Particle Tracking Technique Research Articles

Modeling the effects of agricultural management practices on groundwater in Shelton, USA

An integrated methodology was developed to assess the impact of recharge rates, nitrate leaching from crop root zones, and irrigation pumping rates on groundwater quality and quantity. Monthly values for deep percolation of water, irrigation pumping and leaching of nitrate-nitrogen were calculated with a soilwater-plant model. An Intermediate Vadose Zone Model (IVZM) was developed and used together with models for groundwater flow (MODFLOW) and solute transport (MT3D) to simulate the movement of water and nitrate-nitrogen. The IVZM generates recharge files used by MODFLOW and MT3D. The methodology was applied to an area near the town of Shelton, Nebraska, where a shallow sand-gravel aquifer is highly contaminated by nitrate-nitrogen. MODFLOW was calibrated using historic groundwater level data from 1981 to 1996. Simulation results suggest that concentration reductions of 10% in the upper third of the saturated zone are possible after 10 years of improved irrigation and nitrogen fertilizer management. Groundwater quality changes slowly propagate down-gradient from the field and towards the lower part of the aquifer. A particle tracking technique showed that water from a well does not provide a good indication of the influence of improved management in the adjacent field. The quality of water pumped from a well represents the effect of management over 15 years and from more than 1.5 km up-gradient from the well. Regional groundwater quality depends on local management practices over a long period. Regulatory programs to improve water quality require therefore, widespread adoption and substantial time to provide significant water quality improvements.

Experimental investigation of the particle‐wall‐impact under particular consideration of the wall surface influence on the particle trajectory and the transition between sliding and adhering impact

AbstractWe present results of the experimental investigation of the impact of particles on a rough wall. The particle‐wall impact influences considerably the behavior of particle laden gas flows. The aim of the present work is to study the influence of the wall roughness on the particle trajectory and the particle rotation after impact. The measurements were carried out in a special test facility, which allows the investigation of single particle‐wall impacts. Particle velocities and trajectories were recorded by a video system and evaluated by using a particle tracking technique. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Characterising porosity of multi-component mixtures in rotary mills

The measurement of porosity presents a significant challenge in modelling of slurry transport in rotary mills. This is due to the aggressive environment within rotary mills. In this paper, a method of measuring the porosity of mill charge, using the positron emission particle tracking (PEPT) technique, is presented. In this work, multiple particles are tracked, in turn. The packing density of each size component is proportional to the residence time distribution of its representative tracer particle, based on the ergodicity of the system. The charge porosity is a linear combination of the packing densities of individual components. The porosity is modelled as a function of mill geometric and operating parameters—mill speed and filling fraction. The results show correlations between porosity distribution and operating parameters.

Characterization of solids mixing patterns in bubbling fluidized beds

Behavior of the solid phase in fluidized beds was studied by a 2D CFD-DEM approach to obtain more information on the solid mixing and circulation. Hydrodynamic parameters, including solid diffusivity, and internal and gross circulations were considered in this study. To validate the simulation, time-position data obtained by the Radioactive Particle Tracking (RPT) technique were used. It was shown that the 2D model can satisfactorily predict the axial diffusivity, while the radial diffusivity calculated based on the model is an order of magnitude smaller than the experimental one in 3D. The influence of aspect ratio of the bed, type of distributor, and inlet gas velocity on solids mixing pattern were also studied. The solids flow pattern in the bed changed considerably by increasing the aspect ratio. Different solid circulations were captured by numerical model for the two types of distributors, namely porous and injection types. The results suggested that increasing the superficial gas velocity caused rigorous internal and gross circulations, which in return, improved solids mixing and decreased deviations from well mixed state.

Effect of Bed Diameter on the Hydrodynamics of Gas-Solid Fluidized Beds

Effect of scale on the hydrodynamics of gas-solid fluidized beds was investigated in two fluidized beds of 152 mm and 78 mm in diameter. Air at room temperature was used as the fluidizing gas in the bed of sand particles. The Radioactive Particle Tracking (RPT) technique was employed to obtain the instantaneous positions of the particles at every 20 ms of the experiments. These data were used to calculate hydrodynamic parameters, such as mean velocity of upward and downward-moving particles, jump frequency, cycle frequency and axial and radial diffusivities, which are representative of solid mixing and diffusion of particles in the bed. These hydrodynamic parameters were compared in both scales in order to determine the scale effect on the hydrodynamics of the gas-solid fluidized bed. In all cases, it was shown that solid mixing and diffusivity of particles increase by increasing column diameter. The results of this study would help to understand solid mixing which might be critical in industrial fluidized bed reactors.

