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P. Snabre F. Magnifotcham 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):379-386
The recirculation flow induced by the rising motion of a bubble stream in a viscous fluid within an open-top rectangular enclosure
is studied. The three-dimensional volume averaged conservation equations are solved by a control-volume method using a hybrid
finite differencing scheme to describe the liquid phase hydrodynamics. The momentum exhange between the bubbles and the liquid
phase is modeled with a source term equals to the volumetric buoyancy force acting on the gas in the bubble stream. The volumetric
buoyancy force accounts for in line interactions between bubbles through the average gas volume fraction in the gas liquid
column which depends on the size and the rising velocity of bubbles. The fluid flow within an open-top rectangular enclosure
is further investigated by particle image velocimetry for a bubble stream rising in a water-glycerol solution. The measured
fluid velocities in a vertical plane are compared with the predictions of the numerical model over a wide range of fluid viscosity
(43 mPa s-800 mPa s) and gas flow rates. Finally, the recirculation flows resulting from the interaction of two neighbouring
vertical bubble streams are studied.
Received: 23 July 1997 / Revised: 19 December 1997 / Accepted: 11 May 1998 相似文献
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Christof Grüner Wolfgang Kanther Sren Gtz Karl Strauß 《Particle & Particle Systems Characterization》2004,21(3):219-227
The behavior of the particulate phase in a highly turbulent gas flow has been investigated in a vertical channel. Variations of the flow configuration (1. Flow past a cylinder, 2. flow past a wall‐mounted obstacle and 3. flow around a horizontally injected jet) have been subject to both experiments and numerical simulations. The velocity vector field of the solid phase has been measured by digital particle image velocimetry (DPIV). The measurements have been focused on particle‐obstacle collisions and crossflow in the vicinity of the jet nozzle using the lately developed twinpeak detection method. By application of this method regions of highly inhomogeneous particle behavior could be detected mainly upstream of the flow perturbation. Numerical results have been obtained by an Eulerian‐Lagrangian method on boundary‐fitted grids. Particle‐particle interactions as well as interphase exchange of momentum have been taken into account. The simulation results showed to be well in accordance with the experimental results. 相似文献
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Sbastien Guet RobbertV. Fortunati RobertF. Mudde Gijs Ooms 《Particle & Particle Systems Characterization》2003,20(3):219-230
The possibility to measure the velocity and size of individual bubbles in a high‐void fraction bubbly flow is investigated by using a four‐point optical fiber probe. The air bubbles have an initial spherical equivalent diameter ranging from 4 to 10 mm and the void fraction is up to 0.3. Firstly, single bubble experiments show that intrusiveness effects, i.e. bubble deformations due to the probe, are negligible provided that the bubble approaches the probe at the axis of the central fiber. A selection criterion is utilized for multiple bubble experiments. A good compromise can be found between the required accuracy, the duration of the measurements and the number of validated bubbles required for reliable statistical averaging. In an air‐water high‐void fraction vertical bubbly pipe flow, the void fraction obtained with the instrument is found to be in good agreement with both local single‐fiber probe measurements, and with the volume average void fraction obtained from pressure gradient measurements. The area average volumetric gas flow rate, based on the bubble velocity and void fraction as measured with the four‐point probe, agree with the measured gas flow rate. Also, the liquid velocity is measured by means of a laser‐Doppler anemometer, to investigate the slip velocity. The results show that reliable and interesting measurements can be obtained by using a four‐point optical fiber probe in high void fraction flows. 相似文献
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垂直管内油水两相流局部相分布特性实验研究 总被引:1,自引:0,他引:1
应用双头电导探针测量系统,对垂直上升管内油水两相分散流局部相分布特性进行了系统测量。得到了油水两相分散流的局部含油率分布类型图。研究结果表明低折算水速和低折算油速条件下,局部含油率在实验段截面上呈抛物线型局部分布特征,局部最大值出现在实验段中心区域。随折算油速增大,油滴受到横向力如升力的作用,逐渐向实验段壁面区域迁移,形成局部含油率的壁面峰值分布特性。当折算水速大于0.8 m/s时,局部含油率在实验段截面上呈均匀分布。 相似文献
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We observe electrolysis with gas evolution, a phenomenon occurring in a number of industrial scale electrochemical processes. Here, water electrolysis takes place in a small undivided electrolysis cell consisting of vertical electrodes embedded in a larger glass vessel which contains a dilute NaOH solution. Fluid flow velocities are measured by particle image velocimetry with fluorescent tracers, while size distribution and velocities of the bubbles are determined from bubble shadow images obtained with a high speed camera. Coalescence phenomena are observed in the flow and explain the relatively wide distribution of bubble sizes. Depending on the gap width and the current density, bubbles ascending near the electrodes form two discernible bubble curtains (low average void fraction, wide gaps) or a flow profile more akin to a channel flow (high average void fraction, small gaps). If the flow consists of separate bubble curtains, instabilities develop not unlike to those of a single phase wall jet. Finally, the influence of different wall parallel Lorentz force configurations on the velocity distribution in the cell is investigated. These Lorentz forces are generated by permanent magnets mounted behind the electrodes. Depending on gap width, current density, and magnet configuration, liquid phase velocities can be increased by several times compared to the baseline case. 相似文献
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基于垂直上升管中测取的气液两相流电导波动信号,采用递归定量分析方法,从多尺度角度研究了气液两相流泡状流、段塞流及混状流三种典型流型的动力学运动特征.研究结果表明,低频泡状流及混状流在递归图表现为沿对角线方向比较发育的混沌递归线条纹理特征,表明了低频运动的泡状流及混状流具有较好的确定性运动行为,而随着泡状流及混状流运动频率增加,混沌递归特征变差,其运动特征逐渐向随机方向发展.对于段塞流,在混沌递归图上逐渐呈现间歇的矩形块纹理结构,且段塞流中液塞与气塞的间歇运动特征出现在高频段,而段塞流中的泡状流运动则出现在低频段上,且随着泡状流运动频率增加,泡状流逐渐失去确定性运动行为.表明了基于电导波动信号的多尺度非线性分析方法是理解与表征气液两相流动力学特性的有效途径.
