External Flow of an Acoustically Levitated Droplet

One of the major recent advances for experiments in containerless processing is acoustic levitation. Although there are a lot of previous studies for acoustic levitation, characteristic of external flow of an acoustically levitated droplet is not experimentally examined enough. In this study, external flow field has been observed by using high speed camera and Particle Image Velocimetry. In the case of any levitated droplet at a velocity antinode of standing wave, toroidal vortex are generated around levitated droplet. It is found that toroidal vortex around a levitated droplet is strongly affected by viscosity of levitated samples and input voltage. In terms of water droplet, as input voltage is decreased, location of toroidal vortex is moved from bottom to top of levitated samples.     

Study on Heat Transfer and Flow Characteristic Under Phase-Change Process of an Acoustically Levitated Droplet

Acoustic levitation is one of the levitation technique which is expected to be used for analytical chemistry and manufacturing new materials. Thus, it is important to gather the knowledge about acoustically levitated droplet. The purpose of this study is to investigate the heat transfer and flow behavior under phase change process of an acoustically levitated droplet. The following results were obtained from experiments. Evaporation process and external flow structure of the levitated droplet is visualized by a high speed camera and it is found that they differ by the type of fluid. Toroidal vortices are observed near the surface of the ethanol solution droplet. Heat transfer coefficient is estimated from the volume change and temperature gradient. It is substantially higher than that estimated by the existing experimental correlation.     

Effect of Temperature Change on Interfacial Behavior of an Acoustically Levitated Droplet

Under the microgravity environment, new and high quality materials with a homogeneous crystal structure are expected to be manufactured by undercooling solidification, since the material manufacturing under the microgravity environment is more static than that under the normal gravity. However, the temperature change on the interface of the material in space can affect on the material processing. The purpose of the present study is to investigate effect of the temperature change of interface on the large levitated droplet interface. A water droplet levitated by the acoustic standing wave is heated by YAG laser. In order to heat the water droplet by the laser heating, rhodamine 6G is solved in it to achieve high absorbance of the laser. The droplet diameter is from 4 to 5.5 mm. The deformation of the droplet interface is observed by high speed video camera. The temperature of droplet is measured by the radiation thermometer. It is noticed that the larger droplet under the higher sound pressure tends to oscillate remarkably by the laser heating.     

Effect of Laser Heating on Nonlinear Surface Deformation of Acoustically Levitated Droplet

Under the microgravity environment, new and high quality materials with a homogeneous crystal structure are expected to be manufactured by undercooling solidification, since the material manufacturing under the microgravity environment has no effect of gravity. However, the temperature change on the interface of the material in space is expected to affect on the material processing due to the changing of physical property corresponding temperature. The purpose of the present study is to investigate effect of the laser heating on surface deformation of large levitated droplet. A water droplet levitated in the acoustic standing wave is heated by YAG laser. In order to increase the water droplet temperature, rhodamine 6G is solved in it to achieve high absorbance of the laser. Droplet from 2.5 to 5.5 mm in diameter were levitated and heated. The deformation of the droplet interface has been observed by high speed video camera. We used the radiation thermometer for the measurement of the temperature of droplet surface. It is noticed that the heated droplet deforms with its resonance frequencies. The experimental result of shape oscillation makes it possible to simulate the oscillation.     

IR-Thermography of Evaporating Acoustically Levitated Drops

The surface temperature of evaporating acoustically levitated drops has been monitored by IR-thermography. The thermography system has been calibrated by simultaneous measurements with a thin thermocouple. The integral IR-emission coefficients of a few pure liquids have been derived. Evaporation processes of pure liquids and of binary mixtures of liquids have been studied with levitated drops. Using drop surface temperatures, we were able to calculated analytically binary gas-diffusion coefficients of liquids in ambient air.     

Surface Oscillations of an Electromagnetically Levitated Droplet

The natural oscillation frequency of freely suspended liquid droplets can be related to the surface tension of the material, and the decay of oscillations to the liquid viscosity. However, the fluid flow inside the droplet must be laminar to measure viscosity with existing correlations; otherwise the damping of the oscillations is dominated by turbulent dissipation. Because no experimental method has yet been developed to visualize flow in electromagnetically levitated oscillating metal droplets, mathematical modeling can assist in predicting whether or not turbulence occurs, and under what processing conditions. In this paper, three mathematical models of the flow: (1) assuming laminar conditions, (2) using the k−ɛ turbulence model, and (3) using the RNG turbulence model, respectively, are compared and contrasted to determine the physical characteristics of the flow. It is concluded that the RNG model is the best suited for describing this problem when the interior flow is turbulent. The goal of the presented work was to characterize internal flow in an oscillating droplet of liquid metal, and to verify the accuracy of the characterization by comparing calculated surface tension and viscosity values to available experimental results.     

