两相自然循环系统的静态漂移特性及输热能力限分析

基于分岔理论及其ＤＥＲＰＡＲ数值方法,运用最简单的均相模型计算出典型两相自然循环系统的静态分岔解图,详细讨论了由浮力和阻力随加热功率（含汽率）的非线性变化特性引起的静态分岔机理;导出对应于强迫循环系统的Ｌｅｄｉｎｅｇｇ不稳定性现象及其判断准则;定义稳定性裕度、自然循环系统输热能力限、静态分岔迟滞现象;讨论了系统压力、欠热度、阻力、几何构型等参数对运行稳定性及输热能力限的影响;强调指出了简单理论预测     

低干度自然循环两相流动系统的静态分岔特性

基于一维两相四方程漂移流模型，采用数值模拟的方法对5MW低温核供热堆热工模拟回路（HTRL-5）的自然循环进行模拟，分析在自然循环系统中存在的分岔特性及其参数效应。结果表明：在一定条件下低干度自然循环两相流动系统存在静态分岔现象，并且静态分岔点出现在特征曲线的切点上；当压力高到一定程度或热流密度小到一定程度系统的分岔点消失。     

流动欠热沸腾空泡份额的研究

影响欠热沸腾传热的主要因素是含汽率和系统压力。系统压力直接影响加热面上汽泡的大小,从而影响壁面向液体的传热量。欠热沸腾区任一点的热平衡含汽率可由通道内的热工参数和流动参数求出,然后据此求出通道中某点的空泡份额。文中给出了计算加热通道内流动欠热沸腾区空泡份额的计算关系式,该关系式在给定的参数范围内与实验结果符合较好。     

沸腾两相自然循环回路静态不稳定性的无量纲研究

定义了无量纲分析的参考尺度 ,采用无量纲分析的方法 ,运用一维均相模型 ,从理论上研究了两相自然循环系统的静态不稳定特性 ,总结出了影响两相自然循环系统静态稳定性的几个重要的无量纲参数。运用分岔理论及其DERPAR数值算法 ,得到了由无量纲量Npch m+表示的沸腾两相自然循环系统的静态分岔图 ,详细分析了由浮力和阻力随无量纲的加热功率的非线性的变化特性。并且给出了几个重要系统参数的效应图。     

低压低含汽量自然循环系统密度波振荡的非线性特性研究

用时域方法研究了低压低含汽量自然循环系统的非线性密度波不稳定性。发现存在于系统的两种密度波不稳定的非线性振荡形式,研究了两种振荡的特性、机理及其影响因素。得到如下一些重要结论:1.不稳定区域密度波振荡为有限的持续振荡。靠近稳定边界时,系统发展为等幅的持续振荡,且随着过冷度的增加振幅加大;远离稳定边界时,密度波振荡耦合可压缩性密度波振荡,呈变幅的有限振荡。2.核功率和空泡份额耦合反馈对密度波振荡的影响取决于热流密度滞后的相位,对5MW核供热堆主回路系统来说,起激励作用。3.加大堆芯出口水力提升段的质量惯性能有效地抑制可压缩性密度波振荡,提高系统的稳定性。     

低压低含汽量自然循环系统密度波振荡的非线性特性研究

用时域方法研究了低压低含汽量自然循环系统的非线性密度波不稳定性。发现存在于系统的两种密度波不稳定的非线性振荡形式,研究了两种振荡的特性、机理及其影响因素。得到如下一些重要结论:1.不稳定区域密度波振荡为有限的持续振荡。靠近稳定边界时,系统发展为等幅的持续振荡,且随着过冷度的增加振幅加大;远离稳定边界时,密度波振荡耦合可压缩性密度波振荡,呈变幅的有限振荡。2.核功率和空泡份额耦合反馈对密度波振荡的影响取决于热流密度滞后的相位,对5MW核供热堆主回路系统来说,起激励作用。3.加大堆芯出口水力提升段的质量惯性能有效地抑制可压缩性密度波振荡,提高系统的稳定性。     

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。     

两相自然循环非线性特征及实验研究

采用均相模型,基于分岔理论预测了两相自然循环系统的流量漂移(静态分岔)相关特性,并对其进行了实验验证.同时,对系统的动态参数时序进行了时域和频域分析,研究了特定工况下沸腾喷发弛张动态不稳定性机理.通过对系统相关时序的相空间重构与分维分析,探讨了系统随加热功率变化的非线性演化规律.     

