共查询到20条相似文献,搜索用时 78 毫秒
1.
A novel method is developed for in-line measurements of particle size, velocity and concentration in a dilute, particulate two-phase flow based on trajectory image processing. The measurement system consists of a common industrial CCD camera, an inexpensive LED light and a telecentric lens. In this work, the image pre-processing steps include stitching, illumination correction, binarization, denoising, and the elimination of unreal and defocused particles. A top-hat transformation is found to be very effective for the binarization of images with non-uniform background illumination. Particle trajectories measured within a certain exposure time are used to directly obtain particle size and velocity. The particle concentration is calculated by using the statistics of recognized particles within the field of view. We validate our method by analyzing experiments in a gas-droplet cyclone separator. This in-line image processing method can significantly reduce the measurement cost and avoid the data inversion process involved in the light scattering method. 相似文献
2.
《Particuology》2014
A novel method is developed for in-line measurements of particle size, velocity and concentration in a dilute, particulate two-phase flow based on trajectory image processing. The measurement system consists of a common industrial CCD camera, an inexpensive LED light and a telecentric lens. In this work, the image pre-processing steps include stitching, illumination correction, binarization, denoising, and the elimination of unreal and defocused particles. A top-hat transformation is found to be very effective for the binarization of images with non-uniform background illumination. Particle trajectories measured within a certain exposure time are used to directly obtain particle size and velocity. The particle concentration is calculated by using the statistics of recognized particles within the field of view. We validate our method by analyzing experiments in a gas-droplet cyclone separator. This in-line image processing method can significantly reduce the measurement cost and avoid the data inversion process involved in the light scattering method. 相似文献
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Liquid-solid fluidized beds are used in mineral processing industries to separate particles based on parti- cle size, density, and shape. Understanding the expanded fluidized bed is vital for accurately assessing its performance. Expansion characteristics of the fluidized bed were studied by performing several experi- ments with iron ore, chromite, quartz, and coal samples. Using water as liquid medium, experiments were conducted to study the effects of particle size, particle density, and superficial velocity on fluidized bed expansion. The experimental data were utilized to develop an empirical mathematical model based on dimensional analysis to estimate the expansion ratio of the fluidized bed in terms of particle character- istics, operating and design parameters. The predicted expansion ratio obtained from the mathematical model is in good agreement with the experimental data. 相似文献
5.
两相流显微PIV/PTV系统的开发 总被引:1,自引:0,他引:1
开发了一个能同时测量两相流中两相速度和细颗粒尺寸分布的显微PIV/PTV系统,其硬件系统包括大功率连续激光器、显微镜、高速摄像机;软件系统由改进的球形颗粒图像识别算法、各种图像处理算法和各种先进的PIV/PTV算法组成。其中改进的圆弧识别算法能够进行更准确地进行曲线分割而能对充满噪音并相互重叠的颗粒图像给出较好的识别结果。应用该PIV系统,可以在微秒和微米数量级上捕获细颗粒/气泡图像,并能较准确地同时得到两相速度、颗粒尺寸和浓度分布。对焚香可吸入颗粒物进行了速度和尺寸的同时测量,得到了较满意的结果。 相似文献
6.
A reliable method for the calibration of the measurement volume cross-section has been developed, in order to correct the particle size distribution measured by a phase-Doppler anemometer (PDA) with respect to the counting bias in favour of the large particles. Furthermore, this method allows the measurement of particle concentration or mass flux with high accuracy in two-dimensional two-phase flows. A comparison of the mass flow rate obtained by the integration of the mass flux measured in a water spray by applying this method with the global mass balance showed a difference of about 5%.The basis of the present method is the detection of the amplitude of the filtered Doppler signal in connection with the particle size measured by the PDA. The detection process is performed using an electronic circuit which validates the Doppler burst and has additionally the advantage that the highest amplitude portion of the burst can be selected for digitizing, acquisition and subsequent processing. Therefore, this method has the great advantage that the processed part of the burst has the highest signal-to-noise ratio which results in high accuracies for frequency and phase estimation. 相似文献
7.
This paper reports the first experimental study of liquid neon injection into superfluid helium (He II) through a plain orifice atomizer to explore different means of introducing micron-size tracer particles into a He II bath for particle image velocimetry (PIV) applications. The obtained results verify that the direct injection of liquid neon into He II introduces seed particles into the He II bath. It is also demonstrated that the particle sizes can be controlled by changing the pressure above the injected liquid. Additionally, the size distribution of the particles is calculated from the PIV results through the use of the correlations to the standard drag curve. 相似文献
8.
《Particuology》2015
Information of droplet size and size distribution lays the basis for investigations of atomization mechanisms and performance optimization. However, the laser diffraction and phase Doppler particle analyzers have difficulty in accurately characterizing sprays with a wide range of droplet sizes and very large droplets, especially if a large number of droplets are aspherical. A method to measure size in such large-droplet sprays based on digital imaging with backward illumination was developed, including an image acquisition system and image process programs. Calibration of the measurement system was performed using a dot calibration target with different dot sizes. An experimental setup was designed and established to characterize spray nozzles under different operation loads, as well as different nozzle arrangements. Results show that the droplet size of sprays ranges from dozens of microns to several millimeters. The superiority of wide load range for such nozzles was indicated by the size-measurement results under half-load to full-load operations. The present study revealed that the image processing technique can be effectively implemented for in-line size measurements of sprays with a wide distribution of droplet size and aspherical droplets, which would be difficult to characterize by other methods. 相似文献
9.
