摇摆运动下矩形窄通道内流动沸腾阻力特性

本工作对摇摆运动下水在矩形窄通道内流动沸腾阻力特性进行实验研究分析。一方面利用竖直静止实验数据对已有两相压降的计算方法进行评价,结果表明,应用于常规通道的关系式已不适用于窄通道中流动沸腾压降的计算,基于窄通道的Zhang-Mishima及Sun-Mishima关系式预测结果与实验值符合较好;另一方面得出了摇摆运动下流动沸腾阻力特性,摇摆运动使两相压降周期性波动,但摇摆角度和摇摆周期对压降的波动幅度、两相平均摩擦压降几乎无影响。     

摇摆条件下矩形管内湍流流动特性的LES研究

采用FLUENT软件和大涡模拟方法对摇摆条件下矩形通道内的湍流流体进行了理论研究,分析了各种摇摆条件和矩形通道尺寸对湍流流体流动特性的影响.结果表明,当矩形管比较窄时,管壁会抑制摇摆运动对湍流流体的影响;当摇摆幅度比较小时,摇摆运动对湍流流体的影响比较小;随着矩形管长宽比的减小,管壁上湍流摩擦阻力系数逐渐减小,并呈波形...     

摇摆条件下单相水强制循环阻力特性实验研究

常温常压下,以去离子水为工质,对摇摆条件下当量直径为5.58mm的有机玻璃矩形通道内流动阻力特性进行了实验研究。结果表明：摇摆条件下摩擦阻力系数随时间周期性波动,波动周期等于摇摆运动周期。雷诺数越小,摇摆运动的周期越小,最大摇摆角度越大时,实验段摩擦阻力系数波动幅值越大。通过π定理推导和大量实验数据的拟合,得到了计算摇摆条件下瞬态摩擦阻力系数的经验关系式。     

摇摆运动对窄通道内汽液界面参数的影响

对摇摆运动下矩形窄通道内的过冷沸腾流动进行实验研究,通过数字图像处理技术计算出空泡份额和界面面积浓度等界面参数的变化规律,并分析影响界面参数波动的主要因素。实验结果表明,矩形窄通道内汽液界面参数受摇摆运动影响产生周期性波动,且波动周期与摇摆运动周期相同。摇摆运动下空泡份额和界面面积浓度的波动主要受汽泡等效直径变化的影响。     

窄矩形通道内单相水阻力特性实验研究

文章对两个宽高比不同的窄矩形通道在竖直与倾斜条件下的单相水阻力特性进行了实验研究。通过对实验数据的分析确定了窄矩形通道内单相流动从层流向紊流转变的临界雷诺数为2400左右。在层流区内,竖直和倾斜条件下试验段内单相水的阻力系数实验值均大于圆管经验公式值,紊流区内阻力系数实验值与Blasius经验公式值符合良好。倾斜对试验段内单相水的阻力特性无影响,但宽高比越小,阻力系数越大。     

摇摆条件下矩形窄缝通道单相等温流动摩擦阻力特性研究

通过实验研究和数值计算相结合的方法研究摇摆条件下矩形窄缝通道单相等温流动摩擦阻力特性。研究发现:受摇摆附加惯性力的影响,流道内的微观流场出现变化,但在本实验参数范围内,流场的微观变化较小,摇摆对摩擦阻力特性的影响可以忽略,由流道静止状态获得的摩擦阻力系数计算公式在摇摆条件下仍然适用。     

摇摆对矩形窄通道内单相水流动特性的影响

常温常压下,实验研究摇摆对矩形窄通道内单相水流动特性的影响。结果表明,驱动压头较低时,雷诺数及摩阻系数呈周期性波动,摇摆越剧烈,波动幅度越大;驱动压头较高时,雷诺数周期性波动不明显,摩阻系数波动幅度减小。出口通大气的实验段,摇摆振幅对摩阻系数波动幅值及波形均有影响,摇摆周期只影响摩阻系数波动幅值。摇摆运动对流动特性的影响随雷诺数的增加而减弱。摇摆对矩形窄通道内单相水平均摩阻特性没有明显影响。     

摇摆条件下矩形通道内单相水强制循环流动特性研究

常温常压下,以去离子水为工质,对摇摆条件下矩形通道单相流动特性进行了研究.根据实验测得的压降,求出了摇摆条件下单相水的平均摩擦阻力系数.实验结果表明,摇摆工况下,闭合回路流量呈周期性波动.摇摆运动的频率和振幅越大,则回路的平均流量越小,流量波动幅度越大.摇摆状态下平均摩擦阻力系数比稳态值大,平均摩擦阻力系数值取决于摇摆...     

