孔板汽蚀诱发管道振动问题研究

针对核电厂安全壳喷淋系统(EAS)出现的强烈管道振动问题,采用现场振动试验和数值计算相结合的方法进行研究。研究发现,管道节流孔板过度节流,导致在孔板下游出现汽蚀是诱发管道强烈振动的根本原因;通过数值计算方法对孔板压降、级数、孔径和结构形式等进行一系列优化设计,给出采用三级孔板消除气蚀的减振改造方案,并对改造方案开展完整性评估。通过对改造后的管道进行再鉴定试验表明,采用本文的优化设计分析方法设计的工程改造方案很好地解决了孔板汽蚀诱发的管道强烈振动问题,管道振动和噪声均大幅降低,可以确保EAS管道系统的长期安全运行。     

适用于大压降小间距管道的节流件设计及分析

节流件广泛应用于核电站各类管道系统中,对于大压降和短距离的管道系统,节流孔板设置不合理将导致管道振动程度加剧并伴随节流件的孔径、厚度、偏心度和倒角等关键结构参数对节流效果的敏感性进行分析和计算,在此基础上,提出适用于大压降小间距管道的节流件为多级偏心节流孔板。计算表明:多级偏心节流孔板可有效抑制汽蚀和闪蒸的发生,节流效果较好,适用于大压降小间距管道节流。     

核电站除氧系统孔板后管道减薄机理分析与改进措施研究

田湾核电站1号机组除氧系统某节流孔板后方的直管段在一个换料周期内壁厚由6.6 mm减薄至2.5 mm,极易造成管道泄漏,为机组安全运行带来潜在的隐患。本文就除氧系统孔板后管道减薄磨损位置、汽蚀原理进行分析,对除氧系统孔板设计存在的缺陷、采用多级节流孔板代替单级节流孔板优势及管道减薄改进措施进行综合论述。通过改造,满足了除氧系统给水管线的运行要求,且有效降低了管道腐蚀速率。     

核电厂小支管裂纹泄漏原因分析和改造

采取试验与理论分析相结合的方法,分析诊断了核电厂安全壳喷淋系统小支管裂纹泄漏的根本原因,确定根本原因是主管道上的节流孔板设计不合理导致了小支管振动疲劳失效。设计多级节流孔板代替单级节流孔板,改造方案实施后,小支管振动大幅度降低,消除了影响核电机组安全运行的缺陷。     

大压降管路节流特性分析及孔板优化设计

大压降孔板节流管路面临汽蚀导致的高频振动和孔板间流速过大导致的低频振动这两方面的危害。针对核电厂容积和硼控制系统典型大压降节流管路的振动现象,基于CFD方法分析了单级孔板节流管路中压降、速度、流线、涡流等关键水力特性,发现单级孔板下游产生负压区而发生汽蚀,且因孔板射流导致局部速度过大而形成涡流。采用阻塞压差评估了多级同心孔板的节流性能。相比于单级孔板,多级同心孔板的汽蚀危害得到了较大改善,但最后一级孔板仍存在过度节流的风险。按多级孔板节流压降几何级数递降的原则设计的渐扩型五级孔板可消除汽蚀的发生,但一级孔板压降过大导致其下游流速过大。综合考虑汽蚀特性和流速分布而设计的多级偏心孔板结构既能规避汽蚀危害,又能最大程度降低流速过大引发的管路低频振动,且增大孔板间距可提高上游孔板的节流能力,增加下游孔板的汽蚀裕度,可作为大压降孔板节流管路振动综合治理的优化设计方案。     

某核电厂低压安注泵小流量管线振动原因研究

由于小支管振动超标的敏感管问题是困扰所有核电站的难题。国内外投入了大量的人力和物力来解决敏感管问题。分析判断振动原因是解决敏感管问题的首要因素。本文用综合的技术手段对某核电厂安注系统低压安注泵小流量管线中的敏感管振动原因进行了分析研究。通过在管线上布置加速度计进行现场振动实测获得了管线的振动分布,通过振动加速度的时程的RMS值分布获得了节流孔板后方是振动最大的位置,通过对节流孔板后方的加速度进行频谱分析初步判断为节流孔板过分节流导致通过孔板的流体汽化而出现了汽蚀现象。通过对节流孔板的理论分析获得了节流孔板前后的压差并与阻塞压差进行比较进一步验证了节流孔板的过分节流现象。最后用CFD进行了三维流场分析获得了整个管线的详细流场分布,并得到了经过节流孔板后出现了流场中低于流体饱和蒸汽压的区域,该区域是流体汽化区。通过综合的手段最后确定导致该小流量管线振动高的主要原因是节流孔板的汽蚀。本文所用的方法对其他具有类似的振动现象的振动原因分析具有借鉴的意义。     

孔板对载流管道中流致振动的影响分析

以核电厂反应堆和乏燃料水池冷却和处理系统(PTR)传水管后管线所产生的振动问题为背景,根据工程实际参数,在不同流量、背压相同条件下,开展孔板单个局部阻力件诱发流体扰动产生的脉动压力激励和管道振动的试验.对管线的流场和压力场进行数值模拟,尤其是孔板的流动状况,并将模拟计算结果与试验结果进行分析比较.研究认为,随孔板节流度的增大,能谱增大.在没有其他激励源干扰的条件下,随流量增大,流体扰动增强,压力脉动的谱幅值增大.     

