Particle Tracking Velocimetry Method Research Articles

Integrated monitoring method of flood free surface and surface velocity in a laboratory compound channel

River flooding can pose a significant threat to people's lives and properties on the floodplain. Due to the difficulty and potential danger of monitoring field river floods, laboratory experiments have become the main and key method for exploring flood propagation and evaluating potential flood risks. However, the complex three-dimensional flow state of floods in the compound channel makes current measurement techniques inadequate for meeting monitoring requirements. To this end, a new technique is developed in this study that can simultaneously monitor the flood free surface and the surface velocity in the laboratory compound channel. The developed measurement technique combines stereoscopy and the particle tracking velocimetry (PTV) method through the pixel coordinate fitting method, so that the coordinates of the tracer particles can be reconstructed in the three-dimensional state. This method can not only increase the basic data in the free surface construction but can also capture the complex three-dimensional flood flow behavior. The proposed technology was applied to measure the free surface of flood propagation in a laboratory compound channel. Water level, flow velocity, wave velocity, and wave height were simultaneously measured. The measurement accuracy was verified using wave probes, spatial planes, and fringe projection techniques. The results indicate that the water level measurement error is approximately 1.6 mm, and the flow velocity measurement error is around 3 %. The developed measurement system is simpler than previous methods based on light reflection or absorption. Most importantly, it can simultaneously measure both the flood free surface and surface velocity by only sowing tracer particles on the water surface. The current measurement technology offers a new tool for studying flood propagation in a laboratory compound channel.

Analysis of particle dispersion and cavity formation during bulk particle water entry using fully coupled CFD-DEM-VOF approach

This paper presents the development and validation of a fully coupled computational fluid dynamics—discrete element method—volume of fluid (CFD-DEM-VOF) model to simulate the complex behavior of particle-laden flows with free surfaces. The coupling between the fluid and particle phases is established through the implemented continuity, momentum, and alpha transport equation. The coupled particle forces such as drag, pressure gradient, dense virtual mass, viscous, and interface forces are also integrated, with drag and dense virtual mass forces being dependent on local porosity. The integrated conservative alpha transport equation ensures phase volume conservation during interactions between particles and water. Additionally, we have implemented a trilinear interpolation method designed to operate on unstructured hexahedral meshes. This method has been tested for its ability to properly resolve the coupling effects in the numerical simulations, particularly in cases with a relatively low cell-size ratio. The model is validated through three distinct test cases: single particle water entry, dam break with particles, and water entry of a group of particles case. The experimental setup is built to study the dynamics of the water entry of a group of particles, where three key flow features are analyzed: the evolution of average particle velocity, cavity shape, and particle dispersion cloud profiles in water. The tests involve four different scenarios, including two different water levels (16.1 and 20.1 cm) and two different particle densities (2650 and 4000 kg/m3). High-speed videometry and particle tracking velocimetry (using ImageJ/TrackMate) methods are employed for experimental data acquisition. It is demonstrated that numerical results are in excellent agreement with theoretical predictions and experimental data. The study highlights the significance of vortices in cavity shaping and particle dispersion. The validated CFD-DEM-VOF model constitutes a robust tool for simulating particle-laden flows, contributing valuable insights into the complex interplay between particles and fluids.

Intensifying the particle deposition from a colloidal solution for the purpose of liquid purification: Comparison of deposition mechanisms and rates

