共查询到17条相似文献,搜索用时 125 毫秒
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为分析超声空化的薄层液体中稳定的环状气泡链结构,本文考虑气泡间次级声辐射影响,得到了表征气泡间相互作用的气泡基本动力学方程以及次Bjerknes力的表达式,数值分析了气泡平衡半径、声波频率和声压对纯液体区可能出现的单气泡所受的次Bjerknes力,发现环形泡链能够吸引液体区内的新生的半径小于2μm的气泡,这可能是一定条件下环形气泡链能够稳定存在的原因.随着驱动声波压力增加,气泡数密度增加,气泡间的耦合作用增强,液体区内的环形泡链结构可能被液体区内出现的大气泡或者气泡团破坏,进而导致环形结构演变成柱状、雾状乃至整个液体区均充满空化泡的情况发生.通过高速摄影机观察了强声场作用下换能器辐射面外侧液体薄层内空化初生至形成空化云团簇的整个过程,在空化云团簇中发现了局部同步崩溃并形成类纯液体薄层的现象,该液体薄层边界随时间振荡持续约4个声周期后被空化云团簇吞没,局部类纯液体区出现的位置具有随机性.实验观察结果和理论预测具有很好的一致性. 相似文献
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振动气泡形成辐射场影响其他气泡的运动, 故多气泡体系中气泡处于耦合振动状态. 本文在气泡群振动模型的基础上, 考虑气泡间耦合振动的影响, 得到了均匀球状泡群内振动气泡的动力学方程, 以此为基础分析了气泡的非线性声响应特征. 气泡间的耦合振动增加了系统对每个气泡的约束, 降低了气泡的自然共振频率, 增强了气泡的非线性声响应. 随着气泡数密度的增加, 振动气泡受到的抑制增强; 增加液体静压力同样可抑制泡群内气泡的振动, 且存在静压力敏感区(1–2 atm, 1 atm=1.01325×105 Pa); 驱动声波对气泡振动影响很大, 随着声波频率的增加, 能够形成空化影响的气泡尺度范围变窄. 在同样的声条件、泡群尺寸以及气泡内外环境下, 初始半径小于5 μm 的气泡具有较强的声响应. 气泡耦合振动会削弱单个气泡的空化影响, 但可延长多气泡系统空化泡崩溃发生的时间间隔和增大作用范围, 整体空化效应增强. 相似文献
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在超声快速制取组织细胞病理切片的过程中,发现激励信号对切片制取效果有明显的影响.为了掌握超声激励信号对组织细胞的影响规律,达到快速制取病理切片的最佳状态,从气泡空化模型入手,通过改变激励信号频率、声压、气泡初始半径和液体黏滞系数等参量,研究了声孔效应中气泡动力学激励机制.数值计算表明:空化泡振动随激励声压增强而升高,随液体黏滞系数增强而减弱;一定频率范围内空化泡振动能保持在膨胀、收缩和振荡的稳定空化状态,存在空化泡稳态振动的最佳激励频率;一定初始半径能保证空化泡产生稳定的振动,存在空化泡稳态振动幅度最大的初始半径.实际操作中,在频率、声压、初始半径和黏滞系数综合作用的若干空化阈内,声孔效应使超声快速法制取细胞组织切片获得最佳效果.
