共查询到20条相似文献,搜索用时 15 毫秒
1.
We present two non-intrusive, laser-based imaging techniques for the quantitative measurement of water fluid film thickness.
The diagnostics methods are based on laser-induced fluorescence (LIF) of the organic tracer ethyl acetoacetate added to the
liquid in sub-percent (by mass) concentration levels, and on spontaneous Raman scattering of liquid water, respectively, both
with excitation at 266 nm. Signal intensities were calibrated with measurements on liquid layers of known thickness in a range
between 0 and 500 μm. Detection via an image doubler and appropriate filtering in both light paths enabled the simultaneous
detection of two-dimensional liquid film thickness information from both methods. The thickness of water films on transparent
quartz glass plates was determined with an accuracy of 9% for the tracer LIF and 15% for the Raman scattering technique, respectively.
The combined LIF/Raman measurements also revealed a preferential evaporation of the current tracer during the time-resolved
recording of film evaporation. 相似文献
2.
Cavitation in thin layer of liquid metal has potential applications in chemical reaction, soldering, extraction, and therapeutic equipment. In this work, the cavitation characteristics and acoustic pressure of a thin liquid Ga–In alloy were studied by high speed photography, numerical simulation, and bubble dynamics calculation. A self-made ultrasonic system with a TC4 sonotrode, was operated at a frequency of 20 kHz and a max output power of 1000 W during the cavitation recording experiment. The pressure field characteristic inside the thin liquid layer and its influence on the intensity, types, dimensions, and life cycles of cavitation bubbles and on the cavitation evolution process against experimental parameters were systematically studied. The results showed that acoustic pressure inside the thin liquid layer presented alternating positive and negative characteristics within 1 acoustic period (T). Cavitation bubbles nucleated and grew during the negative-pressure stage and shrank and collapsed during the positive-pressure stage. A high bubble growth speed of 16.8 m/s was obtained and evidenced by bubble dynamics calculation. The maximum absolute pressure was obtained at the bottom of the thin liquid layer and resulted in the strongest cavitation. Cavitation was divided into violent and weak stages. The violent cavitation stage lasted several hundreds of acoustic periods and had higher bubble intensity than the weak cavitation stage. Cavitation cloud preferentially appeared during the violent cavitation stage and had a life of several acoustic periods. Tiny cavitation bubbles with life cycles shorter than 1 T dominated the cavitation field. High cavitation intensities were observed at high ultrasonication power and when Q235B alloy was used because such conditions lead to high amplitudes on the substrate and further high acoustic pressure inside the liquid. 相似文献
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Abstract
Most vehicles have a heating, ventilation, and air-conditioning device that makes the environment in the passenger compartment comfortable. The improvement of climatic comfort is crucial not only to passenger comfort but also to driving safety. Therefore, a better understanding of the flow characteristics of ventilation inside the passenger compartment is essential. Most of the previous studies investigated the ventilation flow using computational fluid dynamics calculations or scale-down water-model experiments. In this study, the ventilation flow inside the passenger compartment of a real commercial automobile was investigated using a particle image velocimetry velocity measurement technique. Under real operating conditions, the velocity fields were measured at several vertical planes for various ventilation modes. The experimental data obtained from this study can be used to understand the detailed flow characteristics in the passenger compartment of a real car and to validate numerical predictions. 相似文献5.
6.
JIN Dawei WANG Yuanyuan WANG Weiqi 《声学学报:英文版》2007,26(3):261-268
In medical Doppler ultrasound systems, a high-pass filter which is usually employed to filter wall clutter components, will remove the information of the low velocity blood flow. To extract intact Doppler ultrasound blood signals, a novel approach is proposed based on the spatially selective noise filtration. The wall signals are firstly estimated by the spatially selective noise filtration from wavelet spatial correlation property. Then the wall clutters are exactly obtained by a wavelet threshold de-noising technique which eliminates the residual blood flow signals. Finally the intact blood flow signals are achieved by subtracting the wall signals from the mixed signals. This approach is applied to both computer simulated and in vivo carotid Doppler ultrasound signals. The experiment results show that the wavelet space based approach can exactly extract the blood flow signals, and achieve about 45% lower results in the mean absolute error than that of the high-pass filtering. This approach is expected to be an effective method to remove the wall clutters in Doppler ultrasound systems. 相似文献
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Using a single high-speed camera and a frequency modulated laser, a novel approach is presented for fast velocity field measurements in unsteady spray flows. The velocity range is from zero up to several 100 m/s, which requires a high measurement rate and a large dynamic. Typically, flow measurements require to seed tracer particles to the fluid. A paradigm shift to seeding-free measurements is presented. The light scattered at the phase boundaries of the fluid droplets is evaluated. In order to validate the high-speed measurement system, a detailed uncertainty analysis is performed by means of measurements as well as simulations. Thereby, variations of the scattered light intensity, which are based on the high temporal velocity gradients, are found to be the main contribution to the uncertainty. The eventually measurement results, obtained at a measurement rate of 500 kHz, exhibit spray velocities ranging from 0 m/s up to 400 m/s in less than 1 ms, and the detection of unsteady and irregular flow phenomena with a characteristic time of several μs is achieved. This demonstrates the high measurement rate, the high temporal resolution and the large measurement range of the proposed high-speed measurement system. 相似文献
9.