核电厂高压安注系统再循环管线节流孔板的分析与改进

某在役运行VVER核电厂高压安注系统（JND）在进行小流量再循环试验时发现再循环流量出现异常波动,导致试验不合格。经过分析认为再循环管线节流孔板发生空化是导致流量波动的主要原因。本文通过相关理论和软件,主要介绍了对再循环节流孔板进行改进设计计算的过程,包括孔板流量、压差、级数、孔径和厚度等参数的计算,重点讨论了如何控制多级孔板的压降以避免孔板发生空化。该项改进已在核电厂中得到实施,实施后再循环流量波动问题得到了明显改善。     

孔板气蚀诱发核级管道振动和噪声问题研究

针对在役核电厂出现的核级管道系统强烈振动和噪声导致结构朱效的问题,采用“数值模拟优先”的研究方法,通过数值计算分析和实验研究,发现节流孔板气蚀是诱发故障的根本原因,提出了工程改造方案。系统改造后的现场调查和评估显示：在保证系统功能和结构完整性满足设计规范的前提下,管系的振动和噪声已控制在可接受的范围内。     

利用节流孔板降低VVER低压安注泵振动

通过对田湾核电站3号机组调试过程中低压安注泵自由端振动高的原因分析和泵循环管线上节流孔板数量和孔径的计算优化,解决了低压安注泵体及其相关管线的振动问题,为后续核电机组低压安注系统管系设计提供重要的经验反馈和参考。     

SCWR single channel stability analysis using a response matrix method

A system response matrix method, which directly solves the linearized differential equations in the matrix form without Laplace transformation, is introduced for the supercritical fluids flow instability analysis. The model is developed and applied to the single channel or parallel channel type instability analyses of a typical proposed Supercritical Water Reactor (SCWR) design. A uniform axial heat flux is assumed, and the dynamics of the fuel rods and water rods are not considered in this paper. The sensitivity of the decay ratio (DR) to the axial mesh size is analyzed and found that the DR is not sensitive to mesh size once sufficient number of axial nodes is applied. The sensitivity of the stability to inlet orifice coefficient is conducted for the hot channel and found that a higher inlet orifice coefficient will make the system more stable. The susceptibility of stability to operating parameters such as mass flow rate, power and system pressure is also performed. It is found that the SCWR stability sensitivity feature can be improved by carefully choosing the inlet orifice coefficients and operating parameters. The stability feature of the average channel is also analyzed with an equivalent inlet orifice coefficient. Finally, the manufacturing feasibility of the inlet orifices for both the hot channel and average channel is studied and found to be favorable.     

Plasma characteristics in the discharge region of a 20A emission current hollow cathode

Numerical calculation and fluid simulation methods were used to obtain the plasma characteristics in the discharge region of the LIPS-300 ion thruster’s 20 A emission current hollow cathode and to verify the structural design of the emitter.The results of the two methods indicated that the highest plasma density and electron temperature,which improved significantly in the orifice region,were located in the discharge region of the hollow cathode.The magnitude of plasma density was about 10~(21)m~(-3)in the emitter and orifice regions,as obtained by numerical calculations,but decreased exponentially in the plume region with the distance from the orifice exit.Meanwhile,compared to the emitter region,the electron temperature and current improved by about 36%in the orifice region.The hollow cathode performance test results were in good agreement with the numerical calculation results,which proved that that the structural design of the emitter and the orifice met the requirements of a 20 A emission current.The numerical calculation method can be used to estimate plasma characteristics in the preliminary design stage of hollow cathodes.     

振动条件下平行孔板间流体的作用力实验

乏燃料贮存格架自由放置在乏燃料水池内,格架 格架、格架 池壁之间有一定间隙。在地震载荷下,这些间隙中流体的流固耦合作用耗散了结构的能量,保证了格架的结构完整性。根据AP1000和CAP1400系列反应堆型的格架储存腔设计,格架的侧壁有平板或孔板两种方案。对格架进行结构动力学分析时,为了简化流体间隙附加质量的计算,工程上一般将孔板直接简化为平板。这样的方法并不能精确反映出实际的流固耦合效应。为获得格架与格架、格架与池壁间流体的流固耦合特性,搭建实验台架,通过振动实验,测量孔板的间隙流体在不同激振频率、不同间隙条件下的流体作用力。实验最终给出孔板的间隙流体的流体力,并给出了不同间隙条件下附加质量,本文可为AP1000和CAP1400系列乏燃料储存格架的流固耦合参数选取提供依据。     

Bubble formation and evolution behavior from vertical wall orifice

Bubble formation is an integral part of the twophase flow science.Through numerical simulation and experiments using different air flow rates and orifice diameters,the present study aims at investigating the behavior of bubble formation and evolution from vertical wall orifice in quiescent pure water.For the experiments,the images of the bubble formation process under different working conditions were recorded using a high-speed camera and analyzed the entire process.The bubble formation process can be divided into three stages,namely nucleation,stable growth,and necking.According to the obtained results,bubble forms only when the air-phase pressure exceeds the threshold pressure at wall orifice.Due to the influence of the threshold pressure and buoyancy,the bubble volume decreases with an increase in the wall orifice diameter for the same flow rate.Moreover,the volume of fluid method is applied to simulate bubble formation in a three-dimensional model and the"buffer volume"is considered in the simulation model.The simulation resultsmatched well with the experimental data,which proves the existence of threshold pressure and the periodic pressure fluctuation at the wall orifice.     

