自然循环过冷沸腾流动不稳定性的实验研究

以氟里昂作工质,对自然循环过冷沸腾流动不稳定性进行了实验研究,重点研究了流动不稳定性的发生机理以及系统操作参数对流动不稳定性的影响规律：实验结果证实,在自然循环系统内,多数运行工况下会同时发生高频脉动和低频脉动两类流动不稳定性：高频脉动属于声波型脉动,低频脉动属于密度波型脉动。通过实验得出了判断系统稳定性的界限,并使用积分方程无因次分析方法得出了预测流动不稳定性的准则关系式,利用准则关系式拟合实验数据,所得的经验公式与实验结果符合良好。     

超临界锅炉并联倾斜内螺纹管两相流密度波型脉动数值研究

采用一维均相流模型,运用Clausse和Lahey提出的非线性两相流垂直上升单管分析法,考虑倾斜角度、内螺纹管因素,发展了多管道系统不稳定性理论模型;对超临界锅炉并联倾斜内螺纹双管汽-水两相流密度波型脉动进行了理论分析和求解.采用时域法求得密度波型脉动发生时,试验段进口质量流量在各个时间点的数值.根据流量随时间发散或收敛的趋势,判断得到发生脉动的阈值.对脉动时的周期、振幅等特征值进行分析,得到进口质量流量随时间的变化规律.计算得到的各工况下的脉动周期范围大多在5～16 s之间,与实验所得的7～19 s 基本吻合.比较可得,该模型的计算结果与试验数据符合较好,可用于判定是否发生密度波型脉动,为确定锅炉安全运行时的水冷壁参数提供参考.     

摇摆运动条件下自然循环复合型脉动的实验研究

对摇摆运动条件下的自然循环两相流动不稳定性进行实验研究。实验结果表明：摇摆运动造成的两相流动不稳定性（波谷型两相流动不稳定性）和密度波型脉动相互叠加形成复合型脉动,加剧了系统的两相流动不稳定性。复合型脉动分为不规则的复合型脉动和规则的复合型脉动两部分,复合型脉动仅发生在高欠热度区域。规则的复合型脉动发生边界与相同热工水力参数下的密度波型脉动边界接近且受摇摆参数影响较小。     

卧式螺旋管压力降脉动瞬态及时均传热特性研究

在中低压条件下，以水为工质，实验研究了卧式螺旋管中发生压力降型脉动时的瞬态和时均换热特性，给出了脉动过程中管截面平均换热系数及周向不同位置处的换热系数分布随时间的变化规律，分析了脉动过程中的瞬态换热特性和机理，获得了压力降脉动时均换热系数计算式。     

大L/d倾斜并联光管汽-液两相流不稳定性实验研究

在高压高温试验台上对倾斜并联管汽-液两相流不稳定性进行了实验研究,观察到了压力降型和密度波型等两类不稳定性脉动。在试验管长与管内径比L/d>1200条件下,没有上游可压缩容积时也发生压力降型脉动。系统压力、质量流速、热负荷和进口过冷度等参数对不稳定性有显著的影响。实验表明,在倾斜并联管中,压力降型脉动出现在含气率较低的水动力曲线负斜率段,为两管整体脉动;而密度波型脉动出现在含气率较高的正斜率区域,呈管间脉动。经过对比发现,倾斜并联光管的脉动特性与垂直并联管类似。     

截面几何形状对并行通道密度波脉动特征影响初步研究

基于170个并行圆管和窄间隙矩形通道间密度波型脉动实验数据点,在统一的密度波型脉动实验方法、脉动识别方法和实验数据分析处理方法的条件下,研究了圆管和窄间隙矩形通道的脉动规律的异同。结果表明,在压力1.0¹9.2 MPa、质量流速101.919.2 MPa、质量流速101.9¹200.0 kg.m-2.s-1、进口过冷度18.01200.0 kg.m-2.s-1、进口过冷度18.0⁸5.2℃时,当量直径相当的圆管和窄间隙矩形通道对密度波型脉动边界规律没有影响。     

低质量流速下不同尺寸垂直并联内螺纹管压力降不稳定试验研究

在高压汽水试验回路上进行低质量流速下两相流压力降不稳定对比试验研究,分析进口压力、质量流速、进口过冷度对两种垂直并联内螺纹管两相流不稳定的影响.结果表明,两种内螺纹管发生压力降型脉动的界限干度范围和脉动周期范围接近;随进口压力、质量流速的增加,发生压力降型脉动的临界热负荷增加;随着进口压力的增加,发生压力降型脉动的界限...     