Droplet Deformation and 2-D/3-D Marangoni Flow Phenomena in Droplets Levitated by Electric Fields

An integrated numerical model is presented for free surface phenomena and Marangoni fluid flows in electrically levitated droplets under both terrestrial and microgravity conditions. The model development is based on the boundary element solution of the Maxwell equations simplified for electrostatic levitation applications and the free surface deformation that is primarily caused from the surface Maxwell stresses resulting from the applied electric fields. The electric and free surface model is further integrated with a finite element model for the surface-tension-induced fluid flows in the levitated droplets. Both 2-D and 3-D fluid flow structures may be developed in the electrically levitated droplets depending on the applied laser heating sources. The integrated model is applied to study the electric field distribution, free surface deformation, and 2-D and 3-D internal fluid flow structures in normal and microgravity for single, symmetric two-beam, four-beam, and six-beam laser heating arrangements. Among these arrangements, the six-beam arrangement with equal heating intensity gives the smallest temperature difference and the smallest maximum velocity.     

Melt Flow Instability and Turbulence in Electro-Magnetically Levitated Droplets

This article addresses fluid flow instabilities and flow transition to turbulent chaotic motions through numerical analysis and turbulence in electro-magnetically levitated droplets through direct numerical simulations. Numerical implementation and computed results are presented for flow instability and turbulence flows in magnetically levitated droplets under terrestrial and microgravity conditions. The linear melt flow stability is based on the solution of the Orr-Sommerfeld linearized equations with the base flows obtained numerically using high order numerical schemes. The resulting eigenvalue problems are solved using the linear transformation or Arnold's method. Melt flow instability in a free droplet is different from that bounded by solid walls and flow transits to an unstable motion at a smaller Reynolds number and at a higher wave number in a free droplet. Also, flow instability depends strongly on the base flow structure. Numerical experiments suggest that the transition to the unstable region becomes easier or occurs at a smaller Reynolds number when the flow structures change from two loops to four loops, both of which are found in typical levitation systems used for micro-gravity applications. Direct numerical simulations (DNS) are carried out for an electro-magnetically levitated droplet in a low to mild turbulence regime. The DNS results indicate that both turbulent kinetic energy and dissipations attain finite values along the free surface, which can be used to derive necessary boundary conditions for calculations employing engineering k--ε models.     

Droplet Dynamics On a Body Surface In a Gas Flow

High Temperature - The results of previous studies of the water droplet dynamics on a horizontal surface blown by air are briefly reviewed. The experiments were carried out on rectangular wing...     

内文丘里管流量计及应用

本文介绍内文丘里管的工作原理、结构、技术性能及优缺点。内文丘里管(又称环形锥管),是新一代差压式流量测量仪表,是对传统文丘里管做了改型的异型文丘里管,它集经典文丘里管、环形孔板和耐磨孔板计量性能优点于一体,并且在能源计量工作中已取得良好的使用效果。     

Non-immersive Ultrasound Scanning and Inspection of Internal Defects Using a Water Droplet Coupling Device

This paper investigates a method for conducting conventional ultrasound image scanning (C-scan) in a non-immersive manner. An ultrasound coupling device is developed to couple a focusing ultrasound transducer with a sample under test through a water droplet. The transducer is immersed in a chamber filled with water. A hole-opening at the chamber’s bottom surface and a polymer film sealing the hole allow focused ultrasound to pass and reach the sample through a water droplet. An ultrasound scanning system is constructed and used for carrying out C-scan on two different samples containing pre-fabricated internal defects. By comparing the images obtained from using both conventional water immersion method and the proposed water-droplet coupling method, we demonstrate the feasibility and capability of this new type of non-immersive ultrasound image scanning method.     

Coalescence of Levitated He II Drops

We describe experiments to study the coalescence of He II drops levitated in a magnetic trap. Using a high speed CCD camera, we have produced movies of drops coalescing at temperatures as low as 0.7 K. We examine some interesting features of the motion during and following coalescence.     

Acoustically driven photon antibunching in nanowires

The oscillating piezoelectric field of a surface acoustic wave (SAW) is employed to transport photoexcited carriers, as well as to spatially control exciton recombination in GaAs-based nanowires (NWs) on a subns time scale. The experiments are carried out in core-shell NWs transferred to a SAW delay line on a LiNbO(3) crystal. Carriers generated in the NW by a focused laser spot are acoustically transferred to a second location, leading to the remote emission of subns light pulses synchronized with the SAW phase. The dynamics of the carrier transport, investigated using spatially and time-resolved photoluminescence, is well-reproduced by computer simulations. The high-frequency contactless manipulation of carriers by SAWs opens new perspectives for applications of NWs in opto-electronic devices operating at gigahertz frequencies. The potential of this approach is demonstrated by the realization of a high-frequency source of antibunched photons based on the acoustic transport of electrons and holes in (In,Ga)As NWs.     

