnetic Microrobots

This paper presents a new generation of wireless resonant magnetic microactuator (WRMMA) type microrobot, named PolyMite. A polymer is used as a spring material in the design of the PolyMite. Compared with the previous generation of such devices, the use of a polymer, i.e., SU-8, as a spring material enables the design of a stable spring system without a significant increase in stiffness. A speed of over 20 mm/s (40 body lengths per second) was measured when the PolyMite was driven in air. Micromanipulation abilities of the PolyMites in wet environments have also been demonstrated. The agents were capable of transporting microobjects such as light polystyrene beads and heavier glass beads in water. The large output force, remote actuation, and biocompatible outer surface (SU-8 and gold) make the PolyMite an exciting candidate for biomedical applications.

Ultrasonic measurement and characterization of a low concentration system of solid particles in liquid, in high shear flow

The objective of this paper is ultrasonic measurement and characterization of solid particles in liquid (20–40 μm glass beads in water) in high shear flow (1.5–2 m/s). Ultrasonic time dependent signals as well as frequency spectra are analyzed, for simultaneous determination of average particle concentration and average flow speed. As a result, the distribution of sound energy in such concentrated systems at given flow speeds is measured. Influence of flow turbulence is demonstrated in measurements. Also, characteristic behaviors of liquid–particle mixtures like particle clustering and influence of gas bubbles have been investigated. Experimental results are complemented with a discussion of factors that influence measurement uncertainty.

Sonochemical enhancement of hydrogen peroxide production by inert glass beads and TiO 2-coated glass beads in water

In this study, a series of experiments were carried out to determine the effects of ultrasound frequency at 28, 580, and 1000 kHz on H 2O 2 production in the presence of both inert and TiO 2-coated glass beads. Several different sizes (no addition, 0.05, 0.1, 1, 2, 3, and 5 mm) and amounts (no addition, 10, 25, 50, 100, and 200 g L −1) of inert glass beads were tested at a power density of 0.2 W mL −1. The production of H 2O 2 with a contact time of 60 min at different frequencies follows the order: 580 kHz (339 μM/no addition–105 μM/2 mm) > 1000 kHz (208 μM/no addition–4.0 μM/1 mm) > 28 kHz (71.2 μM/0.1 mm–18.5 μM/no addition). For a constant glass-bead size of 0.1 mm and at a frequency of 28 kHz, the zero-order rate constant is highest in the presence of glass beads of the amount 10 g L −1 (3.3 μM −1 min −1), and it decreases significantly with increasing inert glass-bead amounts (2.7 μM −1 min −1/25 g L −1 to 0.45 μM −1 min −1/200 g L −1). The zero-order rate constant is the lowest (0.31 μM −1 min −1) with no addition of glass beads. Sonocatalysis at a low frequency of 28 kHz with the addition of TiO 2-coated glass beads (5 mm) of amount 100 g L −1 was significantly more effective (1540 μM) than sonocatalysis carried out with no addition and inert glass beads (12–18 μM) and those carried out at the high frequencies of 580 kHz (33.4 μM) and 1000 kHz (8.77 μM), with the other conditions remaining the same.

Intensified operation of slurry bubble columns using structured gas injection

AbstractWe investigate uniform gas injection using a needle sparger as a structuring methodology to reduce backmixing in slurry bubble columns. Using optical probes, we determined the gas fraction and the bubble behaviour in 2D and 3D slurry bubble columns with a uniform gas injection. Experimental results for air–water–glass beads (ds = 108 µm, Usg = 0–0.10 m/s) indicate that a strong reduction in the vortical structures has been achieved and the homogeneous flow regime can be extended beyond 30% gas fraction. Increasing the solids concentration decreases the gas fraction and widens the bubble velocity distribution. Furthermore, we show by modelling that the reduced backmixing leads to a major improvement of the conversion in case of Fischer–Tropsch synthesis.

Slurry flow modelling by CFD

An attempt has been made in the present study to develop generalized slurry flow model using CFD and utilize the model to predict concentration profile. The purpose of CFD model is to gain better insight into the solid liquid slurry flow in pipelines. Initially a three-dimensional model problem was developed to understand the influence of the particle drag coefficient on solid concentration profile. The preliminary simulations highlighted the need for the correct modelling of the inter phase drag force. The various drag correlations available in literature was incorporated in a two-fluid model (Euler-Euler) along with the standard k-? turbulence model with mixture properties to simulate the turbulent solid-liquid flow in a pipeline. The computational model was mapped on to a commercial CFD solver FLUENT6.2 (of Fluent Inc., USA). To push the envelope of applicability of simulation, the recent data of Kaushal (2005) (with solid concentration up to 50%) was selected to validate the three dimensional simulations. The experimental data consists of water-glass bead slurry at 125& 440 micron particle with different flow velocity (from 1 to 5 m/s) and overall concentration up to 10 to 50% by volume. The predicted pressure drop and concentration profile was validated by experimental data and shows excellent agreement. Interesting findings were come out from the parametric study of velocity and concentration profiles. The computational model and results discussed in this work would be useful for extending the applications of CFD models for simulating large slurry pipelines.

