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竖直矩形窄缝通道内近壁汽泡生长和脱离研究 总被引:1,自引:1,他引:0
可视化研究窄缝通道内汽泡生长和脱离对于揭示窄缝通道内的沸腾传热机理具有重要意义。本文采用高速摄影仪从宽面和窄面可视化观察了常压条件下矩形窄缝通道内汽泡核化生长和脱离规律。研究结果表明,汽泡在核化点生长时,汽泡底部与加热面存在一小的接触面,总体而言,汽泡在生长过程中基本呈球状。在相同热工参数下,不同核化点处汽泡生长规律基本相同,但汽泡脱离直径相差较大。窄缝通道内汽泡生长速率小,脱离时间较长,可采用修正的Zuber公式预测窄缝通道内汽泡生长直径。在同一拍摄窗口内,统计分析了热工参数对汽泡平均脱离直径的影响规律。随热流密度的增加,汽泡平均脱离直径减小;随入口欠热度的增加,汽泡平均脱离直径减小;随主流速度的增加,汽泡平均脱离直径减小。 相似文献
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对窄空间内自然对流条件下的沸腾空泡演化行为进行了可视化实验研究。液相工质为去离子水,实验段采用聚碳酸酯材料,窄小空间尺寸为2 mm×10 mm×250 mm。加热片采用FTO导电玻璃,从而实现从汽泡底部观察其生长特性。本文得到了不同热流密度下的汽泡生长特性曲线,发现在汽泡生长过程中,其长度与宽度的变化均符合指数规律,且长宽比在生长末期在一个固定值附近波动。汽泡生长速度随热流密度的变化不呈线性关系,受多种因素共同影响。同时,还分析了窄空间流道内汽泡聚合过程的受限界面演化特性。 相似文献
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在垂直上升环形通道内进行强制对流过冷沸腾实验。实验工质为水,实验压力为大气压力。由一台高速摄像仪对汽泡核化的动力学过程进行图像捕捉。通过影像获取总共58个工况下的汽泡脱离频率。对本实验的数据和从文献中获取的数据进行无量纲分析。将已有的模型和关系式与汽泡等待时间、生长时间以及脱离频率等实验数据进行比较。由池式沸腾改进的关系式未能很好地应用于强制对流过冷沸腾,同时,由过冷沸腾提出的模型也不能预测宽实验参数范围内的汽泡脱离频率。无量纲汽泡脱离频率与无量纲泡核沸腾热流密度相关。新的关系式与现有的低壁面过热度下的实验数据吻合良好。 相似文献
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为了探讨系统压力变化对窄流道内汽泡生长的影响,在不同系统压力(0.1~1 MPa)下采用高速摄像仪对2 mm竖直矩形窄流道内的汽泡生长进行可视化研究.研究表明,发现在0.1~0.3 MPa下汽泡的生长主要在核化点处进行,但在较高压力(Ps≥0.6 MPa)时汽泡生长主要是在滑移中进行,汽泡的尺寸也显著减小;由于汽泡行为发生变化,不同系统压力下加热壁面上的换热状况有着很大区别.用拉普拉斯数(La)和时间因子(ξ)分别对汽泡半径和汽泡生长时间进行无量纲化后,无量纲汽泡生长曲线遵循指数曲线变化;指数曲线的系数七随系统压力升高而减小. 相似文献
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采用实验方法对窄矩形通道内过冷沸腾时的汽泡聚合行为进行了可视化研究。矩形通道的尺寸为2 mm×40 mm×700 mm。实验参数为:实验段入口处绝对压力pin=0.55 MPa,入口过冷度Δtin=31 ℃,质量流速G=516 kg/(m2•s),平均速度v=0.52 m/s。采用高速摄影仪对实验流道进行拍摄,拍摄速度为5 000帧/s。将汽泡聚合过程分为4个阶段:靠近、融合、调整和稳定阶段。发现聚合后的汽泡运动速度会先增大再减小,最后趋于稳定。调整阶段汽泡形态不断变化,椭球形、圆形交替出现;伴随着形变,聚合汽泡的角度、长短轴长也会有相应的变化。最后发现在汽泡聚合过程中会诱导出一个新的小汽泡。 相似文献
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双探头光学探针识别受热工况两相流流型的基本方法研究 总被引:1,自引:2,他引:1
由于流型识别手段受到限制.目前常用的流型图以及流型转变判据.都是在绝热工况下根据实验得到的;关于受热工况两相流流型还没有足够的实验数据。光学探针的运用为受热工况两相流流型的研究提供了有力的测量手段。本文对双探头光学探针4种流型识别的基本方法进行了研究,包括探针原始电平信号概率密度函数(PDF)分析识别流型、信号时序波形识别流型、空间波形识别流型以及汽泡尺寸PDF分析识别流型。研究结果表明,汽泡贯穿弦长PDF分析可得出满意的流型识别结果。 相似文献
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抑压水池中淹没射流导致的喘振现象对抑压系统的可靠性有较大影响,而气泡行为直接关系到喘振的机理。为更好地识别喘振现象中的气泡行为,本文提出了一种基于改进的分水岭图像分割算法的蒸汽淹没射流图像自动处理方法。基于像素矩阵建立微分模型,提取气泡二维信息并近似估计三维信息,进而获取射流体积变化情况。借助图像灰度方差信息,提取气泡冷凝周期。算法提高了射流气泡的识别精度。通过与人工标定比对,图像区域识别误差控制在10%以内;经验证,简化椭圆模型计算图像投影面积的相对误差较小;气泡参数与冷凝周期提取结果符合实验表征与理论规律。 相似文献
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由于表面张力与惯性力作用,静止流场内较大尺寸气泡[500<气泡雷诺数(Re)<2000]形成不规则几何形状,造成二维图形处理方法等效球体或椭球获取三维体积的方式误差较大。此外,由于不规则界面的散射和反射,引起二维图像处理中边界模糊,难以辨识。本文以高速摄像机获得的静止流场内大尺寸气泡二维灰度图像作为卷积神经网络(CNN)的输入,以图像内气泡二维投影面积及实验获得三维体积训练网络,并用训练好的网络预测气泡体积。实验采用小气泡叠加法获得真实气泡体积,与网络预测结果进行对比。结果表明,该方法与传统图像处理方法相比,不需要对气泡形状进行假设,提高了对大尺寸气泡的适用性。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(8):671-672