关键词:
声孔效应
超声空化
气泡振动
稳态空化域 相似文献
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利用新提出的Gilmore-NASG模型,在考虑液体可压缩效应的边界条件下,研究了可压缩液体中气泡的声空化特性,并与利用原有KM-Vd W模型计算得到的结果进行了比较.结果表明,相比于KM-Vd W模型,由于Gilmore-NASG模型采用新的状态方程来描述气体、液体以及由可压缩性引起的液体密度变化及声速变化,所以用Gilmore-NASG模型得到的空化气泡的压缩比更大、崩溃深度更深、温度和压力峰值更高.随着驱动声压幅值的增大,两种模型给出的结果差别愈加明显,而随着驱动频率的增大,两种模型给出的结果差别逐渐减小.这表明,在充分考虑泡内气体、周围液体在不同温度和压强下共体积的变化所导致的介质可压缩特性下,气泡内的温度和压强可能达到更高值.同时, Gilmore-NASG模型还预测出了气泡壁处液体的密度变化、压力变化、温度变化以及液体中的声速变化.因此, Gilmore-NASG模型在研究高压状态下气泡的空化特性以及周围液体对气泡空化特性的影响方面具有优点. 相似文献
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当声波在含气泡的液体中传播时会出现共振传播现象,即在气泡的共振频率附近声衰减和声速会显著地增大,这是声空化领域的一个重要现象.以往的研究一般假设液体中只存在单一种类的气泡,因此忽略了声波共振传播的某些重要信息.本文研究了含混合气泡液体中声波的共振传播,混合气泡是指液体中包含多种静态半径不同的气泡.结果显示:在这种系统中存在声波共振传播的抑制效应,即与含单一种类气泡的系统相比,在含混合气泡的系统中声波的共振衰减和共振声速会明显变小.对于两种气泡混合、多种气泡混合以及气泡满足某种连续分布的系统,研究了抑制效应的本质和主要特征,此外还探究了黏性和空化率等对抑制效应的影响.本文的研究结果是对该领域现有知识的必要补充. 相似文献
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为了对双泡耦合的声空化过程进行模拟,本文从流体动力学控制方程和流体体积分数模型出发,在Fluent软件中构建双泡耦合超声空化三维有限元仿真模型,对超声波驱动下流体中双泡耦合声空化动力学过程进行数值模拟,并通过对空化气泡周围声场的变化进行分析研究双泡耦合声空化的非线性动力学特性.结果显示:在超声波驱动下,球形气泡先缓慢扩张,扩张到最大半径后迅速收缩直至溃灭;耦合双气泡间存在相互作用力,使得空化气泡的扩张受到抑制、气泡收缩时间增长;空化气泡在收缩阶段的能量转换能力增强,相比单气泡声空化,耦合双气泡溃灭时气泡内部的压强更大.本文分析结果将为超声空化泡群的动力学过程模拟提供参考. 相似文献
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以水为工作介质, 考虑了液体的可压缩性, 研究了驻波声场中空化泡的运动特性, 模拟了驻波场中各位置处空化泡的运动状态以及相关参数对各位置处空化泡在主Bjerknes力作用下运动方向的影响. 结果表明: 驻波声场中, 空化泡的运动状态分为三个区域, 即在声压波腹附近空化泡做稳态空化, 在偏离波腹处空化泡做瞬态空化, 在声压波节附近, 空化泡在主Bjerknes 力作用下, 一直向声压波节处移动, 显示不发生空化现象; 驻波场中声压幅值增加有利于空化的发生, 但声压幅值增加到一定上限时, 压力波腹区域将排斥空化泡, 并驱赶空化泡向压力波节移动, 不利于空化现象的发生; 当声频率小于初始空化泡的共振频率时, 声频率越高, 由于主Bjerknes 力的作用将有更多的空化泡向声压波节移动, 不利于空化的发生, 尤其是驻波场液面的高度不应是声波波长的1/4; 当声频率一定时, 空化泡初始半径越大越有利于空化现象的发生, 但当空化泡的初始半径超过声频率的共振半径时, 由于主Bjerknes力的作用将有更多的空化泡向声压波节移动, 不利于空化的发生. 相似文献
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According to classical nucleation theory, a gas nucleus can grow into a cavitation bubble when the ambient pressure is negative. Here, the growth process of a gas nucleus in a micro-cavity was simplified to two “events”, and the full confinement effect of the surrounding medium of the cavity was considered by including the bulk modulus in the equation of state. The Rayleigh–Plesset-like equation of the cavitation bubble in the cavity was derived to model the radial oscillation and translational motion of the cavitation bubble in the local acoustic field. The numerical results show that the nucleation time of the cavitation bubble is sensitive to the initial position of the gas nucleus. The cavity size affects the duration of the radial oscillation of the cavitation bubble, where the duration is shorter for smaller cavities. The equilibrium radius of a cavitation bubble grown from a gas nucleus increases with increasing size of the cavity. There are two possible types of translational motion: reciprocal motion around the center of the cavity and motion toward the cavity wall. The growth process of gas nuclei into cavitation bubbles is also dependent on the compressibility of the surrounding medium and the magnitude of the negative pressure. Therefore, gas nuclei in a liquid cavity can be excited by acoustic waves to form cavitation bubbles, and the translational motion of the cavitation bubbles can be easily observed owing to the confining influence of the medium outside the cavity. 相似文献