Because of the inherent small size of optical fiberscopes, they provide access and relative handling ease in given closed vessels, which are hardly equipped with extra windows for conventional flow visualization. The use of an optical fiberscope in conjunction with a conventional particle image velocimetry/particle tracking velocimetry (PIV/PTV) system without optimization can lead to degraded transmission of images. The present study proposes a processing technique to filter background noise contained within the coarse bundle image by subtracting the original image of the bundle as reference image. Additionally, efforts were made to increase the reliability of vector processing using particle streak images via judicious pulse interval and duration adjustments. As an applications test we measured classic jet flow using the developed system and using established conventional measurement techniques. Our tests confirmed that our fiberscope PTV system provides vector fields with sufficient accuracy. 相似文献
10.
A digital in-line holographic particle tracking velocimetry (HPTV) system was developed to measure 3D (three-dimensional)
velocity fields of turbulent flows. The digital HPTV (DHPTV) procedure consists of four steps: recording, numerical reconstruction,
particle extraction and velocity extraction. In the recording step, a digital CCD camera was used as a recording device. Holograms
contained many unwanted images or noise. To get clean holograms, digital image processing techniques were adopted. In the
velocity extraction routine, we improved the HPTV algorithm to extract 3D displacement information of tracer particles. In
general, the results obtained using HPTV were not fully acceptable due to technical limitations such as low spatial resolution,
small volume size, and low numerical aperture (NA). The problems of spatial resolution and NA are closely related with a recording
device. As one experimental parameter that can be optimized, we focused on the particle number density. Variation of the reconstruction
efficiency and recovery ratio were compared quantitatively with varying particle number density to check performance of the
developed in-line DHPTV system. The reconstruction efficiency represented the particle number distribution acquired through
the numerical reconstruction procedure. In addition the recovery ratio showed the performance of 3D PTV algorithm employed
for DHPTV measurements. The particle number density in the range of C
o = 13–17 particles/mm3 was found to be optimum for the DHPTV system tested in this study. 相似文献
11.
Numerical simulations based on three-dimensional discrete element model (DEM) are conducted for mono-disperse, binary and ternary systems of particles in a fluidized bed. Fluid drag force acting on each particle depending on its size and relative velocity is assigned. The drag coefficient corresponding to Ergun’s correlation is applied to the system of fluidized bed with particle size ratios of 1:1 for the mono-disperse system, 1:1.2, 1:1.4 and 1:2 for the binary system and 1:1.33:2 for the ternary system b... 相似文献
12.
Klaus Hoyer Markus Holzner Beat Lüthi Michele Guala Alexander Liberzon Wolfgang Kinzelbach 《Experiments in fluids》2005,39(5):923-934
In this article, we present an experimental setup and data processing schemes for 3D scanning particle tracking velocimetry
(SPTV), which expands on the classical 3D particle tracking velocimetry (PTV) through changes in the illumination, image acquisition
and analysis. 3D PTV is a flexible flow measurement technique based on the processing of stereoscopic images of flow tracer
particles. The technique allows obtaining Lagrangian flow information directly from measured 3D trajectories of individual
particles. While for a classical PTV the entire region of interest is simultaneously illuminated and recorded, in SPTV the
flow field is recorded by sequential tomographic high-speed imaging of the region of interest. The advantage of the presented
method is a considerable increase in maximum feasible seeding density. Results are shown for an experiment in homogenous turbulence
and compared with PTV. SPTV yielded an average 3,500 tracked particles per time step, which implies a significant enhancement
of the spatial resolution for Lagrangian flow measurements. 相似文献
13.
A phase discrimination method for two-phase PIV is presented that is capable of simultaneously separating the two phases from
time-resolved stereoscopic PIV images taken in a particle-laden jet. The technique developed expands on previous work done
by Khalitov and Longmire (Exp Fluids 32:252–268, 2002), where by means of image processing techniques, a raw two-phase PIV image can be separated into two single-phase images
according to particle size and intensity distributions. The technique is expanded through the use of three new image processing
algorithms to separate particles of similar size (up to an order of magnitude better than published work) for fields of view
much larger than previously considered. It also addresses the known problem of noisy background images produced by high-speed
CMOS cameras, which makes the particle detection and separation from the noisy background difficult, through the use of a
novel fast Fourier transform background filter. 相似文献
14.
