液滴微粒直径分布的激光散射法测量

本文利用氦氖激光器为光源在自行设计的光散射实验装置上对球形微粒群进行了粒径平均直径及直径分布的理论研究和测量.实验结果表明,本实验装置具有测量精度高、适用范围广和测量粒径范围宽等特点.     

Separation characteristics of alcohol from aqueous solution by ultrasonic atomization

The generation rate of ultrasonically atomized droplets and the alcohol concentration in droplets were estimated by measuring the flow rate and the alcohol concentration of vapors from a bulk solution with a fountain. The effect of the alcohol concentration in the bulk solution on the generation rate of droplets and the alcohol concentration in droplets were investigated. The ultrasonic frequency was 2.4 MHz, and ethanol and methanol aqueous solutions were used as samples. The generation rate of droplets for ethanol was smaller than that for methanol at the same alcohol molar fraction in the bulk solution. For both solutions, at low alcohol concentration in the bulk solution, the alcohol concentration in droplets was lower than that in vapors and the atomized droplets were visible. On the other side, at high concentration, the concentration in droplets exceeded that in vapors and the atomized droplets became invisible. These results could be explained that the alcohol-rich clusters in the bulk solution were preferentially atomized by ultrasonic irradiation. The concentration in droplets for ethanol was higher than that for methanol at low alcohol concentration because the amount of alcohol-rich clusters was larger. When the alcohol molar fraction was greater than 0.6, the atomized droplets almost consisted of pure alcohol.     

Suspension characteristics of water droplet in oil under ultrasonic standing waves

The suspension characteristics of water droplet in oil were investigated under ultrasonic standing waves with high-speed photography in this paper. Firstly, the suspension position of droplet was predicted by theoretical derivation. The motion trajectory of droplet was captured and a kinetic analysis was applied to characterize the suspension position of droplet. The effects of droplet size, acoustic pressure, frequency, as well as density ratio of water and oil on the suspension position of droplet were analyzed in details. It was proved that the droplet size had little effect on the suspension position at different frequencies. The suspension zone approached minimum at 39.4 kHz, and the suspension position of droplet was insensitive to acoustic pressure amplitude and density ratio at this frequency. These would be advantageous to maintain the stability of droplet banding and shorten the width of banding. In addition, it was proved that the suspension position of droplet is approximately linear with the density ratio at different frequencies.     

Experimental study of the effect of helium/nitrogen concentration and initial droplet diameter on nonane droplet combustion with minimal convection

In this paper, we study the influence of inert concentration and initial droplet diameter on nonane (C₉H₂₀) droplet combustion in an environment that promotes spherical droplet flames. The oxygen concentration is fixed while the inert is varied between nitrogen and helium. A range of initial droplet diameters (D_o) are examined in each ambient gas: 0.4 mm < D_o < 0.8 mm; and an oxidizing ambiance consisting of 30% oxygen (fixed) and 70% inert (fixed), with the inert in turn composed of mixtures of nitrogen and helium in concentrations of 0, 25, 50, 75, and 100% N₂. The experiments are carried out at normal atmospheric pressure in a cold ambiance (room temperature) under low gravity to minimize the influence of convection and promote spherical droplet flames. For burning within a helium inert (0% N₂), the droplet flames are entirely blue and there is no influence of initial droplet diameter on the local burning rate (K). With increasing dilution by nitrogen, droplet flames show significant yellow luminosity indicating the presence of soot and the individual burning histories show K reducing with increasing D_o. The evolution of droplet diameter D(t) is nonlinear for a given D_o in the presence of either helium or nitrogen inerts indicating that soot formation has little to do with nonlinear burning. A correlation is presented of the data in the form where the effective burning rate, K′, and ε are concentration-dependent. Correlations for these parameters are presented in the paper.     

Effect of ultrasonic frequency on size distributions of nanosized mist generated by ultrasonic atomization

Ultrasonic atomization is used to produce fine liquid mists with diameter ranges below 100 nm. We investigated the effect of the frequency on the size distribution of ultrasonic mist. A bimodal distribution was obtained for the mist generated by ultrasonic atomization with a wide-range particle spectrometer. The peak diameter decreased with increasing frequency, and the number concentration of the mist increased in the smaller range. We determined the relation between the size distribution of the mist and the ultrasonic frequency, and we proposed a generation mechanism for the ultrasonic nanosized mist based on the amount of water vapor around the liquid column. Increasing the power intensity and density by changing the surface diameter of the ultrasonic oscillator affected the number concentration and size distribution of the nanosized mist. Using this technique, the diameter of the mist can be controlled by changing the frequency of the ultrasonic transducer.     

Interferometric technique for measurement of droplet diameter

The paper considers the optical contact-free method of droplet diameter sizing in the flow cross-section utilizing light interference on a droplet. Distribution of light scattered by a particle was analyzed for different configurations of the measurement system using the Mie theory and approximation of geometrical optics. Basic measurement errors and dynamic range were determined. Possibility of measurements with camera mounting at the angle of 90° to the plane of a laser sheet is shown; this simplifies setup calibration and evens characteristics over the image field. The procedure of measurement system calibration and a set of algorithms for data processing are suggested. The suggested approaches were applied for measurement of characteristics of the gas-droplet jet.     