孔板管道下游流动加速腐蚀速率数值模拟研究

采用计算流体力学方法中的k-ε模型模拟了孔板管道下游管壁与流体间的传质系数分布,并利用Sanchez-Caldera流动加速速率预测模型计算了孔板管道下游的流动加速腐蚀速率分布。结果表明,孔径比的减小会导致流动加速腐蚀敏感部位向孔板下游移动,入口流速的增大对孔板下游流动加速腐蚀敏感部位的位置无明显影响,pH值的增大能有效减小流动加速腐蚀速率。     

Analytical Study of Volumetric Scroll Pump for Liquid Hydrogen Circulating System

The paper presents analytical results of suction process of a volumetric scroll pump, which will be developed for circulating liquid hydrogen in a cold moderator system. The multi-block grid generation approach has been applied to generate a moving boundaries computational model. The finer mesh patterns have been generated in the near-wall regions. The Low-Reynolds number k-ε turbulence model has been solved for predicting Reynolds stresses and turbulent scalar fluxes. The analysis has been carried out under liquid hydrogen flow conditions. The heat transfer effect is neglected to simplify the study. The analytical results show that at the end of suction process the relative pressures increase significantly in a pocket while decrease continuously in another pocket. This phenomenon might damage scroll pump components if the high-pressure side is too high and/or the low-pressure side is too low until the cavitations occur. Therefore, the pocket should open to the discharge chamber before it closes and separates from the suction chamber in order to prevent the cavitations and extremely high-pressure regions.     

Flow-induced vibrations in closed side branch pipes and their attenuation methods

Some problems due to flow-induced vibrations related to closed side branch pipes have been observed in thermal and nuclear power plants. Fluctuating pressure generated in the main pipes was unusually, acoustically excited in closed side branch pipes, and intense vibrations were caused at pipes and components. For example, flow-excited acoustic resonance in closed side branches of stub pipes of safety relief valves caused the failure of steam dryers in the United States Quad City Unit 2 nuclear power plant. Furthermore, there was a possibility that residual air or gas in a closed side branch pipe unexpectedly caused severe vibrations of low frequency in the feed water piping system. We have investigated the root cause and influence of air on severe vibrations. Intense fluctuating pressure was often caused by water hammer due to valve closure and it became larger in the closed side branch pipes. We showed that an additional side branch with an orifice was very effective to suppress the flow-induced acoustic resonance. Design methods of the orifice to attenuate fluctuating pressure generated by water hammer were presented considering Mach number, the pressure loss coefficient of orifice and the intensity of particle velocity. Moreover, suitability of the characteristic curve method was confirmed for evaluation of the attenuation effect of an orifice on fluctuating pressure generated by water hammer. Finally, we considered some flow-induced vibration problems related to closed side branch pipes and their attenuation methods.     

垂直加热通道内超临界水流动稳定性参数敏感性分析

给出了无量纲分析法与频域法相结合的稳定性分析方法的详细描述,并定义了影响稳定性的关键无量纲数。针对垂直加热通道内超临界水进行了密度波稳定性分析,并建立了稳定性边界。对系统入口阻力因数、出口阻力因数、摩擦因数、进出口压降和流动方向等进行了参数敏感性分析,结果表明高的入口阻力因数有利于系统的稳定,但高的出口阻力因数和高的摩擦因数不利于系统的稳定,系统进出口压差对系统的稳定性影响较小,向上流动比向下流动更有利于系统的稳定。计算结果对超临界水堆的堆芯和系统设计具有指导性作用。     

Influence of heating on the discharge characteristics of a hollow cathode

Hollow cathodes are widely used as electron sources and neutralizers in ion and Hall electric propulsion. Special applications such as commercial aerospace and gravitational wave detection require hollow cathodes with a very wide discharge current range. In this paper, a heater is used to compensate for the temperature drop of the emitter at low current. The self-sustained current can be extended from 0.6 to 0.1 A with a small discharge oscillation and ion energy when the flow rate is constant. This is also beneficial for long-life operation. However, when the discharge current is high(1 A), heating can cause discharge oscillation, discharge voltage and ion energy to increase. Further, combined with a rapid decline of pressure inside the cathode and an increase in the temperature in the cathode orifice plate, electron emission in the orifice and outside the orifice increases and the plasma density in the orifice decreases. This leads to a change in the cathode discharge mode.