The deposition of particles from a layer of colloidal solution (water and microparticles) has been experimentally studied in the presence of laser heating. Instantaneous temperature and velocity fields are measured using a thermal imager and the Particle Image Velocimetry and the Particle Tracking Velocimetry methods. The unstable behavior of the velocity field in the presence of heating and a free liquid surface are assumed to be determined by the Bond number (Bo). Of interest is also an additional mechanism for the instability formation when the Peclet number (Pe) exceeds the critical value and when the ratio of characteristic velocities VT/Vavr > 1, where VT is the heat front velocity at the initial moment of laser heating, and Vavr is the average convection velocity. A new mechanism of particle deposition due to the use of local laser heating is proposed for the first time. The control over local heating and local deposition increases the particle deposition rate by 2–3 orders compared with that without convection. The particle deposition rate and the deposit area increase with increasing height of the liquid layer, reach maximum values at a critical height, and then decrease sharply with increasing height. The dependence for determining the area and mass of the deposit is proposed to take into account the deposition time, the height of the liquid layer and the rate of convection. The resulting particle deposition method and calculation method may be used in technologies related to the purification of liquid from solid impurities in small volumes, as well as in problems where deposition in a given direction is required to form an ordered nanocoating.

Hydrate dissociation and mechanical properties of hydrate-bearing sediments under local thermal stimulation conditions

Considering the interaction between hydrate dissociation and the mechanical properties of hydrate-bearing sediment (HBS) facilitates a deep understanding of the relationship between hydrate extraction efficiency and reservoir stability during hydrate exploitation. In this study, a series of tests were carried out to study the effects of hydrate dissociation under local thermal stimulation and the mechanical properties of HBS by using the plane strain shear test apparatus. The characteristics of the local maximum shear strain and volumetric strain were also investigated using the particle tracking velocimetry (PTV) method. The results show that the tested water-saturated host sands have the same heat transfer characteristics under local thermal stimulation, despite having different particle size distributions and mineral compositions. The temperature transfer inside the HBS was slower than that of the host sand sample, and the temperature distribution of the HBS after hydrate dissociation was the same as that of the host sand sample. HBS under an axial loading force higher than that of the peak strength of the host sand would fail after hydrate dissociation. Additionally, even partial dissociation of the hydrate can lead to catastrophic failure of HBS under this condition.

Time-resolved particle-scale dynamics of a particle-laden jet

Particle-laden jet flow is important to both jet-related industry applications and transmission of the virus through violent expiratory events, such as coughing and sneezing. To help understand its dynamics from the particle level, we develop a time-resolved, three-dimensional (3D), particle tracking velocimetry method, coupled with particle image velocimetry measurement of gas flow, and perform experiments on a dilute particle-laden gas jet. The spatial distributions of velocity and fluctuating velocity of the gas and particles are obtained. It is found that the presence of particles significantly changes the gas turbulence and stretch the gas flow field to the downstream. The probability density function of axial particle velocity shows non-Gaussian distribution and deviates much from those of the spanwise velocities, indicating strong non-equilibrium and anisotropic states. A new drag model is derived based on the reconstructed particle trajectories and gas flow field near the ejector exit with particle Reynolds numbers between 30 and 300. It is found in better agreement with the experimental data than the standard single-particle drag model. A simple model relating the particle volume fraction with particle displacement is developed based on the self-similarity theory of jet, showing good agreement with the experimental measurement.

Controlling factors of microplastic fibre settling through a water column.

Microplastic fibres are the most abundant microplastics in waterways worldwide. The settling of fibres is distinct from other particles because of their aspect ratio and shape. In this paper, we test the hypothesis that length, curliness, and settling orientation control the settling velocity of microplastic fibres in a suite of laboratory experiments. Using a Particle Tracking Velocimetry method, we measured the settling velocity of 683 polyester microplastic fibres of 1 to 4 mm in length. Experimental findings support our hypothesis that for microplastic fibre longer than 1 mm, changing settling orientation from horizontal to vertical can increase 1.7 times the settling velocity. Fibre curliness can significantly reduce the settling velocity, where a curly fibre 1.3 times longer than a straight fibre can settle 1.75 times slower. In contrast, short microplastic fibres (less than 1 mm) mostly settle horizontally, and their settling velocity is unaffected by curliness. The drag force exerting on settling microplastic fibres was analysed, and the sphere-equivalent diameter was found to be a good representation of microplastic fibre size to predict the drag coefficient. Measured settling velocity ranges between 0.1 and 0.55 mm/s and exhibits a slight increase with the increasing length of the fibres. This low-velocity range raises concerns that microplastic fibres can favour biological flocculation, form clustered aggregates with microorganisms, feed aquatic organisms and cause bioaccumulation at higher trophic levels.