The authors have been investigating geysering, which may appear during start-up of a natural circulation boiling reactor. From the results, it became clear that a large slug bubble covering the entire channel and its condensation in the upper plenum were indispensable for geysering to occur. In this work, an image processing unit has been developed in order to measure the coalescence process of multiple slug bubbles. The proposed system was used to measure the coalescence process of multiple slug bubbles flow in vertical circular channel on air-water system. It was shown that a following slug bubble was influenced by the preceding slug bubble as the distance between the slug bubbles became 5 times inner channel diameter. The rise velocity of the following slug bubble increased due to the pressure drop induced by the wake behind the preceding slug bubble. The bubbles coalesced together in a fraction of a second. 相似文献
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The bubble motion characteristic is one of the most important fields in two-phase flow research. Based on the image recognition method, the characteristic and dynamics of single bubble rising process in stagnant water were analyzed. The trajectory, deformation extent and instantaneous terminal velocity of single bubble rising process with different equivalent volume diameters were analyzed. The research results show that the peak value of lateral oscillation amplitude is proportional to the peak value of lateral velocity. The instantaneous aspect ratio is inversely proportional to instantaneous axial velocity. The phenomenon that the lateral motion position, aspect ratio and rising speed of a single bubble has periodical change. Based on the quantitative analysis of the relationship between bubble terminal velocity and bubble equivalent volume diameter, the existing prediction formulas were compared and evaluated. A more accurate explicit terminal velocity correlation based on experimental data was obtained. 相似文献
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气泡运动特性是两相流研究的重要领域之一。本文基于图像识别技术对静水中单气泡的上升过程及其动力学特性进行研究,分析了不同等效体积直径下气泡上升过程中轨迹、变形程度、瞬时速度等参数。研究结果表明:椭球型单气泡上升过程中横向振荡幅度峰值与横向速度峰值呈正比,瞬时纵横比与瞬时纵向速度呈反比;单气泡横向运动位置、纵横比、上升速度具有周期性变化的现象。通过定量分析气泡末速度与等效体积直径的关系,对已有预测关系式进行了比较和评价,并基于实验数据拟合得到了一个更为精确的显式末速度关系式。 相似文献
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In two-fluid modelling, accurate prediction of the interfacial transport of mass, momentum and energy is required. Experiments were carried out to obtain a database for the development of interfacial transport models, or correlations, for subcooled water-steam flow in vertical conduits. The experimental data of interest included the interfacial area concentration, interfacial condensation heat transfer and bubble relative velocity. This paper focuses on the interfacial area concentration. The interfacial area concentration was obtained by measuring the distributions of bubble volume and surface area as well as the area-averaged void fraction at various axial locations in subcooled water-steam condensing vertical upward flow under low flow rate and low pressure conditions. The bubble size and surface area were determined using high-speed photography and digital image processing techniques. The area-averaged void fraction was measured by a single-beam gamma densitometer. The results were compared with existing correlations, which were developed on the basis of data obtained for air-water adiabatic flows. Poor agreement between the present data and the existing correlations was obtained. Accordingly, new correlations suitable for subcooled liquid-vapour bubbly flow are proposed. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(11):1017-1027
