超声空化效应对溶液电导率的影响

大功率超声作用于溶液时会产生空化效应,并影响溶液的物理化学性质,如电导率、液体粘度及液体表面张力等。文章对不同功率的超声作用于弱电解质溶液时其电导率的变化进行了实验研究,发现溶液电导率与超声波强度有关。当强度增大到有空化产生时,电导率开始减小;继续增大强度,溶液电导率减小到一定程度后有小幅回升现象出现。且液体内空化效应的出现将导致液体的电导率减小,空化达到一定强度时,空化效应引起的局部瞬态高温高压、冲击波和微射流导致的新导电粒子,会使电导率小幅回升。     

可见光辐照下碘释放现象超声效应的实验研究

1引言 超声波辐照水溶液时,空化泡在声波的作用下形成、振荡、生长、收缩至崩溃.空化泡崩溃时在空化泡周围的极小空间内可以产生5000K以上的高温和高达5×107pa的高压等极端物理条件,同时可以产生氧化电位很高、化学性质十分活泼的羟基自由基(·OH)[1].利用声空化发生时产生的物理化学条件,通过进行超声预处理,可产生一系列声化学效应如超声诱导效应等,提高反应的产率和速率[2,3].本文研究了碘化钾溶液在可见光辐照下碘释放现象的超声效应.实验结果表明:超声的预辐照可以大大增加碘释放量.我们采用临界模型对该现象进行了初步分析.     

仿体中超声空化效应的B超图像处理

0引言使用高强度聚焦超声(HIFU)照射组织,将产生声空化现象。在声空化过程中,声场能量于空化气泡内高度集中,当能量积累到一定阈值后,空化气泡瞬间崩溃。在气泡崩溃的瞬间能量会释放出来,形成局部的高温、高压、强冲击波等极端物理现象[1]。这将使周围的组织细胞遭到损伤。因此,对HIFU空化的监控显得尤其重要[2]。本文主要研究不同脉冲宽度的高强度聚焦超声(HIFU)在体外仿体中引起的空化气泡群面积随时间的变化。从而实现对HIFU空化的实时监控。     

超声波在量块清洗中的应用

1　超声波清洗原理超声波在介质中传播时产生空化效应、力学效应和热效应 ,并由此增强质量传输和热传递 ,对介质产生强的切向力。利用超声振动使液体产生空化作用 ,在空化形成或消失的瞬间 ,造成液体内部压强的突变 ,其突变产生的压力可达几千至一万个大气压。如此大的压力 ,促使固体表面的附着物剥落下来 ,达到清洗之目的。2　超声波在量块清洗中的应用众所周知 ,我们在进行量块检定工作之前 ,对量块的清洗是一个比较细致而繁琐的劳动 ,清洗人员的手长时间受清洗液的腐蚀 ,工作场地受到有害气体的包围。长期在如此恶劣的环境中工作 ,给计量…     

考虑液体空化的火炮制退机性能分析

结合液体空化理论和制退机非工作腔的空化超声检测与压力测试,研究了制退液的空化效应及其对制退机工作性能的影响。结果表明,在火炮后坐冲击作用下,制退液发生了剧烈的空化效应,后坐结束时非工作腔内充满制退液泡沫,并不存在真空段。制退液泡沫在复进过程中逐渐溃灭,因此在复进“真空消失点”处制退机非工作腔并不提供液压阻力。复进过程中非工作腔提供的液压阻力峰值仅为复进节制腔液压阻力平均值的8.91%。考虑制退液空化效应时,火炮复进液压阻力功比传统理论值小4.5%,火炮最大复进速度比传统理论值大10.5%。试验结果证实了计算结果的正确性。该结论为制退机的合理设计与故障诊断提供了理论依据。     

气液混合体内声传播的研究

一引言 在一定频率的超声波作用下,液体的声速和声衰减受到液体内的压力、温度以及外界压力等因素的影响,特别是粘滞性、热传导及散射效应的存在,将使声波衰减较大.当超声波强度增大时,就会产生空化现象[3,4],有大量气泡产生,从而使声速及吸收系数受到影响.本文在声传播方程的基础上[1,2],得出粘滞及含气泡液体内声速及吸收系数的表达式.     