From Pore Scale to Column Scale Dispersion in Capillary Silica Monoliths

We study time and length scales of eddy dispersion in 100 mum i.d. capillary silica monoliths. First, the monolith's macropore morphology was visualized over complete column cross sections by confocal laser scanning microscopy, revealing a wall region with large voids (with a lateral dimension of up to approximately 15 mum) and a homogeneous core region. A bulk segment from the core region was then physically reconstructed to receive a 60 x 12 x 12 mum matrix consisting of approximately 3 x 10(8) cubic voxels of 30 nm edge length for direct numerical simulations of fluid flow by the lattice-Boltzmann method and convective-diffusive mass transport by a random-walk particle-tracking technique on a high-performance computing platform. Pore-scale dispersion was analyzed in detail using the generalized Giddings equation. Eddy dispersion contributions originating in the bulk macropore heterogeneity were quantified and correlated with structural features of the monolith. To complement the simulation results, column scale dispersion was investigated by analysis of chromatographic plate heights. We found a much smaller bulk dispersion than generally assumed for silica monoliths (plate heights of approximately 2 mum over a wide velocity range), promising excellent separation efficiency also at high flow velocities ( approximately 1 cm/s). This potential is not realized by the capillary monolith in chromatographic practice because of the wall defect.

Drs. Allanore and Vacca reply

<h3>Abstract</h3> Optical traps enable nanoscale manipulation of individual biomolecules while measuring molecular forces and lengths. This ability relies on the sensitive detection of optically trapped particles, typically accomplished using laser-based interferometric methods. Recently, precise and fast image-based particle tracking techniques have garnered increased interest as a potential alternative to laser-based detection, however successful integration of image-based methods into optical trapping instruments for biophysical applications and force measurements has remained elusive. Here we develop a camera-based detection platform that enables exceptionally accurate and precise measurements of biological forces and interactions in a dual optical trap. In demonstration, we stretch and unzip DNA molecules while measuring the relative distances of trapped particles from their trapping centers with sub-nanometer accuracy and precision, a performance level previously only achieved using photodiodes. We then use the DNA unzipping technique to localize bound proteins with extraordinary sub-base-pair precision, revealing how thermal DNA fluctuations allow an unzipping fork to sense and respond to a bound protein prior to a direct encounter. This work significantly advances the capabilities of image tracking in optical traps, providing a state-of-the-art detection method that is accessible, highly flexible, and broadly compatible with diverse experimental substrates and other nanometric techniques.

Experimental Analysis of Microchannel Entrance Length Characteristics Using Microparticle Image Velocimetry

The study of the entrance region of microchannels and microdevices is limited, yet important, since the effect on the flow field and heat transfer mechanisms is significant. An experimental study has been carried out to explore the laminar hydrodynamic development length in the entrance region of adiabatic square microchannels. Flow field measurements are acquired through the use of microparticle image velocimetry (micro-PIV), a nonintrusive particle tracking and flow observation technique. With the application of micro-PIV, entrance length flow field data are obtained for three different microchannel hydraulic diameters of 500 μm, 200 μm, and 100 μm, all of which have cross-sectional aspect ratios of 1. The working fluid is distilled water, and velocity profile data are acquired over a laminar Reynolds number range from 0.5 to 200. The test-sections were designed as to provide a sharp-edged microchannel inlet from a very large reservoir at least 100 times wider and higher than the microchannel hydraulic diameter. Also, all microchannels have a length-to-diameter ratio of at least 100 to assure fully developed flow at the channel exit. The micro-PIV procedure is validated in the fully developed region with comparison to Navier–Stokes momentum equations. Good agreement was found with comparison to conventional entrance length correlations for ducts or parallel plates, depending on the Reynolds range, and minimal influence of dimensional scaling between the investigated microchannels was observed. New entrance length correlations are proposed, which account for both creeping and high laminar Reynolds number flows. These correlations are unique in predicting the entrance length in microchannels and will aid in the design of future microfluidic devices.