Nanofluids have shown significant promise in thermal enhancement of many industrial systems and they have been used extensively in energy applications during recent years. Keeping such applications in mind, the present work exhibits a two-dimensional numerical simulation for the boundary layer flow of Graphene oxide (GO)-nanofluids adjacent to a thin needle along with heat transfer. Influence of heat generation/absorption and viscous dissipation have been included to explore the heat transport analysis. The nanofluid flow is generated due to a continuously moving horizontal thin needle. The non-linear expressions governing the flow and heat transfer analysis are changed into dimensionless form by introducing new dimensionless variables. The novelty of current study is to predict the multiple numerical solutions for dimensionless velocity and temperature fields. Numerical computations and graphical delineations were done with the assistance of MATLAB software. This study explores the impacts of several dimensionless key parameters, like, magnetic parameter, Prandtl number, nanoparticles volume fraction and ratio of needle's velocities on the flow and thermal distributions. The computational results have proved that the fluid temperature enhances for higher values of nanoparticles volume fraction while an opposite is true for velocity distributions. In addition, the computed outcomes revealed that for the case of upper branch solution, significant reduction in skin-friction coefficient is seen for higher magnetic parameter. 相似文献
10.
A new incoherent Doppler lidar scheme is proposed using a high resolution Mach-Zehnder interferometer discriminator with sinusoidal transmission functions. A two-channel differential discrimination technique is developed which provides high sensitive velocity measurement. The aerosol and molecular backscatter signals can be separately measured and the backscatter ratio obtained. Principle of the measurement is described and the characteristics of this technique are analyzed and compared. Numerical calculation for a moderate size 1.064 μ lidar shows that an accuracy better than 1 m/s for the velocity measurement and 18% for the backscatter ratio measurement can be obtained up to a height of 10 km by a 500 shot average. 相似文献
11.
The viscose flow and microstructure formation of Fe-Cu peritectic alloy melts are investigated by analyzing the velocity and
temperature fields during rapid solidification, which is verified by rapid quenching experiments. It is found that a large
temperature gradient exists along the vertical direction of melt puddle, whereas there is no obvious temperature variation
in the tangent direction of roller surface. After being sprayed from a nozzle, the alloy melt changes the magnitude and direction
of its flow and velocity rapidly at a height of about 180 μm. The horizontal flow velocity increases rapidly, but the vertical
flow velocity decreases sharply. A thermal boundary layer with 160–300 μm in height and a momentum boundary layer with 160–240
μm in thickness are formed at the bottom of melt puddle, and the Reynolds number Re is in the range of 870 to 1070 in the
boundary layer. With the increase of Re number, the cooling rate increases linearly and the thickness of thermal boundary
layer increases monotonically. The thickness of momentum boundary layer decreases slowly at first, then rises slightly and
decreases sharply. If Re < 1024, the liquid flow has remarkable effects on the microstructure formation due to dominant momentum
transfer. The separated liquid phase is likely to form a fiber-like microstructure. If Re>1024, the heat transfer becomes
dominating and the liquid phase flow is suppressed, which results in the formation of fine and uniform equiaxed microstructures.
Supported by the National Natural Science Foundation of China (Grant Nos. 50121101 and 50395105) 相似文献
12.
Mohammad Rafiqul Haque Mohamed Fayed Amy-Lee Gunter Othman Smadi Lyes Kadem Hoi Dick Ng 《显形杂志》2011,14(4):311-314
Abstract
With the aid of computational fluid dynamics (CFD) and simple flow visualization technique using flowing soap-film, we present here the wake structures behind an array of cylinders for Reynolds numbers corresponding to both laminar and turbulent flow regimes. The image results illustrate interesting vortex interactions past these equally spaced cylinders; for low Reynolds number flow, well-organized wake pattern persists and manifests unsteadily to different symmetry states. An increase of free stream flow velocity causes the wake transition, resulting in the formation of asymmetric flow wake with chaotic mixing at the far wake. Observations from both the numerical simulations and soap-film are in good agreement at least qualitatively. 相似文献13.
