含不凝性气体蒸汽浸没射流冷凝压力振荡实验研究

实验研究了不凝性气体（空气）含量、水温和蒸汽质量流速对蒸汽浸没射流冷凝压力振荡特性的影响,实验工况横跨冷凝振荡（CO）区和稳定冷凝（SC）区。结果表明：对于纯蒸汽射流,压力振荡主频随水温的升高而降低,振荡强度随水温的升高而升高;在CO区,振荡主频和振荡强度均随蒸汽质量流速的升高而升高;在SC区,振荡主频随蒸汽质量流速的升高而降低,振荡强度基本上不随蒸汽质量流速的变化而发生改变;对于含空气射流,随空气质量分数的增加,振荡主频总体呈下降趋势,振荡强度先迅速下降后小幅上升,在空气质量分数为0.05～0.1区域内振荡主频和振荡强度均存在极小值。     

蒸汽射流凝结压力振荡幅值研究

为了得到蒸汽在过冷水中浸没射流凝结引起的压力振荡特性,针对不同的蒸汽质量流率和过冷水温度对压力振荡的影响进行实验研究。通过高频压力传感器测量得到了不同测点位置的压力振荡幅值,并结合蒸汽射流凝结形态分析蒸汽质量流率和过冷水温度对压力振荡幅值的影响规律。结果表明,蒸汽射流凝结在凝结振荡区比较剧烈,在稳定射流区相对缓和,从凝结振荡向稳定射流的形态转变导致了压力振荡幅值随蒸汽质量流率出现先减小后增大的趋势;振荡幅值随水温的升高不断增大,特别是当水温大于40℃时,由于过冷度减小,射流凝结形态变得发散,导致凝结振荡幅值大幅增加。     

稳定蒸汽浸没射流冷凝传热系数评价

为分析稳定蒸汽浸没射流的传热特性,对3类典型冷凝传热系数开展评价。结果表明:平均传热系数实验值精度主要受界面面积计算模型影响,由冷凝驱动势和蒸汽质量流速表征的传统半经验关系式在不同孔径下的预测偏差较大,新增排放孔径为独立拟合变量的纯经验关系式适用范围更广且误差在±30%以内;界面传热系数的预测精度主要受汽羽微观参数取值的影响;由压力振荡主频表征的无量纲传热系数在低池水过冷度下与实验值偏差较大,关系式中纳入汽羽贯穿长度后,预测趋势与实验值类似。      

不凝结气体对蒸汽浸没射流压力振荡强度的影响

对含不凝结气体（空气）的蒸汽浸没射流压力振荡特性进行了实验研究。研究发现,含有少量不凝结气体时,蒸汽浸没射流凝结形态发生显著变化。含不凝结气体的压力振荡强度较纯蒸汽时明显变小,但含有少量不凝结气体的压力振荡强度随空气质量分数的增加整体呈缓慢上升趋势。压力振荡强度随径向距离的增加而单调减小,随轴向距离的增加先增大后逐渐减小,存在压力振荡峰值,且随空气质量分数的增加,压力振荡峰值位置沿轴向后移。压力振荡峰值位置在轴向无量纲距离X=3和X=12之间。不同过冷水温度下,压力振荡峰值随空气质量分数变化的趋势不同。压力振荡峰值的位置即压力振荡最强的位置位于核心汽羽的尾部。     

过冷度对窄缝通道内单蒸汽泡运动特性影响的实验研究

对窄缝通道内过冷条件下单蒸汽泡运动特性进行了实验研究,分析了过冷度对单蒸汽泡运动特性的影响。实验结果表明,过冷条件下,单蒸汽泡在上升过程中,其尺寸不断减小,形状也不断改变;单蒸汽泡界面存在冷凝现象,过冷度越大,直径减小越快,同一直径蒸汽泡的纵横比在一个范围内波动;过冷条件下,单蒸汽泡的z向速度和x向速度都随着直径的增大先增加后减小,均在直径约10 mm时具有最大值;单蒸汽泡z向速度则随着过冷度的增大而增大,而x向速度在零上下波动,随过冷度增大略有增大。过冷度会影响窄缝通道内单蒸汽泡的行为特性,并进一步影响流型形成与演变。      

壁面过冷度对水平管内含空气蒸汽冷凝换热影响

为研究壁面过冷度对含不凝性气体蒸汽流动冷凝换热能力的影响,分别进行水冷却与空气冷却条件下空气-蒸汽混合气在水平管内的流动冷凝实验,分析空气入口质量分数,混合气入口流速以及管外冷却剂体积流量变化时,管内局部换热系数随壁面过冷度的变化规律。结果表明:在环状流及波状流范围内,局部换热系数随壁面过冷度的增加而增大;在分层流范围则随壁面过冷度的增加而减小;空气含量与混合气流速的增加,会使得环状流和波状流下壁面过冷度增大对冷凝换热能力的促进作用更为显著。     