Particles settling studies using ultrasonic techniques

Effects of acoustic velocity and attenuation measurements during settling of 43-, 110- and 168-μm glass beads in water are reported. Ultrasonic waves were generated at a frequency of 3.2 MHz. An abrupt increase in acoustic velocity and a sharp peak in the attenuation characterized the onset of settled bed. The observed attenuation peak at the transition between suspended and settled bed was attributed to dissipation caused by viscous absorption losses. The critical concentration at which increase in acoustic velocity and attenuation peak occurred was estimated for these particle sizes.

Solids flow mapping in a high pressure slurry bubble column

Successful design and scale-up of Slurry Bubble Column Reactors (SBCRs) require proper understanding of how operating conditions affect their flow behavior. Presently, there is little information on the flow dynamics of solids (e.g., distribution of velocities and turbulent parameters) in slurry systems that are operated at industrially relevant conditions of high pressure, high superficial gas velocities, and high solids loading. Computer Automated Radio Particle Tracking (CARPT) is widely recognized as one of a few techniques that can be reliably used even in highly turbulent and opaque slurry flows. This work utilizes an improved CARPT technique to investigate the effect of reactor pressure (0.1–1 MPa) and superficial gas velocity (0.08–0.45 m/s) on solids phase velocity and shear stress in a pilot scale 0.16 m diameter stainless steel column using an air–water–glass beads ( 150 μ m ) system. The solids axial velocity and shear stress were found to increase noticeably with pressure and superficial gas velocity in the churn turbulent flow regime.

Pore-scale characteristics of multiphase flow in porous media: A comparison of air–water and oil–water experiments

Studies of NAPL dissolution in porous media have demonstrated that measurement of saturation alone is insufficient to describe the rate of dissolution. Quantification of the NAPL–water interfacial area provides a measure of the expected area available for mass transfer and will likely be a primary determinant of NAPL removal efficiency. To measure the interfacial area, we have used a synchrotron-based CMT technique to obtain high-resolution 3D images of flow in a Soltrol–water–glass bead system. The interfacial area is found to increase as the wetting phase saturation decreases, reach a maximum, and then decrease as the wetting phase saturation goes to zero. These results are compared to previous findings for an air–water–glass bead study; The Soltrol–water interfacial areas were found to peak at similar saturations as those measured for the air–water system (20–35% saturation range), however, the peak values were in some cases almost twice as high for the oil-water system. We believe that the observed differences between the air–water and oil–water systems to a large degree can be explained by the differences in interfacial tensions for the two systems.

Effects of micron-sized particles on hydrodynamics and local heat transfer in a slurry bubble column

Hydrodynamics and heat transfer in an air–water–glass bead system are investigated to study the effects of particle size (11–93 μm) and slurry concentration (up to 40 vol.%). The effect of particle size on gas holdup is only slight over the range of particle size investigated. This can be attributed to differences in rise velocities of different bubble fractions. Small bubble rise velocities are systematically lower for a particle size of 93 μm compared to 11- and 35-μm particles. Larger bubble rise velocities decreased with increasing particle size. Heat transfer coefficients decreased with increasing particle size at the column center, but no significant difference is observed at the column wall. At the column bottom, the heat transfer behaviour of the 11-μm particles is distinctly different from the 35- and 93-μm particles. With the 11-μm particles, there is a smaller effect of slurry concentration on local heat transfer coefficient. Estimated interfacial area results show a sharp decrease due to addition of fine particles into the liquid. The decrease is more dramatic as the slurry concentration is increased.

Analysis of flow patterns in bubble and slurry bubble columns based on local heat transfer measurements

Flow patterns in two-phase (G–L) and three-phase (G–L–S) bubble columns are investigated based on local time-averaged heat transfer coefficients. The experiments are conducted in a 0.28 m diameter Plexiglas column in air–water and air–water–glass beads (35 μm) systems over superficial gas velocity range 0.05–0.3 m/s and slurry concentration range 0–40 vol.%. The heat transfer measurements are made with a specially designed probe which provided local heat transfer coefficients. The measured heat transfer data are analyzed to illustrate the effects of gas velocities and slurry concentrations on flow patterns in different regions of the column. The heat transfer measurements at different axial and radial positions and for different probe orientations provided further insights into liquid circulation patterns in the column.

