Particle Tracking Velocimeter Research Articles

Magnetic characterization of paramagnetic reagents by particle tracking velocimetry.

Magnetic particle characterization determines the quality of magnetic particles and is of great importance in particle technology, drug delivery, cell separation, in vivo diagnostics, and other biomedical applications. The quality of the sample depends on the particle size, intrinsic magnetic properties of the particles, and the uniformity of these properties. A commercial particle tracking velocimeter was used to record and capture dark field images of particle trajectories in an applied isodynamic magnetic field. The calibrated particle size, magnetophoretic mobility, and additional image data were collected for each magnetic bead imaged. Using twenty-one different de-identified calibration beads and transmission electron microscopy to validate the vendor-reported particle size enabled the estimation of intrinsic magnetic properties, namely, apparent magnetic susceptibility and saturation magnetization, of individual paramagnetic particles. The distributions of volume magnetic susceptibility based on the magnetophoretic mobility and size of the particle for different magnetic beads were determined and displayed as two-parameter distributions. The measured apparent susceptibility and saturation magnetization were found to be directly proportional to the percentage of iron oxide in the reagent particles.

Nanomaterial Endocytosis: Estimation of Particles Per Cell by Magnetic Measurement

We investigated the uptake of superparamagnetic iron oxide nanoparticles (SPIONs) by mammalian cells in monolayer culture by exposing Chinese hamster ovary cells, line CHO-K1 which is frequently used in industrial applications, to Chemicell FluidMagD nanoparticles with diameters of 105 and 150 nm and surface coatings of starch and aminated starch, respectively. The number of particles ingested per cell was determined by measuring the magnetophoretic mobility distributions of treated and untreated cell populations using a Hyperflux magnetic particle tracking velocimeter. Increases in cell volume were evaluated on the basis of cell size data from the Hyperflux velocimeter and used to calculate particles per cell. Starch-coated and positively charged SPIONs were taken up effectively at several concentrations, and these led to quantifiable magnetophoretic mobility and cell volume increases, which, if due to particles only, correspond to several hundred thousand to over one million SPIONs per cell at high SPION feed concentrations. These conclusions are consistent with independent bulk measurements of iron content. Magnetophoretic mobility measurement is a facile and more robust method for measuring SPION uptake.

The influence of inertia and elastic retraction on flow-induced crystallization of isotactic polypropylene

The influence of nonquiescent relaxation of isotactic polypropylene on flow-induced crystallization (FIC) is investigated by a combination of particle tracking velocimeter (PTV) with a cone-plate shearing geometry and synchrotron radiation microbeam wide-angle X-ray diffraction (SR-μWAXD), which is aimed to correlate real flow profile and distribution of crystal orientation. With PTV technique, we observed that flow remains homogeneous during shear, while postshear movement and delayed fracture take place after a step strain when large shear rates and strains were imposed. Delayed fracture slices samples into several layers which move either forward or backward after the cessation of shear imposed externally. SR-μWAXD measurements reveal that the layers moving forward keep high crystal orientations while the layers moving backward show low orientations, which gives an inhomogeneous distribution of crystal orientation across the thickness of sheared samples. The correlation between moving direction and cry...

Application of magnetic particle tracking velocimetry to quadrupole magnetic sorting of porcine pancreatic islets

Magnetic isolation is a promising method for separating and concentrating pancreatic islets of Langerhans for transplantation in Type 1 diabetes patients. We are developing a continuous magnetic islet sorter to overcome the restrictions of current purification methods that result in limited yield and viability. In Quadrupole Magnetic Sorting (QMS) islets are magnetized by infusing superparamagnetic microbeads into islets' vasculature via arteries that serve the pancreas. The performance of the islet sorter depends on the resulting speed of the islets in an applied magnetic field, a property known as magnetophoretic mobility. Essential to the design and successful operation of the QMS is a method to measure the magnetophoretic mobilities of magnetically infused islets. We have adapted a Magnetic Particle Tracking Velocimeter (MPTV) to measure the magnetophoretic mobility of particles up to 1,000 µm in diameter. Velocity measurements are performed in a well-characterized uniform magnetic energy gradient using video imaging followed by analysis of the video images with a computer algorithm that produces a histogram of absolute mobilities. MPTV was validated using magnetic agarose beads serving as islet surrogates and subjecting them to QMS. Mobility distributions of labeled porcine islets indicated that magnetized islets have sufficient mobility to be captured by the proposed sorting method, with this result confirmed in test isolations of magnetized islets.