Experimental study of liquid spreading and atomization due to jet impingement in liquid–liquid systems

Liquid spreading and atomization due to jet impingement in liquid–liquid systems is considered to be crucial for understanding cooling behavior of high temperature molten martial into shallow water pool. This phenomenon takes place where a liquid jet enters a pool filled with another immiscible liquid. The jet spreads radially after impinging on the floor while forming a thin liquid film and atomizing droplets. In this study, we employed three-dimensional Laser-Induced Fluorescence (3D-LIF) measurements and three-dimensional (3D) reconstruction to quantify its unsteady three-dimensional behavior. Under high flow velocity conditions, atomization occurred along with the spreading of the liquid film. To evaluate the spreading behavior of the liquid film, a comparison was made with the existing theory of gas–liquid systems. The spreading of the liquid film was suppressed compared with that of the gas–liquid system. Furthermore, the particle tracking velocimetry method was successfully used to measure the velocity boundary layer and velocity profile in the liquid film, which are important factors that affect the spreading mechanism of the liquid film. The results revealed that in liquid–liquid systems, shear stress at the liquid–liquid interface causes a decrease in the flow velocity and suppressed development of the velocity boundary layer. To evaluate the atomization behavior, the number and diameter distribution of the atomized droplets were measured from the acquired three-dimensional shape data of the jet. The number of droplets increased with the flow velocity. The results show that the jump radius is affected by such atomization behavior, and since the jump radius was lower than the theoretical value, we can conclude that the location of the hydraulic jump is expected to undergo an upstream transition.

Determination of best particle tracking velocimetry method for two-dimensional dusty plasmas.

A practical procedure of determining the best choice of particle tracking velocimetry (PTV) methods for the analysis of two-dimensional (2D) dusty plasmas is provided. Using the measured particle positions with errors, the algorithm of PTV introduces further systematic errors while calculating particle velocities. To better quantify the errors, computer simulations of 2D Yukawa liquids are performed so that the true particle positions and velocities are precisely known. Synthetic data are achieved by varying the time interval between frames and adding the uncertainty with the different magnitude to the particle position data. Various PTV methods are used to calculate the velocity data from the achieved synthetic data, and the obtained velocity data from these PTV methods are compared with the true velocity data using two diagnostics to determine the best PTV method for various conditions. The results of various PTV methods with the simulation data are further confirmed by the demonstration using the 2D dusty plasma experimental data. This practical procedure is also applicable to determine the best PTV method for dusty plasmas in different conditions, such as those in Tokamaks, and for other physical systems, including colloids, granular materials, and fluid mechanics.

Rim Breakups of Impacting Drops on a Superhydrophobic Surface and a Superheated Surface

The rim breakup of an impacting drop is experimentally investigated by comparing the impacts on superheated and superhydrophobic surfaces. The objective of the present study is to experimentally examine whether the Bo = 1 criteria holds for the rim breakups of drops impacting on the surfaces. A transparent sapphire plate was heated to achieve the Leidenfrost impact, which enables us to observe with a high-speed camera from below. The characteristics of the rim breakup were evaluated quantitatively using a particle tracking velocimetry method for both the rim and the drops generated. As a result, we clarified that Bo of the rim increases in the spreading phase and marks the highest value of 0.5 on a superheated surface, which is smaller than that on a pillar, where Bo ≈ 1. On a superhydrophobic surface, the highest Bo was 1.2, which is smaller than that on a wettable solid surface, 2.5, but close to the value on a pillar. We also revealed that diameters of generated drops collapse on a master curve when plotted as a function of pinch-off time for both the impacts on superheated and superhydrophobic surfaces.

