The flow and heat transfer characteristics of turbulent flow in typical rod bundles in ocean environment

The flow and heat transfer characteristic of turbulent flow in typical 4 and 7 rod bundles in ocean environment is investigated theoretically. In ocean environment, the periodic variation of secondary flow in 7 rod bundles is not obvious. Because of the velocity oscillation, there is a periodic heat accumulation on the tube wall. And the restriction of the channel wall on the rolling motion is considerable. In 7 rod bundles, because of the restriction of the channel wall, the effect of the additional force perpendicular to flowing direction is limited, and the turbulent flowing and heat transfer is mainly determined by the axial turbulent intensity and inlet velocity. However, in the 4 rod bundles, the restriction of the channel wall is small. The effect of the additional force perpendicular to flowing direction on the flowing and heat transfer is significant. And the additional force perpendicular to flowing direction can also affect the Reynolds stress.     

中国先进研究堆矩形通道流场数值计算分析

通过SIMPLE数值方法,编制程序,对中国先进研究堆(CARR)全流道进行流场数值模拟.采用对CARR的单个冷却剂通道进行单相水的数值传热计算,并递增地改变流道入口流速,计算获得与入口流速对应的流道速度场与温度场分布,展现其变化规律,分析入口流速对流道热工水力参数分布的影响.采用所编制的程序,对板式燃料组件构成的窄矩形通道进行数值模拟,由此来确定热工水力设计需要的一些反应堆安全参数.这些安全参数为反应堆事故监测系统提供必要的热工过程状态信息,也为CARR提供必要的数据参考.     

A comparative CFD investigation of helical wire-wrapped 7, 19 and 37 fuel pin bundles and its extendibility to 217 pin bundle

Preliminary investigations of sodium flow and temperature distributions in heat generating fuel pin bundles with helical spacer wires have been carried out. Towards this, the 3D conservation equations of mass, momentum and energy have been solved using a commercial computational fluid dynamics (CFD) code. Turbulence has been accounted through the use of high Reynolds number version of standard k– model, with uniform mesh density respecting wall function requirements. The geometric details of the bundle and the heat flux in are similar to that of the Indian Prototype Fast Breeder Reactor (PFBR) that is currently under construction. The mixing characteristics of the flow among the peripheral and central zones are compared for 7, 19 and 37 fuel pin bundles and the characteristics are extended to a 217 pin bundle. The friction factors of the pin bundles obtained from the present study is seen to agree well with the values derived from experimental correlations. It is found that the normalized outlet velocities in the peripheral and central zones are nearly equal to 1.1–0.9, respectively which is in good agreement with the published hydraulic experimental measurements of 1.1–0.85 for a 91 pin bundle. The axial velocity is the maximum in the peripheral zone where spacer wires are located and minimum in the zones which are diametrically opposite to the respective zone of maximum velocity. The sodium temperature is higher in the zones where the flow area and mass flow rates are less due to the presence of the spacer wires though the axial velocity is higher there. It is the minimum in the peripheral zones where the circumferential flow is larger. Based on the flow and temperature distributions obtained for 19 and 37 pin bundles, a preliminary extrapolation procedure has been established for estimating the temperatures of peripheral and central zones of 217 pin bundle.     

核承压热交换器两相流流致振动现象研究

为保障核承压热交换器的安全运行,采用数值模拟以及软件计算相结合的方法,对核承压热交换器两相流流致振动现象及减振措施进行了探究。研究结果表明:基于流致振动发生机理,热交换器横流速度、固有频率、卡门旋涡脱落频率以及紊流抖振频率为重点分析因素;由公式得出流量、换热管直径、换热管壁厚、管束排列等对流致振动有直接影响,无支撑跨距是影响管束流致振动较大因素;最易发生流致振动的部位包括入口区域、出口区域、折流板缺口区域以及无支撑跨距大管束;设计中,应在流量、换热管直径、壁厚、无支撑跨距、管束排列及入口防冲挡板设置等方面优化,以减小流致振动危害。     