Particle capture by turbulent recirculation zones measured using long-time Lagrangian particle tracking

We have measured the trajectories of particles into, and around, the recirculation zone formed in water flowing through a sudden pipe expansion with radius ratio 1:3.7, at Reynolds numbers between 5,960 and 41,700 over a range of particle Stokes number (here defined as $$ St = {\frac{{T_{\text{f}} }}{{\tau_{\text{p}} }}} $$ , where T f is an appropriate mean or turbulent timescale of the fluid flow and a particle relaxation time, τp,) between 6.2 and 51 and drift parameter between 0.3 and 2.8. The particles were thus weakly inertial but nevertheless heavy with a diameter about an order of magnitude larger than the Kolmogorov scale. Trajectories of particles, released individually into the flow, were taken in a Lagrangian framework by a three-dimensional particle tracking velocimeter using a single 25 Hz framing rate intensified CCD camera. Trajectories are quantified by the axial distribution of the locations of particle axial velocity component reversal and the probability distributions of trajectory angle and curvature. The effect of increasing the drift parameter was to reduce the tendency for particles to enter the recirculation zone. For centreline release, the proportion of particles entering the recirculation zone and acquiring a negative velocity decreased from about 80% to none and from about 66% to none, respectively, as the drift parameter increased from 0.3 to 2.8. Almost half of the particles experienced a relatively large change of direction corresponding to a radius of curvature of their trajectory comparable to, or smaller than, the radius of the downstream pipe. This was due to the interaction between these particles and eddies of this size in the downstream pipe and provides experimental evidence that particles are swept by large eddies into the recirculation zone over 1.0 < $$ Z^{*} $$ < 2.5, where $$ Z^{*} $$ is axial distance from the expansion plane normalized by the downstream pipe diameter, which was well upstream of the reattachment point at the wall ( $$ Z^{*} \approx 3. 5 $$ ). Once inside the recirculation zone, the particle motion was governed more by the drift parameter than by the Stokes number.

Flow Style Investigation and Noise Reduction of a Cross-Flow Fan with Varied Rotor-Skew-Angle Rotor

The purpose of this study was investigating the noise emission, flow-style, fan’s performance regarding to cross-fan with three different rotor-skew angle (RSA) rotors. The special flow visualization setups for both vertical and parallel investigation of smoke slice were used to overcome the blind sight of a Laser-Doppler or a particle-tracking velocimeter, and the three-dimensional flow differences were confirmed with streamline images. The experimental results indicated that RSA-5, which is a rotor with a nearly a pitch skew within blade’s two end shrouds, has a lower sound emission and little pressure drops relative to that of no skew angle case, RSA-0. RSA-10, two pitches twisting case, also has a better acoustics quietness than that of RSA-0, but it excited undesired noise in a high frequency components around 2-4kHz. In this work, for a compromise between flow and acoustics performances, RSA-5 shows the most suitable design for cross-flow fan rotor.

Effects of tumble and swirl flows on turbulence scale near top dead centre in a four-valve spark ignition engine

The in-cylinder flowfield and the turbulence scale at the ignition timing play an important role in enhancing the propagation speed of the initial flame and the engine combustion. The aim of this work is to investigate the effect of tumble and swirl flows on the turbulence scale near the top dead centre in a four-valve spark ignition (SI) engine by an experimental method. In this study, various flowfields such as tumble and swirl flows were generated by intake flow control valves. For investigation of the flowfields, the single-frame particle tracking velocimeter (PTV) and the twocolour particle image velocimeter (PIV) techniques were developed to clarify the in-cylinder flow pattern during the intake stroke and the turbulence intensity near the spark plug during the compression stroke respectively. In addition, the flame propagation was visualized by an ICCD camera, and its images were analysed to compare the flowfields. From these experimental results, the effects of tumble and swirl flows on the turbulence scale and the flame propagation speed were clarified.