Rapid change of particle velocity due to volatile gas release during biomass devolatilization

Our earlier study showed significant differences in average particle velocity between simulation and experimental results for devolatilizing biomass particles in an idealised entrained flow reactor [N. Guo et al., Fuel, 2020]. This indicates that the simulations do not accurately describe the physicochemical transformations and fluid dynamic processes during devolatilization. This article investigates the reasons for these discrepancies using time-resolved analyses of the experimental data and complementary modelling work. The experiments were conducted in a downdraft drop-tube furnace with optical access, which uses a fuel-rich flat flame (CH4O2CO2) to heat the particles. Gas flow was characterized using particle image velocimetry, equilibrium calculations and thermocouple measurements. High-speed images of devolatilizing Norway spruce (Picea Abies) particles were captured and analysed using time-resolved particle tracking velocimetry methods. The data were used to estimate the balance of forces and fuel conversion. Thrust and “rocket-like” motions were frequently observed, followed by quick entrainment in the gas flow. Rocketing particles were, on average, smaller, more spherical and converted faster than their non-rocketing counterparts. These differences in conversion behaviour could be captured by a particle-size dependent, 0-D devolatilization model, corrected for non-isothermal effects. The results from this investigation can provide a basis for future modelling and simulation work relevant for pulverized firing technologies.

Probabilistic description of coarse particle motion above threshold by particle tracking velocimetry method in an experimental study

Sediment motion behavior plays an important role in the sediment and hydraulic engineering, though its physics is still not fully understood. Ignoring the stochastic nature of the sediment transport leads to various equations for bedload transport which are now being challenged due to their results. In this study, the non-suspended particle motion (bedload transport) in different hydraulic conditions was assessed by a particle tracking technique called the Particle Tracking Velocimetry (PTV). The results of the PTV were applied to describe the particle behavior throughout the probability distribution functions. Knowing the particle motion behavior would be a guidance to learn more about the parameter/s governing the particle transport in different sediment transport regimes. After calibrating and validating the frames (resulted from the PTV), the instantaneous particle velocity was measured. Different probability distribution functions were assessed with Kolmogorov-Smirnov criterion to find the best function which fits the collected data (i.e. the particle velocity). It was shown that the probability distribution function is Log-Normal for lower particle Reynolds number and on the other hand, in the higher particle Reynolds number, the Normal distribution is best describing the particle velocity. The results of this research also could be applied in similar hydraulic conditions in eco-hydraulic field, specifically macro-plastic movement as bedload in river courses.

Development of multi-cycle rainbow particle tracking velocimetry improved by particle defocusing technique and an example of its application on twisted Savonius turbine

Rainbow particle tracking velocimetry (PTV) is a PTV method that enables three-dimensional (3D) three-component flow measurement using a single camera. Despite the advantage of its simple setup, the accuracy of the particle depth is restricted due to false color caused by image sensor arrays, such as Bayer arrangement. Since the false color occurs near sharp edges in the color gradient of in-focus individual particle images, we here introduced a defocusing technique to rainbow PTV to remove these false colors. Defocusing led to moon-shaped distorted particle images, which we applied an adaptive mask correlation technique to detect. Multi-cycle rainbow illumination was realized as an additional improvement on the defocusing technique. In particular, individual particle coordinates were obtained by a combination of the color and constitution of pixels. This dramatically increased the depth resolution of the 3D particle tracking. The feasibility of the proposed method was demonstrated by a flow driven by rotating impellers and a wake behind a twisted Savonius turbine. By the demonstration, it is confirmed that the twisted turbine suppresses the loss of kinetic energy by shedding streamwise vortices in the wake.