蒸汽射流凝结换热系数计算的一种新方法

基于蒸汽射流凝结的分析模型和压力振荡主频的计算公式,提出通过汽羽穿透长度将平均凝结换热系数和压力振荡主频联系起来,得到一种新的平均凝结换热系数的计算方法。通过实验得到不同蒸汽质量流率和水温下的压力振荡主频,根据本实验得到的主频和先前学者的实验值计算得到的平均凝结换热系数在1.71~2.93 MW/m~2·℃之间,换热系数出现了随着蒸汽质量流率的增大变化很小,随水温的增大略有增大而后减小的趋势。     

喷洒器蒸汽浸没射流汽羽长度实验研究

以孔径分别为4、10、16 mm的侧开孔I型喷洒器为实验件,对质量流速为300~1100 kg·m?2·s?1的饱和蒸汽浸没在温度为35~65℃的过冷水中的直接接触式冷凝开展实验研究。结果表明:孔径不变时,汽羽贯穿长度基本随蒸汽质量流速和池水温度的升高而增大;大孔径喷洒器的汽羽长度与直管式喷嘴的汽羽长度接近,拟合值与实验值的偏差在±15%以内;小孔径喷洒器的汽羽长度明显低于直管式喷嘴,拟合值与实验值的偏差最高达80%;采用收缩喷管流量公式对蒸汽质量流速进行修正,拟合值与实验值的偏差在±20%以内,由实验值拟合的新关系式的预测误差在±10%以内。      

低过冷流场中蒸汽水下喷注直接接触冷凝声学特性研究

低过冷流场中蒸汽水下喷注直接接触冷凝（DCC）是核动力舰船冷凝器热井鼓泡除氧的热力基础,该过程涉及强湍动、相变、多相流等复杂行为,可诱发强烈的流场压力脉动与辐射噪声,是影响舰船声隐身性能的重要因素。针对该问题,本文通过实验对流场过冷度2.8~14.7 ℃范围内蒸汽水下喷注DCC过程的汽羽流型演化和声学特性进行研究。结果表明,蒸汽质量流速和流场过冷度对汽羽流型演化具有不同的作用机制和影响规律。低过冷流场中,蒸汽水下喷注冷凝噪声具有宽频特征;流场过冷度极低时,低频噪声占辐射噪声的主导地位,随流场过冷度的增大,高频噪声的贡献逐渐提升。     

矩形窄缝通道内汽泡脱离直径可视化研究

以去离子水为介质,研究热流密度、入口过冷度和质量流速等热工参数对矩形通道内汽泡脱离直径的影响。主要参数如下:主流流体流动方向分别为竖直向上和纵倾45o,压力为0.16 MPa,质量流速G=300~700 kg/(m2.s),热流密度q=27.6~228.3 kW/m2,入口过冷度ΔTsub=20~40℃。研究发现,热流密度和入口过冷度对汽泡脱离直径的影响不明显;随着质量流速的增大,汽泡脱离直径明显减小。     

振荡区下蒸汽冷凝过程的热工水力模型建立及验证

蒸汽射流冷凝过程具有强烈的凝结换热能力,广泛应用于先进非能动反应堆安全系统中,但该过程会产生强烈的压力振荡现象。为研究蒸汽浸没射流冷凝振荡现象的本质,从基本守恒方程式出发,建立了气泡边界层质量交换模型、气泡控制方程模型、气泡内蒸汽压力计算模型、水池中任意位置处压力计算模型等关键模型,构建了模拟水池中蒸汽气泡冷凝振荡过程的热工水力模型。运用建立的气泡半径和水池内压力的计算模型获取气泡半径和压力随时间变化的规律,并与Chun实验和Fukuda实验的实验数据进行比对,验证了模型的有效性,为后续开展冷凝振荡机理研究打下理论基础。     

Pressure and Fluid Oscillations in Vent System due to Steam Condensation, (I)