关键词:
两相流
流动特性
多尺度分析
递归分析 相似文献
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Countercurrent flooding data have been obtained using air and water for vertical-to-downwardly inclined pipes containing elbows of varying angles. Experiments were performed with six different test sections, all having an inner diameter of 51 mm and a 1-m-tong vertical tube connected to an inclined or horizontal tube The flooding data for 112.5° and 135° elbow angles were almost identical and showed that these geometries required the largest gas flow rates for flooding among all the geometries tested. The flooding gas velocities for the 157.5° elbow were slightly less than those of the 112.5° and 135° elbows but greater than those of the vertical pipe without any elbow and vertical-to-horizontal pipes at low to moderate liquid flow rates In all vertical-to-inclined pipes, flooding was initiated in the inclined section at about 15 to 50 cm downstream of the elbow. Due to the countercurrent flow of gas, the liquid stream just downstream of the elbow became highly agitated and a frothy mixture was carried upstream by gas at flooding. At moderate to high liquid flow rates, the liquid was deflected off at the elbow to form a turbulent, jetlike stream that partially broke up into droplets, These droplets were, at the onset of flooding, entrained and carried over by the gas stream Comparison of the data with the slugging correlation at low liquid flow rates and with the liquid entrainment/carryover model at high liquid flow rates suggested that these mechanisms are likely responsible for flooding in vertical-to-inclined pipes. 相似文献
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A. Saint-Jalmes M.U. Vera D.J. Durian 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):67-73
An apparatus is described for rapidly producing large quantities of foam via turbulent mixing of gas with a narrow jet of a surfactant solution inside a delivery tube. By controlling relative flow rates,
the gas volume fraction in the resulting foam may be easily varied across . Using such foams, we present a comprehensive set of data for free drainage as a systematic function of gas fraction and
sample geometry. The qualitative behavior can be understood in terms of simple theoretical considerations, emphasizing the
importance of controlling the initial foam conditions. Quantitative features are compared with two approximate versions of
the drainage equation, highlighting the crucial role of capillarity for very dry foams and small samples.
Received 15 February 1999 相似文献
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Results of experimental investigation of the bubbly gas-liquid flow in a vertical annular channel are presented. The average and pulsation shear stresses and distributions of local void fraction were measured by the electrochemical method on both channel walls. It is shown that with a rise of gas flow rate ratio the value of wall shear stress increases significantly, and this effect becomes higher at a decrease in superficial liquid velocity. A presence of the gas phase effects significantly shear stress on the inner wall. Relative intensity of shear stress pulsations increases similarly on both channel walls. 相似文献
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基于在液态金属实验回路上的实验,对非均匀磁场中液态金属射流的MHD稳定性进行了研究,建立了一个描述射流性能的简化模型。由此简化模型所得的结果与从实验获得的结果相比较表明,它们相当吻合,并发现在此液态金属射流中存在一个固有稳定性区域。 相似文献
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气体相与颗粒相混合流场的声速研究, 由于具有重要的基础理论价值与广泛的工程应用背景, 逐渐受到人们重视. 针对稠密可压缩气粒两相流动, 综合考虑颗粒相所占空间体积以及颗粒间相互作用, 推导给出了新的等熵声速计算公式; 新公式包含了已有的纯气体、稀疏气粒两相流情形的计算公式作为其特例, 一方面验证了公式推导的正确性, 另一方面说明新公式更具有通用性; 分析了不同颗粒质量分数条件下的声速变化规律, 相应结果与普朗特的理论分析符合, 特别对于稠密气粒两相流动工况得到了一些新的物理认识; 开展了颗粒间相互作用建模参数的物理分析, 揭示了其对气粒两相流动声速的影响机理. 本文取得的成果为稠密可压缩气粒两相流动研究以及相关工程应用提供理论支撑. 相似文献