LES and URANS simulations of turbulent flow in 4 rod bundles in ocean environment

The flow and heat transfer of turbulent flow in typical 4 rod bundles in rolling motion is investigated with LES and URANS. The effect of rolling motion consists of two parts, the axial additional force which causes velocity oscillation and the radial additional force. The effect of rolling motion on the flowing similarity is considerable. The effect of radial additional force on the flow should not be neglected. In ocean environment, the effect of radial additional force on the flow should not be neglected. The average parameters are determined by the drive force and axial additional force, but the parameter profiles in the cross section are mainly determined by the radial additional force.     

核主泵屏蔽电机内部水路三维流场研究

核主泵屏蔽电机是核电站核岛一次回路系统的重要组成部分,而屏蔽电机内部的冷却水的流动状态直接影响电机内的热量传递的效果。对此建立了一种屏蔽电机整机的三维流场模型。基于计算流体力学理论中的有限体积法,利用Ansys Fluent软件,以实验得到的额定工况时的一次水流速为边界条件,反演计算出屏蔽电机内部的流场速度分布。针对结果分别对屏蔽电机内的关键部位的三维流场进行了分析,得出屏蔽电机内部的轴向及径向速度分布规律。计算结果表明,在靠近旋转壁面处,水速较大,且沿轴向以螺旋线形式向上流动,在下飞轮、屏蔽套间隙流体沿径向速度梯度较大。该研究可为后续的温度场研究提供不同位置处速度分布和数值。     

轴向非均匀加热对并联通道流动不稳定性的影响

基于均相流模型建立并联通道系统的控制方程,采用交错网格技术和半隐式差分离散控制方程,并使用追赶法求解来模拟并联通道的两相流动特征。采用轴向余弦功率加热模拟轴向非均匀功率加热。运用小扰动法,获得了不同压力、入口过冷度和轴向功率加热方式下的稳定性边界（MSB）和三维不稳定性空间。对于余弦和均匀功率加热,系统稳定性均随系统压力的增大而增强。余弦功率加热在高过冷度区降低并联通道系统稳定性,而在低过冷度区增强系统稳定性。随进口阻力系数的增加,处于余弦功率加热的并联通道系统稳定性增强,MSB的拐点逐渐向高过冷度区移动。     

Flow Structure of Subcooled Boiling Water Flow in a Subchannel of 3 × 3 Rod Bundles

In this paper, the interfacial flow structure of subcooled water boiling flow in a subchannel of 3 × 3 rod bundles is presented. The 9 rods are positioned in a quadrangular assembly with a rod diameter of 8.2mm and a pitch distance of 16.6 mm. Local void fraction, interfacial area concentration, interfacial velocity, Sauter mean diameter, and liquid velocity have been measured using a conductivity probe and a Pitot tube in 20 locations inside one of the subchannels. A total of 53 flow conditions have been considered in the experimental dataset at atmospheric pressure conditions with a mass flow rate, heat flux, inlet temperature, and subcooled temperature ranges of 250–522 kg/m s, 25–185 kW/m², 96.6–104.9°C, and 2–11 K, respectively. The dataset has been used to analyze the effect of the heat flux and mass flow rate on the local flow parameters. In addition, the area-averaged data integrated over the whole subchannel have been used to validate some of the distribution parameter and drift velocity constitutive equations and interfacial area concentration correlations most used in the literature.     

