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1.
牟静  陶超  朱哲民  杜功焕 《声学技术》2003,22(Z2):51-53
1引言 液体中气泡振动学是一个具有理论及实用意义的课题,以往已有很多研究,并取得了相当的进展[1-4].一般自由气泡在液体中容易溶解,而如在气泡外附加一粘弹材料表面层则可使气泡在液体中的稳定性大大提高.因此包膜气泡更具有实用价值,已作为超声造影剂获得重要应用.包膜气泡的应用研究已涉及气泡的线性散射,非线性二次谐波成像.近年来更出现次谐波成像的研究,Church推导了包膜气泡模型并给出了弱非线性情况下的逐级近似解[5].但是至今尚无用动力学方法分析包膜气泡非线性特性的相关工作.  相似文献   

2.
本文测定了射流搅拌发酵罐中自由射流气泡区的气含率、气泡直径和液体循环量。研究了混合器,喷嘴尺寸、气速、清液层高度、液体粘度、表面张力对自由射流气泡区的液体循环量,气含率、气泡直径的影响。由理论分析及实验数据获得了液体循环量、气含率、气泡直径的关联式。模型关联式与实验值吻合良好。  相似文献   

3.
许兆峰  罗锐  杨献勇 《工程力学》2005,22(3):63-67,51
含气泡液体流动的雷诺应力主要是由气泡存在及液体湍动而引起的,它们分别在层流和湍流流动中占主导地位。通过对粘性流体绕球形颗粒的流场进行研究,运用单元系综平均方法推导出由气泡引起的剪切雷诺应力关系式,并根据Sato(1981)的方法获得最佳剪切雷诺应力系数。此关系式与雷诺数的平方根成正比,且仅适用于空泡率较小的含气泡液体流动。通过模型预测及与Sato(1981)所得关系式进行比较,显示同意所得关系式更具有理论性,更合理。  相似文献   

4.
超声造影剂SDA的巨非线性参量   总被引:3,自引:0,他引:3       下载免费PDF全文
1 引 言近年来 ,含微气泡液体的非线性声学特性引起了人们极大的兴趣。液体中的空气泡是很好的声散射体 ,能产生强的超声散射信号。液体中气泡的非线性振动 ,尤其是在它们的共振频率附近的非线性振动 ,使得它们的存在能够增强液体的声学非线性效应。因此 ,研究含有微气泡的液体的非线性声学特性是非线性声学领域也是它的应用领域的一个重要课题。例如 ,利用含微气泡液体的非线性声特性是水声学中用来增强声参量阵效率的一个有效方法。媒质的非线性声特性可以用非线性声参量 B/A来描述。到目前为止的所有文献上 ,液体、生物流体和组织的非…  相似文献   

5.
1.引言 近年来在临床医学超声诊断与成像的领域中,超声造影剂受到越来越多的关注,其物理模型为气泡外面覆盖一层包膜用来提高其稳定性.对于这种含包膜气泡流体非线性的探索则是这一领域的一个重要课题.当声波在这种流体中传播时,由于非线性效应的存在,往往会激发出二次谐波等种种高次谐波.作为反应其二次谐波性质的一个非线性声学中的基本参量,B/A描述了超声波通过媒质非线性效应的大小,而利用B/A进行医学成像也正成为国际上的一个热点1,2.但是,这方面的工作大都基于实验,在理论上对这种含包膜气孔流体的非线性特性的研究尚未有报道.本文运用等效媒质法,研究了这种含包膜气孔流体的一阶,二阶非线性声场,并从理论上计算的这种流体的等效非线性参量(B/A)e并与含自由气泡流体的非线性参量进行了比较.  相似文献   

6.
针对液体射流的真空闪蒸特性,建立气泡动力学模型分析了射流内部的气泡生长特性,并提出用无量纲数C_h描述真空射流中的气泡生长条件。通过数值仿真方法模拟了气泡在真空射流中的生长过程,研究了气泡初始半径、液体粘度、射流温度和射流半径等参数对气泡生长的影响。在真空环境中开展了不同液体工质的真空喷射试验,试验结果与C-h数预测结果吻合良好;开展水射流的闪蒸试验,获得了破碎距离的变化规律,并与计算结果进行了对比分析。  相似文献   

7.
为提高液体表面张力测量的准确性和稳定性,提出一种基于气泡运动的液体表面张力系数测量方法。根据气泡在液相中的受力情况,建立气泡在液相中脱离体积及瞬时稳态上浮速度数学模型,基于搭建的气体水下生成及控制平台,采用水浴加热法改变液相温度,将6种不同温度下蒸馏水及空气,分别作为实验的液相和气相进行实验测量,使用高速摄像机采集气泡运动图像,所采集图像使用Matlab软件进行图像处理与数据分析,将实验数据及液相物性,代入到所建立的模型中,推导出不同温度下蒸馏水的表面张力系数大小,采用最小二乘法线性对测算结果进行拟合。结果表明该方法具有可行性。  相似文献   