Statistical properties of a 2D granular material subjected to cyclic shear

This work focuses on the evolution of structure and stress for an experimental system of 2D photoelastic particles that is subjected to multiple cycles of pure shear. Throughout this process, we determine the contact network and the contact forces using particle tracking and photoelastic techniques. These data yield the fabric and stress tensors and the distributions of contact forces in the normal and tangential directions. We then find that there is, to a reasonable approximation, a functional relation between the system pressure, P, and the mean contact number, Z. This relationship applies to the shear stress τ, except for the strains in the immediate vicinity of the contact network reversal. By contrast, quantities such as P, τ and Z are strongly hysteretic functions of the strain, e. We find that the distributions of normal and tangential forces, when expressed in terms of the appropriate means, are essentially independent of strain. We close by analyzing a subset of shear data in terms of strong and weak force networks.

Quantitative investigation of powder flow during die filling using positron emission particle tracking

The flow behaviour of powders during die filling was investigated using the positron emission particle tracking (PEPT) technique, from which quantitative information on the flow of individual particles was obtained. Two grades of spherical microcrystalline cellulose powders with different particle sizes were used as the model powder systems. It is shown that the trajectories of tracked particles at different initial positions are consistent with the overall flow patterns observed using a high-speed video system and linear kinematics (i.e. displacement and velocity) of the tracked particles in the moving direction of the feed shoe correspond very well with the specified shoe motion. Furthermore, a close examination of the vertical velocity component (i.e. in the gravitational direction) of the tracked particles that were deposited into the die reveals that for the system with large particles, the particles flow into the die at a higher falling velocity, compared to the system with small particles. This is primarily due to the effect of the presence of air in the die, which can significantly inhibit the flow of small particles, while its effect on the flow of large particles is small.

Development of particle tracking algorithms for various types of finite elements in multi-dimensions

Suk and Yeh (2009) previously reported the development of an accurate and efficient particle tracking algorithm for simulating the pathline under complicated steady and unsteady flow conditions. However, a mathematical derivation of only quadrilateral and hexahedral elements was reported. This study extends the applicability of the particle tracking technique previously proposed by Suk and Yeh (2009) to various types of elements within finite elements in multi-dimensions. Accordingly, an extension of the particle tracking method by Suk and Yeh (2009) (herein referred to as extended method) was designed to incorporate quadrilateral and triangular elements in two dimensions, including triangular prism, tetrahedral, and hexahedral elements in three dimensions. In addition, the performance of the extended method was evaluated by a comparison with the results of Pollock's method. Various examples and applications were used to illustrate the applicability and practicality of the extended method in the field of groundwater flow and transport.

Hydrodynamic characteristics of gas–solid fluidization at high temperature

AbstractEffect of temperature on the hydrodynamics of bubbling gas–solid fluidized beds was investigated in this work. Experiments were carried out at different temperatures ranged of 25–600°C and different superficial gas velocities in the range of 0.17–0.78 m/s with sand particles. The time‐position trajectory of particles was obtained by the radioactive particle tracking technique at elevated temperature. These data were used for determination of some hydrodynamic parameters (mean velocity of upward and downward‐moving particles, jump frequency, cycle frequency, and axial/radial diffusivities) which are representative to solids mixing through the bed. It was shown that solids mixing and diffusivity of particles increases by increasing temperature up to around 300°C. However, these parameters decrease by further increasing the temperature to higher than 300°C. This could be attributed to the properties of bubble and emulsion phases. Results of this study indicated that the bubbles grow up to a maximum diameter by increasing the temperature up to 300°C, after which the bubbles become smaller. The results showed that due to the wall effect, there is no significant change in the mean velocity of downward‐moving clusters. In order to explain these trends, surface tension of emulsion between the rising bubble and the emulsion phase was introduced and evaluated in the bubbling fluidized bed. The results showed that surface tension between bubble and emulsion is increased by increasing temperature up to 300°C, however, after that it acts in oppositely.