Turbulent Air Flow Measurement with the Aid of 3- D Particle Tracking Velocimetry in a Curved Square Bend.

A three-dimensional particle tracking velocimeter (3-D PTV) was applied to air-flow measurement in a strongly curved U-bend of a square cross-section. He-filled neutral-buoyant soap bubbles were employed as a flow tracer, and turbulent statistics including all Reynolds stress components were measured. The pressure-induced secondary flow, of which magnitude reached about 30% of the bulk mean velocity, was observed. The present experimental result is mostly in good agreement with the LDA data at higher bulk-mean Reynolds number taken by Chang et al. The effect of the secondary flow on the production mechanism of turbulent kinetic energy as well as on the distributions of the invariants of stress anisotropy tensor was examined in detail.

Turbulent Air Flow Measurement with the Aid of Three-Dimensional Particle Tracking Velocimetry in a Curved Square Duct.

A three-dimensional particle tracking velocimeter (3-D PTV) was successfully applied to turbulent air flow measurement in a strongly curved U-bend of square cross-section. He-filled bubbles, of which specific density was very close to that of air were employed as a flow tracer. Distributions of the mean velocities and Reynolds stresses were obtained at 90°downstream of the inlet to the curved section. The secondary flow as strong as 20% of the bulk mean velocity is observed in the cross-stream plane ; it results in a marked trough in the streamwise velocity at a distance of about 0.3 times the channel height from the inner wall. The present experimental result is mostly in good agreement with the LDV data of Chang et al. (1983). Moreover, turbulent statistics including all Reynolds stress components are obtained. The production mechanism of turbulent kinetic energy as well as the distributions of invariants for stress anisotropy tensor are discussed in detail.

Flow visualization and pressure characteristics of a cylinder for water impact

This study examines the water impact of a cylinder by using a modern digital imaging system and a high speed data acquisition system to measure simultaneously the impact pressure motion and flow field. The measurement system can be triggered by an external optic sensor; real-time display of flow field information and pressure variation can be obtained in each time step. The scaling effects of model and pressure gage that Takemoto [J. Soc. Naval Arch. 156 (184) 314] observed are also considered, along with a comparison of experimental and theoretical pressures. Moreover, the flow characteristics are observed via a flow following ‘seeding’ particles and the digital particle tracking velocimeter, thereby allowing that the flow field velocity distribution to be measured.

Simultaneous measurements of water impact on a two-dimensional body

This study utilizes a high-speed charge coupled device (CCD) camera as the data acquisition system to simultaneously measure the pressure and flow field. The measurement system can be triggered by an external optical sensor, to obtain the free surface and pressure variations in each time step of the initial stage of water impact. The whole field image was observed by a high-speed area scan sensor camera. Almost no interval between photographing moving objects was allowed owing to the extremely short transfer time and high exposure sensitivity of the camera. Following image transfer, this characteristic and the hardware computational function of a video card not only allowed for binarization, accumulative addition but we could also quickly identify the track of a moving object and obtain the image and numerical data which we needed. Moreover, the flow characteristics are observed via a flow following “seeding” particles, and the digital particle tracking velocimeter (DPTV) so that the flow field velocity distribution can be measured.

Three-dimensional particle-tracking velocimetry measurement of turbulence statistics and energy budget in a backward-facing step flow

Using a three-dimensional (3-D) particle-tracking velocimeter, detailed turbulent flow measurements were made in a plane channel with a one-sided 50% abrupt expansion, which acted as a backward-facing step. The turbulent channel flow reached a fully developed state well upstream of the step. The Reynolds number based on the upstream centerline velocity and the step height H was 5540. With the mean reattachment point located at 6.51 H downstream of the step, the measurement region ranged from −2 H upstream to 12 H downstream of the step. Various turbulent statistics and the energy budget were calculated from numerous instantaneous vector distributions. As in previous experimental investigations, the Reynolds normal and shear stresses had maximum values upstream of the reattachment. The stress anisotropy tensor revealed a peculiar phenomenon near the reattachment wall, wherein the spanwise normal stress was the largest among the three normal stresses. The triple velocity correlations indicated large values in the separating shear layer, and hence the turbulent diffusion was a major term in the energy budget. Comparison was made between the present results and those of the direct numerical simulation (DNS) of Le et al. (1993), and it was found that the mean and fluctuating velocities, the Reynolds shear stress, and the turbulent energy budget were in excellent agreement, although there was a considerable difference in the inflow conditions.