The formation of metal powders by ultrasonic atomization of molten metals

Ultrasonic liquid automization was first described in 1927. Since then the subject has caught the imagination of both academics and industrialists. This paper describes the continuation of work started by Stamm on the ultrasonic automization of molten metals. In this work experiments were extended to atomization of metal melts with melting points up to 700°C and to frequencies up to 0.8MHz. The example of ultrasonic atomization is used to show that the mechanism of atomization is in accord with the surface wave theory.     

微流控芯片流道特征超声C扫描分析

微流控芯片流道宽度处于微米尺度,存在特征辨识困难的问题。该文选取两种具有不同流道宽度和布局的典型微流控芯片,采用超声C扫描技术进行流道特征成像。利用标称中心频率15 MHz、10 MHz和5 MHz聚焦探头实施水浸C扫描检测,并分析中心频率、焦斑直径、扫描步进等关键参数对流道表征的影响。实验结果表明,对于流道宽度200μm的微流控芯片,当探头中心频率不低于10 MHz、扫描步进不超过0.1 mm时,成像分辨力和流道表征效果最佳,且流道中心间距测量误差不超过5%。同时,超声C扫描图像可以反映流道宽度变化,辨识发生堵塞的微流控芯片。     

Size-selective separation of submicron particles in suspensions with ultrasonic atomization

Aqueous suspensions containing silica or polystyrene latex were ultrasonically atomized for separating particles of a specific size. With the help of a fog involving fine liquid droplets with a narrow size distribution, submicron particles in a limited size-range were successfully separated from suspensions. Performance of the separation was characterized by analyzing the size and the concentration of collected particles with a high resolution method. Irradiation of 2.4 MHz ultrasound to sample suspensions allowed the separation of particles of specific size from 90 to 320 nm without regarding the type of material. Addition of a small amount of nonionic surfactant, PONPE20 to SiO₂ suspensions enhanced the collection of finer particles, and achieved a remarkable increase in the number of collected particles. Degassing of the sample suspension resulted in eliminating the separation performance. Dissolved air in suspensions plays an important role in this separation.     

Correlations to predict droplet size in ultrasonic atomisation.

In conventional two fluid nozzles, the high velocity air imparts its energy to the liquid and disrupts the liquid sheet into droplets. If the energy for liquid sheet fragmentation can be supplied by the use of ultrasonic energy, finer droplets with high sphericity and uniform size distribution can be achieved. The other advantage of ultrasound induced atomisation process is the lower momentum associated with ejected droplets compared to the momentum carried by the droplets formed using conventional nozzles. This has advantage in coating and granulation processes. An ultrasonic probe sonicator was designed with a facility for liquid feed arrangement and was used to atomise the liquid into droplets. An ingenious method of droplet measurement was attempted by capturing the droplets on a filter paper (size variation with regard to wicking was uniform in all cases) and these are subjected to image analysis to obtain the droplet sizes. This procedure was evaluated by high-speed photography of droplets ejected at one particular experimental condition and these were image analysed. The correlations proposed in the literature to predict droplet sizes using ultrasound do not take into account all the relevant parameters. In this work, a truly universal correlation is proposed which accounts for the effects of physico-chemical properties of the liquid (flow rate, viscosity, density and surface tension), and ultrasonic properties like amplitude, frequency and the area of vibrating surface. The significant contribution of this work is to define dimensionless numbers incorporating ultrasonic parameters, taking cue from the conventional numbers that define the significance of different forces involved in droplet formation. The universal correlations proposed are robust and can be used for designing ultrasonic atomisers for different applications. Among the correlations proposed here, those ones that are based on the dimensionless numbers and Davies approach predict droplet sizes within acceptable limits of deviation. Also, an empirical correlation from experimental data has been proposed in this work.     

Influence of adding salt on ultrasonic atomization in an ethanol-water solution

Ethanol was enriched by ultrasonic atomization. Enrichment ratios were increased by adding salt to the ethanol solution. Different enrichment ratios were observed for different types of salts in a range of low ethanol concentrations. The enrichment ratio was significantly improved by adding K(2)CO(3) or (NH(4))(2)SO(4). It is concluded that this is due to enhanced interfacial adsorption of the ethanol. Addition of Na(2)CO(3) to the ethanol solution also enhanced the interfacial adsorption of the ethanol, but the effect was relatively small. Addition of NaCl to the ethanol solution did not enhance the interfacial adsorption of the ethanol.     

