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1.
A particle image velocimetry system for microfluidics 总被引:20,自引:0,他引:20
J. G. Santiago S. T. Wereley C. D. Meinhart D. J. Beebe R. J. Adrian 《Experiments in fluids》1998,25(4):316-319
A micron-resolution particle image velocimetry (micro-PIV) system has been developed to measure instantaneous and ensemble-averaged
flow fields in micron-scale fluidic devices. The system utilizes an epifluorescent microscope, 100–300 nm diameter seed particles,
and an intensified CCD camera to record high-resolution particle-image fields. Velocity vector fields can be measured with
spatial resolutions down to 6.9×6.9×1.5 μm. The vector fields are analyzed using a double-frame cross-correlation algorithm.
In this technique, the spatial resolution and the accuracy of the velocity measurements is limited by the diffraction limit
of the recording optics, noise in the particle image field, and the interaction of the fluid with the finite-sized seed particles.
The stochastic influence of Brownian motion plays a significant role in the accuracy of instantaneous velocity measurements.
The micro-PIV technique is applied to measure velocities in a Hele–Shaw flow around a 30 μm (major diameter) elliptical cylinder,
with a bulk velocity of approximately 50 μm s-1.
Received: 26 November 1997/Accepted: 26 February 1998 相似文献
2.
Astigmatism or wavefront deformation, microscopic particle tracking velocimetry (A-μPTV) (Chen et al. in Exp Fluids 47:849–863,
2009; Cierpka et al. in Meas Sci Technol 21:045401, 2010b) is a method to determine the complete 3D3C velocity field in micro-fluidic devices with a single camera. By using an intrinsic
calibration procedure that enables a robust and precise calibration on the basis of the measured data itself (Cierpka et al.
in Meas Sci Technol 22:015401, doi:, 2011), accurate results without errors due to spatial averaging or bias due to the depth of correlation can be obtained. This
method takes all image aberrations into account, allows for the use of the whole CCD sensor, and is easy to apply without
expert knowledge. In this paper, a comparative study is presented to assess the uncertainties of two state-of-the-art methods
for 3C3D velocity field measurements in microscopic flows: stereoscopic micro-particle image velocimetry (S-μPIV) and astigmatism
micro-particle tracking velocimetry (A-μPTV). First, the main parameters affecting all methods’ measurement uncertainty are
identified, described, and quantified. Second, the test case of the flow over a backward-facing step is analyzed using all
methods. For comparison, standard 2D2C μPIV measurements and numerical flow simulations are shown as well. Advantages and
disadvantages of both methods are discussed. 相似文献
3.
PIV measurements of a microchannel flow 总被引:24,自引:0,他引:24
A particle image velocimetry (PIV) system has been developed to measure velocity fields with order 1-μm spatial resolution.
The technique uses 200 nm diameter flow-tracing particles, a pulsed Nd:YAG laser, an inverted epi-fluorescent microscope,
and a cooled interline-transfer CCD camera to record high-resolution particle-image fields. The spatial resolution of the
PIV technique is limited primarily by the diffraction-limited resolution of the recording optics. The accuracy of the PIV
system was demonstrated by measuring the known flow field in a 30 μm×300 μm (nominal dimension) microchannel. The resulting
velocity fields have a spatial resolution, defined by the size of the first window of the interrogation spot and out of plane
resolution of 13.6 μm× 0.9 μm×1.8 μm, in the streamwise, wall-normal, and out of plane directions, respectively. By overlapping
the interrogation spots by 50% to satisfy the Nyquist sampling criterion, a velocity-vector spacing of 450 nm in the wall-normal
direction is achieved. These measurements are accurate to within 2% full-scale resolution, and are the highest spatially resolved
PIV measurements published to date.
Received: 29 October 1998/Accepted: 10 March 1999 相似文献
4.
We address the problem of making quantitative measurements of local flow velocities in turbulent liquid helium, using tracer
particles. We survey and evaluate presently available particles and previous work to establish the need to develop new particles
for the purpose. We present the first practical solution for visualizing fluid motions using a suspension of solid hydrogen
particles with diameters of about 2 μm. The hydrogen particles can be used to study flows with Taylor-microscale Reynolds
numbers between 85 and 775. The particles can be used equally well with the PIV, LDV, or particle-tracking techniques. 相似文献
5.
