低质量流速垂直并联内螺纹管密度波型不稳定性试验

在高压汽-水两相流实验台上进行了低质量流速垂直并联内螺纹管密度波型不稳定性的试验研究,观察到了垂直并联内螺纹管气-液两相流密度波型不稳定性的一些主要特征。在试验参数范围内就热负荷、系统压力、质量流速、进口过冷度和不对称加热对密度波型不稳定性的影响进行了研究和分析。同时根据试验结果,采用均相流模型得到了密度波型不稳定发生的界限关系式。     

非均匀加热蒸发管内两相流动不稳定性数值分析

针对蒸发管非均匀加热工况,采用包含水平、倾斜上升、垂直上升和垂直下降流动的优化内螺纹管,建立了基于均相流模型的蒸发管数学模型,采用时域法模拟了蒸发管内两相流动不稳定性。计算了不稳定发生时,进口流量在各时间点的数值,并与Siemens公司的计算结果进行了对比,结果符合良好,表明本文采用的数学模型和数值方法在模拟两相流动不稳定性上具有一定的可靠性。分析了系统参数对两相流动不稳定性的影响,并与均匀加热工况进行了比较。结果表明:非均匀加热工况系统参数影响规律与均匀加热工况具有相似性,增加进口压力或进口流量系统的稳定性提高;减小进口阻力系数或增大出口阻力系数系统的稳定性降低。     

水平管冷凝流动不稳定性分析

通过搭建水平管模型,采用RELAP5程序模拟计算了冷凝管内冷凝流动不稳定性现象,程序计算的稳定性边界与Bhatt理论稳定性公式计算结果符合良好。瞬态分析结果表明,冷凝管内气体压力与两相段长度不匹配是造成冷凝流动不稳定性的主要原因,进而引起冷凝出口流量震荡。冷凝管参数影响分析表明,更小的流动管径与更大的流通截面积有助于冷凝流动稳定,而入口流量的影响则相对复杂。     

低压流动稳定性实验研究(英文)

在5MW核供热反应堆模拟热工水力学实验回路HRTL-5上研究了在低压(P=0.1,0.24MPa)自然循环各种进口过欠热度条件下,单相及两相流流动特性。研究了不同种类的流动不稳定性,如,欠热沸腾不稳定性,欠热沸腾引起的闪蒸不稳定性,纯闪蒸不稳定性,密度波-闪蒸耦合不稳定性及高频流动振荡。研究结果表明:低压自然循环系统在绝大部分进口欠热度条件下,其两相流流动是不稳定的,仅在小进口欠热度条件下可获得稳定的两相流流动;在高进口欠热度条件下,加热段中的欠热沸腾控制流动不稳定,在中进口欠热度条件下,加热段中的欠热沸腾及上升段中的空泡闪蒸控制流动不稳定。     

螺旋管内汽液两相流密度波型脉动流动传热试验研究

详细介绍了在沸腾通道内部发生汽液两相流水动力不稳定性而出现周期性密度波型脉动时,脉动流动过程中瞬态和时均传热系数的实验研究结果。实验在以水为工质、以螺旋管作沸腾蒸发试验段的中低压闭式循环系统上进行,试验参数范围为：压力p=05～35 MPa,质量流速G=200～2 100 kg/(m2·s),工质进口过冷度ΔTsub=20～90 ℃,试验段壁面热负荷qw=0～540 kW/m2,密度波脉动的周期为T=125～14 s,且主要集中在4～10 s范围内。对密度波脉动过程中瞬态及时均传热系数和其它主要参数的基本特征与变化规律作了分析和描述,提出了表征密度波脉动传热的新的特征准则数和传热系数计算式。     

核态沸腾存在时垂直管内环状流换热数值计算

建立了垂直管内流动沸腾换热与阻力特性的数值计算模型。该模型以环状流为研究对象,认为强制对流与核态沸腾两种换热方式同时存在。通过求解质量守恒、动量守恒、能量守恒方程,获得液膜厚度、速度与温度等参数。由汽泡脱离频率、脱离直径、汽化核心密度及抑制因子等参数计算核态沸腾换热。换热系数根据热流密度叠加原理确定。对一种有机工质在垂直管内向上流动时的沸腾换热进行了数值预测,计算值与实验结果符合良好。随着干度的增加,核态沸腾在总换热系数中的比例由约20％下降至1％。     

管束外垂直上升汽液两相流沸腾传热特性的数值模拟

以唐琦琳的管束外垂直上升汽液两相流沸腾传热试验台为原型,进行基于CFX的管束外垂直上升汽液两相流沸腾传热特性数值模拟,得出了不同入口温度、热流密度、质量流速下管束外狭窄通道的热工水力特性。沿管束高度流体温度的模拟结果与实验结果的最大相对偏差为3.5%,从而证明了数值计算的有效性和正确性。在此基础上,探讨了汽液两相流速度分布、沸腾压降与含汽率及其影响因素。     