8.
超声造影剂的非线性参量研究   总被引:3,自引:3,他引:0       下载免费PDF全文
龚秀芬  冯绍松 《声学技术》1996,15(4):208-210
近年来对超声造影剂的研究兴趣日趋增加是由于它有可能改进超声临床诊断的效果,含有微气泡的液体可用和有效的超声造影剂,液体中气泡的存在提高液体的非线性参量值,本文用检测二次谐波的方法实验上测定了5种超声造影剂的非线性参量,四种含气泡的液体(声振后)和半乳糖Echovist300。结果表明,含有微气泡的液体具有非常大的非线性参量值,对这种高非线性值的现象文中进行了可能的解释和讨论。  相似文献   

9.
近年来对超声造影剂的研究兴趣日趋增加是由于它有可能改进超声临床诊断的效果。含有微气泡的液体可用作有效的超声造影剂。液体中气泡的存在可提高液体的非线性参量值。本文用检测二次谐波的方法实验上测定了5种超声造影剂的非线性参量:四种含气泡的液体(声振后)和半乳糖Echovist300。结果表明,含有微气泡的液体具有非常大的非线性参量值。对这种高非线性值的现象文中进行了可能的解释和讨论  相似文献   

10.
气泡泵提升管内气液两相流动特性直接影响工质提升性能。本文借助高速摄像仪观察了不同加热功率(400、600、800、1 000、1 200、1 400 W)下多管气泡泵中液体提升过程,并与单管气泡泵液体提升过程进行了对比。研究结果表明,对于多管气泡泵,液体提升总量与液体提升速率随加热功率的增大而提高,与加热功率为1200 W时相比,当加热功率为1400 W时,气泡泵液体提升总量提高了15.16 kg,液体提升速率提高了5.08 g/s;多管气泡泵中心位置提升管气泡数量较多,提升效果最好。对于单管气泡泵,当加热功率为400 W时,提升管数量的增加不能提高气泡泵液体提升性能;当加热功率为600~800 W时,多管与单管的气泡泵液体提升性能相差较小;当加热功率为1 000~1 400 W时,多管气泡泵的液体提升总量、最大提升速率和泵效率均比单管相应性能显著提高。  相似文献   

11.
《材料科学技术学报》2019,35(7):1388-1392
Synchrotron X-ray radiography was used to carry out an in-situ observation of the hydrogen bubble evolution in the liquid Al/solid Ni interconnection. The individual bubble mainly grows in a stochastic way during heating. The size distribution for groups of bubbles follows a Gaussian distribution in the early stage and Lifshitz-Slyozov-Wagner (LSW) diffusion controlled distribution in the final stage. The intermetallic compounds (IMCs) first form during solidification, following by the hydrogen bubbles. The bubbles between two adjacent Al3Ni grains grow unidirectionally along the liquid channel, with the bottom being impeded by the Al3Ni phase and the radius of the growth front being smaller. For the bubbles at triple junctions, they grow along the liquid channel and the crack with morphology transition.  相似文献   

12.
The formation of bubbles in a flow‐focusing (FF) junction comprising multiple rectangular sections is described. The simplest junctions comprise two sections (throat and orifice). Systematic investigation of the influence on the formation of bubbles of the flow of liquid and the geometry of the junction identifies regimes that generate monodisperse, bidisperse, and tridisperse trains of bubbles. The mechanisms by which these junctions form monodisperse and bidisperse bubbles are inferred from the shapes of the gas thread during breakup: these mechanisms differ primarily by the process in which the gas thread collapses in the throat and/or orifice. The dynamic self‐assembly of bidisperse bubbles leads to unexpected groupings of bubbles during their flow along the outlet channel.  相似文献   

13.
Human ocean activities are inseparable from the supply of energy. The energy contained in the gas-phase components dispersed in seawater is a potential universal energy source for eupelagic or deep-sea equipment. However, the low energy density of bubbles dispersed in water introduces severe challenges to the potential energy harvesting of gas-phase components. Here, a super-aerophilic biomimetic cactus is developed for underwater dispersive microbubble capture and energy harvesting. The bubbles captured by the super-aerophilic biomimetic cactus spines, driven by the surface tension and liquid pressure, undergo automatic transport, coalescence, accumulation, and concentrated release. The formerly unavailable low-density dispersive surface free energy of the bubbles is converted into high-density concentrated gas buoyancy potential energy, thereby providing an energy source for underwater in situ electricity generation. Experiments show a continuous process of microbubble capture by the biomimetic cactus and demonstrate a 22.76-times increase in output power and a 3.56-times enhancement in electrical energy production compared with a conventional bubble energy harvesting device. The output energy density is 3.64 times that of the existing bubble energy generator. This work provides a novel approach for dispersive gas-phase potential energy harvesting in seawater, opening up promising prospects for wide-area in situ energy supply in underwater environments.  相似文献   