The atomization current and droplet size of ethanol in two different small-scale electro-spraying systems

An experimental study on electro-spraying from small-scale combustors is carried out using liquid ethanol as fuel. Two systems of electro-spraying are employed in the present study; one is a nozzle system (without a ring electrode) and the other is a nozzle-ring system (with a ring electrode). The photos of electro-spraying at the cone-jet mode are taken by a digital camera. The voltage drop across the resistance in the loop is measured by a data acquisition instrument, and the atomization current is calculated according to Ohm's Law. The size and velocity of electro-spraying droplets are measured by a Phase Doppler Anemometer. A non-dimensional analysis on atomization current is completed to explain the electro-spraying phenomena of liquid at the stable cone-jet mode. The results show that, the lower atomization current and droplet velocity corresponds to smaller size of droplet. Based on the results of non-dimensional analysis, it is found that the dimensionless atomization current in both the nozzle system and nozzle-ring system obeys the scaling law as square root of the dimensionless flow rate. The charge density is of a −1.5 power dependence on droplet diameter. Both of the nozzle and the nozzle-ring systems show a good agreement with Rayleigh instability.     

Enrichment of surfactant from its aqueous solution using ultrasonic atomization

Dilute aqueous solutions of dodecyl-benzenesulfonic acid sodium salt (DBS-Na) and polyoxyethylenenonylphenyl ethers (PONPEs) were ultrasonically atomized. The surfactants were concentrated in collected mist droplets. The enrichment ratio increased with decreasing surfactant concentration. Depending on the surfactant’s molecular weight and affinity to water, different enrichment ratio was observed in the range of low feed concentrations. For anionic surfactant, DBS-Na, the enrichment ratio was significantly improved by KCl addition and a peak appeared on the plot of the ratio against KCl concentration. Addition of NaCl or CaCl₂ · 2H₂O to the surfactant solution also enhanced the enrichment ratio; however, the effect was relatively small. Such behaviors of the ratio were interpreted as enhanced interfacial adsorption of the surfactant and a lack of supply of surfactant monomers from liquid bulk because of slow breaking of surfactant micelles. Time required for collecting an amount of mist was also observed. Among the three salt systems, the time for KCl system was twice as long as others. This fact suggested that the formation of smaller droplets in KCl system.     

Determination of biomass concentration by measurement of ultrasonic attenuation

Experimental results are presented that demonstrate that ultrasonic attenuation can be used to estimate the biomass concentration of a biological suspension. The attenuation approach avoids the temperature sensitivity of established ultrasound velocity test methods, which have hindered their application in process environments. An empirical model is presented for the estimation of the biomass of Microcystis aeruginosa suspensions based on acoustic attenuation, temperature, and frequency, and is compared with experimental results.     

Changes of water solution properties under the processes of their ultrasonic atomization

Acoustical Physics - Transformation of diluted water solutions of medicines into medicinal aerosols in ultrasonic inhalers leads to variation of concentration ratios for solution components in an...     

超声波盐酸浓度计的研制

本文介绍了一种根据盐酸浓度、温度和声速三者之间的相互关系来进行在线检测的超声波盐酸浓度计。通过实验,作者精确地测定了不同浓度和温度的盐酸溶液中的超声波声速,给出了盐酸的声速浓度系数和声速温度系数。     

Production of Fine Particles from Melts of Metals or Highly Viscous Fluids by ultrasonic standing wave atomization

Ultrasonic standing wave atomization (USWA) is a new process capable of atomizing both high surface energy liquids and highly viscous liquids. Atomization is achieved through acoustic forces acting upon a liquid jet which is guided into the central pressure node of a standing wave field. Spherical metal powders with minimum mass median diameters of less than 15 μm have been produced from metal melts with surface tensions of about 0.5 N/m. Organic liquids with viscosities between 1 and 10 Pas have been atomized, yielding mass median diameters from 20 to 330 μm. The influence of different operating parameters on the mass median diameter of metal melts and highly viscous liquids was evaluated. Parameters which were varied were ambient gas pressure, vibration amplitude of the transducers, mass flow rate, density of liquid, viscosity of the liquid, surface tension and the outlet diameter. The powders and sprays were analyzed with laser diffraction particle sizers. The physical background of the atomization process is discussed and an equation for the prediction of the mass median diameter is derived.     

Experimental studies on droplet characteristics in a microfluidic flow focusing droplet generator: effect of continuous phase on droplet encapsulation

The European Physical Journal E - Interaction of cytoskeletal filaments, motor proteins, and crosslinking proteins drives important cellular processes such as cell division and cell movement....     

Electrical characteristics of metal-dielectric-semiconductor structures with silicon nitride prepared by reactive cathode atomization

The effect of the technology of preparation of silicon nitride in a low temperature gas discharge plasma upon the volt-ampere and volt-farad characteristics of metal-dielectricsemiconductor (MDS) structures (Al-Si₃N₄-Si-Al) is studied. It is shown that by using a heterogeneous Si₃N₄ formation reaction with ionic purification of the silicon surface, it is possible to obtain MDS structures with lower and more stable surface charge in comparison to similar structures in which the Si₃N₄ is grown by other methods (for example, gas transport reaction methods). The conductivity of the Si₃N₄ film is described approximately by the well known Frankel model, and its value is close to that of Si₃N₄ films prepared by other methods.