共查询到16条相似文献,搜索用时 156 毫秒
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利用平面激光诱导荧光技术(PLIF)结合数字图像处理对不同Re下液膜厚度的实时变化进行测量。通过MATLAB内建功率谱密度计算函数对液膜波动的时间序列进行进一步的处理,获得了液膜波动特性的功率谱密度(PSD)曲线,对不同Re下的液膜波动规律进行了频谱分析。结果表明:液膜波动具有显著的多频特性,且各频率有优劣之分,孤立波数量虽少,却携带液膜波动的大部分能量,对液膜波动的贡献不可忽略。液膜波动幅度与Re有关并呈现出一定的规律性:小Re时,液膜的波动幅度与Re有强烈的相关性,随Re的增大而增大;中等Re时,液膜的波动幅度基本保持稳定;大Re时,孤立波的出现使液膜波动幅度急剧增大,液膜波动不稳定性增强。 相似文献
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为避免在极端事故工况下,乏燃料水池会长期失去补水和冷却,第3代核电站如AP1000和CAP1400,引入了喷淋冷却系统。在喷淋条件下,乏燃料棒上液膜流动特性是影响冷却效果的重要因素,国内外学者还未对其做过详细的研究。本文使用光学法研究了在不同雷诺数(Re)条件下,对单根乏燃料棒进行喷淋冷却所形成的液膜厚度随时间和空间的变化。利用CCD相机采集液膜图像,并经过处理得到了清晰的液膜厚度图像和与图像吻合良好的数据。实验结果表明:当Re为608~7 538时,瞬态液膜厚度最大值出现在Re=7 085的条件下,其值为2.36 mm;随着Re的增加,时均液膜厚度会随之增加,并且液膜波动的振幅也会随之增加;在沿棒方向上,随着距棒顶距离的增加,液膜厚度会逐渐减小并趋于平稳,并且随着Re的增加,平稳部分会出现在距棒顶更远的位置。对乏燃料单棒冷却液膜流动特性的研究,为确定具有有效冷却能力的最小喷淋流量奠定了基础。 相似文献
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液膜在安全壳表面的流动铺展性能对非能动安全壳冷却系统有重要的影响。采用三维数值模拟方法研究了降膜板表面形貌、接触角与液相雷诺数对液膜铺展性能的影响,并将结果与前人的实验和理论结果对比,吻合良好。研究发现,当降膜板为横向波纹板时液膜完全铺展时间、液膜厚度及界面湍动程度明显大于平板与纵向波纹板,此时波纹板波谷处会有循环流动产生。随接触角的增加或液相雷诺数的减小,液膜逐渐从完整流转变为片状流、溪流、滴状流。在纵向波纹板对液膜的导流与撕裂综合作用下,随接触角的变化,液膜的铺展性能与平板相比也发生较大的变化。 相似文献
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气弹速度和液膜厚度作为弹状流工况下的关键参数,在传热分析和力学分析中具有重要意义。本文以空气-水为介质,采用高速摄影机和印刷电路板式(PCB)液膜厚度传感器,对高1.9 mm×宽68 mm的水平窄矩形通道内气弹运动特性进行研究。液相雷诺数(Rel)<2500,矩形通道内为层流区;Rel≥2500,矩形通道内为湍流区,基于气-液两相混合速度分别拟合了气弹运动速度的预测关系式,结果表明,层流区分布系数(C0)可采用Ishii关系式计算且漂移速度为0;而湍流区C0为1.0。当气弹雷诺数(Reb)<3100时,气弹底部液膜厚度(δb)随毛细管数的增大而增大;而在Reb≥3100时,δb表现出波动性。现有的δb预测关系式不适用于窄矩形通道,在考虑通道高宽比的影响下提出了一个新的δb预测关系式,对文献中210个数据进行了验证,预测误差均在±20%内。 相似文献
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为探明环状流液膜界面扰动波形成机制,以准确预测液膜质量输运和干涸(Dryout)型临界热流密度特性,本研究通过将高速摄像与液膜厚度电导传感结合的方法,分别对液膜界面波的演化行为和液膜厚度进行定性可视化分析和定量测量实验。结果表明,高湍动的气芯与液膜的相互作用在液膜界面上形成毫秒级不规则演变的涟波,高频涟波先驱经过一系列秒级自卷积演化成随机分布的扰动波;扰动波形成机制的数学模型表明,液膜界面扰动波的形成时间间隔符合伽马分布,伽马分布阶数与气相速度正相关但独立于液相流速。 相似文献
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波形板干燥器是船用核动力系统中重要的汽水分离设备,其壁面上自由下降液膜的流动特性对干燥器的汽水分离效率及船用核动力装置的安全性指标有着较大的影响。基于平面激光诱导荧光技术(PLIF)对不同雷诺数下的壁面薄层液膜厚度进行测量。通过小数据量法计算不同工况下的液膜厚度时间序列的最大Lyapunov指数,分析壁面液膜的混沌特性并进行相空间重构。利用反向传播(BP)神经网络解决非线性问题的优势对液膜厚度进行预测,完成了单隐层BP神经网络预测模型的建立并实现了自由液膜厚度的非线性特征分析。结果显示:最大Lyapunov指数与液膜雷诺数呈正相关关系;在大雷诺数区生成的孤立峰同重力及液膜间的叠加作用相互耦合,使液膜混沌特性变得更加明显。 相似文献
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Disturbance waves play an important role in interfacial transfer of mass, momentum and energy in annular two-phase flow. In spite of their importance, majority of the experimental data available in literature on disturbance wave properties such as velocity, frequency, wavelength and amplitude are limited to near atmospheric conditions (Azzopardi, B.J., 1997. Drops in annular two-phase flow. International Journal of Multiphase Flow, 23, 1-53). In view of this, air-water annular flow experiments have been conducted at three pressure conditions (1.2, 4.0 and 5.8 bar) in a tubular test section having an inside diameter 9.4 mm. At each pressure condition liquid and gas phase flow rates are varied over a large range so that the effects of density ratio, liquid flow rate and gas flow rate on disturbance wave properties can be studied systematically. A liquid film thickness is measured by two flush mounted ring shaped conductance probes located 38.1 mm apart. Disturbance wave velocity, frequency, amplitude and wavelength are estimated from the liquid film thickness measurements by following the statistical analysis methods. Parametric trends in variations of disturbance wave properties are analyzed using the non-dimensional numbers; liquid phase Reynolds number (Ref), gas phase Reynolds number (Reg), Weber number (We) and Strouhal number (Sr). Finally, the existing correlations available for the prediction of disturbance wave velocity and frequency are analyzed and a new, improved correlation is proposed for the prediction of disturbance wave frequency. The new correlation satisfactorily predicted the current data and the data available in literature. 相似文献
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矩形窄缝通道内水稳态和瞬态流动换热特性实验 总被引:1,自引:0,他引:1