The turbulent fluid and particle interaction in the turbulent boundary layer for cross flow over a cylinder has been experimentally
studied. A phase-Doppler anemometer was used to measure the mean and fluctuating velocities of both phases. Two size ranges
of particles (30μm–60μm and 80μm–150μm) at certain concentrations were used for considering the effects of particle sizes
on the mean velocity profiles and on the turbulent intensity levels. The measurements clearly demonstrated that the larger
particles damped fluid turbulence. For the smaller particles, this damping effect was less noticeable. The measurements further
showed a delay in the separation point for two phase turbulent cross flow over a cylinder.
The project supported by the National Natural Science Foundation of China 相似文献
6.
A particle image velocimetry (PIV) method has been developed to measure the velocity field inside and around a forming drop
with a final diameter of 1 mm. The system, including a microscope, was used to image silicon oil drops forming in a continuous
phase of water and glycerol. Fluorescent particles with a diameter of 1 μm were used as seeding particles. The oil was forced
through a 200 μm diameter glass capillary into a laminar cross-flow in a rectangular channel. The velocity field was computed
with a double-frame cross-correlation function down to a spatial resolution of 21 × 21 μm. The method can be used to calculate
the shear stress induced at the interface by the cross-flow of the continuous phase and the main forces involved in the drop
formation process. 相似文献
7.
Spatially averaged time-resolved particle-tracking velocimetry in microspace considering Brownian motion of submicron fluorescent particles 总被引:2,自引:0,他引:2
A time-series measurement method is proposed to detect velocity fields in a microchannel taking into account Brownian motion of submicron tracer particles. The present study proposes spatially averaged time-resolved particle-tracking velocimetry (SAT–PTV), which can detect temporal variations of fluid flow and eliminate errors associated with Brownian motion without losing temporal resolution. Velocity vectors of tracer particles obtained by PTV are spatially averaged in each interrogation window of particle-image velocimetry, yielding full velocity field information with temporal resolution. Synthetic particle images, which include Brownian motion of submicron fluorescent particles in flow fields with linear velocity gradients, are generated to validate the ability of SAT–PTV to track particles. SAT–PTV correctly captures the velocity gradient profiles. The spatial resolution based on the size of the first interrogation window and the measurement depth of the microscope system is 6.7 m×6.7 m×1.9 m, within which several vectors are averaged. SAT–PTV is shown to measure the velocity field of a pulsating flow generated by an electrokinetic pump.An earlier version of this paper appeared in the Fourth International Symposium on Particle Image Velocimetry at Göttingen, Germany, 17–19 September 2001. 相似文献
8.
Stereoscopic micro particle image velocimetry 总被引:1,自引:0,他引:1
A stereoscopic micro-PIV (stereo-μPIV) system for the simultaneous measurement of all three components of the velocity vector in a measurement plane (2D–3C) in a closed microchannel has been developed and first test measurements were performed on the 3D laminar flow in a T-shaped micromixer. Stereomicroscopy is used to capture PIV images of the flow in a microchannel from two different angles. Stereoscopic viewing is achieved by the use of a large diameter stereo objective lens with two off-axis beam paths. Additional floating lenses in the beam paths in the microscope body allow a magnification up to 23×. The stereo-PIV images are captured simultaneously by two CCD cameras. Due to the very small confinement, a standard calibration procedure for the stereoscopic imaging by means of a calibration target is not feasible, and therefore stereo-μPIV measurements in closed microchannels require a calibration based on the self-calibration of the tracer particle images. In order to include the effects of different refractive indices (of the fluid in the microchannel, the entrance window and the surrounding air) a three-media-model is included in the triangulation procedure of the self-calibration. Test measurement in both an aligned and a tilted channel serve as an accuracy assessment of the proposed method. This shows that the stereo-μPIV results have an RMS error of less than 10% of the expected value of the in-plane velocity component. First measurements in the mixing region of a T-shaped micromixer at Re = 120 show that 3D flow in a microchannel with dimensions of 800 × 200 μm2 can be measured with a spatial resolution of 44 × 44 × 15 μm3. The stationary flow in the 200 μm deep channel was scanned in multiple planes at 22 μm separation, providing a full 3D measurement of the averaged velocity distribution in the mixing region of the T-mixer. A limitation is that this approach requires a stereo-objective that typically has a low NA (0.14–0.28) and large depth-of-focus as opposed to high NA lenses (up to 0.95 without immersion) for standard μPIV. 相似文献
9.