中国需要高速磁悬浮列车

20世纪,高速磁悬浮列车的发展令人瞩目,高速磁悬浮列车技术已成熟到可建造实用运营线的程度,从而使人类地面客运的速度可望在21世纪中前期达到550km/h的新水平。文章简要叙述了高速磁悬浮列车的发展、特点与优势,它主要适用于长距离、大城市间、大流量的客运。从我国的国情与未来需求出发,指出它最适合于我国高速客运专线网的发展,就京沪高速铁路而言,也比高速轮轨列车有着明显的优越性,发展高速磁悬浮列车体系是当务之急,并对当前应抓紧试验运营线的建设等工作提出了建议。     

A Model of Polydisperse Vapor–Droplet Mixture Flow in a Vortex Chamber

Journal of Engineering Physics and Thermophysics - A thermo- and hydrodynamic model of polydisperse vapor–droplet mixture flow in a vortex evaporation chamber has been described. The motion...     

Study of Interaction of Disturbances in an Internal Flow

Data on narrowband acoustic disturbances that arise in manifold pipes with one or two blind branches and in wind tunnels with an open working section are analyzed. The ranges of acoustic instability that correspond to excitation of selfoscillations in a flow in the cases mentioned are determined. The dependence of the intensity of acoustic radiation in two blind branches and in the manifold between them on the multiplicity of the length of the resonance section to the length of halfwaves of resonance frequency is considered. The possibility of attenuation of selfoscillations by organizing hydrodynamic structures that interact with formations generating acoustic oscillations is determined.     

Probing Cell Deformability via Acoustically Actuated Bubbles

An acoustically actuated, bubble‐based technique is developed to investigate the deformability of cells suspended in microfluidic devices. A microsized bubble is generated by an optothermal effect near the targeted cells, which are suspended in a microfluidic chamber. Subsequently, acoustic actuation is employed to create localized acoustic streaming. In turn, the streaming flow results in hydrodynamic forces that deform the cells in situ. The deformability of the cells is indicative of their mechanical properties. The method in this study measures mechanical biomarkers from multiple cells in a single experiment, and it can be conveniently integrated with other bioanalysis and drug‐screening platforms. Using this technique, the mean deformability of tens of HeLa, HEK, and HUVEC cells is measured to distinguish their mechanical properties. HeLa cells are deformed upon treatment with Cytochalasin. The technique also reveals the deformability of each subpopulation in a mixed, heterogeneous cell sample by the use of both fluorescent markers and mechanical biomarkers. The technique in this study, apart from being relevant to cell biology, will also enable biophysical cellular diagnosis.     

Shape Oscillations in Levitated He II Drops

We describe experiments to study the shape oscillations of levitated He II drops. Drops of approximately 0.5 cm diameter are levitated magnetically with a superconducting solenoid, and shape oscillations are induced with an ac electric field. We have measured the damping of shape oscillations as a function of temperature. The damping rate is compared to that predicted by a two fluid, hydrodynamic model, which takes account the effect of the motion in the vapor. The effects of condensation and evaporation on the motion of the drop are also considered.     

基于Fluent的气液两相流喷嘴内部流动特性仿真

目的探究气液两相流喷嘴内部流动特性及工作参数对流动特性的影响。方法测量得到气液两相流喷嘴的结构图,利用Fluent软件建立喷嘴模型,并选择流体体积(VOF)两相流模型和RNG(重整化群)k-?湍流模型,以常温状态下液态水和空气为研究介质,并以气压和液压为变量,进行多参数的流动特性分析,并引入气液比的概念。结果得到了不同时刻喷嘴内部的压力、速度及液相分布云图。其中最大压力为827 kPa,出现在出口段和进气段交叉的壁面上,由于喷嘴内部出现缩口,故出口段存在负压(?1.53 MPa);喷嘴内部最高速度出现在气液两相交汇处,为134 m/s;液相在最初迅速充满喷嘴后,逐渐与气相混合,最终出口段中心液相体积占比为0.543,混合情况良好。还得到了多参数对喷嘴内部压力、速度及液相分布的影响。结论使用软件仿真的方法得到了喷嘴内部的流动特性和多参数对流动特性的影响规律,并为进一步研究优化喷嘴结构及喷雾提供了建议和参考。     

Acoustically resonant pulsed photoacoustic technique for liquids

The use of resonant piezoceramic transducers in the pulsed photoacoustic technique and the effect of the focusing of the probing beam have been investigated experimentally. The improved sensitivity for resonant detection and for more tightly focused probing beams has been verified. The constraints imposed when working with tightly focused beams are noted.