改进型低温供热堆二次侧非能动余热排出系统不稳定性分析

研究了改进型低温供热堆非能动余热排出系统不稳定性问题。采用RELAP5程序计算分析了非能动余热排出系统瞬态响应情况,余热排出系统冷凝管内由于压力与两相段长度不匹配出现冷凝两相流不稳定性。采用RELAP5程序数值计算所得冷凝流动稳定性边界与Bhatt公式理论分析结果符合良好。增大冷凝管入口节流,增加冷凝管流通面积、换热面积,可以避免冷凝流动不稳定性。     

开式自然循环系统启动特性实验研究

对开式自然循环系统的启动过程进行了实验研究,并详细分析了不同加热功率和不同入口过冷度条件下系统出现的实验现象和流动特性,最后给出了自然循环系统在启动过程中的流动不稳定性边界图。结果如下:在低加热功率下,随着入口过冷度的减小系统会依次经历单相稳定、两相振荡和两相稳定流动;增大加热功率会使系统的两相流动不稳定范围增大,甚至很难形成稳定的两相流动。在两相振荡阶段,系统会出现由闪蒸诱发的不稳定流动以及由沸腾喷发和闪蒸共同诱发的不稳定流动两种模式,这两种不同模式的流动不稳定性均属于密度波不稳定性。     

基于一维漂移流模型的并联矩形双通道密度波流动不稳定性数值模拟

基于一维漂移流模型构建了并联矩形双通道密度波流动不稳定性数学模型。模型中采用Zuber推荐的经验关系式计算两相流体空泡份额,采用Chisholm关系式和中国核动力研究设计院自拟关系式计算两相流体的摩擦压降。求解过程中将质量方程、能量方程与动量方程解耦,并在计算域内沿流动方向依次求解方程组。计算过程中,首先开展稳态计算,在稳态解的基础上,通过添加流量或功率扰动,诱发流体周期性振荡,通过辨识瞬态计算中得到的流量振荡模式来获得流动不稳定边界。采用数值计算获得的密度波脉动图像与实验中观察到的密度波脉动现象的特征基本一致。最后,针对16组典型实验工况开展数值模拟,结果表明,大部分工况下计算不稳定界限热流密度与实验值的相对偏差小于±20%。     

物理模型及边界条件对直流蒸发管两相流不稳定性边界影响研究

本文研究不同边界条件及物理模型对两相流不稳定性边界的影响。采用RELAP5程序模拟直流蒸发管内的两相流不稳定性实验工况，对计算程序和模型进行验证，分析恒定流量及恒定压降两种边界条件、并联管数量、轴向功率分布形式和传热管热容等不同边界条件和物理模型对不稳定性边界的影响。结果表明：恒定压降边界条件下，单根管、2根并联管和多根并联管的不稳定性边界差别小于5%；恒定流量边界条件下，多根并联管不稳定性边界和2根并联管相比差别小于5%，而与单根管不稳定性边界的差别则超过100%；并联管根数相同时，恒定流量边界条件的稳定性好于恒定压降边界条件；沿流动方向（轴向）功率递增分布时，系统稳定性好于沿流动方向功率均匀分布，沿流动方向功率均匀分布时，系统稳定性好于沿流动方向功率递减分布；当管壁厚度为0~20 mm时，管壁热容对不稳定性边界几乎没有影响。     

Study on the stability behaviour of two-phase natural circulation systems using a four-equation drift flux model

Theoretical investigations were carried out to study the influence of two-phase flow parameters such as friction factor multiplier, drift velocity and void distribution parameter on the stability of boiling two-phase natural circulation systems. The theoretical model considers a four-equation drift flux model which solves the linearised conservation equations of mass, momentum and energy applicable to boiling two-phase natural circulation systems. The model was applied to three boiling natural circulation loops wherein Type I and Type II instabilities were observed over a wide range of operating pressures. The two-phase friction loss was predicted using different friction factor multiplier models available in literature. It was found that these models influence the steady state and threshold powers for stability, especially the Type II instabilities in natural circulation significantly. Since the void fraction depends on the drift velocity and the void distribution parameter in two-phase flow, these parameters were varied and their effects on the natural circulation flow stability were investigated. It was found that an increase in either the drift velocity or the void distribution parameter reduces the unstable regions observed in the Type I or Type II flow instabilities in two-phase natural circulation systems.Further, investigations were carried out to study the effect of loop diameter on the Type I and Type II instabilities in natural circulation. This study is important to reveal the capability of the reduced diameter scaled facilities of the prototype systems to simulate natural circulation instabilities. The results indicate that with increase in the loop diameter, the threshold power of the Type I instability and the Type II instability increases. Moreover, the stability of natural circulation greatly enhances with increase in the diameter of the loop.     

