超声法测量高浓度矿浆两相流粒径分布和浓度

研究了超声衰减谱法和超声多次回波反射法测量高浓度矿浆两相体系粒径分布和浓度。实验测量了多个浓度下硫矿浆在3～6 MHz频率下的声衰减谱,结合反演算法由实验数据计算得到矿浆两相流粒径分布。同时测量了不同浓度下硫矿的声阻抗值,由超声多次回波反射法计算得到浓度。粒径分布与浓度测量得到的结果与标准配置值较为吻合,表明超声法适用于高浓度矿浆两相流粒径分布和浓度的在线检测。     

多频声衰减法测量低密度差异液固两相流粒径分布

针对低密度差异液固两相流的分散相粒径分布测量问题,提出多频超声衰减测量方法。以ECAH (Epstein Carhart Allegra Hawley theory)理论模型为基础,分析了不同物性参数对多频超声衰减的影响,建立了分散相粒径分布与多频超声衰减之间的理论关系,用于计算被测流体中超声衰减的理论预测值。通过构造实测多频衰减与待求粒径分布间的目标函数,将粒径分布的反演表示为优化问题,利用高斯量子粒子群算法对不同粒径颗粒浓度参数寻优,实现粒径分布的反演。以微米级聚苯乙烯颗粒与水制备的悬浮液作为研究对象,在搅拌条件下进行动态实验。实验结果表明,利用4~11 MHz的多频超声衰减测得的粒径分布,与Mastersizer 2000激光粒度分析仪的测量结果基本一致,平均粒径误差为5.60%。     

超声法测量高浓度水煤浆若干问题研究

利用超声法在线测量高浓度水煤浆具有无需稀释、快速、在线、非接触等优势.本文探讨了水煤浆中的浓度测量问题.在理论分析和实验基础上得出了水煤浆中声速与浓度的关系,指出水煤浆温度、稳定性、粒径与声速的关系和对浓度测量的影响,并从理论上提出了水煤浆中粒径测量的方法.本文设计的实验装置适合在线测量中的应用.     

高密度超细颗粒高浓度悬浊液超声衰减的数值模拟分析

以拓展耦合相ECP理论模型为基础,通过对高浓度超细二氧化钛-水悬浊液和玻璃微珠-水悬浊液中超声衰减的数值计算分析,讨论了高密度差异颗粒两相介质在高浓度情况下,超声频率、颗粒粒径大小、颗粒浓度对超声波衰减的影响,为高密度超细颗粒在高浓度悬浊液中颗粒粒度和浓度的超声波测量提供理论支持。     

超声衰减法测量油水分散流中颗粒粒度分布

针对油水分散流的颗粒粒度测量问题,提出一种基于多频率下超声衰减作用的测量方法。根据多相流体中超声衰减的BLBL模型,推导出超声衰减系数与颗粒粒度分布存在的数学表达关系。通过多频率条件下所获得的超声衰减系数进行联合比较分析,求解被测流体中颗粒粒度分布.通过对含油率低于30%的5个样本中4种颗粒粒度分布的油水分散流进行数值模拟仿真实验,得到颗粒粒度占比分布的测量结果,并对结果进行分析,得到BLBL模型在毫米尺度油相颗粒作为离散相的油水分散流中的适用条件和范围。     

非侵入式超声波浆料浓度测量技术研究*

设计了一种基于非侵入式超声波透射衰减法的浆料浓度测量系统,根据超声传播衰减原理,建立超声衰减值与浆料浓度之间的关系。实验中采用生物显微镜和激光粒度仪对颗粒标称粒径进行验证,采用中心频率为200 kHz的超声波换能器,利用一发一收模式对超声波在有机玻璃管内的浆料进行非侵入式测量并分析透射波信号,对体积百分浓度小于25%、不同粒径的石英砂浆料进行测量,通过拟合方法获得浆料温度、体积百分浓度与声衰减对应的关系,并据此构造浓度求解方程,通过现场实时在线测量并与取样结果进行对比验证方程的准确性,结果显示,本方法可有效测量浆料浓度。     

超声脉冲背向散射法测量悬浊液浓度的研究

本文报导了在不同浓度和不同粒径的水泥浆悬浊液中超声脉冲背向散射讯号的数字特征,主要是幅域和频域特征.对于不同的浓度范围,可以取不同的背向散射讯号特征量(如散射声强或散的衰减)来表征是浊液的浓度和粒径.对于低浓度范围,相对散射声强与浓度有较好的线性关系,对于高浓度范围,声强的散射衰减与浓度有较好的线性关系,高浓度与低浓度之间存在着过渡区域,在此区域内,散射声强随浓度的增加与散射衰减随浓度的增加呈动态平衡,因而在过渡区域内散射声强将与浓度无关,并与频率或粒径有关,当频率一定时,可确定粒径分布.     

