竖直向下大、小支管气相夹带起始可视化研究

已有气相夹带起始模型均是基于竖直向下的小支管夹带所得到的,用于分析大支管气相夹带时并不适用。本文基于可视化实验,对竖直向下的大、小尺寸T型管的气相夹带起始点进行对比研究。选择与主管道直径比为0.625和0.1的大、小支管,并采用有机玻璃作为实验管道材料,空气和水为实验工质。其实验现象表明:大、小支管夹带起始均有漩涡,且漩涡现象大致相同,但在大支管条件下会出现气室,夹带气体进入支管后也会在气室下翻腾,且在相同液相折算速度下,大支管夹带起始液位会高于小支管。     

竖直向下大支管T型管气相夹带实验研究

基于可视化夹带实验,本文对由水平主管段和大尺寸支管组成的T型管进行夹带起始和稳态夹带研究,并与RELAP5中的气相夹带模型进行对比。结果表明:本实验中夹带起始时所出现的漩涡形式与前人的研究结果相似;稳态夹带实验中观察到一种全新的无旋夹带形式;压差与气相夹带基本为线性关系,T型管主管与支管压差越大,气相夹带越小。     

AP1000中ADS-4液体夹带实验研究

以AP1000核电厂中自动泄压管线(ADS-4)与热管段形成的T型结构为研究对象,开展缩小比例的T型管夹带实验。实验结果表明:大尺寸支管的夹带与小尺寸支管的夹带有明显差别。分层流情况下的夹带研究中发现两种夹带机理;在较低气相Froude数及较低气腔高度时,容易产生间歇流夹带;在较高气相Froude数情况下,往往出现环状流夹带。此外,实验研究发现,大尺寸支管中回流现象显著。支管形状对起始夹带有重要影响,而液体横流似乎并不影响起始夹带。     

AP1000 ADS-4空气-水夹带试验研究

为研究核电厂中ADS-4卸压夹带过程,以AP1000核电厂为原型设计建造了ADS-4喷放卸压试验回路ADETEL。用高速摄像仪拍摄夹带起始和夹带率的试验过程,将试验数据与现有试验数据和模型进行对比。结果表明:ADETEL试验数据和其他试验数据及理论模型之间存在较大差异;RELAP5和ATLATS的夹带率模型不能准确估算AP1000核电厂中的ADS-4夹带量;当热管段内液位较低时,夹带量会随热管段内液位降低而迅速减小;夹带起始在小支管-主管直径比(d/D)工况下更容易发生;在相同的热管段相对液位下,AP1000中ADS-4支管内液体的夹带率较AP600的低。     

AP1000中ADS-4液体夹带模型研究

研究了由AP1000核电厂一回路热管段和ADS-4管道组成的大尺寸支管T型管液体夹带的实验和理论模型,主要包括起始夹带和稳态夹带模型的研究。通过实验和理论分析,建立了与实验数据符合良好的起始夹带模型和稳态夹带模型。通过分析实验段入口长度对夹带的影响,确定了合适的入口段长度。不同液体流量下的研究表明,ADS-4管道中,液体流量对起始夹带和稳态夹带的影响可忽略。     

AP1000中ADS-4第4级自动降压系统夹带试验研究

为研究AP1000反应堆第4级自动降压系统(ADS-4)夹带卸压过程,以AP1000核电厂为原型,按1:5.6模化比例设计建造了ADS-4喷放卸压试验回路(ADETEL)。用高速摄像仪记录试验现象并进行了详细分析。将试验数据和现有试验数据和模型进行对比,并得出以下结论:当热管段内液位较低时,夹带量会随着热管段内液位降低而迅速减小;在热管段内流动情况相同(流动参数相同)情况下,夹带起始在,竖直支管和水平主管管径比较小的工况下更容易发生;在相同的热管段相对液位下,AP1000中ADS-4支管内液体的夹带率较AP600低。     

大型先进压水堆ADS-4夹带试验研究

针对大型先进压水堆的ADS-4夹带现象,按照实际比例1∶1搭建了全尺寸ADS-4试验台架(FATE),在不同工况下进行了多组夹带试验。将试验数据与不同模型的结果进行对比,并将试验数据进行拟合,得到夹带起始的模型关系式。试验结果显示：拟真实工况与纯水工况的现象较相似,支管弗劳德数随夹带起始气腔高度的增加而增加;在不同工况的组合中均出现了回滞现象;由于黏性和表面张力的作用,拟真实工况的夹带起始相比纯水工况更难发生。无论是纯水工况、硼酸工况还是杂质工况,除少部分试验数据外,大部分稳态夹带率的试验数据与Welter模型存在较大差异,相对误差均大于20%。     

