Experimental investigation of electrohydrodynamic instabilities in micro channels

The European Physical Journal Special Topics - An electric field is applied to destabilize the interface between two Newtonian and immiscible liquids flowing in a rectangular micro channel. The...     

Velocity imaging of highly turbulent gas flow

We introduce a noninvasive, quantitative magnetic resonance imaging (MRI) wind-tunnel measurement in flowing gas (>10 m s(-1)) at high Reynolds numbers (Re>10(5)). The method pertains to liquids and gases, is inherently three dimensional, and extends the range of Re to which MRI is applicable by orders of magnitude. There is potential for clear time savings over traditional pointwise techniques. The mean velocity and turbulent diffusivity of gas flowing past a bluff obstruction and a wing section at realistic stall speeds were measured. The MRI data are compared with computational fluid dynamics.     

Study on successively preparation of nano-TiO2 ethanol colloids by pulsed laser ablation and fluorescence property

Nano-TiO₂ colloids have been successively prepared by focused, pulsed laser ablation (PLA) at the interface of solid titanium dioxide and flowing liquid. Three factors influenced the luminescence of the nano-TiO₂ colloids. The first factor was the flowing rates of the flowing liquid. The second factor was the pulsed laser output power. The third factor was the age of the colloids. The nano-TiO₂ colloids products were characterized by transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV-vis) and fluorescence spectroscopy. The results revealed that anhydrous ethanol was the best flowing liquid, and cyclohexane or water was found to be not suitable for this system; under the conditions of the lowest flowing rates of the flowing liquids in the range of 0.017-0.15 mL/s, the highest pulsed laser output power in the range of 100-250 mJ/pulse and with the proper aging time of the colloids, nano-TiO₂ ethanol colloids with strong fluorescence emission intensity at about 414 nm can be obtained.     

相对法测量表面张力系数

从细管缓慢流出的液体,并不是呈现连续的液流,而是一些继续的液滴。通过对不同液体液滴大小的比较,可测得表面张力系数。     

Qualitative estimation of the contents of seeping water and estimation of the flow velocity in clay barriers by impedance spectroscopy

In this work, the flow of different kinds of liquids (differences in polarity, aromaticity, molecular size) through a layer of Friedland clay and the interaction of these liquids with the clay particles are investigated by means of electrical impedance measurements. The instationary flow can be described by data obtained from complex impedance plots. The gradient of the ohmic part of the impedance gives information about the strength of the driving force and the speed of flow/diffusion of the liquid through the clay. Different kinds of liquids lead to completely different impedance spectra. From time-dependent impedance measurements on a layer of defined thickness, information can be gained about the contents of the liquid flowing or diffusing through the clay. The impedance spectroscopy could be a powerful method for the development of an in situ monitoring system in waste disposal sites having clay barriers. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Correlated displacement-T2 MRI by means of a Pulsed Field Gradient-Multi Spin Echo Method

A method for correlated displacement-T2 imaging is presented. A Pulsed Field Gradient-Multi Spin Echo (PFG-MSE) sequence is used to record T2 resolved propagators on a voxel-by-voxel basis, making it possible to perform single voxel correlated displacement-T2 analyses. In spatially heterogeneous media the method thus gives access to sub-voxel information about displacement and T2 relaxation. The sequence is demonstrated using a number of flow conducting model systems: a tube with flowing water of variable intrinsic T2's, mixing fluids of different T2's in an "X"-shaped connector, and an intact living plant. PFG-MSE can be applied to yield information about the relation between flow, pore size and exchange behavior, and can aid volume flow quantification by making it possible to correct for T2 relaxation during the displacement labeling period Delta in PFG displacement imaging methods. Correlated displacement-T2 imaging can be of special interest for a number of research subjects, such as the flow of liquids and mixtures of liquids or liquids and solids moving through microscopic conduits of different sizes (e.g., plants, porous media, bioreactors, biomats).     