摇摆条件下自然循环流动不稳定性的混沌特性研究

对摇摆条件下两相自然循环系统不规则复合型脉动进行了非线性时序分析。通过相空间重构计算了不规则复合型脉动时间序列的关联维、K₂熵和最大Lyapunov指数值,在几何不变量的计算结果基础上,结合密度波型脉动和波谷型脉动的对比,分析了不规则复合型脉动的混沌特征和产生机理。分析结果表明：不规则复合型脉动为典型的混沌运动,热驱动力、流动阻力和摇摆引起的附加外力的相互作用和耦合导致了混沌的出现。     

低压自然循环复合流量脉动实验研究

在低压流动沸腾不稳定性实验中,研究了自然循环流动在不同入口过冷度下的演化过程。对实验中的流动沸腾不稳定性入口流量信号进行快速傅里叶变换,基于振幅和频率特性区分了3种流动脉动模式：小幅流量脉动、复合流量脉动和逆流。分析了加热功率和入口过冷度对自然循环不稳定性的影响。根据加热段出口水温变化得到了出口的流型变化,当流量波动振幅较小时加热段出口流体始终是饱和状态,而当流量波动振幅较大时,加热段出口为单相液体和两相混合物交替通过。给出了这3种流量脉动的边界图,分析了热流密度和入口过冷度对流量脉动模式的影响。结果表明：出口含气率大于0时发生流动不稳定性,热流密度达到间歇干涸型临界热流密度时发生逆流。     

低压低含汽率工况下两相自然循环流动不稳定的实验研究

在系统压力０．２ＭＰａ－０．６ＭＰａ,进口过冷度５～４０℃,质量流密度４５０～１６００ｋｇ／（ｍ２ｓ）的范围内,研究了当试验段出口质量含汽率１％左右时垂直上升单管内自然循环两相流动不稳定现象,得到了系统发生密度波型脉动的曲线,并分析了脉动产生的机理。应用微分方程无因次分析方法导出了描述系统极限状态下各参数相互关系的极限状态方程式,由实验数据拟合得出系统发生不稳定界限的经验关系式。     

Experimental Study of the Effect of Applied Magnetic Field on Plasma Properties of Unbalanced Magnetron Sputtering

An experimental study of the effect of applied magnetic field on the properties of the plasma and electrostatic oscillations in an unbalanced magnetron sputtering discharge was carried out. The apparatus consists of a magnetron sputtering target, using the conventional magnetic field configuration, and a coaxial coil around the target for an applied axial magnetic field. The dependencies of plasma parameters on the coil current were studied by two Langmuir probes. The resonance properties of electrostatic oscillations were observed. The results indicate that the applied magnetic field affects the plasma properties for the coil current in a range of 0 to 8 A. The frequency bandwidth of the electrostatic oscillations in the unbalanced magnetron sputtering plasma is in a range of 0 to 300 kHz. From the spectrum analysis, the eigenfrequency near the target is in a range of 20 to 50 kHz under typical experimental conditions where all the magnetic field, pressure, and power etc are able to have full impact on the spectrum characteristics. The calculated value of the electron temperature as per an ion acoustic standing wave pattern inside the magnetic trap is in good agreement with the experimental result.     

Root Cause Analysis of Vibration Exceeding and Design Optimization of Stagnant Branch of Reactor Coolant Loop

During the hot function test of nuclear power plant, it was found that the vibration of a stagnant branch of reactor coolant loop (RCL) exceeded the limit. According to the natural modal analysis, acoustic modal analysis and the variation trend of measured vibration with temperature, it is inferred that the acoustic vibration of the fluid in the pipeline causes the resonance of the pipeline. According to the calculation of vortex shedding frequency and acoustic vibration frequency, it is inferred that the acoustic vibration and the vortex shedding frequency of fluid at the tee are locked, which leads to the amplification of acoustic vibration excitation. Based on the analysis result and measured data above, it is determined that the cause of the vibration exceeding is the fluid-acoustic-structure coupling vibration. The pipe supports were optimized to avoid resonance frequency of acoustic structure coupling. The fillet at the tee was used to weaken the vortex shedding, so as to reduce the amplitude of flow-excited acoustic resonance. The vibration of the optimized branch will be significantly reduced to ensure the safety of the pressure boundary.     

主回路滞流分支管振动超标的原因分析与设计优化

在某核电厂热态功能试验中,巡视发现主回路的某滞流分支管振动超标。根据实测振动随温度变化的趋势、管道固有声模态分析和模态分析等,推测管道内流体的声振动激励引发管道共振。根据滞流管三通处流体的漩涡脱落频率计算和声振动频率计算,推测漩涡脱落与滞流管内流体的固有声振动频率锁定,引发声振动激励放大。综合分析计算和实测结果,确定滞流管振动超标的原因为流声固耦合振动。对管道支架进行了优化,以错开声固耦合共振频率,在三通处倒圆角削弱漩涡脱落,以降低流声耦合的声振动幅值。优化后的分支管振动会明显降低,以保证承压边界的安全。     

Air/steam flow and steam wetness dependence on acoustic resonance in safety relief valves