14.
Bubble formation and growth play an important role in various processes and industries, where the dispersion of gas bubbles in a liquid medium occurs frequently. In this paper, the formation, growth, and detachment of gas bubbles produced from a submerged needle in water are numerically and experimentally investigated. The effect of injected gas properties on bubble characteristics, including bubble diameter, contact angle, and the frequency of bubble formation, is evaluated. In particular, the changes in bubble characteristics during the injection process are investigated for three different gases to evaluate the effect of density and surface tension on the bubble detachment criteria. The present numerical results show an acceptable agreement with experiments under different operating conditions. The results show that the increase in surface tension, and the decrease in gas density result in larger bubble sizes before detachment occurs. Moreover, the bubble generation frequency is found to strongly depend on the contact angle and the surface tension.  相似文献   

15.
为实现液氢在空间中安全高效应用,针对微重力条件下液氢膜态沸腾现象,建立了加热细丝浸没在过冷液氢池中的数值计算模型。采用VOF方法捕捉相界面,相变模型选取Lee模型,利用文献中的实验数据验证了模型的准确性。从气泡运动行为和换热特性两方面开展研究,结果发现液体过冷度和重力水平是影响换热机理的两个重要因素。在高重力水平、低液体过冷度的条件下,加热细丝上方持续产生气泡并脱离,随着重力水平的降低,气泡脱离直径和气泡生长时间逐渐增大,流体与壁面间换热量随之降低。在低重力水平、高液体过冷度条件下,气膜附着在加热丝表面不断晃动,没有气泡的产生与脱落现象。对于液体过冷度为2 K,壁面过热度为30 K的工况,气泡是否脱落的临界重力在0.1 g至0.15 g之间。  相似文献   

16.
17.
Results are given of theoretical study into the propagation of acoustic disturbances in mixtures of liquid with vapor-gas bubbles in view of interphase diffusion mass transfer. A unified general dispersion relation is obtained, which defines the propagation of harmonic disturbances in two-phase mixtures of liquid with bubbles of vapor and gas in the plane, spherical, and cylindrical cases. Numerical calculations are performed of the evolution of weak pulse disturbances of pressure of different geometries in liquids with vapor-gas bubbles at different values of parameters of the medium. It is demonstrated that the velocity of propagation of waves significantly decreases with increasing initial concentration of vapor in vapor-gas bubbles, and the wave damping significantly increases. In so doing, the effect of vapor content on the dynamics of acoustic disturbances significantly increases with the initial volume content of bubbles. The nonmonotonic dependence of damping of pulse disturbance of pressure on the initial radius of bubbles in liquid with vapor-gas bubbles in the presence of phase transformations is demonstrated.  相似文献   

18.
蓝宝石单晶的气孔形成研究   总被引:1,自引:0,他引:1  
采用冷心放肩微量提拉法(SAPMAC法)生长的蓝宝石晶体,气孔是其主要缺陷.本文探讨了影响气孔形成的工艺因素,从晶体生长动力学角度分析了气孔形成机理.结果表明,通过优化温场、选择合适的生长速度及控制微凸固/液界面形状,可有效降低晶体中气孔的数量.  相似文献   

19.
分析了液体模塑成型工艺(LCM)下织物预成型体中双尺度流动以及由此造成的空气裹入,进而产生细观及微观气泡的现象。基于多相流(VOF)方法建立了树脂空气两相流体在单胞内部流动的数学模型,并确定了该模型中多孔介质阻力源项和毛细力源项的具体形式。基于Fluent软件的UDF功能实现了上述两相流模型的数值求解,研究了平纹织物单胞中的两相流动以及2种气泡的生成过程。对Rovcloth 2454织物的气泡生成仿真结果显示,毛细数 Ca 对气泡的产生有决定性作用:当毛细数接近临界毛细数 Cac时,气泡产生量最低,而当Ca小于Cac时,容易产生细观气泡,反之容易产生微观气泡。通过与文献中的理论预测和实验数据对比,验证了本文算法的正确性。  相似文献   

20.
The objectives of this paper are to visualize the bubble behavior for an ammonia–water absorption process, and to study the effect of key parameters on ammonia–water bubble absorption performance. The orifice diameter, orifice number, liquid concentration and vapor velocity are considered as the key parameters. The departing bubbles tend to be spherical for surface tension dominant flow, and the bubbles tend to be hemispherical for inertial force dominant flow. A transition vapor Reynolds number is observed at a balance condition of internal absorption potential (by the concentration difference) and external absorption potential (by the vapor inlet mass flow rate). As the liquid concentration increases, the transition Reynolds number and the initial bubble diameter increase. The initial bubble diameter increases with an increase of the orifice diameter while it is not significantly affected by the number of orifices. Residence time of bubbles increases with an increase in the initial bubble diameter and the liquid concentration. This study presents a correlation of initial bubble diameter with ±20% error band. The correlation can be used to calculate the interfacial area in the design of ammonia-water bubble absorber.  相似文献   

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