声流条件下超声空化气泡分布研究

研究了频率为 20 kHz的超声作用在圆柱形料腔中出现声流现象时超声空化效应的空间分布特性。结合大振幅声源条件下的声辐射力,对声场内的声流现象进行了仿真分析,获取了不同超声功率和液位高度下的声流速度场分布,初步探究了声流条件下空化气泡的运动分布规律。采用超声空化效应的声致化学发光实验,对比研究了有、无声流条件时超声空化效应的空间分布特性。结果表明：功放电流高于 80 mA(电功率为 17.6 W)时,超声场可形成稳定的声致流动现象且可有效提高其声能辐射效率,大大增加了空化效应的作用区域,进而提高了声化学反应效率;声流条件下料腔内超声空化效应的分布区域与超声功率(振幅)、料腔液位高度相关,功放电流从 40 mA(电功率为8.8 W)增加至 120 mA(电功率为 26.4 W)时,空化面积占比提高了 100.86%,液位高度为 60 mm时的空化面积占比较50 mm和 70 mm时分别提高了 13.11%和 73.91%,提高超声功率及选择合理的料腔液位高度,可有效提高空化气泡扩散距离,增大空化分布面积;对于固定形状及尺寸料腔中的声场,声流速度达到一定阈值时,会出现空化效应增强,空化效应增强区域位于大于声流速度阈值的区域内;空化气泡的扩散分布与声流速度场密切相关,表现为随声流速度场的变化在料腔中部沿径向扩散、沿变幅杆轴向且在料腔底部沿径向扩散、沿变幅杆轴向扩散三种扩散分布模式。     

超临界CO2流体中超声速的特性

超临界CO2流体声速随压力和温度变化规律,对超声技术强化超临界流体萃取应用具有理论指导作用。为研究超临界CO2流体的超声速特性,设计了单探头脉冲回波法的声速测量探头,频率2.5MHz。采用汕头超声研究所生产的CTS-3600数字式超声探伤仪与声速测量探头连接。以温度每5℃和压力每1MPa为间隔,测量了温度为25℃～55℃,压力为7MPa～26MPa的CO2流体声速,根据不同温度下声速随压力变化的一组等温线,采用多项式拟合得到超临界CO2流体声速随压力和温度变化关系模型,在T=300K时计算模型计算值和文献参考值的相对误差。结果表明:超临界CO2流体声速随压力增加而增大,随温度升高而降低,在T=300K时模型计算值和文献参考值的相对误差在7%以内。     

多频同振超声波清洗器

一、超声波频率与超声波清 洗器 超声波清洗的机理主要是在清洗液中引入强的超声声场,因而在清洗液中产生空化、声流、声波的辐射压力和声学的毛细效应等现象。清洗主要依赖未炸裂的空化泡的强裂振动,以及空化泡炸裂时产生的微冲击波。它克服了被清洗物表面与污垢之间的附着力,起到了剥离和粉碎污垢的作用。声波的辐射压力与毛细效应可促使清洗液加速渗入被清洗物表面的微小隙孔。声流则可促使污垢加速从表面脱离。超声振动的引入还加强和促进了清洗液的乳化和增溶。因此超声波的清洗工艺适用于几何形状复杂的工件,但是要想达到预期的理想效…     

激光冲击中的"应变屏蔽"和"约束击穿"

讨论了约束状态和激光冲击的高压、高能、超快及超高应变率对材料响应之间的2个共性问题。激光冲击时,当被冲击材料本身与表面自由约束层能完全约束受冲击区域表面的宏观形变而不影响强化效应时,称为应变屏蔽,此时被冲击件可视为厚件,材料内部将保留大量的应变微结构;反之,当被冲击材料不能约束冲击能量而产生宏观形变时,称为约束击穿,此时被冲击件可视为薄件,冲击效果以塑性变形为主。最后扼要介绍了这2种现象在材料表面强化和微成形制造领域中的应用。     

液态CO2爆破系统压力动态响应及爆炸能量分析

为了研究液态CO_2爆破系统的压力响应特性和爆炸能量,通过实验室测定液态CO_2爆破系统爆破管内压力,获得压力与时间关系曲线,分析了压力曲线变化规律,结合SpanWagner CO_2状态方程,对常用的两种爆炸能量公式进行了分析与讨论,给出了液态CO_2爆破系统的爆炸能量的计算方法。结果表明:整个液态CO_2汽化过程的时间为0.026~0.086 s,高压流体释放时间约为0.18~0.26 ms。对外做功过程是一个压力值动态震荡衰减过程:首先高压流体以峰值压力作用于介质,随后以70%~80%峰值压力对介质产生二次破坏作用,最后以较低水平压力对介质产生气楔作用。两种常用的爆炸能量公式可以在一定程度上评估液态CO_2爆破系统爆炸能量产生的危害级别,但准确性不够,结合SpanWagner状态方程和爆破管内压力可以提高计算液态CO_2爆破系统的爆炸能量的准确性。     