The present paper studies numerical modelling of near-wall two-phase flows induced by a normal shock wave moving at a constant speed, over a micron-sized particles bed. In this two-fluid model, the possibility of particle trajectory intersection is considered and a full Lagrangian formulation of the dispersed phase is introduced. The finiteness of the Reynolds and Mach numbers of the flow around a particle as well as the fineness of the particle sizes are taken into account in describing the interactions between the carrier- and dispersed-phases. For the small mass-loading ratio case, the numerical simulation of flow structure of the two phases is implemented and the profiles of the particle number density are obtained under the constant-flux condition on the wall. The effects of the shock Mach number and the particle size and material density on particle entrainment motion are discussed in detail. The obtained results indicate that interphase non-equilibrium in the velocity and temperature is a common feature for this type of flows and a local particle accumulation zone may form near the envelope of the particle trajectory family. 相似文献
15.
《Particuology》2023
The resuspension of graphite dust is an important phenomenon in the release of radioactivity and the safety of nuclear reactors during severe accidents. In this study, a visualization experimental platform is constructed to study effects of particle size, flow velocity, and wall roughness on the resuspension characteristics of graphite particles. A statistical model of particle resuspension applicable to monolayer dispersed particles is developed based on the moment equilibrium of the particles and the flow field characteristics, as calculated by the large-eddy simulation framework. The results show that particle resuspension can be divided into short- and long-term resuspension stages. Most particle resuspension occurs during the short-term stage. With increases in flow velocity and particle diameter, the aerodynamic or adhesion force acting on the particles increases, and corresponding particle resuspension fraction increases. The influence of rough walls on particle resuspension is related to both the force on the particles and the arm ratio between the wall morphology and the particle diameter. A comparison with the experimental results demonstrates that the particle resuspension model developed in this study accurately predicts the impact of flow velocity, particle size, and wall roughness on particle resuspension. 相似文献
16.
New insights into particle image velocimetry data using fuzzy-logic-based correlation/particle tracking processing 总被引:2,自引:0,他引:2
M. P. Wernet 《Experiments in fluids》2001,30(4):434-447
Digital particle image velocimetry (DPIV) data processing has been developed to the point where DPIV image data are processed
via auto- or cross-correlation techniques in near real time and the results are displayed on screen as they are processed.
Correlation techniques are highly desirable, since they provide velocity measurements on a regular grid, which are readily
comparable to CFD predictions of the flow field. In high-speed flows, particle lag effects are always of concern; however,
the correlation operation does not provide any means for minimization or elimination of systematic errors in the recorded
particle image data. In this paper, we present a combined correlation processing/particle tracking technique providing “super-resolution”
velocity measurements. Fuzzy-logic principles are employed to maximize the information recovery in the correlation operation
and to determine the correct particle pairings in the tracking operation. The combined correlation/particle tracking technique
is applied to DPIV data obtained in the diffuser region of a high-speed centrifugal compressor producing velocity vector maps
with an average density of 6 vectors/mm2. Inspection of the particle tracking results revealed large particles that were not following the flow. Using preknowledge
of the flow field, the biased velocity estimates arising from large particles in the flow were removed, thereby improving
the accuracy of the measurements.
Received: 21 October 1999/Accepted: 19 August 2000 相似文献
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Three different particle image processing algorithms have been developed for the improvement of PIV velocity measurements
characterized by large velocity gradients. The objectives of this study are to point out the limitations of the standard processing
methods and to propose a complete algorithm to enhance the measurement accuracy. The heart of the PIV image processing is
a direct cross-correlation calculation in order to obtain complete flexibility in the choice of the size and the shape of
the interrogation window (IW). An iterative procedure is then applied for the reduction of the size of IW at each measurement
location. This procedure allows taking into account the local particle concentration in the image. The results of this first
iterative processing, applied to synthetic images, show both a significant improvement of measurement accuracy and an increase
of the spatial resolution. Finally, a super-resolution algorithm is developed to further increase the spatial resolution of
the measurement by determining the displacement of each particle. The computer time for a complete image processing is optimized
by the introduction of original data storage in Binary Space Partitions trees. It is shown that measurement errors for large
velocity gradient flows are similar to those obtained in simpler cases with uniform translation displacements. This last result
validates the ability of the developed super-resolution algorithm for the aerodynamic characterization of large velocity gradient
flows. 相似文献
20.
We present a cost-effective solution of the three-dimensional particle tracking velocimetry (3D-PTV) system based on the real-time
image processing method (Kreizer et al. Exp Fluids 48:105–110, 2010) and a four-view image splitter. The image processing algorithm, based on the intensity threshold and intensity gradients
estimated using the fixed-size Sobel kernel, is implemented on the field-programmable gate array integrated into the camera
electronics. It enables extracting positions of tracked objects, such as tracers or large particles, in real time. The second
major component of this system is a four-view split-screen device that provides four views of the observation volume from
different angles. An open-source ray-tracing software package allows for a customized optical setup for the given experimental
settings of working distances and camera parameters. The specific design enables tracking in larger observation volumes when
compared to the designs published up to date. The present cost-effective solution is complemented with open-source particle
tracking software that receives raw data acquired by the real-time image processing system and returns trajectories of the
identified particles. The combination of these components simplifies the 3D-PTV technique by reducing the size and increasing
recording speed and storage capabilities. The system is capable to track a multitude of particles at high speed and stream
the data over the computer network. The system can provide a solution for the remotely controlled tracking experiments, such
as in microgravity, underwater or in applications with harsh experimental conditions. 相似文献