摇摆对窄缝通道内高压两相摩擦阻力影响的研究

对矩形窄缝通道内高压两相摩擦阻力特性开展实验研究,分析摇摆运动对矩形窄缝内两相摩擦阻力的影响。结果表明:摇摆运动条件下,两相摩擦阻力会随着摇摆运动而呈现近似正弦的波动,两相摩擦阻力波动时均值与静止条件下的相等;摇摆运动引起的摩擦阻力相对变化量随着全液相雷诺数、含汽率、摇摆周期的增大而减小,随着摇摆幅值的增大而增大;摩擦阻力相对变化量与最大摇摆角加速度没有明显单调关系。提出用于计算摩擦阻力相对变化量的经验关系式。     

摇摆对窄缝通道内高压两相摩擦阻力影响的研究

对矩形窄缝通道内高压两相摩擦阻力特性开展实验研究,分析摇摆运动对矩形窄缝内两相摩擦阻力的影响。结果表明:摇摆运动条件下,两相摩擦阻力会随着摇摆运动而呈现近似正弦的波动,两相摩擦阻力波动时均值与静止条件下的相等;摇摆运动引起的摩擦阻力相对变化量随着全液相雷诺数、含汽率、摇摆周期的增大而减小,随着摇摆幅值的增大而增大;摩擦阻力相对变化量与最大摇摆角加速度没有明显单调关系。提出用于计算摩擦阻力相对变化量的经验关系式。     

稠密栅元内湍流流体的流动传热

本文对稠密栅元内的湍流流动和传热特性进行了分析。首先利用实验数据对计算结果进行了验证,然后分析了Re和P/D等参数对稠密栅元内的摩擦阻力系数和传热系数的影响。Re和P/D均会对稠密栅元内的流动传热特性产生显著影响,但传统的理论模型无法描述P/D对栅元内的摩擦阻力系数和传热系数的影响。P/D=1.03是一临界点,这种条件下的稠密栅元内的流动和传热是最安全的,也是最高效的。此时核反应堆的功率和系统的传热能力可同时达到最大。     

空气-水在垂直非圆截面通道内流型研究

采用可视化方法研究了水力直径分别为15mm和10mm的两种正方形截面、14.43mm的三角形截面以及14mm的圆形截面通道内空气-水垂直上升流动,表观气速0.04～80m/s,表观水速0.001～6m/s.观察到了泡状流、弹状流、块状流、环状流和弥散泡状流等常见流型.此外,在表观气速很大而表观水速很小时,在非圆截面通道内发现了爬动流,证实了非圆截面直通道内存在"二次流"现象,且对气-液两相流动的相分布有较大影响,证明截面形状对两相流流型及其转变具有重要影响.由实验得到了流型转变界限,并首次获得了包括爬动流的两相流流型图.比较本文的实验结果及与前人的研究结果对比发现,水力直径的大小对两相流流型的转变具有一定影响.     

竖直和倾斜条件下气-液两相流型转变研究

以去离子水和空气为两相介质,研究了竖直和倾斜条件下气-液两相流型,发现通道内存在弥散泡状流、泡状流、弹状流、搅拌流和环状流5种流型。通过对流型间转变特性的机理分析,构建了竖直和倾斜条件下各流型的转变准则,与实验数据进行了对比,符合很好。     

Flow Regime Transition to Wavy Dispersed Flow for High-Pressure Steam/Water Two-Phase Flow in Horizontal Pipe

A wavy-dispersed flow regime was observed between slug and annular-dispersed flow regimes in TPTF high-pressure steam/water horizontal pipe experiments, employing the video probe visual observation. The onset OF entrainment was identified to cause slug to wavy-dispersed flow transition. The wavy-dispersed flow regime extended towards lower gas flow rates as pressure was increased. Furthermore, it was found that the gas-liquid relative velocity for the onset of entrainment decreases significantly, resulting in decrease in the minimum void fraction. Consequently, the slug flow regime was found to disappear for pressures above 8.6MPa, as observed in the previous TPTF experiments. Applicability of available models and correlations on the onset of entrainment was assessed against the TPTF data. Steen-Wallis parameter correlated the data well when the superficial gas velocity term in this parameter 1s replaced by the gas-liquid relative velocity.     

