“超声技术——功率超声及其应用”评介

功率超声是利用超声振动形式的能量使物质的一些物理、化学和生物特性或状态发生改变,或使这种改变的过程加速的一门科学技术。与检测超声不同,功率超声是利用超声能量来对物质进行处理、加工,最常用的频率范围,是从几千赫到几十千赫,功率范围由几瓦到几万瓦。声能对物质的作用机制是功率超声较为独特的问题,也是一个比较复杂的问题,为此必须了解和究各种应用中的作用机理。     

混响场中脉冲超声空化效应的研究

本文实验研究了不同脉冲宽度的８２０ｋＨｚ超声波的空化效应，结果得出，空化致自基产量随脉冲宽度及声强呈现规律性变化，尤其观察到了“脉冲空化峰”现象，本文从液面受迫振动角度出混响场中“脉冲空化峰”现象的机制。     

气泡的大振幅振动及其在声致发光和空化核聚变中的应用

评述了气泡大振幅振动方程，特别是R—P方程的来龙去脉，指出了该方程所存在的缺陷并对它进行了修正，将修正方程的数值解和R—P方程的数值解作了比较，在此基础上，对与气泡振动方程有关的应用(如声致发光和空化核聚变)情况作了分析。     

超声作用加速骨折愈合

许多研究表明,低强度的超声辐照对细胞和组织有深远影响,特别在动物和人体骨折的愈合方面。这里报告的是,特定的超声加速了兔子腓骨骨折、人体的科利斯骨折和腔骨骨折的愈合。 试验选用的是175只成熟的雌性新西兰白兔(3.5—5.0kg),用无损的脉冲超声辐照锯开的腓骨。脉冲超声的载频为1.5MHz,它在软组织中衰减较小。为避免引起声空化和使组织发热,对超声幅值和平均功率加以限制。脉冲宽度取200μs、重复作用频率1kHz、输入声强(SATA)25±5mW/cm~2。为造成双侧“C”形腓骨骨折,采用了1mm的季格利(Gigli)锯,以确保骨骼横向接合并稳定愈合线。从切骨手术     

面内场和静态偏磁场作用下条畴和泡畴的稳定性

实验研究面内场H_in和静态偏磁场H_b作用下,(111)面磁泡膜内条畴的消失过程。保持H_b恒定,增加H_in,测量条畴消失场H_s^*和泡畴消失场H_k^*与面内场方向β的变化关系。计及立方磁晶各向异性的影响,建立H_in和H_b共同存在时的条畴稳定性理论。定性解释了实验的主要特点。导出黑、白条畴同时消失时的角度 β_n=1/3(2nπ±arc cos│3/(2^1/2)(M_sH_b)/K₁│)(n=0,±1,±2,…)与实验基本符合。 关键词：     

液体中空化声场的统计测量及其在评估空化设备性能中的应用

利用液体中声空化现象制成的各类设备,有一个评估其性能优劣的问题.本文提出了基波谱级、谐波总声级、相对谐波总声级、内爆波谱级、总线谱声级和非线性转移效率几个参数的定义,并以这些参数来评估空化设备的性能.对统计测量上述参数的方法作了说明.     

微型超高压宝石喷嘴内部的空化与磨损

宝石喷嘴是影响超高压水射流切割系统工作效率的重要部件,而宝石内部的空化直接影响射流的形成,也是宝石磨损的重要原因之一。对400 MPa压力范围内宝石孔内部的空化两相流进行了数值模拟,阐述了射流在宝石内的形成过程,分析了长径比、压力和入口形状对宝石内空化的影响,并在相应压力下对宝石喷嘴的磨损进行了实验研究。结果表明:宝石内部的空化发展程度随着长径比的增大而减弱;在一定的长径比范围内,空化可以发展到喷嘴出口,并最终使射流的初始直径小于喷嘴直径,且在此条件下当压力升高时,射流的初始直径增大;良好的入口形线可以降低空化的发展程度;宝石入口的磨损较出口更显著,空蚀和高压水的冲蚀造成了宝石孔边缘形状的破坏,这种破坏随着压力的升高而加剧,选择合适的长径比是减少冲蚀磨损的有效途径。     

A Thermodynamic Cavitation Model for Cavitating Flow Simulation in a Wide Range of Water Temperatures

A thermodynamic cavitation model is developed to simulate the cavitating water flow in a wide temperature range. The thermal effect on bubble growth during cavitation is introduced in the developed model by considering both pressure difference and heat transfer between the vapor and liquid phase. The cavitating turbulent flow over a NACA0015 hydrofoil has been simulated at various temperatures from room temperature to 150°C by using the present cavitation model, which has been validated by the experimental data. It is seen that the thermodynamic effects of cavitation, vapor depression and temperature depression are much more predominant in high temperature water compared with those in room temperature water. These results indicate that the proposed thermodynamic cavitation model is reasonably applicable to the cavitating water flow in a wide temperature range.     

Binary-component micelle and vesicle:Free energy and asymmetric distributions of amphiphiles between vesicle monolayers

The real-space two-dimensional self-consistent field theory(SCFT) is employed to study the free energies of micelles and vesicles constituted by binary amphiphilic diblock copolymer AB in homopolymer A.With an increasing volume fraction of copolymer AB,there are morphological transitions from circle micelles to oblate circle-like micelles,to a compound structure with inverted micelles in the inner center and micelles outer layer,and to vesicles.Special attention is paid to the role of the copolymer AB in controlling the free energies of the micelles and vesicles by examining the effect of the length ratio of A/B with the fixed whole chain length of the AB copolymer,the length effect of A or B block with the corresponding fixed length of B or A block,for one component of copolymer,and the effect of different amphiphile compositions for a binary-component copolymer system.The quantity η is provided to describe the asymmetric density distribution of amphiphiles between the inner and outer monolayers of vesicles,and to quantify the relative asymmetric extent of the density distribution between two species of copolymers in binary component vesicles.