钠冷快堆燃料组件热工水力特性数值模拟与分析

利用CFD程序CFX,分别对7、19、37、61根棒组成的三角形排列螺旋绕丝定位的钠冷快堆燃料组件棒束通道进行了热工水力特性的分析研究,并将结果与子通道程序SuperEnergy进行了对比验证。重点考察了棒束通道轴向流动分布、横向流交混效应及子通道轴向温升,分析了定位绕丝的影响。结果表明,绕丝对棒束通道的横向流交混效应、轴向流动分布及子通道温升有着重要影响,且随棒束的增多,通道内的流动趋向复杂化,轴向流动不均匀性有升高趋势。     

海洋条件对棒束间湍流流动传热的影响

对海洋条件下典型7棒束和4棒束通道内的流体流动传热特性进行理论分析.分析结果表明,在海洋条件下,由于流速的波动,加热管壁上始终有周期性变化的蓄热存在.在7棒束通道内,由于四周壁面和加热管管壁的限制作用,垂直于流动方向的附加力对流体的影响非常小,流体的流动和传热特性主要由轴向湍流强度和入口流速决定.而在4棒束通道内,由于...     

Thermal-hydraulic modeling and analysis of a tank in pool reactor for normal operation and loss of flow transient

A transient thermal-hydraulic model entitled Tank in Pool Reactor Thermal-Hydraulic Analysis (TPRTHA) has been developed to simulate the steady-state operation and loss of flow transient for a tank in pool type research reactor. The model solves the momentum equation, energy equation and general conduction equation in cylindrical coordinates in order to predict the coolant velocity, coolant temperature and fuel rod temperature distribution respectively. The analytical solution is utilized for steady-state calculation while the finite difference technique with implicit scheme is adopted for transient calculation. The model divides the active core into a specified axial regions and the fuel rod into a specified radial zones, then a nodal calculation is performed for both average and hottest rods with a chopped cosine shaped heat generation flux. The model also predicts the heat flux leading to onset of nucleate boiling and the critical heat flux as well as the flow inversion phenomenon. The model is used to simulate a 2 MW reactor with downward flow direction and different types of fuel bundles of different powers and different flow rates. The best-estimate thermal-hydraulic safety margins are determined and the model results are analyzed and discussed.     

铅铋快堆螺旋管直流蒸汽发生器热工水力特性数值研究

本研究以铅铋快堆螺旋管直流蒸汽发生器（HOTSG）设计结构为研究对象,采用精细网格与多孔介质相结合的物理建模方法,通过一次侧三维湍流计算与二次侧用户自定义函数（UDF）分区传热计算相耦合的手段,在FLUENT求解器中开展了蒸汽发生器的热工水力特性数值分析研究。研究表明:铅铋入口附近的流量分配孔和腔室对应的直管段区域出现铅铋流速峰值,径向最大速度为0.431 m/s;入口腔室至管束区位置受到阻力突变的影响,压力、横流速度、轴向速度变化较大;热工参数变化符合流动与传热机理,临界热流密度（CHF）点附近一二次侧温差最大为109.61 K,此处最大热流密度为323.55 kW/m2。该研究将为铅铋快堆HOTSG结构设计、流致振动及安全评价提供重要的参考。      

Dynamics of a rod-shell system conveying fluid

The dynamics of a rod-shell system simulating nuclear reactor fuel rod bundles subjected to a parallel flow is studied analytically. Frequency spectra are presented and the effects of the flow velocity are discussed. It is shown that the natural frequency and critical flow velocity of the coupled rod-fluid-shell system are smaller than those of an isolated rod subjected to an axial flow.     

有界域轴向流动中棒束流致振动和稳定性研究

基于Ｃｈｅｎ有界域静止流体中棒束流致振动数学模型,给出了棒束稳定分析的数值方法。作为应用研究,分析了有界域轴向流动中棒束（４根）流致振动的特性及稳定性,给出了不同条件下轴向及横向的振型。     

Forced convection condensation in the presence of noncondensable gas in a horizontal tube; experimental and theoretical study