Shannon entropy for local and global description of mixing by Lagrangian particle tracking

If 100 dice cannot be cast simultaneously, one single die can be cast 100 times. On the basis of this simple principle, the experimental technique of positron emission particle tracking has been used to develop and implement a new methodology for quantifying the local and global mixing characteristics within a mechanically agitated fluid batch system. This Lagrangian technique uses a single positron-emitting particle as flow follower. Using a high data acquisition rate, such a tracer is continuously tracked in 3D space and time to accurately determine its trajectory over a considerable period of time. By partitioning its long trajectory, the single particle tracer can be regarded as thousands of simultaneously tracked particles which are instantaneously, locally and non-invasively injected in the mixing system at varying feed positions. A large amount of PEPT data were collected for impeller rotational speeds ranging from 100 to 500 rpm which allowed new statistical tools derived from information theory, such as Shannon entropy and uncertainty, to be implemented in the data analysis. Thus, measurements of entropy mixing indices were obtained as a function of position, time and impeller speed. The method also allowed the determination of characteristic time parameters including the macroscale mixing time which agreed very well with correlations of the dimensionless mixing time available in the mixing literature. Detailed local information is provided on minimum mixing time positions for feed and withdrawal of material, which can be used to optimise the design or operation of stirred batch mixing systems.

상판이 없는 직사각형 단면의 미세채널에서 모세관 유동 분석

초록:소형분석시스템에서미세채널의상판이제거되면상판에의한빛에너지손실이대폭감소되어광학측정법으로대상을분석할때장점을갖는다. 본연구에서는상판이없는사각단면미세채널내액체유동을이해하려는목적으로실험과전산유체역학해석을수행하였다. 개방형사각단면미세채널에서입자추적기법으로유속을측정하였고, 채널의단면적변화에따른모세관유동현상을이론적으로해석하였다. 단면의너비와높이가각각20 μm로제작된미세채널의주입부에물을떨어뜨렸을때물은오직모세관힘에의해미세채널을따라이동하였다. 액체의젖음현상에영향을미치는중요한유동파라미터는채널의크기와표면장력, 점성등으로볼수있으며, 미세채널에서액체유동을조절하는데이용될수있다.Abstract: Our study aims to understand the flow of liquid in an open-top rectangular microchannel that canbe used in micro total analysis systems (μ-TAS) because it has advantages in terms of light transmission andenergy efficiency. We measured the liquid velocity using particle tracking technique and conducted asimulation with computational fluid dynamics by altering the area of channel cross section and channel lengthfor the capillary-driven flow in the open-top rectangular microchannel. When liquid water drops to anentrance of the fabricated microchannel with a height of 20 μm and a width of 20 μm, it flows along themicrochannel by only capillary force. In the wetting behavior of the liquid, important parameters of this floware channel size, contact angle and liquid properties such as surface tension and viscosity, which are used tocontrol the flow of liquid in the microchannel.

Applications of Holography in Fluid Mechanics and Particle Dynamics

The quantification of three-dimensional (3D) flow structures and particle dynamics is crucial for unveiling complex interactions in turbulent flows. This review summarizes recent advances in volumetric particle detection and 3D flow velocimetry involving holography. We introduce the fundamental principle of holography and discuss the debilitating depth-of-focus problem, along with methods that have been implemented to circumvent it. The focus of this review is on recent advances in the development of in-line digital holography in general, and digital holographic microscopy in particular. A mathematical background for the numerical reconstruction of digital holograms is followed by a summary of recently introduced 3D particle tracking and velocity measurement techniques. The review concludes with sample applications, including 3D velocity measurements that fully resolve the flow in the inner part of a turbulent boundary layer, the diffusion of oil droplets in high–Reynolds number turbulence, and predator-prey interactions among swimming microorganisms in dense suspensions, as well as oceanic and atmospheric field experiments.

Hyperspectral Line Scanning Microscopy for High-Speed Multicolor Quantum Dot Tracking

One of the fundamental goals in observing protein-protein interactions on the cell membrane is achieving nanometer scale spatial resolution along with temporal resolution sufficient to study live cell behavior. Traditional fluorescence microscopy methods have been unsuccessful in studying these interactions due to the diffraction limit with visible light. Single particle tracking techniques using quantum dots have provided single particle localizations to well below the diffraction limit, however, clustering of multiple particles limits the unique identification and thus tracking of individual particles throughout the (possibly dynamic) clustering process. This problem can be solved by tracking multiple quantum dot colors using a high-speed hyperspectral microscope.We have developed a high-speed hyperspectral microscope based on a line scanning design that is capable of up to 30 frames/sec with 128 spectral channels per pixel (ranging from 500-800 nm) with a sample area of ∼30 υm2. We describe the details of the microscope optical design details and layout, and show the results of excitation and emission path characterization. We image RBL-2H3 cells with IgE that has been conjugated with various colors of QDs (to give a near 1:1 QD:IgE ratio) and image at 30 frames per second. By imaging in both the presence and absence of crosslinking DNP-BSA, we demonstrate the ability to identify dynamic interactions and/or oligomers at spatial scales below the diffraction limit.