Fission gas release in the bump tests was correlated to the deformations of claddings via mathematical product of the number of gas atoms and their residing time on grain boundaries. A positive correlation of the deformations with the product indicated that gas bubble swelling of pellets contributed to the pellet-cladding mechanical interaction (PCMI). Residual gaps prior to the bump tests turned out to be filled in at the bump terminal level by differential thermal expansion of pellet and cladding. Visible macro cracks existing in the central part of the pellet virtually vanished during the tests due to bubble swelling of the pellet. Together with these observations, quantitative image analysis of pellet porosity showed that the aforementioned PCMI was brought about by combination of differential thermal expansion and bubble swelling. A model to unify gas release, bubble growth and PCMI simulated well the observed behaviors of fission gas release from bump-tested rods. It was deduced by the model that higher burnup retains a higher potential for PCMI, while power reductions and associated gas releases reduce PCMI. In the analysis in this paper were used the data of the Rise Transient Fission Gas Release Project. 相似文献
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本文研究了常温、常压条件下自由液面单气泡破裂产生的膜液滴现象。利用染色液滴撞击熟宣纸表面不洇散特性,加工宣纸纸筒进行稀释墨水中气泡破裂产生膜液滴空间分布实验,并通过后续图片扫描及编写Matlab图像处理程序获得膜液滴在圆柱纸筒上的尺寸分布、空间分布信息。通过改变实验条件,讨论分析气泡尺寸及纸筒半径对膜液滴空间分布结果的影响,获得了常温、常压条件下自由液面单气泡破裂产生膜液滴空间分布规律。 相似文献
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Gas-lift pump in liquid metal cooling fast reactor (LMFR) is an innovative conceptual design to enhance the natural circulation ability of reactor core. The two phase flow characteristics of gas–liquid metal make significant improvement of the natural circulation capacity and reactor safety. It is important to study bubble flow in liquid metal. In present study, the rising behaviors of a single nitrogen bubble in 5 kinds of common stagnant liquid metals (lead bismuth alloy (LBE), liquid kalium (K), sodium (Na), potassium sodium alloy (Na–K) and lithium lead alloy (Li–Pb)) and in flowing lead bismuth alloy have been numerically simulated using two-dimensional moving particle semi-implicit (MPS) method. The whole bubble rising process in liquid was captured. The bubble shape, rising velocity and aspect ratio during rising process of single nitrogen bubble were studied. The computational results show that, in the stagnant liquid metals, the bubble rising shape can be described by the Grace's diagram, the terminal velocity is not beyond 0.3 m/s, the terminal aspect ratio is between 0.5 and 0.6. In the flowing lead bismuth alloy, as the liquid velocity increases, both the bubble aspect ratio and terminal velocity increase as well. This work is the fundamental research of two phase flow and will be important to the study of the natural circulation capability of Accelerator Driven System (ADS) by using gas-lift pump. 相似文献