关于一维两流体模型中界面阻力计算的研究

一维两流体模型中,界面阻力是决定相间耦合程度的关键参数,其计算方法目前有漂移流模型法和阻力系数法。本研究利用子通道程序,基于圆管空气-水两相实验数据,对这2种计算方法进行了评估,结果表明一维两流体模型中漂移流模型法的预测能力要优于阻力系数法。同时评估了两相流动中分布效应对界面阻力计算的影响,结果表明在低空泡份额区分布效应影响较小,而高空泡份额区其影响明显。      

非稳态流体力作用下两相流管束流弹失稳研究

流弹失稳会引起传热管振幅过大而发生磨损破坏，是两相流作用下蒸汽发生器管束流致振动的重要机理。为了较为准确地预测两相流作用下圆柱管的失稳临界流速，对试验测量的两相流非稳态流体力进行参数拟合，建立了气-水两相流作用下单管的动力学模型。通过无量纲化，运用Galerkin方法对方程变量进行离散后，联立求解方程得到了不同空泡份额的临界流速。数值结果表明，数值解与试验测得失稳临界流速较为吻合，验证了该模型可用于两相流传热管临界流速的预测。      

Fluctuation characteristics of heating surface temperature near an obstacle in transient boiling two-phase flow in a vertical annular channel

When a flow obstruction such as a spacer is set in a boiling two-phase flow within an annular channel, the inner tube of which is used as a heater, the temperature on the surface of the heater tube is severely affected by the existence of the spacer. In some cases the spacer has a cooling effect, and in other cases it causes the dryout of the cooling water film on the heating surface resulting in the burnout of the tube. In the present paper we will discuss temperature fluctuations in relation to the change in the flow configuration near the cylindrical spacer in transient boiling two-phase flow caused by the stepwise change of the operation parameters such as the heat flux, the mass flow rate, and the inlet quality of the test section. As a result it is concluded that: Even if the flow pattern changes rapidly by a stepwise change of an operation parameter, the transition of flow proceeds safely provided that the change causes the increase of vapor velocity, i.e. the increase of the shear force which is acting on liquid film flow. On the other hand if the change causes the decrease of the vapor velocity, it must be noticed that the transient burnout possibly occurs even when the operating condition after the change is less than the steady burnout condition.     

SENHOR-IV: A computer code for small pipe-break analysis of pressure-tube type reactors

A computer program SENHOR-IV was developed which describes blowdown phenomena associated with a small pipe-break accident in pressure-tube type reactors. Thermal-hydraulic transients of single-phase and two-phase flow in a primary cooling system, which is composed of the pressure tubes, a steam drum, downcomers, a lower header and pipings connecting these components, were calculated from the conservation equations of mass, momentum and energy by assuming pressure propagation and flow rate distribution to be quasi-steady and by applying the method of characteristics to enthalpy transport. The void propagation velocity in two-phase flow was given from Smith's equation for void-quality relationship to the program. Calculation of a flow transient, which has an exact solution, with use of this program showed small deviations from the exact solution. Predicted transients of pressure and water level in the steam drum indicated a good agreement with those observed in a full scale test facility at O-arai Engineering Center.     

New algorithm for the numerical simulation of two-phase stratified gas–liquid flow and its application for analyzing the Kelvin–Helmholtz instability criterion with respect to wavelength effect

In this article, the transient condition of two-phase stratified gas–liquid flow was investigated using numerical simulation. The basis of the method involves the one-space dimensional transient solution of the governing equations using the two-fluid model. In this paper, an analogy between the SIMPLE algorithm in two-space dimensional single-phase flow and one-space dimensional two-phase stratified flow is established through the application of a special algorithm created to solve the conservation equations. After the modeling was established and justified, wave growth was examined in two-phase stratified flow in a horizontal duct. The results were then compared with the results of the previously published articles. The results show that the classical criterion for the Kelvin–Helmholtz (K–H) instability is consistent when the long wavelength with small amplitude is considered. In this case (of the K–H instability criterion), the wavelength effect on this instability and pressure variation on the two phases interface was consistent with prior researchers’ correlations. However, as the wavelengths decreased, the results indicated that the K–H instability criterion is over-predicted and must be modified. The application of the present numerical simulation method improved the results, and the consistency with the analytical solution is higher in comparison with other well-known computer codes.     

两相横流作用下的旋转三角形管束流弹失稳研究

为了较为准确的预测两相流作用下圆柱管的失稳临界流速，采用试验测量的两相流准稳态流体力系数，对单向流的准稳态模型进行扩展，建立了气-水两相流作用下的旋转三角形管束中间悬臂自由管的动力学模型，运用Galerkin方法对方程变量进行离散后，求解特征方程得到了不同空泡份额的临界流速，并运用龙格-库塔法求解动力学方程得到位移时程响应。数值结果表明，临界流速随着空泡份额的增大而增大，且所建模型计算结果与试验测量值较为吻合。因此，本研究所建模型可用于两相横流作用下的旋转三角形管束流弹失稳临界流速预测。