Settling behaviour of irregular-shaped polystyrene microplastics

Microplastics are emerging pollutants that can pose threats to aquatic ecosystems by carrying toxic additives to the food web. Their abundance has been reported in many waterways globally, including the Sai Gon River, Vietnam. A good understanding of microplastic sinking behaviours can help predict the distribution and removal of these pollutants in water. Microplastic dynamics are still mostly assumed to be similar to that of suspended sediment. However, MPs possess many artificial properties that can make them move distinctly in the water from suspended sediment like densities, structures, shapes, and surface properties. This research, therefore, aims to investigate the correlation of the polystyrene microplastic size and irregular shapes with its vertical movement. The experiments employed the Particle Tracking Velocimetry (PTV) method and an automatic image processing algorithm to simultaneously measure MP geometrical properties and settling velocity while freely settling in a still water column. We found that the circumscribed diameter is the most appropriate geometrical parameter to represent MP size. The settling velocity of irregular-shaped polystyrene microplastics in size of 0.2 to 0.9 mm is mostly between 0.5 and 2 mm/s, half of the sediment but four-fold that of biological aggregates at the same size. The settling velocity increases two-fold when MP size enlarges from 0.2 to 0.9 mm. The shape irregularity can slow down the sinking of large microplastics but do not affect the vertical movement of microplastics smaller than 0.32 mm. The ratio between microplastic projected area and the area of the smallest circumscribed circle was found to be the two-dimensional representation of three-dimensional shapes in the correlation between size and settling velocity. Therefore, the fitting curve equations suggested herein can be used as a simple tool to estimate the settling velocity of irregular-shaped polystyrene microplastics found in many in-situ sampling campaigns.

Influence of the number of flights on the dilute phase ratio in flighted rotating drums by PTV measurements and DEM simulations

Particle distribution in the cross-section of the flighted rotating drum (FRD) is critical to the analysis of heat and mass transfer between gas and solids. In this work, the particle tracking velocimetry (PTV) method is applied to study the influence of the number of flights on the particle motion in FRDs. The drum, installed with 1, 4, 8, or 12 rectangular flights, is filled with plastic balls to 15% and operated at various rotating speeds ranging from 10rpm to 30rpm. The results show that the number of flights has different effects on the holdup ratio and cascading rate of single flight and active flights. With 8 and 12 flights, the FRD produces a larger and more stable particle ratio of the dilute phase. Moreover, DEM simulations agree with PTV measurements, whereas literature models show significant deviations.

A particle tracking velocimetry method to measure size and charge distributions in tribocharged powder particles

Simultaneous charge and size of tribocharged particles suspended in a gas stream are measured using image analysis. Under the action of a homogeneous electric field, drag, and electric forces are the main factors influencing particle trajectory, from which electric charge and polarity are derived. We could check that the system operates in a laminar gas regime inside the analysis cell since high flow turbulences would alter the particle “electrical” path, thus invalidating the measurement. Single component granular materials and binary mixtures are studied, all cases showing bipolar distributions and dependence on particle size. Mixture composition affects the overall charge polarity in the dispersed powder, and this effect can not solely be attributed to the weight proportion of the components. PTV is a powerful tool in techniques used for triboelectric dry separation of organic and inorganic products since their efficiency relies much on the charge to mass ratio.

The influence of key parameters on combustion of double gas hydrate

The combustion and dissociation of the double hydrate of propane-methane have been studied in terms of several key parameters: the velocity of the forced air flow U0, heat flux, temperature difference, and geometry of the work area. Simple expressions relating the dissociation rate with the specified key parameters have been obtained. The ratio of dissociation rates J1/J2 was determined, where the dissociation rates J1 and J2 correspond to the experiment with and without combustion, respectively. At U0 = 0 m/s, the ratio J1/J2 equals 8–9, and in the presence of forced gas flow J1/J2 = 11–12. Forced convection increases this ratio. Approximate correlations have been obtained for assessing the time of combustion beginning and the duration of the gas hydrate burning. The dissociation rate is nonlinearly related to the velocity U0. Two characteristic modes of gas hydrate dissociation are distinguished. Measurements of velocity fields obtained using the Particle Tracking Velocimetry (PTV) method show that the interaction of forced and free convection flows leads to a decrease in the maximum resultant velocity. Due to fuel excess over the oxidizer (violation of stoichiometric ratio), there are periodic emissions of gas bubbles, leading to incomplete combustion of the fuel. To improve the efficiency of combustion, it is advisable to use velocities U0 = 1.2–3 m/s. A further increase in U0 leads to the extinguishing of the flame.