ADS-4空气-硼酸夹带试验研究

为研究真实工况下的ADS-4夹带现象,以CAP1400为原型按1∶1的比例设计搭建了FATE试验台架。硼酸溶液用来模拟反应堆堆芯中真实工况的流体。利用数据采集系统和高速摄像仪记录夹带过程,将所得的试验数据与纯水工况和已有的模型进行比较。结果表明：对于夹带起始和稳态夹带率,硼酸工况和纯水工况的试验结果与之前的模型均不同。硼酸工况和纯水工况的现象基本相似,弗劳德数随夹带起始液位的增加而减小。两者的夹带起始均有回滞效应,且自上而下的夹带起始更易发生。硼酸工况和纯水工况之间也存在着差异,这主要是由于两者的物理特性参数不同而造成的,尤其是密度和黏度的影响。     

快堆气体夹带实验研究

正快堆本体中的一些设备贯穿钠池的自由液面及氩气空间,如果布置不当会导致本应平滑的自由液面产生强烈波动、强大的表面环流、漩涡以及气芯等异常流动现场,进而导致在中间热交换器入口窗等冷却剂向下流动的通道处存在覆盖气体被夹带进入下腔室(冷池)的风险。如果被夹带气体通过主循环泵吸入堆芯将会导致堆功率振荡、     

基于REVENT实验的气溶胶再夹带模型适用性分析

在核反应堆事故后卸压等特定场景下,安全壳内液体大量蒸发,液相中气溶胶在蒸汽作用下被夹带回气相中的现象称为再夹带。本文基于Revent实验结果对KataokaIshi's和Cosandey's再夹带模型的适用性进行了评估。首先将模型转化为程序语言,针对实验建立分析模型并对不同工况开展模拟研究;然后通过对比分析模型预测结果与实验测量结果,评估了在不同压力、气体组分条件下,KataokaIshi's各夹带区域模型预测可溶性气溶胶再夹带行为的适用性,Cosandey's模型预测可溶性、不可溶性气溶胶再夹带行为的适用性。结果表明:Cosandey's模型更适用于预测核电厂事故工况下安全壳内不同种类气溶胶粒子再夹带行为。     

Off-take and Slug Transition at T-junction of Vertical-up Branch in the Horizontal Pipe

The off-take and the slug transition on air-water interface are experimentally investigated at the T-junction of the horizontal pipe with a vertical upward branch to simulate the loss-of-residual-heat-removal during a mid-loop operation in the Korea standard nuclear power plant. Scaling analysis is performed to scale down the experimental facility to the reference nuclear power plant. Two different diameters of branch pipes are used to verify the scaling laws and their scale effects. Air is used as working gaseous fluid and no water flow exists. Off-take behavior on horizontal stratified and slug flows is visually observed in the horizontal pipe. The experimental data are divided into three categories; onset of liquid entrainment at T-junction, onset of slug transition in the horizontal pipe, and discharge quality in the branch pipe. It is found out that the scale effect of the branch diameter on the onset of liquid entrainment is small and the existing correlations for it are applicable. Also, the onset of slug transition shows a discrepancy with Taitel-Dukler's correlation and has a strong influence on the discharge quality. New correlations for discharge quality are developed considering the critical dependency of the onset of slugging.     

On the relevance of low side flows for thermal loads in T-junctions

The mixing of coolant streams of different temperatures in pipe junctions leads to temperature fluctuations that may cause thermal fatigue in the pipe wall. Numerous T-junction experiments are known from literature, which were performed to study the nature of thermal loads in the pipe walls occurring during the mixing of hot and cold liquid. It is common to all known experiments that the experimental boundary conditions are set to reflect cases, in which the flow velocities in both main and side branches of the T-junctions are of the same order of magnitude. In the present experiments, carried out using wire-mesh sensors, it was observed that very low flow velocities in the side branch compared to the main pipe may lead to conditions potentially severe for thermal fatigue due to the low frequency of the temperature fluctuations occurring. The T-junction presented here consists of a perpendicular connection of two pipes of 50 mm inner diameter. The straight and the side branches are supplied with water of different electrical conductivities, to enable performing generic, isothermal tests on turbulent mixing with the idea to model the temperature fluctuations in thermal mixing processes. A pair of wire-mesh sensors, each with a grid of 16 × 16 measuring points, are used to record conductivity distributions in the downstream of the T-junction as well as directly at the junction in both branches. At very low flow rates in the side branch, a characteristic entrainment of liquid from the main branch into the side branch was found. Typically the entrainment flow in the side branch results in relatively high fluctuations at the low-frequency range. While the sensor in the main flow shows fluctuations with a power spectrum similar in character to mixing experiments with comparable flow velocities in both branches of the T-junction. The phenomenon of entrainment of water from the main branch into the side branch against the main flow direction vanishes at a certain critical velocity in the side branch.     

