对液体表面张力系数实验方法的改进

本文提出用双毛细管代替单毛细管测定液体表面张力系数，这种方法不仅提高了测量精度，而且适宜于测定微量液体的表面张力系数。     

毛细管探针法测定液体表面张力系数的进一步研究

采用较大直径的毛细管对探针法测量液体表面张力系数做了进一步研究.文中引用了Prokhorov提出的改进的瑞利公式,介绍了表面张力系数α的各相关公式的适用范围.实验中利用毛细管探针法测量了几个不同温度下蒸馏水在一直径为5.744.nm的毛细管中的上升高度,用Prokhorov公式计算α.实验测得的蒸馏水的表面张力系数与公认值的百分误差约小于0.13%.最后对实验结果的误差原因进行了分析.     

设计控温装置研究液体表面张力系数与温度的关系

介绍了自行设计、搭建的测量液体表面张力系数与温度关系的实验装置,用毛细管法测量了不同温度下水和乙醇的表面张力系数,得到了它们与温度的线性关系.利用此装置还可以进行其他对样品温度测控要求较高的实验.     

最大气泡压力法测定溶液表面张力的改进

最大气泡压力法测定溶液表面张力的改进谷里鹏（华中工学院汉口分院）最大气泡压力法测定溶液表面张力时气泡的增大速度不易控制，因此很难在气泡半径等于毛细管半径时及时读准压差△ｈ，造成较大的实验误差．最大气泡压力法测量表面张力装置采用医用输液瓶代替抽气机将取...     

表面张力的定性定量分析

通过自制实验装置演示镜子起雾现象证明了液体表面张力的存在,同时也证明了表面活性剂对表面张力的大小存在影响.对于表面张力系数的测量,该实验定量装置提出了基于大气压强原理测量液体表面张力系数的新方法.实验发现,该实验定性定量装置具有精度更高、成本更低、可操作性更强等优点.     

毛细管探针法测定液体的表面张力系数

在毛细管法测定液体表面张力系数的实验中,利用被测液体导电的性质,在螺旋测微计的测微螺杆上沿轴线方向加装一根金属探针,通过电学方法探测毛细管内液面及容器内液面的位置,实现液体在毛细管内上升高度的测量.利用探针法分别测量了蒸馏水在几个不同温度下的毛细上升高度,利用瑞利公式计算表面张力系数.实验结果表明,探针法测量毛细上升高度的重复性好,所测得蒸馏水的表面张力系数与其公认值的百分误差约小于0.12%.     

基础实验题A:液体的表面张力系数测量

介绍了第5届全国大学生物理实验竞赛基础实验题A的实验内容,给出了参考解答,并分析了竞赛结果.基础实验题A涵盖毛细管法和最大泡压法测量液体的表面张力系数2部分,分5道试题.毛细管法和最大泡压法在理论上具有相似性,毛细管法从液体的表面张力系数的定义出发,引导学生从最基础的层面上理解液体表面张力系数的定义,从而自拟实验方案,自组实验器材进行实验测量;最大泡压法考查学生举一反三的学习能力,在相似的理论下自拟、自组实验.试题整体考查了学生对理论知识的理解运用能力以及基本的实验操作能力.     

酒精杂质对水的表面张力系数的影响

利用毛细管测量液体的表面张力系数α是一个重要的物理实验,它是根据毛细现象,利用公式α=ρghR/2来测量的,式中的ρ为被测液体的密度,g为重力加速度,h为液体在毛细管中上升的高度,R为毛细管的半径.此实验经常用水和酒精两种液体来做.在做这个实验的过程中发现水中混入少量的酒精杂质会对水的表面张力系数的测量结果产生很大的影响.为此,笔者专门对酒精杂质的影响进行了研究,介绍于下.     

对测定液体表面张力系数实验的一点改进

为了提高实验质量,我们对现行的测定液体表而张力系数实验方法进行了如下改进.用毛细管升高法测定液体表面张力系数σ公式为:     

测量毛细管中液面上升高度的另一种方法

从流体动力学角度推出了液体在毛细管中上升的高度，从而指出的测量液体表面张力系统数中传统方法的欠缺，提出了采用下降法测量液体在毛细管内的高度的方法，使得测量液体表面张力系数的系统误差大大降低。     

Dynamics of a cavitation bubble near a solid wall

The cavitation bubble dynamics, the variation of pressure and velocity fields of the surrounding liquid in the process of the bubble axisymmetric compression near a planar solid wall are considered. It is assumed that the liquid is at rest at the initial moment of time, and the bubble has a spheroidal shape. The liquid is assumed inviscid and incompressible, its motion being potential. The bubble surface deformation and the liquid velocity on the surface are computed by the Euler scheme using the boundary element method until the moment of the collision of some parts of the bubble surface with one another. The influence of the distance of the bubble from the wall and its initial nonsphericity on the liquid pressure and velocity fields, the bubble shape, and the pressure inside the bubble at the end of the time interval under consideration are studied. The maximum pressure in liquid is shown to realize at the bottom of the cumulative jet arising at the bubble collapse with direction to the wall. In the upper part of this jet, the velocity and pressure are practically constant, and the pressure in the jet is approximately equal to the pressure in the bubble.     

