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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
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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
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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
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《真空科学与技术学报》2016,(7)
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
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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
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《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
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Michinao Hashimoto George M. Whitesides 《Small (Weinheim an der Bergstrasse, Germany)》2010,6(9):1051-1059
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
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Yu Du Ping Li Yumei Wen Zhibin Guan 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(18):2207256
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
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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
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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
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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
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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
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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