基于后向散射的高浓度纳米颗粒粒度分布测量方法研究

传统的动态光散射法通常采集侧向散射进行纳米颗粒粒度分布的测量,由于多次散射的影响,利用侧向散射不能准确测量高浓度样品的颗粒粒度分布。针对该问题,对后向散射测量方法进行了研究,在实验基础上提出了后向散射最佳光程的判断准则。在不同样品浓度下,用侧向散射和后向散射方法对标称粒径分别为110 nm、220 nm的聚苯乙烯乳胶球颗粒进行了测量。实验结果表明,对于高浓度的待测样品,后向散射测量方法通过自适应调整光程,在最优光程处进行测量,能够有效得到高浓度纳米颗粒的粒径及粒度分布,测量结果相对误差为2.72%。     

基于二阶滤波器的消光起伏谱颗粒测量结果

消光起伏频谱法是一种新的测量两相流系统中颗粒粒径分布和浓度的方法,装置简单,操作方便,适合实时、在线测量。采用二阶低通滤波器对起伏的透射率信号分析,得到消光起伏频谱实验数据,并利用改进的Chahine循环方法计算得到颗粒的粒径分布和浓度信息。重点讨论高浓度情况,包括对特征函数频率响应的修正和对其阶高修正两个方面,得到修正参量并运用到反演算法中从而得到正确的测量结果。测量结果表明,通过高浓度修正,消光起伏频谱法可以在很大的颗粒浓度动态范围得到合理的测量结果,其可测颗粒最大体积分数视颗粒的大小而定。     

超声波多次回波反射法测量两相流密度实验研究

本文利用超声波在一侧壁面内的多次反射确定两相流的声阻抗值,从一侧壁面通过两相流到另一侧壁面再反射回来的二次回波时差确定两相流中声速,对这两个数据采用超声多次回波测量理论进行处理,可以得到两相流密度和浓度.不同浓度下的水煤浆实验结果表明,该方法测量得到的结果与珲论值较为吻合.并且超声波多次回波反射法的测量装置具有结构简单,非侵入式测量,实时处理数据以及不受超声发射功率影响等优势,适合高浓度两相流密度和浓度的在线测量.     

考虑晶粒分布的多晶体材料超声散射统一理论

现有超声散射统一理论可通过多晶体材料的微观结构和力学特性，实现全频域范围内衰减和相速度的正演建模，但其忽略晶粒尺寸分布的影响，进而降低了正演模型的计算精度.本文对不均匀介质的波动方程进行二阶Keller近似，用全频域格林函数推导介质中的平均波；以截断对数正态分布描述晶粒分布，构建加权的空间相关函数；结合材料的弹性模量协方差，建立含晶粒分布的超声散射统一理论，揭示晶粒分布对超声散射的影响规律；制备304不锈钢试块并开展超声散射实验.结果表明考虑晶粒分布特性后，纵波衰减谱和相速度谱相对于实验结果的相异性降低约49%和64%，横波衰减谱和相速度谱相对于实验结果的相异性降低约12%和4%.可见，本文的统一理论模型能有效修正晶粒分布导致的衰减谱和相速度谱偏差，为晶粒分布反演评价提供理论基础.     

