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。     

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、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。     

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 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%。     

矩形窄缝过冷沸腾汽泡滑移起始点可视化初步研究

采用高速摄像仪对矩形窄缝汽泡滑移起始点进行了可视化实验初步研究.实验发现.在1.3mm的矩形窄缝中,汽泡滑移起始点在壁面上的分布呈抛物线形状,质量流密度、热流密度和系统压力对汽泡滑移起始点位置影响较大;表面粗糙度和流体波动对汽泡滑移起始点位置和滑移起始点汽泡尺寸大小有较为明显影响.     

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。     

定位格架搅混翼附近气泡运动特性可视化实验研究

针对3×3棒束采用可视化实验技术研究棒束通道内气-液两相流动过程,获得了定位格架搅混翼附近的气泡行为特性。通过实验发现在搅混翼背流面存在气泡滞留的现象。在稳定工况下,滞留气泡的高度基本不变,滞留气泡相界面在流动、来流气泡合并过程中存在波动,并在液相的夹带下从滞留气泡末端分裂成多个小气泡。滞留气泡末端被液相夹带分裂是棒束通道中气泡尺寸变化的主要原因之一,并且分裂后的气泡尺寸小于来流气泡尺寸。在相同空泡份额条件下,随着液相流量的增加,滞留气泡高度增加,从滞留气泡上分裂的气泡尺寸相比来流气泡减小、数量增加;在相同液相流量条件下,随着空泡份额的增加,滞留气泡大小基本不变。来流气泡尺寸影响滞留气泡相界面的波动幅度,同时搅混翼背面存在滞留气泡时,气泡从搅混翼迎流面和背流面经过搅混翼时,在下游具有不同的运动特性,导致格架下游子通道间相态分布的差异性。     

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.     

Penetration of a turbulent jet with negative buoyancy into the upper plenum of an LMFBR

The penetration of a turbulent jet with negative buoyancy in a uniform environment is investigated. The jet generated from a finite source is treated by using the integral representation of the governing equations. The entrainment is assumed to be dependent on the local Froude number. Numerical solutions are compared with experimental results to suggest values for three empirical constants: the entrainment coefficients and the spreading ratio of density and velocity profiles. Good agreement is obtained over a large range of initial Froude number, which determines the maximum penetration distance.     

T型三通管内热分层流动3D数值模拟

针对主管和支管流体温度不同的等径三通管,利用AQUA程序,对该三通管内的热分层流动进行了三维数值流场模拟。模拟结果显示,高流速的支管流体自上部射入,深入到主管的主流内部,迫使主管内上游来流贴着主管下壁面流动。在支管人流的背流面有一涡存在,主支流在此涡下部的狭窄通道内被加速到较支流速度更高的速度。对三通管内的温度分布计算表明,支流人流的迎流面存在着很大的温度梯度,两种流体的混合主要存在于远离支流人流的下游地区。     

Experimental study on scale effect on gas entrainment at free surface

It is necessary to understand effects of scale and fluid properties on gas entrainment phenomena for prediction of gas entrainment in a fast breeder reactor (FBR). In the present study, three models of different scales but of similar geometry were used for water tests to examine the effects of scale and viscosity. The results have shown that the critical Froude (Fr) number, above which gas entrainment appears, drastically decreases as the scale increases. A prediction method using the Fr-Re map is proposed in the present paper for the sodium flow in an FBR.