三次元画像処理流速計による複雑形状流路内流れの測定

The three-dimensional particle tracking velocimeter (3-D PTV) is a powerful tool for measuring the instantaneous three-dimensional distributions of the velocity vectors. Despite of its significant ability, it can be applied only to the flow field in a simple geometry, because of its complex camera calibration procedure. Although there have been made some modifications that handle the refraction at the glass walls implicitly in the camera parameters, but their applications are still limited to the case of parallel planes. Presently, a new method is proposed that calculates all the refractions at any surface explicitly. Thus, one can avoid the complexity in the camera calibration and can measure any flow field in the complex geometry, if the shape of which is known by the numerics. The principle of the new camera calibration technique and the procedures for the practical measurement in a circular curved pipe is shown in this study.

2 三次元画像処理流速計による複雑形状流路内流れの測定

The three-dimensional particle tracking velocimeter (3-D PTV) is a powerful tool for measuring the instantaneous three-dimensional distributions of the velocity vectors. Despite of its significant ability, it can be applied only to the flow field in a simple geometory, because of its complex camera calibration procedure. Although there have been made some modifications that handle the refraction at the glass walls implicitly in the camera parameters, but their applications are still limited to the case of parallel planes. Presently, a new method is proposed that calculates all the refractions at any surface explicitly. Thus, one can avoid the complexity in the camera calibration and can measure any flow field in the complex geometry, if the shape of which is known by the numerics. The principle of the new camera calibration technique and the procedures for the practical mesurement in a circular curved pipe is shown in this study.

Turbulent Air Flow Measurement Using Three-Dimensional Particle Tracking Velocimetry.

A three-dimensional particle tracking velocimeter for turbulent air flow measurement was developed. As a tracer particle, spherical plastic capsules and He-filled bubbles were tested. The plastic capsule's traceability was anticipated to be insufficient for high-frequency components of turbulence because its density was thirty times larger than that of air, its diameter was small enough compared with the turbulent microscale, and the image was clear enough to track. On the other hand, the bubble, which was neutrally buoyant, had a relatively large diameter and its image had two peaks in brightness. The previous 3-D PTV system was modified so that two successive instantaneous particle images could be recorded on two successive TV fields with an arbitrary time interval. In order to evaluate the present technique, a fully developed turbulent air flow in a square-cross-section duct was measured. Cross-stream distributions of the mean velocities and of the full Reynolds stress tensor components were obtained and some of them were compared with a separate hot-wire measurement. The agreement was generally good for both tracers. However, part of the plastic particles adhered to the bottom wall of the duct and caused serious errors in the measurement.

Budgets of the Reynolds Stresses in an Axisymmetric Free Jet.

In the previous study an axisymmetric free jet was measured with the aid of a three-dimensional particle tracking velocimeter, and a database of the turbulent statistics was constructed. In this study, by using the database, the budgets of the turbulent kinetic energy and the Reynolds normal and shear stresses are calculated. The dissipation term of the turbulent kinetic energy is estimated as a residual of its budget neglecting the pressure diffusion term. The pressure terms in the budgets of the Reynolds stresses are also obtained as closing terms of each budget equation in which the dissipation term is calculated with an assumption of local isotropy. The mechanism of energy exchange among the stresses is revealed, i.e., the mean flow energy is first fed to the streamwise normal stress through the Reynolds shear stress and then redistributed to the radial and azimuthal normal stresses via the pressure term. The production terms in the budgets of the radial and azimuthal stresses are found to be negative around the flow axis.