Michael J. Patrick Chia-Yuan Chen David H. Frakes Onur Dur Kerem Pekkan 《Experiments in fluids》2011,50(4):887-904
In hemodynamics, the inherent intermittency of two-phase cellular-level flow has received little attention. Unsteadiness is
reported and quantified for the first time in the literature using a combination of fluorescent dye labeling, time-resolved
scanning confocal microscopy, and micro-particle image velocimetry (μPIV). The near-wall red blood cell (RBC) motion of physiologic
high-hematocrit blood in a rectangular microchannel was investigated under pressure-driven flow. Intermittent flow was associated
with (1) the stretching of RBCs as they passed through RBC clusters with twisting motions; (2) external flow through local
obstacles; and (3) transitionary rouleaux formations. Velocity profiles are presented for these cases. Unsteady flow clustered
in local regions. Extra-cellular fluid flow generated by individual RBCs was examined using submicron fluorescent microspheres.
The capabilities of confocal μPIV post-processing were verified using synthetic raw PIV data for validation. Cellular interactions
and oscillating velocity profiles are presented, and 3D data are made available for computational model validation. 相似文献
10.
Patrick E. Freudenthal Matt Pommer Carl D. Meinhart Brian D. Piorek 《Experiments in fluids》2007,43(4):525-533
Quantum Nanospheres™ (QNs) have been developed as a new type of flow-tracing particle for micron resolution particle image
velocimetry (PIV). The 70 nm diameter QNs were created by conjugating quantum dots to polystyrene beads. The fluorescent QNs
have a large Stokes’ shift and are impervious to photobleaching. The use of QNs as flow-tracing particles for micro-PIV was
demonstrated by measuring fluid motion in a 30 × 300 μm channel. Using an interrogation region of 1 × 1,024 pixels and ensemble
averaging 1,800 image pairs, the physical volume of the interrogation region was 117 μm × 117 μm × 2 μm. 相似文献
11.
Large polymer filaments can form when drag reducing polymers are injected through wall slots. The presence of these structures enhances the performance of the drag reducing function by mechanisms which are not understood. This paper shows how particle image velocimetry (PIV) techniques can be used to study changes in the configuration of the injected polymer and in the structure of the velocity field with increasing drag reduction. The filaments are found to behave as solid bodies which break up in high shear regions close to a boundary. The breakup process provides an explanation of why the filaments are not observed close to a wall and offers the possibility of providing a heterogeneous distribution of small aggregates of polymers which could be more effective than uniformly distributed molecules as suggested by Hoyer and Gyr (J Non-Newton Fluid Mech 65:221–240, 1996; J Fluids Eng 120:818–823, 1998), Dunlop and Cox (Phys Fluids 20:203–213, 1977) and Vlachogiannis et al. (Phys Fluid 15:3786–3794, 2004). PIV measurements show dramatic qualitative changes in the velocity patterns at maximum drag reduction. 相似文献
12.
Yannis Hardalupas Srikrishna Sahu Alex M. K. P. Taylor Konstantinos Zarogoulidis 《Experiments in fluids》2010,49(2):417-434
A new approach for simultaneous planar measurement of droplet velocity and size with gas phase velocities is reported, which
combines the out-of-focus imaging technique ‘Interferometric Laser Imaging Droplet Sizing’ (ILIDS) for planar simultaneous
droplet size and velocity measurements with the in-focus technique ‘Particle Image Velocimetry’ (PIV) for gas velocity measurements
in the vicinity of individual droplets. Discrimination between the gas phase seeding and the droplets is achieved in the PIV
images by removing the glare points of focused droplet images, using the droplet position obtained through ILIDS processing.