On-Line Particle Size Analysis Using Ultrasonic Velocity Spectrometry

A new method is described for the determination of particle size distribution of slurries based on ultrasonic velocity spectrometry combined with gamma-ray transmission. This method shares the advantages of ultrasonic attenuation spectroscopy of being capable of analyzing highly concentrated samples without dilution. However the ultrasonic velocity method is better suited to fine particles of diameter from about 0.1 to 30 μm, a greater volume of slurry is analysed and therefore sampling errors are reduced, and precise theoretical models are readily available to permit the accurate determination of size distribution by inversion of ultrasonic velocity measurements. The method can also be used to accurately determine particle size cut points by linear correlation. Using either inversion or correlation methods, the accuracy of particle size information from ultrasonic velocity spectroscopy is significantly enhanced by the independent measurement of solids loading by gamma-ray transmission. In addition, larger sizes can be measured by combining the ultrasonic velocity method with ultrasonic attenuation measurements. The method has been tested in the laboratory on a wide variety of mineral and paint slurries. The method determined the size distribution of single component silica and alumina samples in water in agreement with laser diffraction measurements and the method successfully distinguished well and poorly dispersed TiO₂ suspensions. For composite samples the method discriminated separate TiO₂ and CaCO₃, components and determined their proportions to within 0.25% volume. In addition the method, in combination with ultrasonic attenuation measurements, determined the size fractions of iron ore slurries below 10 and 30 μm to within 1.3% and 1.0% relative respectively, when compared with laser diffraction measurement of particle size. The CSIRO is presently designing an industrial gauge which will be manufactured and installed in an industrial slurry stream in 1997.     

Absorption and velocity dispersion due to crystallization and melting of emulsion droplets

The influence of droplet crystallization and melting on the ultrasonic properties of oil-in-water emulsions has been investigated. The ultrasonic velocity and attenuation were measured in a series of 3 wt% n-hexadecane-in-water emulsions as a function of frequency (0.3–4 MHz), droplet diameter (0.4 and 1 μm) and temperature (0–25°C). The emulsified n-hexadecane crystallized at about 5°C due to supercooling effects and melted at about 18°C. As solid and liquid n-hexadecane have significantly different ultrasonic properties, an appreciable change in the velocity and attenuation is observed during the phase transition. This behaviour is modified significantly in systems where the emulsion droplets are partially crystalline because the temperature fluctuations associated with the ultrasonic wave can perturb the phase equilibria solid liquid causing excess attenuation and velocity dispersion. The magnitude of this effect depends on the ultrasonic frequency and the average droplet size.     

Influence of milk fat globule membrane and milk protein concentrate treated by ultrasound on the structural and emulsifying stability of mimicking human fat emulsions

The primary objective of the present study was to investigate the effectiveness of ultrasonic treatment time on the particle size, molecular weight, microstructure and solubility of milk fat globule membrane (rich in phospholipid, MPL) and milk protein concentrate (MPC). The mimicking human fat emulsions were prepared using modified proteins and compound vegetable oil and the structural, emulsifying properties and encapsulation efficiency of emulsions were evaluated. After ultrasonic treatment, the cavitation caused particle size decreased and structure change of both MPL and MPC, resulting in the enhancement of protein solubility. While, there was no significant change in molecular weight. Modified proteins by ultrasonic may cause a reduction in particle size and an improvement in emulsifying stability and encapsulation efficiency of emulsions. The optimal ultrasonic time to improve functional properties of MPL emulsion and MPC emulsion were 3 min and 6 min, respectively. The emulsifying stability of MPL emulsion was superior to MPC emulsion, which indicated that MPL is more suitable as membrane material to simulate human fat. Therefore, the obtained results can provide basis for quality control of infant formula.     

Enhanced creaming of milk fat globules in milk emulsions by the application of ultrasound and detection by means of optical methods

The effects of application of ultrasonic waves to recombined milk emulsions (3.5% fat, 7% total solids) and raw milk on fat destabilization and creaming were examined. Coarse and fine recombined emulsions (D[4,3]=9.3 μm and 2.7 μm, respectively) and raw milk (D[4,3]=4.9 μm) were subjected to ultrasound for 5 min at 35°C and 400 kHz or 1.6 MHz (using a single transducer) or 400 kHz (where the emulsion was sandwiched between two transducers). Creaming, as calculated from Turbiscan measurements, was more evident in the coarse recombined emulsion and raw milk compared to that of the recombined fine emulsion. Micrographs confirmed that there was flocculation and coalescence in creamed layer of emulsion. Coalescence was confirmed by particle size measurement. These results imply that ultrasound has potential to pre-dispose fat particles in milk emulsions to creaming in standing wave systems and in systems with inhomogeneous sound distributions.     