自然循环过冷沸腾截面平均空泡份额实验与计算方法研究

采用RBI高温高压光学探针,对自然循环过冷沸腾截面平均空泡份额进行了实验研究通过实验数据与应用较为普遍的Saha模型、Levy模型以及孙奇提出的真实质量含汽率模型计算值的比较发现．基于强迫循环实验数据的截面平均空泡份额计算模型无法适用于自然循环工况,且经过比较初步判定相同系统参数下高过冷沸腾区自然循环较强迫循环空泡份额偏高,另外,根据模型的比较分析结果对真实质量含汽率模型进行了拓展,使其可适用于自然循环过冷沸腾工况。     

汽液两相流动不稳定性的小波包研究法

利用小波包对信号的精确细分特性,对汽液两相流动密度波不稳定性的脉动信号进行分析,并由此得到两相密度波不稳定性脉动的特征向量。由这些特征向量可得到汽液两相流动脉动能量随脉动频率的分布状况,开创了对汽液两相流动密度波不稳定性研究的新视角。     

低干度自然循环流量漂移的特征曲线图谱分析

在5MW低温核供热堆全模拟试验回路(HRTL-5)上,实验观察到了低干度自然循环条件下的流量漂移现象.通过一个考虑了加热段欠热沸腾、上升段冷凝、闪蒸等物理过程的两相流动数学模型,编制了相应的计算程序,获得了自然循环特征曲线图谱及其运行曲线,确定了自然循环分岔图和静态不稳定边界图,进而提出了通过自然循环特征曲线图谱研究流量漂移的分析方法.分析表明:特征曲线图谱方法是研究自然循环静态不稳定的有效手段.增大系统压力、减小热流密度、增加入口单相阻力、减小出口两相阻力有利于避免自然循环流量漂移的发生.     

低压高过冷度下自然循环流动不稳定性实验研究

对具有长直上升段的自然循环系统,开展了流动不稳定性实验研究。同时,详细分析了低压、高入口过冷度条件下典型的流动不稳定现象。实验表明：自然循环系统的结构、流体的热边界条件会影响自然循环的运行特性及流动不稳定性类型。较高入口过冷度下,高热流密度导致系统脱离稳态后,很难重新回到稳定的两相自然循环流动状态。随着热流密度的提高,系统会经历间歇沸腾、复合动态流动不稳定性等状态。依据实验结果得到了高入口过冷度下的不稳定性边界图。在两相振荡期间,自然循环驱动压头和回路阻力的主要影响因素集中在长直上升段和加热段。加热段出口积聚的大量气泡对上、下游流体的强烈挤压作用是流量大幅振荡及逆流的主要原因。     

Two-phase instability analysis in natural circulation loops of China advanced research reactor

In this paper, two-phase flow instability in natural circulation loops of China Advanced Research Reactor (CARR) has been investigated. CARR is a low pressure and low power density research reactor. A natural circulation instability analysis model is developed for the natural circulation loop of CARR. The homogeneous flow model is used to establish the system control equations. The non-uniform heating and subcooled boiling heat transfer is included. The accumulation heat of the wall is also included. Numerical method of Gear is employed to solve the system equations documented in terms of ordinary differential equations. According to the calculation results, stability maps of the natural circulation loop, which confirm the presence of an instability region under the conditions of low equilibrium quality in the outlet and low pressure, are obtained. It is a special kind of density wave oscillation (DWO) that occurs in very low equilibrium quality region with the characteristics of geysering and ‘Type-I’ DWO at the same time. The calculation results show such oscillation course clearly. The variations of the mass flow rate, the pressure drop and the boiling boundary are analyzed separately. Especially, the phase-space trajectory of the boiling boundary and the mass flow rate is discussed. Finally the oscillation frequency is discussed. The calculated results have important significance for the safety operation and accidental analysis of CARR.     