Nanotube Electron Drag in Flowing Liquids

We show that electric current can be generated in metallic carbon nanotubes immersed in liquids flowing along them. Molecular layers of the liquid coat the nanotube, slip along its surface, and excite there a phonon wind, which drags free carriers in the tube. The induced electric current should allow building of nanoscale detectors or power cells.     

Ultrasonic flow measurement and wall acoustic impedance effects

An examination of the influence of wall acoustic impedance effects on sound propagation in flowing liquids confined by cylindrical walls is presented. Special focus is given to the importance of the wall acoustic impedance value for ultrasonic flow meter performance. The mathematical model presented allows any radially-dependent axial flow profile to be examined in the linear flow acoustics regime where fluid flow speed is much smaller than the fluid sound speed everywhere in the fluid medium.     

Identification of a low-frequency elastic behaviour in liquid water

This article deals with the identification of solid-like properties measured at room temperature at a sub-millimetre length scale in liquid water. At a macroscopic scale, normal liquids (i.e.?above melting temperature), and in particular water, are typically and empirically defined by the absence of shear elasticity, in contrast to solids or plastic fluids that require a stress threshold for flowing. A novel method optimizing the transmission of the shear stress to the sample enables a more complete probe of the mechanical response of liquids. It reveals that glass formers and viscous alkanes actually exhibit finite macroscopic shear elasticity away from any phase transition. This protocol is here applied for the first time to liquid water at room temperature, revealing, at the sub-millimetre scale, a low-frequency solid-like property.     

Inactivation of pathogenic and spoilage microorganisms in a testliquid using pulsed electric fields

Experiments have been carried out to investigate the effect of pulsed electric fields (PEFs) on the inactivation of microbial populations suspended in liquids using nonflowing and continuous flowing test chambers. Electric fields of ~30 kV/cm, and a pulse duration of 500 ns, were generated from a coaxial table Blumlein pulse forming network (PFN) and applied to a parallel plate, circular electrode test configuration. Sample microorganisms were grown under standardized conditions and were introduced into test liquids in order to produce known population densities within the treatment celt. The organisms investigated include the mold Aspergillus niger, the yeast Sacckaromyeces cerevisiae, and the bacterial pathogens Bacillus cereus, Staphylococcus aureus, and Pseudomonas aeruginosa. The PEF studies were undertaken at a sample temperature range of 25°C-30°C, and the effect of the number of pulses on the test microbial population was studied. The results of this investigation showed that the greater the number of pulses applied, the larger the corresponding reduction in microbial cells/spores obtained. With the exception of dormant fungal spores, all of the test organisms were reduced by -3 to 4 log orders after 3000 pulses. The number of B. Cerus cells was reduced by -7.5 log orders after 15 000 pulses, of which 10 000 pulses were applied in a flowing system followed by 5000 pulses in a static system     

Mathematical Study of the Water-Vapor Permeability of the Surface Layer of a Homogeneous Porous Material

Permeability in relation to gases and liquids is one of the most important characteristics of porous materials. A porous material can interact with gases and liquids flowing through it in different ways that depend on a material’s permeability. Studies of the interaction of water vapor with materials with uniformly distributed pores are of considerable practical interest, since many of these materials are used in building and construction. Interest is also due to the possibility of expanding the study results obtained for an individual pore to a porous medium if this medium can be represented as a structure with uniformly distributed pores with sufficient accuracy. The dependence of the permeability of an individual cylindrical pore on its radius, length, and characteristics of the process of water-molecule interaction with the pore walls is studied.     

Flow-induced transverse electrical potential across an assembly of gold nanoparticles

We report the generation of a potential difference, of the order of tens of millivolts, induced by the flow of polar liquids over an assembly of gold nanoparticles. The device consisted of two conducting glass plates, one of which contained the gold nanoparticle multilayer assembly. The potential generated is in transverse direction to the flow and is dependent on the nature of the flowing liquid. We propose a simple theoretical model to account qualitatively for the generation of the flow-induced transverse potential.     