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借助高速摄影和图像分析技术对首次发现的附壁气泡的绕圈现象进行了实验研究,重点研究游移气泡的运动轨迹、附壁气泡的布阵过程、气泡的来源以及气泡的振动细节.研究发现游移绕圈气泡的运动轨迹呈现出不稳定、不规则、不光滑的特点.阵列气泡源于游移气泡,而游移气泡变成阵列气泡的方式主要是通过合并增大体积,从而减小所受的Bjerknes力,降低活性的方式实现的.游移气泡源于ALF(acoustic lichtenberg figure)空化云中大量空泡的合并,使以径向振动为主的空泡逐渐过渡到以表面波动为主的气泡.阵列气泡在Bjerknes力的作用下呈现出规则的表面波动,而体积更小受力更大的游移空泡的表面完全失稳,呈现极不规则的形貌,并对附近阵列气泡的表面波动产生影响.阵列气泡呈现出十分规则的排布,相邻阵列气泡之间的振动相位是相反的,表现为相互排斥. 相似文献
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《Ultrasonics sonochemistry》2014,21(4):1496-1503
Changes in the cavitation intensity of gases dissolved in water, including H2, N2, and Ar, have been established in studies of acoustic bubble growth rates under ultrasonic fields. Variations in the acoustic properties of dissolved gases in water affect the cavitation intensity at a high frequency (0.83 MHz) due to changes in the rectified diffusion and bubble coalescence rate. It has been proposed that acoustic bubble growth rates rapidly increase when water contains a gas, such as hydrogen faster single bubble growth due to rectified diffusion, and a higher rate of coalescence under Bjerknes forces. The change of acoustic bubble growth rate in rectified diffusion has an effect on the damping constant and diffusivity of gas at the acoustic bubble and liquid interface. It has been suggested that the coalescence reaction of bubbles under Bjerknes forces is a reaction determined by the compressibility and density of dissolved gas in water associated with sound velocity and density in acoustic bubbles. High acoustic bubble growth rates also contribute to enhanced cavitation effects in terms of dissolved gas in water. On the other hand, when Ar gas dissolves into water under ultrasound field, cavitation behavior was reduced remarkably due to its lower acoustic bubble growth rate. It is shown that change of cavitation intensity in various dissolved gases were verified through cleaning experiments in the single type of cleaning tool such as particle removal and pattern damage based on numerically calculated acoustic bubble growth rates. 相似文献
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Joost Rooze Evgeny V. Rebrov Jaap C. Schouten Jos T.F. Keurentjes 《Ultrasonics sonochemistry》2013,20(1):1-11
The physics and chemistry of nonlinearly oscillating acoustic cavitation bubbles are strongly influenced by the dissolved gas in the surrounding liquid. Changing the gas alters among others the luminescence spectrum, and the radical production of the collapsing bubbles. An overview of experiments with various gas types and concentration described in literature is given and is compared to mechanisms that lead to the observed changes in luminescence spectra and radical production. The dissolved gas type changes the bubble adiabatic ratio, thermal conductivity, and the liquid surface tension, and consequently the hot spot temperature. The gas can also participate in chemical reactions, which can enhance radical production or luminescence of a cavitation bubble. With this knowledge, the gas content in cavitation can be tailored to obtain the desired output. 相似文献