Experiments and CFD Predictions of Solid Particle Distribution in a Vessel Agitated with Four Pitched Blade Turbines

The distribution of solid particles in a high aspect-ratio baffled tank agitated with four 45° pitched blade turbines (PBT) was investigated using both experimental measurements and CFD simulations. Dilute suspensions of glass beads in water and moderately viscous liquids were considered. The measurement of axial particle concentration profiles was conducted by means of a light attenuation technique. Fully predictive simulations of solid-liquid suspensions were performed using a Sliding-Grid approach coupled with the Eulerian-Eulerian Two Fluid Model and the ‘homogeneous’ two-phase k-ɛ turbulence model. The simulated particle axial concentration profiles were compared with the experimental data and good agreement was found.

Optimization of optical particle sizing in multiphase flows

Simultaneous measurements of particle size and velocity with different media are important in the experimental study of multiphase flows. Especially, when one of the dispersed media has a relative refractive index close to unity (m? 1.0), the optical configuration requires extra consideration in phase-Doppler anemometry (PDA). Such measurements are often encountered when water flows are composed of air bubbles and glass beads with relative refractive indices of m1 = 0.75 and m2= 1.13, respectively. Large uncertainty in measurements may arise if optical parameters fall into the region of so-called scattering angles.'' Furthermore, the scattering intensities from air bubbles and glass beads in water are found to have two-order-of-magnitude differences at an off-axis angle in between 60 to 85 deg, which narrows the measurable dynamic range and causes bias in the size distribution of different dispersed phases. We use a scheme based on the recently developed combined refraction-reflection model and Mie scattering theory to optimize the off-axis angle to minimize the measurement uncertainty. The variation of the critical scattering angles and scattering intensity ratios of media are quantitatively described. The predictions are validated by conducting experiments to measure glass spheres and vapor bubbles in water.

Novel mixing tank for improved gas–liquid mass transfer and solids suspension

A novel, baffleless, mixing tank configuration presented provides greater mixing efficiency than conventional technologies under a wide variety of operating conditions. The concept uses a cylindrical tank with a contoured bottom and a shroud that surrounds an axial flow impeller and supports a set of stationary antiswirl fins positioned in close proximity to the impeller blades. The angle and pitch of the fins impart an angular component to the flow that is equal and opposite to the swirl induced by impeller rotation, thereby eliminating the need for wall baffles. The contoured bottom eliminates dead space beneath the impeller and n the corners of flat-bottom mixing tanks. This alternative mixing system, named the ASSET system, is compared to conventional mixing configurations through experiments of power consumption, gas-liquid mass transfer, and solids suspension. Measurements of Power number vs. Reynolds number reveal that it has power requirements similar to those of high-efficiency axial-flow turbines in a conventional tank geometry. Unsteady-state oxygen absorption and stripping experiments are used to determine the interphase mass-transfer coefficient as a function of power input for each configuration at superficial gas feed velocities of 0.057 to 0.17 cm/s. With this system, K{sub L}a values are on average 30 tomore » 50% greater than those obtained in a conventional mixing tank at the same power input. Measurements of the height of the well-mixed region of suspended solids in a 15 wt. % mixture of 0.1-cm-dia. glass beads in water indicate that the ASSET system requires {approximately} 30% less power to achieve equivalent extents of solids suspension than the conventional setup.« less

Diffusive transport of acoustic waves in strongly scattering media

The diffusive transport of multiply scattered ultrasonic waves is investigated experimentally and theoretically in a simple system consisting of glass beads in water. New experimental results are presented using a novel method for measuring the frequency correlation function of the transmitted acoustic field. The wave diffusion coefficient D is found to vary strongly with frequency when the wavelength is comparable to the size of the scatterers, reflecting a substantial slowing down of wave propagation when the scattering is strongest. The results are interpreted using a model based on a spectral function approach that gives good agreement with experiment.

Comparative evaluation of hydrodynamic and gas—liquid mass transfer characteristics in bubble column and airlift slurry reactors

Three pneumatically agitated reactors — a bubble column and two airlift devices — with identical rectangular cross-sections (0.456 m × 0.153 m), working heights (1.64 m) and equivalent gas sparging arrangements were compared in terms of the hydrodynamic and oxygen transfer performance. The two airlift reactors had identical riser-to-downcomer cross-sectional area ratios of 1.0, but differed in being sparged either in the central draft-tube or in the peripheral risers. The reactors produced comparable overall gas holdups for otherwise identical conditions in air—water or air—water—glass bead (0.069 mm particle diameter, 0%–5% (v/v) solids loading) systems. For the airlifts, irrespective of the sparging configuration or the solids loading, the same linear equation could relate the riser and the downcomer gas holdups. The velocity of the induced liquid circulation was not affected by solids loading, but the central draft-tube sparged design produced consistently higher velocities than did sparging in peripheral tubes. The bubble column had the poorest mixing performance. Complete suspension of solids occurred in all reactors in the range of superficial air velocities (0.01–0.08 m s −1) tested; however, the distribution of solids was non-uniform in the bubble column. The airlift devices achieved homogeneous distribution. The oxygen transfer capability of the three reactors was comparable, with the bubble column performing slightly better.