超声微泡造影剂的低频动力学行为

低频超声联合微泡造影剂有可能用于治疗肿瘤,因此开展造影剂低频的动力学特性研究是十分重要的。将低频声场(26.2kHz)中有壳和无壳的微泡造影剂视为以流体为负载的非线性振子,由带耗散函数的拉格朗日方程导出在不可压缩的粘滞流体中造影剂球对称振动的运动方程,利用球谐振腔和Mie散射技术对CO2微泡和带人白蛋白壳的全氟丙烷造影剂微泡进行了气泡散射光强I(t)曲线的实验测定,结果与数值模拟曲线相一致。表明:有壳和无壳的造影剂微泡在低频稳态空化时同样呈现大幅膨胀、迅速塌缩和回弹的非线性振荡;如处于内径较小的微血管中,微泡周期性大幅度(>血管内径)膨胀收缩将会引起血管轴向破裂,形成微血管栓塞;而在塌缩相,微泡内的气体被急剧压缩,泡内压强急剧增大,易在泡壁不稳定处形成高速微射流,诱发内皮细胞损伤而形成血栓。     

超临界CO_2在电子膨胀阀内流动特性的数值分析

建立了超临界CO_2通过电子膨胀阀(EEV)降压过程的二维计算模型,采用均相流模型对超临界CO_2通过EEV的两相流动过程进行了数值模拟。结果表明超临界CO_2进入膨胀阀后,沿着工质的流动方向,其状态参数在开始变化不大,在接近阀芯最下端的部分,各状态参数开始剧烈变化。越靠近膨胀阀对称中心,CO_2压力越大,接近壁面处的压力最小。工质的流速最大的位置位于阀芯尖端,可达到179 m/s。CO_2工质流过阀芯尖端流阻最大处时,CO_2的压力急剧降低,两相间的质量传递率急剧增加,CO_2发生相变。随着EEV内CO_2压力的降低,CO_2气体份额持续增大,气体份额大小值与压力大小成反相关。     

UV-Visible Spectroscopic Measurement of Solubilities in Supercritical CO(2) Using High-Pressure Fiber-Optic Cells

The design and construction of a microscale, fiber-optics-based system for the measurement of solubilities in supercritical CO(2) by UV-visible spectroscopy is described. This system consists of three high-pressure fiber-optic cells, with path lengths ranging from 38 μm to 1 cm, constructed from standard (1)/(16)-in. stainless steel fittings and silica fibers. It is capable of withstanding pressures in excess of 300 atm, and spectra over the entire UV-visible range (200-900 nm) can be obtained. Use of three cells with different path lengths enables compounds of high or low solubility to be measured over a concentration range of several orders of magnitude. The solubility of a uranium complex, UO(2)(tta)(2)·TBP, in supercritical CO(2) at 40 °C and over the pressure range 100-325 atm was determined, and it was found to be possible to attain solubilities in excess of 10(-)(2) M for metal species in unmodified supercritical CO(2). Also, the small volume of this system allows solubilities to be measured with relatively small amounts of compounds.     

FT-IR studies of acetylacetonates in supercritical CO2 using a capillary cell at pressures up to 3.1 kbar

The keto-enol equilibria of the beta-diketones acetylacetone, trifluoroacetylacetone, and hexafluoroacetylacetone were determined using Fourier transform infrared spectroscopy in a novel high-pressure capillary cell. Acetylacetone and its fluorinated analogues were studied as neat liquid and as supercritical CO2 solutions at pressures up to 3.1 kbar. The keto form was found to be favored at high pressure and low temperature. The change in partial molar volume and enthalpy between the keto and enol forms was determined for the acetylacetone and trifluoroacetylacetone. Under all conditions studied, only the enol form of hexafluoroacetylacetone was observed. Based on the thermodynamic data obtained, there appears to be no advantage gained in conducting metal extractions at high pressures and low temperatures using acetylacetone or trifluoroacetylacetone.     