Combination of the two optical arrangements can result in a discrepancy in the location of the centre of a droplet, when imaging
through ILIDS and PIV techniques, of up to about 1 mm, which may lead to erroneous identification of the glare points from
droplets on the PIV images. The magnitude of the discrepancy is a function of position of the droplet’s image on the CCD array
and the degree of defocus, but almost independent of droplet size. Specifically, it varies approximately linearly across the
image along the direction corresponding to the direction of propagation of the laser sheet for a given defocus setting in
ILIDS. The experimental finding is supported by a theoretical analysis, which was based on geometrical optics for a simple
optical configuration that replicates the essential features of the optical system. The discrepancy in the location was measured
using a monodisperse droplet generator, and this was subtracted from the droplet centres identified in the ILIDS images of
a polydisperse spray without ‘seeding’ particles. This reduced the discrepancy between PIV and ILIDS droplet centres from
about 1 mm to about 0.1 mm and hence increased the probability of finding the corresponding fringe patterns on the ILIDS image
and glare points on the PIV image. In conclusion, it is shown that the proposed combined method can discriminate between droplets
and ‘seeding’ particles and is capable of two-phase measurements in polydisperse sprays. 相似文献
13.
Tomographic particle image velocimetry (PIV) is a recently developed method to measure three components of velocity within a volumetric space. We present a visual hull technique that automates identification and masking of discrete objects within the measurement volume, and we apply existing tomographic PIV reconstruction software to measure the velocity surrounding the objects. The technique is demonstrated by considering flow around falling bodies of different shape with Reynolds number?~1,000. Acquired image sets are processed using separate routines to reconstruct both the volumetric mask around the object and the surrounding tracer particles. After particle reconstruction, the reconstructed object mask is used to remove any ghost particles that otherwise appear within the object volume. Velocity vectors corresponding with fluid motion can then be determined up to the boundary of the visual hull without being contaminated or affected by the neighboring object velocity. Although the visual hull method is not meant for precise tracking of objects, the reconstructed object volumes nevertheless can be used to estimate the object location and orientation at each time step. 相似文献
14.
An experimental method based on confocal microscopy and particle image velocimetry (PIV) is used to characterize the flow
in a polymer solution during solvent casting. The flow inside a 200-μm-thick film of a poly(vinyl alcohol) (PVA) solution
is visualized near a vertical wall of a mold using confocal microscopy of seed particles during solvent evaporation at 25,
35, and 45°C, and the corresponding velocity vector fields are determined from projections of the confocal images. Flow toward
the vertical wall is observed inside the film as well as a slower Marangoni-type counter flow at the film surface during the
initial phase of solvent evaporation, resulting from a polymer concentration gradient along the film due to a local variation
in evaporation rate. Total volume of the polymer solution in the observation volume as well as solvent evaporation rate are
determined as a function of time, both revealing close correlation to average horizontal velocity data from PIV. The PIV measurements
show significant differences in the flow velocity fields at different temperatures. The PIV measurements correlate with the
solvent evaporation rates as well as the final polymer thicknesses on the vertical wall of the mold. Surface tension and viscosity
measurements are taken for different concentrations of PVA solution. 相似文献
15.
16.
We present in this paper a novel approach dedicated to the measurement of velocity in fluid experimental flows through image
sequences. Unlike most of the methods based on particle image velocimetry (PIV) approaches used in that context, the proposed
technique is an extension of “optical-flow” schemes used in the computer vision community, which includes a specific enhancement
for fluid mechanics applications. The method we propose enables to provide accurate dense motion fields. It includes an image based integrated version of the continuity equation. This model is associated to a regularization
functional, which preserve divergence and vorticity blobs of the motion field. The method was applied on synthetic images
and on real experiments carried out to allow a thorough comparison with a state-of-the-art PIV method in conditions of strong
local free shear. 相似文献
17.
Shahram Pouya Manoochehr M. Koochesfahani Andrew B. Greytak Moungi G. Bawendi Daniel G. Nocera 《Experiments in fluids》2008,44(6):1035-1038
Near-surface velocity measurements are carried out with quantum dot (QD) nanoparticles using evanescent wave illumination.