超声波对多孔介质中两相流动的影响

近年来，超声技术已被应用于采油工程中，在油井解堵，水井增注等方面发挥了重要的作用。     

Correlation-induced memory effects in transport properties of low-dimensional systems

We demonstrate the remnant presence of initial correlations in the steady-state electrical current jS flowing between low-dimensional interacting leads. The leads are described as Luttinger liquids and electrons can tunnel via a quantum point contact. We derive an analytic result for the time-dependent current and show that ground-state correlations have a large impact on the relaxation and long-time behavior. In particular, the I-V characteristic is not reproduced by quenching the interaction in time. We further present a universal formula of jS for an arbitrary sequence of interaction quenches and it is established that jS is history dependent for nonsmooth switching process.     

Visualization of blood flow by ultrasound speckle interferometry

A new method for the visualization of flowing liquids is suggested. The method makes it possible to obtain images of dynamic objects located in an inhomogeneous medium. The main requirement for the realization of this method is the stability of the field during two successive measurements. The dimensions of the irradiating beam depend on the value of the spatial correlation interval characterizing the inhomogeneities of the medium, while the amplitude distribution in the beam can be arbitrary. A numerical modeling of the method is performed, and images of the models of blood vessels lying under an inhomogeneous layer are presented.     

Slip, immiscibility, and boundary conditions at the liquid-liquid interface

The conventional boundary conditions at the interface between two flowing liquids include continuity of the tangential velocity. We have tested this assumption with molecular dynamics simulations of Couette and Poiseuille flows of two-layered liquid systems, with various molecular structures and interactions. When the total liquid density near the interface drops significantly compared to the bulk values, the tangential velocity varies very rapidly there, and would appear discontinuous at continuum resolution. The value of this apparent slip is given by a Navier boundary condition.     

Analysis of KrF excimer laser beam modification resulting from ablation under closed thick film flowing filtered water

The application of a closed thick film flowing filtered water to immerse the ablation etching mechanism of an excimer laser poses interesting possibilities concerning debris control, modification of machined feature topography and modification of the ablation rate. Furthermore, these parameters have been shown to be dependent on flow velocity; hence, offering further user control of machining characteristics. However, the impact of this technique requires investigation. This contribution offers comparison of the calculated ablation pressure and the effect on feature surface characteristics given for laser ablation of bisphenol A polycarbonate using KrF excimer laser radiation in ambient air against laser ablation of the same substrate under closed thick film flowing filtered water immersion. Also, an impact of such immersion equipment on the optical performance of the micromachining centre used is quantified and reviewed. The pressure is calculated to have risen by a magnitude of 48, when using the liquid immersed ablation technique. This increase in pressure is proposed to have an increased surface roughness, promoting the number of asperities with a surface area lower than 16 μm²; resulting in a diffuse reflection of light and an apparent darkening of features. The focal length of the optical system was accurately predicted to increase by 2.958 mm, when using the closed flowing liquid immersion equipment. This equipment is predicted to have increased the optical depth of focus via reduction in the angle of convergence of the two defining image rays; yet the perceived focus, measured discretely by mean feature wall angle, was found to be 25% smaller when using the closed thick film flowing filtered water immersion technique instead of similar laser ablation in ambient air. A compressed plume interaction is proposed as a contributing factor in this change.     

机载机电公共设备自动化测试技术研究

为研究机载机电公共设备装机后的电缆导通特性、配电功率装置供电功能、传感器性能、综合管理计算机与其它相关系统通信状态的自动化测试技术,设计了一套地面测试用途的测试系统。首先明确了测试对象和测试项目,而后设计了硬件测试环境及其与机载设备交联的电缆,基于LabWindows/CVI开发了软件测试程序,将硬件与软件集成并测试,最后进行了应用。结果表明,设计的测试系统能够对机电公共设备进行全面自动化测试,准确给出测试结果并生成报告,具有应用推广价值。