PEPT measurements of solid–liquid flow field and spatial phase distribution in concentrated monodisperse stirred suspensions

The technique of positron emission particle tracking (PEPT) has been used to determine the two-phase flow field and spatial phase distribution in a stirred vessel containing coarse glass particles suspended in water. The Lagrangian flow data provided by PEPT have been converted to give a detailed Eulerian description of the two-phase flow generated by a pitched blade turbine (PBT) operating in up-pumping or down-pumping mode. For the first time, it has been possible to determine the full 3D velocity and concentration fields of both the liquid and the solid phase within an opaque dense slurry of this type containing up to 40 wt% solids. The detailed PEPT measurements have also enabled the solids mass balance and the mass continuity of the two phases to be accurately verified throughout the vessel. The data show that the pumping effectiveness of the PBT is unaffected at moderate solid fractions, but is considerably reduced at high fractions and even more so in the up-pumping mode. A uniformity index based on the variance of the local solids concentration in the vessel shows that, overall, a down-pumping PBT achieves a significantly better homogeneity than an up-pumping PBT.

Evaluation of different disinfection calculation methods using CFD

Computational Fluid Dynamics combined with a particle tracking technique provides valuable information concerning residence times and contact times in chemical reactors. In drinking water treatment, for example an accurate estimation of the disinfection is important to predict the microbial safety. Ozone contactors are widely used for disinfection, but the complex geometry of the system causes suboptimal hydraulics and requires optimizations of the flow. This results in a lower ozone dosage, which may reduce the formation of unwanted disinfection-by-products and the consumption of energy. To that end disinfection needs to be calculated precisely, accounting for the complex hydraulics. Several calculation methods estimating the disinfection performance of ozone contactors were evaluated using Computational Fluid Dynamics. For an accurate disinfection prediction, the full distribution of ozone exposures (CT values) is needed, only a mean CT value or residence time distribution provides insufficient information for an accurate disinfection prediction. Adjustments to the geometry of the ozone contactor that reduce the short-circuit flows resulted in an increase in disinfection capacity, whereas the mean CT value remained the same. A sensitivity analysis with respect to the kinetics was conducted. The gain in disinfection capacity obtained by optimizing the hydraulics was significant for typical values used in practice.

Particles-Vortex Interactions and Flow Visualization in 4He

Recent experiments have demonstrated a remarkable progress in implementing and use of the Particle Image Velocimetry (PIV) and particle tracking techniques for the study of turbulence in He4. However, an interpretation of the experimental data in the superfluid phase requires understanding how the motion of tracer particles is affected by the two components, the viscous normal fluid and the inviscid superfluid. Of a particular importance is the problem of particle interactions with quantized vortex lines which may not only strongly affect the particle motion, but, under certain conditions, may even trap particles on quantized vortex cores. The article reviews recent theoretical, numerical, and experimental results in this rapidly developing area of research, putting critically together recent results, and solving apparent inconsistencies. Also discussed is a closely related technique of detection of quantized vortices negative ion bubbles in He4.

Spatial Phase-Shifting Digital Holography for Three-Dimensional Particle Tracking Velocimetry

This paper presents a holographic technique for three-dimensional particle tracking. The complex amplitude on an image sensor is measured with two pairs of spatially phase-shifted digital holograms captured in a short time interval using a phase-shifting technique. Pairs of digital holograms are used to track small tracer particles in three-dimensional space and the phase-adjusted complex amplitude is employed in numerical image reconstruction to accurately detect the particles. The performance of the method is evaluated by numerical simulation. In order to demonstrate the feasibility of the method for real flow measurement, it is applied to the velocity measurement of tracer particles in a small water channel along which a high voltage is applied. The resulting components of the velocity vector in three-dimensional space are compared to those obtained using a conventional single-shot phase-shifting technique.