Relying on the small size of QDs, their correspondingly small hydrodynamic radius and high Brownian diffusion coefficient,
we consider the situation where the tracer diffusion length over the inter-frame time Δt is large compared to the size of the interrogation region next to the wall. While keeping all other experimental parameters
fixed, we systematically increase Δt by as much as a factor of 25, resulting in an increase of the QD diffusion length by a factor of 5. Data indicate a significant
overestimation of the “apparent” mean velocity measured experimentally. These results provide a direct confirmation of the
phenomenon of diffusion-induced bias described by the simulations of Sadr et al. (2007). 相似文献
18.
A stereomicroscopic particle image velocimetry (SμPIV) system has been developed for millimeter scale flows. The SμPIV system
is based on an off-the-shelf stereomicroscope, with magnification between 0.69× and 30×, and a field of view between 7.5 × 6 mm
and 250 × 200 μm. Custom calibration targets were devised using printed circuit board technology, and applied at a magnification
factor of 1.74, with a field of view of 4.75 × 3.8 mm. Measurement errors were assessed by moving a test block with fixed
particles. Total system uncertainty in test block displacement transverse to the optical axis was 0.5% of the field of view,
and 3% of the depth of field for motion along the optical axis. Approximately 20% of this uncertainty was due to the calibration
target quality and test block procedures. 相似文献
19.
R. Camussi 《Experiments in fluids》2002,32(1):76-86
A new technique based on wavelet transform is applied to bidimensional velocity fields obtained by particle image velocimetry
(PIV) measurements, in order to extract and characterize swirling motion associated with coherent structures. The proposed
technique is based on the selectivity property of the wavelet transform and permits the detection of regions of the flow field
associated with coherent structures and their spatial localization. Furthermore, being the method based on the analysis of
the local energy content at separated scales, it is possible to extract the typical wavenumber associated with structures
and therefore the typical length-scale. The procedure is validated by the application to velocity vector fields obtained from
PIV measurements in different flow conditions and turbulence levels. Results are compared with those obtained by other more
standard procedures, and the advantages and limitations of the proposed method are then discussed.
Received: 16 October 2000 / Accepted: 18 June 2001 Published online: 29 November 2001 相似文献
20.
The technical basis and system set-up of a dual-plane stereoscopic particle image velocimetry (PIV) system, which can obtain
the flow velocity (all three components) fields at two spatially separated planes simultaneously, is summarized. The simultaneous
measurements were achieved by using two sets of double-pulsed Nd:Yag lasers with additional optics to illuminate the objective
fluid flow with two orthogonally linearly polarized laser sheets at two spatially separated planes, as proposed by Kaehler
and Kompenhans in 1999. The light scattered by the tracer particles illuminated by laser sheets with orthogonal linear polarization
were separated by using polarizing beam-splitter cubes, then recorded by high-resolution CCD cameras. A three-dimensional
in-situ calibration procedure was used to determine the relationships between the 2-D image planes and three-dimensional object
fields for both position mapping and velocity three-component reconstruction. Unlike conventional two-component PIV systems
or single-plane stereoscopic PIV systems, which can only get one-component of vorticity vectors, the present dual-plane stereoscopic
PIV system can provide all the three components of the vorticity vectors and various auto-correlation and cross-correlation
coefficients of flow variables instantaneously and simultaneously. The present dual-plane stereoscopic PIV system was applied
to measure an air jet mixing flow exhausted from a lobed nozzle. Various vortex structures in the lobed jet mixing flow were
revealed quantitatively and instantaneously. In order to evaluate the measurement accuracy of the present dual-plane stereoscopic
PIV system, the measurement results were compared with the simultaneous measurement results of a laser Doppler velocimetry
(LDV) system. It was found that both the instantaneous data and ensemble-averaged values of the stereoscopic PIV measurement
results and the LDV measurement results agree well. For the ensemble-averaged values of the out-of-plane velocity component
at comparison points, the differences between the stereoscopic PIV and LDV measurement results were found to be less than
2%.
Received: 18 April 2000/Accepted: 2 February 2001 相似文献