Assessment of Some Cross Section Libraries through Analyses of Coupled-Core Critical Experiments by Monte Carlo Calculations

An experiment was performed on the natural circulation test loop HRTL-5, which simulates the geometry and system design of the 5 MW full power natural circulation nuclear heating reactor. Different flow modes, including density wave oscillation and flow excursion et al., were observed in a wide range of inlet sub-cooling at 1.5MPa. By means of self-developed computational codes, the bifurcation chart has been obtained. Consequently the flow excursion boundary has been determined. Through the analysis on the excursion boundary, the method to avoid the flow excursion during startup has been presented. Analytical results show: (1) with the decreasing heat flux or the increasing system pressure, the static flow excursion occurs at higher inlet temperature and its range in the instability maps becomes narrower correspondingly; (2) to decrease the outlet two-phase resistance or increase the inlet single-phase resistance is beneficial to avoid the flow excursion; (3) by means of increasing the system pressure to start up the reactor with low heat flux, the flow excursion and low steam quality density wave oscillation can be successfully avoided. This investigation is meaningful to the reactor safety and the design of the nuclear heating reactors.     

开式自然循环流动不稳定性的频域法分析

非能动安全壳热量导出系统依靠自然循环导出事故后排入安全壳内的热量,但在运行过程中也可能发生流动不稳定性现象。本文以某开式自然循环非能动安全壳热量导出系统为对象,建立了描述该系统行为的数学模型和本构关系,运用小扰动法对守恒方程进行线性化,通过Laplace变换获得系统质量流速随加热段进口焓变化的传递函数。基于Nyquist稳定性判据,分析了热工参数变化对该自然循环系统稳定性的影响。结果表明:系统的流动稳定性本质上受空泡份额随质量含气率的变化关系的制约,在一定范围内,随着质量含气率的增大,空泡份额对质量含气率的敏感性减弱,系统趋于稳定。     

An analytical investigation of role of expansion tank in semi-closed two-phase natural circulation loop

Role of the expansion tank in a semi-closed two-phase natural circulation loop was examined analytically with the emphasis placed on the flow instability. Loopwise steady circulation rate was obtained, and conditions for flow instability were examined by using the method of the linear stability analysis with perturbations. The homogeneous two-phase model was adopted for the analysis. As well as the pressure at the expansion tank, the length and the cross-sectional area of the tube connected to the expansion tank appeared to be the important parameters determining the flow instability. The system was predicted to be stable with the longer length and the smaller cross-sectional area of the expansion-tank line and also with the higher expansion-tank pressure.     

Experimental observation of flow instability in a semi-closed two-phase natural circulation loop

In this experimental study, the flow instabilities within a semi-closed two-phase natural circulation loop were examined, with an emphasis placed on the role of the expansion-tank-line resistance. Six different modes of loopwise natural circulation were identified: the single-phase natural circulation, periodic two-phase natural circulation with a nonboiling period between the cycles, two-phase continuous circulation (stable circulation), and three other modes of the two-phase natural circulation characterized by different ranges of the cyclic period. The results were also shown in the instability map in the plane of the heat flux and the heater-inlet subcooling. When the frictional resistance at the expansion-tank line becomes larger, the circulation becomes stable, especially at the high heat-flux and high inlet-subcooling conditions, and, as a whole, the stable operation region becomes larger in the instability map. Similarly, the longer expansion-tank line stabilizes the system. However, unlike the analytical prediction, the excursive instability was not identified with the semi-closed loop due to the flow restriction at the expansion-tank line.     

细长自然循环系统流动不稳定性实验研究

以水为工质,在常压下对拥有细长回路和较长水平段的自然循环系统进行可视化实验研究,并以典型的实验现象（ P =1.46 kW）为例分析该系统的瞬态运行特性和不稳定性机理。结果表明：阻力系数较大的细长自然循环回路难以产生有效的单相自然循环,只能通过间歇性沸腾和两相流动将热量导出。这是因当回路阻力较大时,过冷沸腾产生的驱动力无法驱动回路产生有效的自然循环,而只有当加热段内流体发生饱和沸腾时才能驱动系统产生循环流动。较大的回路阻力和沸腾过程中产生的系统降压闪蒸是细长自然循环系统难以维持稳定的流动驱动压头从而产生间歇性沸腾和强烈流动不稳定性的根本原因。