To have a better understanding on forced convection condensation with noncondensable gas inside a horizontal tube, an experimental research and theoretical investigation were conducted under annular and wavy flow. The effects of noncondensable gas mass concentration, mixture gases velocity, pressure and inner wall sub-cooling on the condensation heat transfer have been analyzed. The results indicate that the local heat transfer coefficient increases with the increase of the mixture inlet velocity and pressure while decreases with the increase of the noncondensable mass fraction and wall sub-cooling. Based on the above conclusions, an empirical correlation for predicting the local heat transfer coefficient was proposed which showed a good agreement with the experimental data with an error of ±20%. Furthermore, a theoretical model using the heat and mass transfer (HMT) analogy method was developed including the suction effect. The heat transfer capacity for the film, gaseous boundary and convective heat transfer of the bulk gases were compared along the tube. Besides, the axial distribution of the bulk gases and liquid–gas interface temperatures inside the tube were analyzed. The present theoretical model fits better with the experimental data compared with Lee's and Caruso's models for stratified flow.     

Flow Characteristics in Spacer Grids Measured by Rod-embedded Fiber Laser Doppler Velocimetry

Precise measurement of velocity in fuel bundles is required to improve the thermal-hydraulic properties of Pressurerized Water Reactor (PWR) spacer grids. To better understand the cross-flow characteristics in rod bundles for developing spacer grids, we used the rod-embedded fiber laser Doppler velocimetry (rod LDV) to measure the flow velocities inside the spacer grid flow channels. As the result of measurement, we found that the flow distribution inside the spacer grid depends on the local flow resistance of the grid straps and is clearly affected by the presence of a mixing vane. We also clarified the relationship between cross-flow velocity in the fuel bundle downstream of the spacer grid and the axial flow inside the spacer grid.     

不同约束条件和几何参数对有界域轴向流动棒束稳定性的影响

基于有界域轴向流动中棒束流致振动数学模型和棒束稳定性的分析方法,作为应用研究,分析了棒束端约束条件和系统几何参数对系统失稳时临界流速的影响。     

入口流量分配对矩形窄缝多通道流动交混的影响

在实际的工程中,矩形窄缝多通道得到广泛的应用,各通道之间的流动交混特性是设计者非常关心的问题之一。采用CFD程序CFX数值模拟了主通道入口流量分配对矩形多通道内流动交混的影响。研究结果表明,入口流量分配对多通道内的流动交混行为影响较大,主通道给定入口平均流量时,各个通道内的流量在轴向上基本不发生变化;主通道入口流量按照一定的比例分配后,流体在轴向交混段存在交混行为,其比例分配偏差越大,主通道的交混越强烈;流体经过全部轴向段的交混后,各个通道内的流量都趋于一致,以前4段的流动交混较为明显。     

绕丝棒束组件低流速时摩擦阻力实验研究

钠冷快堆在事故停堆余热排放期间,堆芯组件内钠流为自然循环流动,流速很低,因此准确确定绕丝棒束组件低流速时的摩擦阻力系数对钠冷快堆非能动余热排出系统的设计具有重要意义。本文以水为流动介质,准确测量了37棒和19棒绕丝棒束组件在低流速（Re<1 000）时的摩擦阻力系数。实验结果表明,随着流速的降低,绕丝棒束组件的摩擦阻力系数迅速升高,流动从层流向过渡流转变时,摩擦阻力系数有明显跃升。将实验测量值与绕丝棒束摩擦阻力系数经验公式的计算结果进行比较,发现在低流速时,经验公式计算结果较实验测量值明显偏小,同时经验公式计算的绕丝棒束层流向过渡流转变的临界Re较实验值偏大。     

摇摆条件下子通道内湍流流体的数值分析

利用FLUENT软件分析了摇摆条件对典型四棒束间的湍流流体流动和传热特性的影响机理。摇摆运动会对棒束间流体的流动传热特性产生一定影响。RSM模型可以很好地描述摇摆条件下子通道内的参数分布。摇摆周期变化带来的径向附加力的变化不会对摩擦阻力系数、传热系数和Reynolds应力产生影响。在摇摆条件下,摩擦阻力系数、传热系数和Reynolds应力呈周期性变化,但最大摩擦阻力系数所在时刻并不固定,而最大传热系数却始终是在流速最大的时刻。