以去离子水为工质,在压力0.5~5.0 MPa的范围内,对矩形窄缝通道内水稳态及瞬态流动换热特性进行了实验研究。结果表明:矩形窄缝通道在水平和竖直放置以及稳态和瞬态条件下,水的流动换热特性呈现出基本相同的规律。层流向紊流过渡区域的雷诺数(Re)为900Re1300,比常规通道提前,单相摩擦阻力系数比常规通道大;采用Dittus-Boelter公式的形式拟合得到了新的换热实验关联式,其系数较Dittus-Boelter公式的系数约小11.3%。在稳态条件下,紊流区换热系数随质量流速的增加而增大,增大趋势比较明显;换热系数随热流密度的变化不明显;压力对单相强迫对流换热特性基本没有影响。 相似文献
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The use of thin liquid metal layers as shield against erosion and thermal loads of the inner reactor walls continues to be of interest. The degree and reliability of the protection depend on the stability of the liquid metal layer under the influence of the surrounding magnetic field. In this paper we treat analytically the problem dealing in particular with the stability of the liquid metal layer under the influence of a uniform surface normal magnetic field and its control by means of a transversal electrical field. The Karman–Polhausen integral method is used to reduce the system into two equations that describe the spatio-temporal variations of the flow rate and the film thickness. The proposed model improves the formulation of Korsunsky (1999) for high Reynolds numbers by including the second order terms. It is shown that Korsunsky's formulation overestimates the cut-off frequency and it does not foresee periodic stationary waves to develop on the free liquid surface. The electrical and magnetic fields’ abilities to stabilize or destabilize the flow, as a function of the critical Reynolds number, are examined. The influence of the electromagnetic fields on the cut-off wave-number and growth rate of the perturbations in terms of the Reynolds number and wave-number is also presented. 相似文献
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Experimental studies of the effect of functional spacers to annular flow in subchannels of a BWR fuel element 总被引:1,自引:0,他引:1
For the prediction of dryout in fuel elements of boiling water reactors, the dynamic behavior of the water film covering the fuel rod has to be understood. This paper provides high resolved experimental data of the liquid film and gives insight into the dynamic film behavior.The experiments of this work were conducted in a vertical channel representing a pair of neighboring subchannels of a BWR fuel rod bundle. Air and water at ambient pressure and temperature are used as model fluids, creating an annular flow in the test section. The influence of different functional spacer shapes on the liquid film has been studied.The heart of the instrumentation is a liquid film sensor (LFS), which measures the film thickness distribution around a half cylinder with a matrix of 64 × 16 measuring points with a time resolution of 10,000 frames per second and a spatial resolution of 2 mm × 2 mm. The high resolution allows for a visualization of the dynamic liquid film as a movie animation. Principals of the dynamic behavior of the liquid film are observed.The time-averaged film thickness distributions show that the spacers structure the liquid film significantly. The gaseous phase is accelerated due to the cross-section blockage caused by the spacer. This leads to a local thinning of the liquid film downstream of the spacer.Two statistical evaluation methods are presented to determine different dynamic wave properties: The wave velocity as function of the wave height, the traveling path of the waves and the location of wave separation and merge events.The first evaluation method shows that big waves move generally faster than small waves. The analysis further shows wave acceleration in close proximity of the spacer with subsequent deceleration further downstream.Analyzing the wave as a two-dimensional entity it can be seen that the wave paths are clearly structured by the spacer and hence do not travel circumferentially around the fuel rod. Wave separation and merge has a higher occurrence probability in the subchannel gap, if there is no spacer present. With spacer the merge and separation locations are only found along the main flow paths of the waves. 相似文献