Improvement in properties of coal water slurry by combined use of new additive and ultrasonic irradiation

Coal water slurry (CWS) was prepared with a newly developed additive from naphthalene oil. The effects of ultrasonic irradiation on coal particle size distribution (PSD), adsorption behavior of additive in coal particles and the characteristics of CWS were investigated. Results showed that ultrasonic irradiation led to a higher proportion of fine coal in CWS and increased the saturated adsorption amount of additive in coal particles. In addition, the rheological behavior and static stability of CWS irradiated by ultrasonic wave were remarkably improved. The changes on viscosity of CWS containing 1% and 2% additive are qualitatively different with the increasing sonication time studied. The reason for the different effect of sonication time on CWS viscosity is presented in this study.     

A study on measuring distribution of nanoparticle size based on ultrasonic attenuation spectrum

Through varying the ultrasonic path length,the ultrasonic attenuation spectrum of the nanometer particle suspensions is measured.Based on the McClements and BLBL model, the Optimum Regularization Technique is employed to inverse the distribution of particle size for nanometer particles.Experiments are carried out to measure the distribution of particle size of aqueous nanometer titanium dioxide suspension with volume fraction of 1%.The ultrasonic measurement results show good consistence with those from TEM(Transmission Electron Microscope) and centrifugal sedimentation particle size analyzers,which indicate that measuring distribution of the particle size of nanometer particles with the ultrasonic attenuation spectrum is feasible and reliable.     

平面波经颅超声成像相位校正及散斑跟踪*

准确的脑血流成像对脑功能监测和脑疾病的快速诊断具有重要意义,然而颅骨对超声传播的影响会导致成像质量下降、速度或位移估计不准确等问题。论文采用平面波相干复合结合散斑跟踪方法进行颅内散射目标成像和速度估计,以实现脑血流速度矢量检测;针对颅骨存在导致的超声相位畸变,利用数值仿真和体模实验研究了其对成像及散斑跟踪效果的影响,并采用近似射线声学理论方法进行校正。数值结果表明颅骨的存在造成目标运动速度估计的相对误差达到55%左右,校正后误差降至约12%;体模实验中对目标位移大小和角度估计的平均误差在校正前分别约为16%和28%,校正后均降至1%左右。该研究结果可为超声颅脑疾病诊疗设备的研制提供理论指导和技术支持。     

Ultrasound pre-fractured casein and in-situ formation of high internal phase emulsions

Traditional preparation of protein particles is usually complex and tedious, which is a major issue in the development of Pickering high internal phase emulsions (HIPEs). In this study, a facile and in-situ method for the preparation of food-grade Pickering HIPEs was developed using ultrasound pre-fractured casein flocs. The ultrasonic-treated casein protein and resulting Pickering HIPEs were characterised using particle size distribution, confocal laser scanning microscopy (CLSM), cryo-SEM, and rheological measurement. The results indicated that pH values of casein and ultrasonic power level were key parameters for casein protein dispersion into nanoparticles to form o/w Pickering HIPEs. In optimal conditions, the hexagons of emulsion droplets were close together, and the emulsions formed with ultrasonic caseins exhibited gel-like behaviour. Additionally, ultrasonic microscale-sized caseins (about 25 μm) disappeared upon the use of high speed homogenisation during the formation of HIPEs, while the chemical distribution revealed by confocal laser scanning microscopy indicated that the dispersive nanoparticles from casein proteins were evidently absorbed on the interface of HIPEs (cryo-SEM). These findings prove that ultrasound is an effective tool to loosen casein flocs to induce the in-situ formation of stabilised Pickering HIPEs. Overall, this work provides a green and facile route to convert edible oil into a soft solid, which has great potential for applications in biomedical materials, 3D printing technology, and various cosmetics.     

Ultrasonic attenuation and velocity properties in rat liver as a function of fat concentration: a study at 100 MHz using a scanning laser acoustic microscope

This study examines the extent to which ultrasonic attenuation coefficients and velocity properties change between normal and fatty rat liver. The view of this problem is toward the application in clinical medicine in the future. Fatty livers were produced in rats by feeding them alcohol diets in liquid form. The animals were sacrificed and the fat concentration of the liver specimens determined. The fat concentration varied from 2.5% to 16.8% wet weight. The ultrasonic attenuation coefficient and velocity properties in 28 specimens were measured at 100 MHz with the scanning laser acoustic microscope (SLAM). Regression analysis was applied to the liver's ultrasonic propagation properties as a function of fat concentration. The results show that the attenuation coefficient increases at a rate of 1.08 dB/mm/% fat and the velocity decreases at a rate of 2.3 m/s/% fat as the fat concentration increases.