Flow Behavior and Phase Distribution in Two-Phase Flow around Inverted U-Bend

Experimental results are presented on the flow behavior, phase distribution, average void fraction and slip ratio in air-water two-phase mixture flowing through an inverted U-bend. The curved test section of transparent acrylic resin tubing with 24 mm I. D. was used, comprising a riser, an inverted U-bend with radius of 96 mm, and a downcomer. From the visual observation, a flow map was derived, which indicates the relation between the flow patterns and velocities. Distributions of local void fraction along a diameter lying in the central plane of the bend and over the whole cross section of bend tube were measured, and those distribution mechanisms were explained by the effect of centrifugal and gravitational forces. The average void fraction around the bend was obtained by numerical integration of the measured local void fraction, and the slip ratio was calculated using the average void fraction.     

低流量下蒸汽发生器一次侧流量分配研究

采用CFD方法对低流量下倒U型管式蒸汽发生器一次侧内的流动特性进行了分析研究.结果表明,在自然循环模拟试验装置的U型管结构参数条件下,倒流只发生在内层的短管内.低流量时,随单管平均流量的增大,倒流管内的流量相对减小,倒流管数量相对减少,最终倒流消失;随二次侧温度升高,倒流管内的流量也相对减小,倒流管数量相对减少.     

Applicability of Annular Flow Model to Counter-Current Flow in Debris Beds

Counter-current flow limitation (CCFL) is dominant phenomena for dryout in a debris bed which may be formed during a severe accident as observed in the Three-Mile Island unit-2. Actual CCFL situation in debris bed is very complex. It is difficult to treat the CCFL in the debris bed as it is. On the other hand, an annular flow model was developed to predict CCFL in a pipe by assuming a two-dimensional turbulent flow. If hypothetical flow channel were assumed for CCFL in the debris bed, CCFL in the debris bed could be treated with the same manner as for CCFL in a pipe. 'The purpose of this study is to investigate whether the annular flow model developed for CCFL in a pipe is applicable for CCFL in the debris bed or not. As the results, it is clarified that qualitative tendency of the CCFL in the debris bed consisting of larger particles than 3 mm is estimated by the annular flow model developed for CCFL in a pipe, although the difference between the calculation and the data is large in higher and lower gas velocity. It is also clarified that wall friction factor calculated with the present analysis is twice to forth larger than that in the single phase flow through porous media.     

组合阀步降流道三维流场数值分析

运用计算流体力学程序CFX对组合阀步降流道内三维流场进行了分析和计算,流道水力学特性计算结果与组合阀步降流道流动阻力实验结果符合良好。在此基础上,对流道内流速和压力分布进行了研究,结果表明:阀芯流道侧壁入口上端流体流速达到峰值,回零水腔内流体的流速分布均匀,流道内压力损失最大的部位处于入口流道竖管段与横管段之间,可通过增大管径或加缓变过渡段的方法来减少该部位的流动阻力损失。     

Calculation for Three-Dimensional Structures of Two-Phase Flow in Enlarged Flow Area

Superconducting tunnel junctions in use for X-ray detection ale expected to produce an excellent energy resolution. An inclusive model is employed to give an overview of the detector characteristics. This method is devised to implicitly take properties of superconductor materials into account. With introducing an empirical relationship between junction parameters, the detector characteristics such as signal magnitude and energy resolution are reproduced to an acceptable degree. This method gives a helpful suggestion for understanding the detector performance such as a Fano-like factor, and may also serve as a guide line for designing tunnel junctions.     

环形窄缝通道单相流动特性研究

对环形窄缝通道内单相流动特性进行了分析，提出了理论模型预测环形窄缝通道内单相流动阻力特性。根据该模型，对窄缝宽度分别为1.0、1.5、2.0mm环形通道内单相湍流流动摩擦阻力系数进行了理论计算，并与实验结果进行了比较。理论预测值与实验结果符合较好，且窄缝间隙大小对环形窄缝通道内流动特性有着重要影响，随着间隙的减小，摩擦阻力系数相应减小。间隙对流动阻力系数的影响还依赖于Re大小，其影响随Re的减小而降低。