Speckle Velocimetry or high-image density PIV gives a velocity vector map of a twodimensional flow field by point-by-point spatial frequency analysis of local pattern at an interrogation spot in a double- or a multiple-exposed image of laser speckle or pseudo-speckle pattern generated by pulsed laser-light-sheet illuminations of a plane in the flow densely seeded with fine particles. The whole field spatial frequency analysis of the double- or multiple-exposed PIV image gives more useful information of the flow field. Optical Fourier transform is a conventional technique not only for the local spatial frequency analysis but for the whole field analysis. Filtering of spatial frequency is one of the typical techniques for the latter which can reconstruct a velocity contour or a component velocity contour map of the flow. Fundamentally this technique is a simple and efficient analogue method to get more information in the velocity field analysis of the flow than a digital image processing, but in practical applications the measurement is restricted to simple flows because of optical noise and low spatial resolution. In order to improve the technique, the fundamental characteristics of the filtering and the noise yielded in the filtering process must be investigated. Meanwhile, wavelet analysis can also be applied to the whole field spatial frequency analysis of PIV image. In this paper the filtering technique is examined by numerical convolution integral, and the results obtained are compared with ones obtained by the wavelet analysis. 相似文献
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Abstract
An experimental investigation was conducted to study the characteristics of turbulent swirling flow in an axisymmetric annuli. The swirl angle measurements were performed using a flow visualization technique using smoke and dye liquid for Re = 60,000–80,000. Using the two-dimensional particle image velocimetry method, this study found the time-mean velocity distribution and turbulent intensity in water with swirl for Re = 20,000, 30,000, and 40,000 along longitudinal sections. There were neutral points for equal axial velocity at y/(R − r) = 0.7–0.75, and the highest axial velocity was recorded near y/(R − r) = 0.9. Negative axial velocity was observed near the convex tube along X/(D − d) = 3–23. 相似文献15.
《Current Applied Physics》2015,15(11):1529-1533
In this paper, we carried out the two-dimensional (2D) strain measurement in sub-10 nm SiGe layer; images were obtained by dark-field electron holography (DFEH). This technique is based on transmission electron microscopy (TEM), in which dark-field holograms were obtained from a (400) diffraction spot. The measured results were compared to the X-ray diffraction (XRD) results in terms of the strain value and the depth of strain distribution in a very thin SiGe layer. Subsequently, we were able to successfully analyze the 2D strain maps along the [100] growth direction of the nanoscale SiGe region. The strain was measured and found to be in the range of 1.8–2.4%. The strain precision was estimated at 2.5 × 10−3. As a result, the DFEH technique is truly useful for measuring 2D strain maps in very thin SiGe layers with nanometer resolution and high precision. 相似文献
16.
In this work, we present the performance improved InGaZnO thin film transistors by inserting low temperature processed 10 nm thick SiOCH buffer layers between SiNx insulator and InGaZnO channel layer. The influences of oxygen flow rate during the deposition of SiOCH buffer layer have been intensively investigated. Basing on the analysis of hall effect measurement and Fourier transform infrared spectrum, the SiOCH buffer layer can effectively increase the carrier concentration of the channel layer by the hydrogen doping due to re-sputtering and diffusion effect. The InGaZnO thin film transistor with buffer layer exhibits an enhanced performance with mobility of 13.09 cm2/vs, threshold voltage of −0.55 V and Ion/Ioff over 106. 相似文献
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《Current Applied Physics》2014,14(5):659-664
To study the influence of defects in the hole blocking layer (HBL) on the dark current of amorphous selenium (a-Se) based photosensors, we prepared ZnO thin films by reactive sputter deposition (RSD) for the use as the HBL of the photosensors. The ZnO HBL layers prepared with different oxygen flow rates were characterized by X-ray photoelectron spectroscopy, Raman scattering analysis and photoluminescence, indicating that the density of oxygen vacancies in the ZnO thin films is significantly affected by the oxygen flow rate. The deep level transient spectroscopy measurement reveals two hole trap levels present in the RSD deposited ZnO thin films; one is at 0.94 eV and the other at 0.24 eV above the valence band edge. The electrical performance of the a-Se photosensor is largely influenced by the amount of oxygen vacancies in the ZnO thin film. The a-Se photosensor with the ZnO HBL of the most oxygen vacancies has the lowest dark current and demonstrates the highest breakdown field. 相似文献
19.
I. V. Marchuk 《Journal of Engineering Thermophysics》2009,18(3):227-237
In this paper, steady thermocapillary flow in a thin horizontal layer of a viscous incompressible liquid with a free surface
is considered. An axially symmetric steady problem with a localized thermal action on a horizontal liquid layer with a deformable
free surface is solved in a thin-layer approximation. In addition to the thermocapillary effect, the model takes into account
the capillary pressure caused by the free surface variable curvature and the convective mechanism of heat transfer in the
liquid. Analytical expressions for the velocity vector components as functions of the liquid layer thickness and surface temperature
are obtained. The free surface and velocity profiles caused by various kinds of heating are calculated. The influence of convective
heat transfer on the flow pattern is analyzed. 相似文献
20.
分层薄膜-基底结构广泛应用于微电子器件等诸多领域,但薄膜材料参数超声测量尤其是横波速度的定征是一个困难的问题。本文对液固界面Scholte界面波的频散特性和脉冲激励的声压响应进行了理论分析。结果表明,液固界面Scholte波频散与分层膜-基底结构的速度分布密切相关。薄膜材料各层的厚度和横波速度对界面波频散特性有显著影响。基于Scholte界面波的频散特性,提出了一种多层膜的多参数反演定征方法。首先针对理论信号进行薄膜参数反演,验证了该方法的可行性。后续对不同类型的多层膜材料样品进行了液固界面波激发与采集实验,实验信号的薄膜参数反演结果进一步验证了该方法的可行性和有效性。 相似文献