Turbulence measurement in a separated and reattaching flow over a backward-facing step with the aid of three-dimensional particle tracking velocimetry

With a three-dimensional particle tracking velocimeter, detailed turbulent flow measurement was made in a plane channel with a one-sided 50% abrupt expansion, which acted as a backward-facing step. The plane channel flow reached a fully developed state well upstream of the step. The Reynolds number based on the center-line velocity, U c, and the step height, H, was about 5540. The measurement region ranged from −2H upstream to 12H downstream of the step, and it was divided into about 300 × 120 sub-regions when the turbulence statistics were calculated. The mean reattachment position, where the forward flow fraction near the wall equaled to 0.5, was found to be located at 6.51H downstream of the step. All the distributions of mean and fluctuating velocities well demonstrated characteristics of the separated flow. As in the previous experimental investigations, the Reynolds normal and shear stresses had the maximum values upstream of the reattachment. The anisotropy tensor, which was calculated from the Reynolds stress tensor, revealed a peculiar phenomenon near the reattachment point that, even without any direct production mechanism, the spanwise normal stress was the largest among the three normal stresses. The ratio between the Reynolds shear stress and the turbulent kinetic energy showed considerably large values in the free shear layer downstream of the step shoulder.

Turbulence measurement in a separated and reattaching flow over a backward-facing step with the aid of three-dimensional particle tracking velocimetry

With a three-dimensional particle tracking velocimeter, detailed turbulent flow measurement was made in a plane channel with a one-sided 50% abrupt expansion, which acted as a backward-facing step. The plane channel flow reached a fully developed state well upstream of the step. The Reynolds number based on the center-line velocity, U c , and the step height, H, was about 5540. The measurement region ranged from −2H upstream to 12H downstream of the step, and it was divided into about 300 × 120 sub-regions when the turbulence statistics were calculated. The mean reattachment position, where the forward flow fraction near the wall equaled to 0.5, was found to be located at 6.51H downstream of the step. All the distributions of mean and fluctuating velocities well demonstrated characteristics of the separated flow. As in the previous experimental investigations, the Reynolds normal and shear stresses had the maximum values upstream of the reattachment. The anisotropy tensor, which was calculated from the Reynolds stress tensor, revealed a peculiar phenomenon near the reattachment point that, even without any direct production mechanism, the spanwise normal stress was the largest among the three normal stresses. The ratio between the Reynolds shear stress and the turbulent kinetic energy showed considerably large values in the free shear layer downstream of the step shoulder.

Turbulence Statistics in the Self-Preserving Region of an Axisymmetric Free Jet.

Turbulence measurement was carried out in the self-preserving region of an axisymmetric free jet with the aid of the three-dimensional particle tracking velocimeter. Approximately 420 instantaneous velocity vectors on average were acquired from each of 126000 TV fields. The self-similarity and axisymmetry of turbulence statistics distributions are confirmed. The power-law requirements are fulfilled for the streamwise evolutions of the mean centerline velocity and the velocity half width. Detailed radial distributions of the turbulent statistics are obtained, which include mean velocities and all the one-point velocity correlations up to the fourth-order. Skewness and flatness factors of velocity fluctuations and the invariants of the Reynolds stress anisotropy tensor are also calculated. The mean radial velocity agrees with that calculated from the continuity equation and the mean streamwise velocity. The Reynolds shear stress is also in good agreement with that estimated from the momentum equation. These results demonstrate the accuracy and consistency of the present data.

A color-coded particle tracking velocimeter with application to natural convection

This paper introduces a novel concept of the image-processing technique to visualize a two-dimensional flow field and to generate streaks with embedded time marks in real time. Grey levels of a pixel are used in this work to encode the temporal information rather than the intensity of particle trajectories used in conventional image-processing systems. To do this, the incoming video image is first binarized by a step function predefined in an input look-up table, with the height of the step varying with time to bear temporal marks. A real-time arithmetic-logic unit and an image-frame buffer are used to accumulate the images. These processes result in continuous streaks with embedded time marks which have many advantages over those recorded by conventional techniques. Pseudo-color output look-up tables and color monitor provide more direct and intuitive means for human visual perception. This color-coded particle tracking velocimetry was applied to investigate natural convection in an enclosure heated from below with an isothermal extrusion. By quantifying the color-coded streaks, velocity vectors were obtained at a discrete number of points with less labor. The present technique provides an elaborate tool for simultaneous qualitative and quantitative realizations of steady and slowly varying flow fields.