Modelling of urea aggregation efficiency via particle tracking velocimetry in fluidized bed granulation

This work presents a predictive model to estimate the particle size distribution (PSD) and aggregation efficiency of wet granulation of urea in top spray fluidized bed. To elucidate the model solution, the experimental granulation process of urea particles was performed. Urea particles with an average size of 250 µm, were charged and fluidized at the granulator by spraying a binder solution. Urea granule samples were withdrawn at different granulation time, and the respective particle size distributions were characterized using the sieving method. An empirical model for aggregation rate constant has been developed based on the experimental data at various operating conditions and used in population balance model to estimate the PSD. Furthermore, the model has been extended to determine aggregation efficiency using particle tracking velocimetry method (PTV). The developed model could be employed to estimate the urea granulation performance and kinetics in fluidized bed for design and scale-up purpose.

PTV measurement and DEM simulation of the particle motion in a flighted rotating drum

To investigate the particle motion in the flighted rotating drum (FRD), a laboratory drum with four rectangular flights is horizontally arranged and filled with plastic particles in this work. The FRD is operated by varying the drum rotating speed (10, 20, and 30 rpm) and filling degree (10, 15, and 20%). The particle tracking velocimetry (PTV) method and DEM simulation (with LIGGGHTS software) are applied to analyze the particle movements.The results have shown that, as the drum rotating speed is increased, the holdup ratio and cascading rate of an individual flight increase. The drum rotating speed also affects the particle ratios in three phases and the falling time distribution of the dilute phase. Moreover, the average velocities and granular temperatures of the particle system in FRD increase as the drum rotating speed increases and the filling degree decreases. Good agreements are observed between the PTV measurements and DEM simulations.

Study of Induced EHD Flow by Microplasma Vortex Generator

For flow control, plasma actuators have the advantages of no moving parts. An experimental study was carried out to generate vortexes using a microplasma actuator. Also, a 3-D numerical simulation code was developed to calculate the flow generated by the microplasma actuator. The numerical simulation used the Suzen–Huang model coupled with Navier–Stokes equations. Our microplasma actuator has a thin dielectric layer with a thickness of $25~\mu \text{m}$ between the grounded and high-voltage energized electrodes, which enables to drive our device at less than 1 kV. The high-voltage and grounded electrodes have both holes. In the series of experiments, an ac voltage with an amplitude 1 kV and a frequency of 20 kHz was applied to the electrode. The induced flow was visualized using an Nd: YVO4 532-nm laser, and the flow velocity was measured using the particle tracking velocimetry (PTV) method. Incense smoke was utilized as a tracer particle. The electrohydrodynamic (EHD) flow was induced around the holes of high-voltage electrode, thus vortexes appeared above these holes. In order to study the basic phenomena of the flow, one and four holes were isolated from the electrode; thus, the phenomena could be observed in a simplified version of the electrode. The 3-D numerical simulation code showed similar results both in values and flow configuration compared with the experimental results.

A novel particle tracking velocimetry method for complex granular flow field**Project supported by the National Natural Science Foundation of China (Grant Nos. 11572201 and 91634202).

Particle tracking velocimetry (PTV) is one of the most commonly applied granular flow velocity measurement methods. However, traditional PTV methods may have issues such as high mismatching rates and a narrow measurement range when measuring granular flows with large bulk density and high-speed contrast. In this study, a novel PTV method is introduced to solve these problems using an optical flow matching algorithm with two further processing steps. The first step involves displacement correction, which is used to solve the mismatching problem in the case of high stacking density. The other step is trajectory splicing, which is used to solve the problem of a measurement range reduction in the case of high-speed contrast The hopper flow experimental results demonstrate superior performance of this proposed method in controlling the number of mismatched particles and better measuring efficiency in comparison with the traditional PTV method.