共查询到19条相似文献,搜索用时 109 毫秒
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空隙率波是气液两相流系统的特殊物理现象,理解空隙率波的传播特性对揭示两相流流型转变与流速测量物理机理具有重要意义.本文首先考察了典型非线性系统的多尺度互相关特性,发现去趋势互相关分析方法可有效揭示系统的多尺度非线性动力学特征;然后,通过采集垂直上升小管径气液两相流电导传感器阵列上下游空隙率波动数据,提出采用多尺度去趋势互相关分析方法探测空隙率波传播的多尺度互相关特性,并提取了低尺度空隙率波互相关水平增长率;另外,通过计算空隙率波空间衰减因子,考察了气液两相流空隙率波传播的结构不稳定行为.结果表明,空隙率波结构的多尺度互相关特性与其空间衰减特性具有较好的物理关联性:对于气液两相流过渡流型,低尺度空隙率波互相关水平增长率较高,且与较为稳定的空隙率波传播特性相对应;而当气液两相流空隙率波明显衰减或放大时,空隙率波互相关水平增长速率一般较低. 相似文献
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气液两相流压力波色散特性实验研究 总被引:1,自引:0,他引:1
设计了可调频式压力扰动源的气液两相流压力波实验装置,实验研究了垂直上升管内气液两相流泡状流、弹状流压力波的色散规律。实验结果表明,对泡状流,在实验范围内,压力波的传播速度及其衰减跟扰动频率有关,随着扰动频率的增加,波速及其衰减都增加;工质的流速对压力波的色散特性没有影响。结合数值模拟结果,验证了泡状流压力波色散特性的临界频率现象,即高于临界频率,压力波色散特性消失,本文分析了相应的物理机制。对弹状流,压力波同样具有典型的色散特性,已有研究结果还不能预测其色散规律。 相似文献
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本文通过实验研究了空气与非牛顿流体在小尺寸矩形微通道中的两相流动特性,给出了在不同气液两相流速下的流型图。同时比较了气液两相流速,液相黏度,表面张力,微通道尺寸对各流型分布区域以及Taylor气泡/液柱长度的影响。发现气液两相流流速变化对流型区域的影响极为明显,而黏性力和表面张力只是在局部范围改变了流型分布。Taylor气泡长度随气液两相流速比增大而增大,随液相黏度及表面张力增大而减小。液柱长度随液相黏度增大而增大,随两相流速比及表面张力增大而减小。最后,我们给出了基于无量纲数JG/JL,Re和Ca的Taylor气泡/液柱长度预测公式,公式预测结果与实验结果基本一致。 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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水平管气液两相泡状流紊流结构的准三维测量 总被引:2,自引:0,他引:2
用两个X型热膜探针对内径为35mm的水平管内气液两相泡状流的三维紊流结构进行了准三维测量,得出了沿不同直径的轴向、径向和周向的紊流脉动速度和雷诺应力分布。发现在水平管下部脉动速度和雷诺应力与单相流动时的分布规律相似;在管子上部由于空气泡的存在增强了脉动速度;在某些区域内,周向的脉动值甚至比径向和轴向的相应值还要高。水平气液两相泡状流中雷诺应力-uw不为零,在管子的上部甚至和-uv有相同的量级。给出了由于气泡引起的紊流脉动与总素流脉动比值沿径向的分布。 相似文献
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Tadeusz Bohdal 《实验传热》2013,26(2):103-117
This article describes investigations of bubbly boiling in flow of a refrigerating medium under conditions of impulse disturbances occurring in refrigeration engineering systems. The development and decay of boiling is induced by impulsively changing parameters, such as pressure and mass flux density, of the two-phase system in a tubular channel. It is confirmed that the two-phase systems exhibit wave properties and the induced disturbances propagate with a finite velocity. Correlations are elaborated to evaluate the propagation velocity of disturbance signals during the development and decay of boiling in a coil tube. Investigations are conducted by feeding under pressure a heat exchanger with an environment-friendly refrigerant R404A. 相似文献
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Convective heat transfer coefficients were measured experimentally for a tube immersed vertically in a circulating fluidized bed. Circulating fluidized beds operate in the dilute transport regime of two-phase (solid/gas) flow. The dominant mechanism for heat transfer to surfaces is particle-induced convection. In this study, experiments were carried out in a circulating fluidized bed of15 cm diameter and 11 m height. An instrumented tube of 9.5 mm diameter and 1.3 m length was placed vertically at the centeriine of the fluidized bed to measure convective heat transfer coefficients at several different elevations in the bed. Three types of particles, with mean diameters ranging from 68 to 2S1 urn, were used in the experiments at superficial gas velocities in the range of 1.3 to 8.2 m/s. Results showed that the convective heat transfer coefficients with solid/gas two-phase circulation were two to three times greater than those for single-phase gas convection at the same velocity. For a given gas velocity, the coefficients increased with increasing solid mass flux, but decreased with elevation. It was demonstrated that the heat transfer coefficients for the immersed tube and for the bed wall could be correlated with different functional dependence on the two-phase suspension density. 相似文献
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The intermittent excitation of geodesic acoustic mode by resonant Instanton of electron drift wave envelope in L-mode discharge near tokamak edge 下载免费PDF全文
Zhao-Yang Liu 《中国物理 B》2022,31(4):45202-045202
There are two distinct phases in the evolution of drift wave envelope in the presence of zonal flow. A long-lived standing wave phase, which we call the Caviton, and a short-lived traveling wave phase (in radial direction) we call the Instanton. Several abrupt phenomena observed in tokamaks, such as intermittent excitation of geodesic acoustic mode (GAM) shown in this paper, could be attributed to the sudden and fast radial motion of Instanton. The composite drift wave—zonal flow system evolves at the two well-separate scales:the micro-scale and the meso-scale. The eigenmode equation of the model defines the zero-order (micro-scale) variation; it is solved by making use of the two-dimensional (2D) weakly asymmetric ballooning theory (WABT), a theory suitable for modes localized to rational surface like drift waves, and then refined by shifted inverse power method, an iterative finite difference method. The next order is the equation of electron drift wave (EDW) envelope (containing group velocity of EDW) which is modulated by the zonal flow generated by Reynolds stress of EDW. This equation is coupled to the zonal flow equation, and numerically solved in spatiotemporal representation; the results are displayed in self-explanatory graphs. One observes a strong correlation between the Caviton-Instanton transition and the zero-crossing of radial group velocity of EDW. The calculation brings out the defining characteristics of the Instanton:it begins as a linear traveling wave right after the transition. Then, it evolves to a nonlinear stage with increasing frequency all the way to 20 kHz. The modulation to Reynolds stress in zonal flow equation brought in by the nonlinear Instanton will cause resonant excitation to GAM. The intermittency is shown due to the random phase mixing between multiple central rational surfaces in the reaction region. 相似文献