Pressure and fluid oscillation in vent tubes and a header induced by steam condensation were measured with a test apparatus. Pressure oscillation consists of low-, middle- and high-frequency components. The frequencies measured in the present apparatus are around 2–8Hz, 15 Hz and 100–150 Hz for low, middle and high frequency respectively. The chugging phenomenon occurs in a certain range of steam flow rate. When the amplitude of fluid oscillation becomes maximum, the amplitude of pressure oscillation in the header also becomes maximum. High frequency component is predominant in the pressure oscillation in vent tubes. When the temperature of pool water becomes lower, the amplitude becomes larger. As the temperature of pool water gets higher, high-frequency component of pressure oscillation disappears, and middle, low frequency in order. Based on the experimental facts mentioned above, the theoretical analysis was conducted by considering the header as one volume and by modeling chugging as one-dimensional motion of water column in and out of vent tubes. As the result, the characteristics of chugging phenomenon got in the experiment coulbd well be simulated. Chugging phenomenon, accompanying back flow of water into vent tubes, is a kind of low-frequency oscillation which is predominant in the pressure oscillation in the header.     

单棒通道流动振荡诱发沸腾临界可视化实验研究

为深入分析沸腾两相流动振荡诱发沸腾临界的影响特性,本文以去离子水为工质,横截面19 mm×19 mm、中心为外径9.5 mm的单棒通道为研究对象,通过在不同热工参数下开展沸腾两相流动特性可视化实验研究,结合汽泡行为和汽-液界面特性,分析流动振荡诱发沸腾临界的影响特性。研究结果表明,低压力、低质量流速和低入口过冷度下,极易出现流动振荡,并导致沸腾临界提前发生,此时的临界热流密度与稳定工况下相比明显偏低;随着壁面热流密度不断增加,流道中两相流型先后出现泡状流、弹状流、合并弹状流、搅混流、剧烈搅混流、不稳定环状流;当流动出现剧烈振荡时,流道存在回流;发生沸腾临界时流道压降波动最大,对应的流型为不稳定环状流。因此,单棒通道内流动振荡可能会导致沸腾临界提前发生。      

Condensation regime diagram for supersonic/sonic steam jet in subcooled water

This study was designed to determine the behaviour of the flow patterns of supersonic and sonic steam jet condensation in subcooled water. The effects of steam mass flux, water temperature and pressure ratio on the flow pattern were discussed. The results indicated that the flow pattern was not only affected by steam mass flux and water temperature, but also affected significantly by pressure ratio. The expansion and contraction ratios of the steam plume were influenced significantly by pressure ratio, and a correlation for predicting the expansion and contraction ratio was given based on the theoretical expansion ratio of sonic steam jet. At relatively low steam mass flux and high water temperature, the transition of flow pattern from stable jet to unstable jet was observed, and a criterion of stable-unstable jet transition was given. Moreover, the three-dimensional condensation regime maps, including stable steam plume shapes and unstable jet, for sonic and supersonic steam jet under different conditions were discussed. Four different shapes of the steam plume occurred in sonic steam jet regime map, and six different shapes of the steam plume occurred in supersonic steam jet regime map. The regime maps were also validated against the previous experiments.     

两相自然循环密度波不稳定性的实验研究

在自然循环水回路上进行了两相流密度波不稳定性的实验研究，得到了不同工况下的实时脉动曲线。分析了系统压力、质量流密度、进口欠热度对系统稳定边界的影响。得出了用无量纲量相变数Ｎｐｃｈ、欠热度数Ｎｓｕｂ、弗劳德数Ｆｒ表示的系统稳定边界图及稳定性判别准则式。     

Density Wave Instability of Sodium Boiling Two-phase Flow in a Vertical Annulus at Low Pressure

Experiments of density wave instability in a sodium boiling two-phase flow in an annulus were carried out with the parameters of heat flux from 80 to 976kW/m², inlet subcooling from 25.6 to 226.8°C, mass flow rate from 7.92 to 68.9 kg/h, and system pressure from 2,600 Pa to 0.06 MPa. It was found that the density wave instability occurred in the case of low exit quality, and the oscillation of flow rate was so large that the flow would be reversal. The lower inlet temperature, the higher system pressure and the larger mass flow rate could result in a more stable boiling two-phase flow. The oscillation period of the instability increased with the system pressure and the inlet subcooling, but it decreased with the mass flow rate. A correlation for the onset condition of the density wave instability was obtained from the experimental data.     

双孔对直接接触冷凝特性影响的实验研究

本文对双孔直接接触冷凝进行了实验研究。实验的蒸汽质量流速范围为50～500 kg/(m²·s),水箱温度范围为35～85 ℃。实验获得了压力脉动和高速摄像机的同步数据,重点研究分析了双孔对冷凝流型和压力脉动特性的影响。结果表明：单孔和双孔冷凝相图不同,孔数的变化导致冷凝相图流型界线的改变,且双孔造成冷凝的压力脉动强度和频率随热工参数变化的转折点提前发生。