Many experimental studies related to the flow-induced acoustic resonance closed side branches have been reported. However, few studies have reported on the effects of air/steam flow and steam wetness dependence on fluctuating pressure amplitude. Therefore, we investigated the effect of air/steam flow and steam wetness dependence on fluctuating pressure amplitude by conducting a high temperature and high pressure tests at the Hitachi Utility Steam Test Leading Facility (HUSTLE). The test section consisted of a main pipe and a side branch. The side branch was mounted on the long straight main pipe. Fluctuating pressures at the end face of the side branches were measured. The following two results were obtained; the first is that the air/steam flow had little effect on the fluctuating pressure amplitude normalized by dynamic pressure and frequency normalized by the resonance frequency; the second is that under the acoustic resonance (St = 0.41) and non-resonance (St = 0.55) conditions, fluctuating pressure and frequency changed little with steam wetness. The steam wetness during the boiling water reactor operation was less than 0.1%; thus, there was no effect of steam wetness on the acoustic pressure amplitude and the frequency under this operating condition.     

Simulation Study on the Self-Sustained Oscillations in DC Driven Glow Discharges at Atmospheric Pressure Under Different Gas Gaps

In this paper,a one-dimensional plasma fluid model is employed to study the selfsustained oscillations in DC-driven helium glow discharges at atmospheric pressure under different gas gaps.Our simulation results indicate that a harmonic current oscillation with tiny amplitude always occur at the onset of instability and transits into a relaxation one as the conductivity of the semiconductor is decreased.It is found that the dynamics of the oscillations are dependent on the gas gaps.The discharge can only exhibit a simple oscillation with unique amplitude and frequency at smaller gas gaps(2 mm) while it can exhibit a more complex oscillation with several different amplitudes and frequencies at larger gas gaps(2 mm).The discharge modes in these current oscillations have also been analyzed.     

Parametric effects on reactivity instabilities and nonlinear oscillations in a nuclear-coupled double channel natural circulation boiling system

Natural circulation boiling systems consisting of parallel channels can undergo different types of oscillations (in-phase or out-of-phase) depending on the geometric parameters and operating conditions. The coupling between the neutronics and thermal-hydraulics has a strong influence on the modes of oscillations in a multi-channel system. In the present study a natural circulation double channel system is modeled. The reactor kinetics is represented by multi-point neutron kinetics model which includes the spatial variation of neutrons. Parametric effects on stability of the system, frequency, and the oscillation modes (reactivity instabilities) are investigated. It is found that at high powers compact cores will be more stable compared to larger cores, while the opposite will be the case at low powers. Further, nonlinear analysis is carried out to investigate the parametric effects on the bifurcation characteristics, transition from one mode to the other mode and chaotic oscillations. The delay in heat transfer and strong neutron interactions between the subcores delays the occurrence of chaotic oscillations.     

Effects of electron temperature on the ion extraction characteristics in a decaying plasma confined between two parallel plates

In this paper, a one-dimension particle-in-cell (PIC) code (EDIPIC) is employed to simulate the parallel-plate ion extraction process under an externally applied electrostatic field, focusing on the analysis of the influence of the initial electron temperature on the extracted ion fluxes to the metal plates during the ion extraction process. Compared with previously published results, the plasma oscillations on a timescale of the electron plasma period, and the excitation of the ion acoustic rarefaction waves resulting from the plasma oscillations originating from both the negative and positive electrodes, are studied for the first time. The modeling results show that both the negative and positive extractors can collect ions due to the plasma oscillations and the propagation of the ion acoustic rarefaction waves. With the increase of the initial electron temperature achieved by keeping other parameters unchanged, on the one hand, both the ion speed and flux to the negative and positive plates increase, which leads to a significant decrease of the ion extraction time, while on the other hand, the ion flux to the positive plate after the formation of a Child–Langmuir sheath is much more sensitive to an increase of the initial electron temperature than that to the negative plate. The PIC simulation results provide a deeper physical understanding of the influence of the initial electron temperature on the characteristics of the entire ion extraction process in a decaying plasma.     

Free particle oscillation frequency in an isochronous cyclotron as affected by space charge

Theoretical and experimental results are presented from a study of the effect of ionic space charge on the frequency of the free axial oscillations in an isochronous synchrotron. The axial oscillation frequency was determined by resonance excitation of free oscillations with an external electric field. It is shown that the change in frequency of the axial oscillations as a function of space charge density agrees with the results of the theoretical treatment. An experimental determination was made of the azimuthal dimension of the accelerated particle burst at different radii. The studies were made in the Nuclear Problems Laboratory of the United Institute of Nuclear Studies, on a cyclotron with spatial variation of the magnetic field.Translated from Atomnaya Énergiya, Vol. 15, No. 3, pp. 205–209, September, 1963