High Speed Visualization and Dynamic Measurement of Heat Driven Pumps

We provide the high speed flow visualization and dynamic measurement results for the U-shaped and the inverted U-shaped heat driven pumps. The U-shaped heat driven pumps at the high heating powers consist of a succession of tiny bubble nucleation, growth and coalescence process. Once the “larger” spherical bubble or the bubble slug forms, it expands quickly in both upstream and downstream directions. The increased pressure leads to the liquid discharge through the outlet check valve. When the advancing vapor/liquid interface reaches a higher position in the vertical discharge branch, the condensation heat transfer in the discharge branch shrinks the bubble slug, leading to the decreased pressure and initiating the open of the inlet check valve. Thus the fresh liquid can be sucked into the system. Heat driven pumps operating at the low heating powers display the similar process. However, two major differences are identified: (1) A full cycle includes a set of positive pressure pulses corresponding to a set of tiny bubble nucleation, growth and coalescence process in each substage. Only at the end of the cycle, an apparent negative pressure pulse is created. (2) For each substage in each cycle, when the newly formed bubble slug is chasing the ahead “old” bubble slug, the deformed liquid bridge is formed due to the gravity force effect. When the two bubble slugs are merging together, a wave vapor/liquid interface occurs along the bottom of the capillary tube. For the inverted U-shaped heat driven pumps, there are fewer positive pressure pulses included, corresponding to lesser number of new bubble nucleation, growth, and coalescence process. The bubble slug in the capillary tube is very standard with the smooth vapor/liquid interface. The cycle periods and the pumping flow rates are given versus the heating powers.     

Experimental investigation on the effects of the standoff distance and the initial radius on the dynamics of a single bubble near a rigid wall in an ultrasonic field

Bubble behaviors near a boundary in an ultrasonic field are the fundamental forms of acoustic cavitation and of substantial importance in various applications, such as industry cleaning, chemical engineering and food processing. The effects of two important factors that strongly affect the dynamics of a single acoustic cavitation bubble, namely, the initial bubble radius and the standoff distance, were investigated in this work. The temporal evolution of the bubble was recorded using high speed microphotography. Meanwhile, the time of bubble collapse and the characteristics of the liquid jets were analyzed. The results demonstrate that the intensity of the acoustic cavitation, which is characterized by the time of bubble collapse and the liquid jet speed, reaches the optimum level under suitable values of the initial bubble radius and the normalized standoff distance. As the initial bubble radius and the normalized standoff distance increase or decrease from the optimal values, the time of the bubble collapse increases, and the first liquid jet’s speed decreases substantially, whereas the speeds of the second and third liquid jets exhibit no substantial changes. These results on bubble dynamics in an ultrasonic field are important for identifying or correcting the mechanisms of acoustic cavitation and for facilitating its optimization and application.     

单液滴撞击倾斜液膜飞溅过程的耦合Level Set-VOF模拟

采用耦合水平集--体积分数法(CLSVOF)对液滴撞击倾斜表面液膜后液膜的形态演化及飞溅过程进行数值模拟, 并对液滴撞击液膜过程中形成的空气卷吸现象进行研究并探讨了撞击角对此的影响, 分析了液滴撞击后液体内部的压力和速度分布, 对液滴撞击倾斜表面液膜的飞溅过程进行讨论, 并与实验结果进行了对比, 验证了CLSVOF方法研究液滴撞击倾斜液膜的可行性. 结果表明, 液滴撞击倾斜液膜时前后两部分飞溅现象产生的机理不同, 前半部分飞溅是由于压差引起的颈部射流, 而后半部分则是由液膜径向流动产生的飞溅现象. 随着撞击角的增大, 空气卷吸气泡数量减少.     

Physical investigation of acoustic waves induced by the oscillation and collapse of the single bubble

The objective of this paper is to apply both experimental and numerical methods to investigate acoustic waves induced by the oscillation and collapse of a single bubble. In the experiments, the schlieren technique is used to capture the temporal evolution of the bubble shapes, and the corresponding acoustic waves. The results are presented for the single bubble generated by a low-voltage bubble generator in the free field of water. During the numerical simulations, a three-dimensional (3D) weakly compressible model is introduced to investigate the single bubble dynamics, including the generation and propagation of acoustic waves. The results show that (1) Compression wave, rarefaction wave and shock wave are generated during expansion stage, collapse stage and rebound stage of the bubble respectively. (2) Compression waves are induced by the rapid expansion of the bubble and eventually steepen into one shock wave propagating outward in the liquid, then another strong shock wave is emitted at the final collapse stage. The velocity and pressure of the liquid field increases after the shock wave. (3) Rarefaction waves are generated during the collapse stage due to the contraction of the bubble. The rarefaction wave reduces the liquid pressure and its spatial distribution is dispersive. The pressure of these acoustic waves and their effect on the liquid velocity attenuate with the increase of propagation distance.     

