共查询到18条相似文献,搜索用时 31 毫秒
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采用高速摄像仪对矩形窄缝通道内垂直上升流过冷流动沸腾区域汽泡脱离频率进行可视化实验研究。结果表明,汽泡脱离频率随质量流速的增大而减小,随入口过冷度的增大而减小,随热流密度的增大而增大。将实验数据与文献中汽泡脱离频率计算模型进行比较,发现基于池式沸腾和饱和流动沸腾开发的计算模型不能准确预测过冷沸腾区域汽泡脱离频率。本文以无量纲参数的形式,分别用液相雷诺数、过冷雅各布数和核态沸腾热流密度表示质量流速、主流过冷度和热流密度对汽泡脱离频率的影响,获得矩形窄缝通道内过冷沸腾区域汽泡脱离频率预测关系式,关系式的平均预测误差为±17.1%。 相似文献
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通过汽泡受力分析,构建窄缝通道内汽泡脱离直径预测模型。基于可视化实验获得的汽泡轴心倾斜角、前后接触角以及底部接触直径等数据,评价分析汽泡界面参数对脱离直径预测的影响,进而确定适用于本实验工况下窄缝通道内汽泡受力模型求解的界面输入参数,获得了窄缝通道汽泡脱离直径的预测值。利用竖直和倾斜条件下可视化实验获得的58个数据对汽泡脱离直径预测模型进行了验证,预测值和实验值符合较好。基于验证的汽泡脱离直径模型评估了各个力的地位和作用,应用分析了热工参数对汽泡脱离直径的影响。 相似文献
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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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低压下水欠热流动沸腾的两相CFD数值模拟研究 总被引:2,自引:2,他引:0
采用两流体(汽相和液相)基本数学模型,结合汽相和液相之间的界面传热、传质和动量交换封闭模型、汽泡平均直径模型、汽泡脱离直径模型、汽泡成核模型、汽泡脱离频率模型、欠热沸腾起始点模型和壁面热流密度分配模型,在CFD软件CFX4.4中采用用户自定义函数将相变引起的传热、传质和动量交换作为源项分别添加到汽相和液相的能量、质量和动量守恒方程中,对低压下内管加热外管绝热的环形通道内的欠热沸腾进行了数值研究,得到了欠热流动沸腾下汽相体积份额、液相速度、汽相速度分布等。采用Lee等的环形通道内低压下欠热沸腾体积份额实验数据对计算结果进行了验证,吻合良好。 相似文献
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铬(Cr)涂层锆合金包壳是最有前途的耐事故燃料(ATF)的新型包覆材料之一,对其表面的气泡动力学进行研究有助于评估是否具有更好的传热性能。在常压下的Cr涂层锆合金包壳池式沸腾实验装置中对不同工艺方法下制备的Cr涂层锆合金包壳进行实验,研究了粗糙度等表面状态对气泡产生、长大以及脱离等气泡行为的影响。结果表明,气泡接触角与Cr涂层表面粗糙度有关,粗糙度越大,表面气泡接触角越小;不同涂层工艺下制备的4种Cr涂层锆合金包壳样件表面的气泡脱离直径范围为1.256 ~1.446 mm,气泡脱离频率范围为29.99 ~50.97 Hz;气泡脱离直径与粗糙度呈负相关,脱离频率与粗糙度呈正相关;气泡脱离直径预测模型与实验数据之间的偏差为±6%,脱离频率预测模型与实验数据之间的偏差为±3%。 相似文献
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Experimental data are presented for the void fraction distribution in low flow rate forced convection subcooled boiling of water in a heated vertical tube at steady-state conditions. The measurements are based on gamma attenuation and X-ray radiography techniques. The measured local equilibrium quality at the point of net vapor generation and the void fraction profiles are compared with theoretical and empirical models of subcooled boiling. A close fit to the experimental results is obtained by the Levy model and by the Saha and Zuber correlation. 相似文献
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Visual experimental study focusing on bubble growth and departure behaviors in a narrow rectangular channel was carried out in this paper. Deionized water was used as working fluid, and the experiment was performed at atmospheric pressure. The cross section of the narrow rectangular channel is 2 mm × 8 mm. A high speed digital camera was applied to capture the behaviors of bubble growth and bubble departure from the nucleation site. The bubble departure diameter, bubble inclination angle, upstream contact angle, downstream contact angle and bubble contact diameter were obtained according to the observation. An analysis of force balance on a growing bubble was performed to predict the bubble departure diameter in the narrow channel, and the effect of bubble interface parameters on the prediction of bubble departure diameters was discussed in this paper. The result of predicted model agrees well with the experimental result with a maximum relative deviation less than 25%. According to the study proposed in this paper, the mechanism of bubble departure from a nucleation site can be explained based on the force balance analysis of a growing bubble, and the major forces dominating the bubble departure are the buoyancy force, surface tension force and quasi-steady drag force. 相似文献
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Erfeng Chen Yanzhong Li Xianghua Cheng Lei Wang 《Nuclear Engineering and Design》2009,239(10):1733-1743
Applying a three-dimensional two-fluid model coupled with homogeneous multiple size group (MUSIG) approach, numerical simulations of upward subcooled boiling flow of water at low pressure were performed on the computational fluid dynamics (CFD) code CFX-10 with user defined FORTRAN program. A modified bubble departure diameter correlation based on the Unal's semi-mechanistic model and the empirical correlation of Tolubinski and Kostanchuk was developed. The water boiling flow experiments at low pressure in a vertical concentric annulus from reference were used to validate the models. Moreover, the influences of the non-drag force on the radial void fraction distribution were investigated, including lift force, turbulent dispersion force and wall lubrication force. Good quantitative agreement with the experimental data is obtained, including the local distribution of bubble diameter, void fraction, and axial liquid velocity. The results indicate that the local bubble diameter first increases and then decreases due to the effect of bubble breakup and coalescence, and has the maximum bubble diameter along the radial direction. Especially, the peak void fraction phenomenon in the vicinity of the heated wall is predicted at low pressure, which is developed from the wall repulsive force between vapor bubbles and heated wall. Nevertheless, there is a high discrepancy for the prediction of the local axial vapor velocity. 相似文献
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沸腾是一个复杂的换热过程,大量实验表明,不同核化点的脱离直径存在区别,即使在同一工况下,同一核化点产生的汽泡脱离直径也会大小不一,因此汽泡尺寸分布不可忽略。尽管目前已有较多用于汽泡平均尺寸的计算关系式,但对于尺寸分布的研究仍较少。因此,本文针对流动沸腾下汽泡脱离直径的尺寸分布进行研究,对比常用的伽马函数和正态分布函数描述这一分布时的准确度,确定概率函数后,再对概率密度函数中两个重要的参数均值和标准差进行分析,最后得到一套预测不同工况下汽泡尺寸分布的关系式,该关系式准确度较高,并考虑了壁面过热度、质量流速等因素的影响。 相似文献