垂直管内气液两相逆流极限管径效应实验

在压水堆安全性分析中,需准确预测气液逆流极限(CCFL)工况下两相流动关系。本文采用水下淹没排气的实验方法,对相同管长不同管径垂直管的CCFL特性进行可视化实验,并对垂直管CCFL关联式模型进行分析,主要结论有:①在CCFL工况下垂直管内流型为环状流动;表观气速较大时,大管径管内液膜呈搅拌状,小管径管内液膜呈波动状;随表观气速减小,均转为液面光滑的自由降膜流动;②Wallis数模型过度关联了管径变化对垂直管CCFL特性的影响;Kutateladze数和Froude-Ohnesorge数模型也不能良好关联垂直管CCFL特性的管径效应;③提出了新的CCFL无量纲参数和相应的实验关联式,由此可使垂直管CCFL特性的管径效应得以统一表征,还可以关联物性参数变化的影响。     

Experimental analysis of off-take phenomena at the header–feeder system of CANDU

An experimental study has been performed to investigate the off-take phenomena at the T-junction installed between the header and feeder pipes in CANadian Deuterium Uranium (CANDU) reactor. Previous works have been made to correlate the onset condition and the quality at the branch for the representative directions such as top, side and bottom. However, for the actual branches with specific direction such as ±36° and ±72° to the horizontal header in the header–feeder system of CANDU, the direct application of the conventional correlations to the safety analysis needs experimental verification. A 1/2 scaled test facility from the prototype plant of Wolsong Units 2, 3 and 4 (CANDU 6 type) is used to measure the onset conditions for the gas pull though and liquid entrainment in the seven different orientations of the branch pipe with 0°, ±36°, ±72° and ±90° angles. The horizontal pipe has a diameter of 184 mm. The branch pipes are attached on the horizontal pipe with, and have diameters of 16.7, 20.7 and 24.8 mm, respectively. Air and water are used as working fluids under the conditions of room temperature and of pressures up to 0.95 MPa. The present experimental data were compared with the existing experimental data set such as UCB and KfK and with the horizontal stratification entrainment model (HSEM) in RELAP5/MOD3.3. It was found that The HSEM does not show good agreements with the present data obtained from the specific branch angles, ±36° and ±72°. At the bottom branch, the quality data are compared with the previous data in terms of h/D. The present data can be used for an improvement of the off-take model in order to predict the onset of off-take and the branch quality at specific angles between −90° and +90° in CANDU.     

Prediction of flooding gas velocity in gas–liquid counter-current two-phase flow in inclined pipes

The purpose of the experimental study is to investigate the effects of pipe inclination, pipe length, pipe diameter and surface tension of the working liquid on the onset of flooding of gas–liquid adiabatic counter-current two-phase flow in inclined pipes. Flooding in inclined pipes were observed by using the combination of visual observation, measurement of discharged liquid flow rate and time variation of liquid hold-up. And it was defined as the maximum air flow rate at which the discharged liquid flow rate is equal to the inlet liquid flow rate. As a result we proposed a correlation to predict the flooding gas velocity in inclined pipes under a given liquid flow rate, and the predictions agreed well with the experimental observations.     

AP1000 ADS-4夹带卸压试验模拟分析

第4级自动降压系统（ADS-4）是AP1000极为重要的非能动安全设施。ADS-4能在AP1000小破口失水事故中为反应堆系统提供可控卸压。然而,大量的冷却剂可通过卸压过程中ADS-4夹带和上腔室夹带被带到安全壳中,从而引发堆芯裸露和堆芯熔化事故。为研究小破口事故中的ADS-4夹带卸压和上腔室夹带过程,在以AP1000为原型、按直径/高度比1∶5.6设计建造的ADS-4喷放卸压试验回路（ADETEL）中,研究了不同初始压力、压力容器混合液位和加热功率下的夹带和卸压行为,以及反应堆内部构件的夹带沉积效应。试验数据表明,大量的水在短时间内迅速通过ADS-4支管被夹带出来。液体的夹带率和压力容器混合液位的降低速率随系统初始压力的增加而增大。值得注意的是,在本试验特定工况下,初始压力为0.5 MPa时出现堆芯裸露。堆内构件对夹带量和压力容器混合液位无显著影响。