Lesion generation through ribs using histotripsy therapy without aberration correction

This study investigates the feasibility of using high-intensity pulsed therapeutic ultrasound, or histotripsy, to non-invasively generate lesions through the ribs. Histotripsy therapy mechanically ablates tissue through the generation of a cavitation bubble cloud, which occurs when the focal pressure exceeds a certain threshold. We hypothesize that histotripsy can generate precise lesions through the ribs without aberration correction if the main lobe retains its shape and exceeds the cavitation initiation threshold and the secondary lobes remain below the threshold. To test this hypothesis, a 750-kHz focused transducer was used to generate lesions in tissue-mimicking phantoms with and without the presence of rib aberrators. In all cases, 8000 pulses with 16 to 18 MPa peak rarefactional pressure at a repetition frequency of 100 Hz were applied without aberration correction. Despite the high secondary lobes introduced by the aberrators, high-speed imaging showed that bubble clouds were generated exclusively at the focus, resulting in well-confined lesions with comparable dimensions. Collateral damage from secondary lobes was negligible, caused by single bubbles that failed to form a cloud. These results support our hypothesis, suggesting that histotripsy has a high tolerance for aberrated fields and can generate confined focal lesions through rib obstacles without aberration correction.     

超声强化超临界流体萃取技术及其最新进展

文章较系统地介绍了超声强化超临界CO2萃取装置的设计,讨论了超声强化超临界CO2萃取技术的应用、萃取模型及其超声强化机理。超声强化与其他强化方法相比较,具有无污染、强化效率高等优点,超声波加入不仅降低了萃取系统的压力、萃取温度以及夹带剂用量和萃取时间,而且提高了萃取率,同时萃取对象的结构并没有发生变化。文章还提出了以后研究的重点。     

A polymer NMR cell for the study of high-pressure and supercritical fluid solutions

Nuclear magnetic resonance (NMR) offers researchers unique, highly localized molecular information. The importance of this technique is well established in studies using chemical shift, spin coupling, and relaxation times providing detailed structural information, determining chemical equilibria and kinetics, and understanding molecular dynamic processes. However, the widespread application of NMR spectroscopy to high-pressure liquids and supercritical fluids has been limited due to the complexity of the necessary instrumentation. One approach to these studies is to build a dedicated high-pressure probe. Another involves the utilization of a high-pressure cell designed to fit in commercially available probes. Here we present the design and implementation of a simple, three-piece, high-pressure NMR cell constructed of high-performance polymers. The present cell has pressure capabilities of up to 400 bar; however, the ultimate temperature and pressure limits will be determined by the specific polymer chosen. High-resolution NMR spectra of methanol modified and tributyl phosphate (IBP) modified supercritical CO2 are presented. An example of supercritical fluid phase behavior monitored with NMR is demonstrated for the TBP system in which the chemical shift changes in the 31P nucleus as a function of density are indicative of solution phase separation. The multinuclear NMR data demonstrate the utility of this cell for studying supercritical fluid solution systems relevant to analytical separations and extractions.     

低温流体空化特性的数值计算研究

采用数值计算的方法研究了液氮和液氢的空化流动特性。为了考虑温度影响,控制方程采用了连续方程、动量方程及能量方程,并应用二次开发方法在商业软件中引入Merkle 空化模型及物质属性,物性参数随流场温度变化而不断更新。分别对液氮和液氢几个工况进行了计算,并与实验结果进行了对比。结果发现,在液氮和液氢中,当流体温度接近临界点时,热力学效应表现显著。热力学效应显著主要表现在空穴变短、水蒸汽含量减少和汽液界面变的模糊。由于密度比、饱和蒸汽压随温度变化梯度等物质属性的不同,相对液氮,液氢的热力学效应更加明显。     

Preparation of carbon fibre reinforced aluminium via ultrasonic liquid infiltration technique

Abstract

An ultrasonic liquid infiltration technique has been developed for the fabrication of carbon fibre reinforced aluminium (CF/Al) precursor wires. The principal effect of ultrasound on aluminium infiltration into carbon fibres is considered to be caused by cavitation. The acoustic power required to produce cavitation in the present experimental system has been approximately calculated to be about 150 W, which is much greater than the requirement, several tens of watts, for overcoming the capillary pressure among carbon fibres. The observations on the morphology of the CF/Al precursor wires show that there are generally four states of infiltration: totally non-infiltrated, non-infiltrated in the centre and in some local regions of the wires, and completely infiltrated. It is found that carbon fibres can be sufficiently impregnated by molten aluminium given the appropriate application of ultrasound. Furthermore, a single fibre tensile test shows that there is no strength degradation of carbon fibres after aluminium infiltration. The CF/Al precursor wires obtained have an average fibre volume fraction of 26%. The maximum longitudinal tensile strength of the CF/Al wires is 605 MN m^?2, which implies a fibre strength transfer efficiency of 0·76.

MST/1715