空化泡液体外围压强的分布

本文从空化泡动力学理论出发,分别讨论了空化泡在压缩和膨胀时液体中的压强分布情况,并作了数值模拟。研究结果表明,空化泡在膨胀和压缩时其外围压强分布明显不同,不能将其一并而论。发现当空化泡的半径增大时液体的压强在不断变化,压强是先变小后变大。而且这个压强的变化还与待测点距空化泡的距离有关。当空化泡的半径在不断变小时外界的压强在不断增大,当空化泡刚开始压缩时液体中的压强变化情况不是很明显,但当空化泡的半径变到1μm时,空化泡外界压强出现明显变化。当空化泡压缩到较小时,此时再增加外界压强空化泡的半径也不会在有很大的变化。     

Surface tension effects on the behaviour of a rising bubble driven by buoyancy force

In the inviscid and incompressible fluid flow regime,surface tension effects on the behaviour of an initially spherical buoyancy-driven bubble rising in an infinite and initially stationary liquid are investigated numerically by a volume of fluid (VOF) method. The ratio of the gas density to the liquid density is 0.001, which is close to the case of an air bubble rising in water. It is found by numerical experiment that there exist four critical Weber numbers We₁,~We₂,~We₃ and We₄, which distinguish five different kinds of bubble behaviours. It is also found that when 1≤We2, the bubble will finally reach a steady shape, and in this case after it rises acceleratedly for a moment, it will rise with an almost constant speed, and the lower the Weber number is, the higher the speed is. When We >We₂, the bubble will not reach a steady shape, and in this case it will not rise with a constant speed. The mechanism of the above phenomena has been analysed theoretically and numerically.     

Effects of surface tension on the dynamics of a single micro bubble near a rigid wall in an ultrasonic field

Acoustic cavitation is a very important hydrodynamic phenomenon, and is often implicated in a myriad of industrial, medical, and daily living applications. In these applications, the effect mechanism of liquid surface tension on improving the efficiency of acoustic cavitation is a crucial concern for researchers. In this study, the effects of liquid surface tension on the dynamics of an ultrasonic driven bubble near a rigid wall, which could be the main mechanism of efficiency improvement in the applications of acoustic cavitation, were investigated at the microscale level. A synchronous high-speed microscopic imaging method was used to clearly record the temporary evolution of single acoustic cavitation bubble in the liquids with different surface tension. Meanwhile, the bubble dynamic characteristics, such as the position and time of bubble collapse, the size and stability of the bubbles, the speed of bubble boundaries and the micro-jets, were analyzed and compared. In the case of the single bubbles near a rigid wall, it was found that low surface tension reduces the stability of the bubbles in the liquid medium. Meanwhile, the bubbles collapse earlier and farther from the rigid wall in the liquids with lower surface tension. In addition, the surface tension has no significant influence on the speed of the first micro-jet, but it can substantially increase the speed of second and the third micro-jets after the first collapse of the bubble. These effects of liquid surface tension on the bubble dynamics can explain the mechanism of surfactants in numerous fields of acoustic cavitation for facilitating its optimization and application.     

The pressure field in the liquid column in the tube-arrest method

We have been using the method of tube-arrest as a means of producing transient single cavitation bubble. In the present paper we seek to comprehend the mechanism of production and inquire into the structure of the ab initio pressure field in the arrested liquid column. The generated pressure wave is shown by combining the theoretical analysis with the experimental observation to be a slightly varied version of water hammer. With relatively clean liquid, the magnitude of the tension peak generating the TSB is likely to reach of several millions Pa. It is also shown that the so generated cavitation bubble originating from the gas-containing bulk liquid is in ‘violent’ motion.     

声场中双空化泡的运动特性

空化泡的运动特性是声场作用下的动力学行为,受空化泡初始半径,声压幅值,驱动声压频率,液体特性等众多因素的影响,是个复杂工程。本文从双空化泡运动方程出发,考虑到液体粘滞系数、空化泡辐射阻尼项的影响,研究了不同初始半径、驱动声压频率、驱动声压幅值、液体粘滞系数下空化泡泡壁的运动情况,研究结果表明不同初始半径、外界驱动声压频率、驱动声压幅值、液体粘滞系数均会对空化泡的膨胀比和空化泡的溃灭时间有一定影响。