安全壳过滤排放系统文丘里洗涤器除碘性能分析北大核心CSCD

本文通过CFD(Computational Fluid Dynamics)数值模拟方法,对文丘里洗涤器运行工况进行模拟计算。分析入口气相流速、系统压力的改变对引射量的影响,并与实验方法结合,探讨文丘里洗涤器引射能力对除碘效率的影响,并对某核电厂安全壳过滤排放系统排放工况提出指导性建议。结果表明:提高入口气相流速可提升引射量,且引射量呈现近似线性增长关系,同时吸液管内外侧压差呈现近似抛物线规律,系统除碘效率在初始阶段与引射量的增长趋势保持一致,随后在引射量达到一定水平后趋于稳定。为保证较高除碘效率,系统排放风量应保持在3300 m^(3)/h以上;在0.1~0.5 MPa系统压力范围内,除碘效率均可保持在较高水平,压力增大有助于引射量提升,并且在高流量区提高更加明显。     

自吸式文丘里水洗器结构设计程序开发

开发了1套自吸式文丘里水洗器结构设计程序,该程序给出了完善的热工参数计算和喉部结构设计逻辑。在实验研究的基础上,提出了阻力计算修正关系式,修正后的计算结果与实验值的相对误差在8.6%以内。     

基于FLUENT的核电用文丘里管稳流性能研究

采用Realizable k-?湍流模型和Zwart空化模型对某核电用空化型文丘里管的空化流动进行了数值模拟。模拟在特定工况条件下文丘里管内流动情况,得到流量变化曲线,预测空化区域,分析稳流原理和规律。模拟不同喉部直径文丘里管稳流性能,探究喉部直径变化对空化的影响。研究结果表明:随着入口压力的增大,文丘里管将发生空化塞流。将流量变化控制在一定范围内,达到相对稳流的作用。稳流时,管路压力每升高0.1 MPa,流量增加0.06 m3·h-1;喉部直径的尺寸直接影响水力空化初生与流量增幅;在一定范围内,文丘里管喉部直径大,空化流动发展迅速且流量增幅大,喉部直径小,管路流量增长幅值小。      

鼓泡层内气态甲基碘的去除特性研究

以安全壳过滤排放系统对甲基碘的去除为背景,采用碱性硫代硫酸钠溶液作为吸收工质,对甲基碘气体的去除特性进行实验研究。结果表明:溶液温度、系统压力、气体流量以及液位是影响甲基碘去除效果的重要因素;溶液温度对甲基碘气体去除的影响表现出分区效应;在0~80℃范围内,随着温度的增加去除效率变化明显,化学反应过程是限制该区域去除效率的主要因素;当温度高于80℃时,去除效率对温度的变化不再敏感,传质过程成为影响效率的主要因素;系统压力和液位对去除效率的影响均表现为线性关系,压力和液位的提高能够显著改善气体吸收过程;相反,气相容积流量的增加会导致甲基碘气体吸收效率明显降低。研究中还进一步发现,入口气体浓度的变化对去除效率的影响很小。     

核电站主给水文丘里流量计磨损和破损影响的数值研究

针对某核电站主给水文丘里流量计受高温高速的蒸发器给水冲刷产生的磨损和破损问题,通过建立三维模型,应用计算流体力学方法,对其磨损和破损进行定量计算和分析。结果表明：文丘里流量计上下游的缩放区磨损厚度为1 mm时,测得的流量将比实际值偏大不超过0.1%;磨损量为3 mm时,偏大最大达到了0.32%。当文丘里流量计喉部发生磨损,磨损厚度为1 mm时,各流量平台下,测得的流量将比实际值偏小接近2%;随着磨损量的增大,偏差进一步增大,磨损量为3 mm时,流量测量偏小最大达到了6.16%。当文丘里流量计喉部发生破损,汇入缝隙为1 mm时,测得的流量比真实值偏大10%左右;当汇入缝隙扩大到2 mm时,偏大增大到20%。主给水文丘里流量计喉部的磨损和破损对计量的影响较大,将影响蒸发器的水位控制,应该在制造和运行阶段予以重视。     

文丘里式气泡发生器内气泡输运过程研究

利用可视化方法研究文丘里式气泡发生器内气泡的输运和破碎过程。实验以水和空气为工质,水流量范围为15～20 m³/h,气流量范围为0.6～0.7 L/min,空泡份额在0.2%～0.3%之间。结果表明：不同于常规通道,气泡在从文丘里管喉部流出后具有一个明显的减速过程,使得气液相对速度随之增加,该减速过程对气泡变形和破碎存在极大影响;水流量对气泡的破碎位置无明显影响,气泡破碎位置通常发生在渐扩段距喉部8～10 mm左右的范围,处于壁面涡流区与主流的交界附近。     

自吸式文丘里水洗器阻力特性实验研究

以空气、水为工作介质,对自吸模式运行的有机玻璃文丘里水洗器阻力特性进行了实验研究。研究结果表明,经验公式计算值与实验结果的趋势较为一致,但相对偏差较大,高达±50%以上。在实验的基础上,给出了阻力计算实验关联式,计算值与实验结果符合很好,相对偏差在±15%以内。     

文丘里气泡发生器气泡在喉部和扩张段的运动和碎化研究

文丘里式气泡发生器因其结构简单、能够有效产生所需均匀粒径的微气泡等优点,被熔盐堆脱气系统所采用。本文在脱气回路水力试验台架的实验基础上,借助高速相机来研究气泡在文丘里气泡发生器喉部和扩张段处的运动和碎化特性。研究表明:气泡运动可以分为4个阶段:1)气泡高速稳定运动阶段;2)气泡速度剧烈变化阶段;3)气泡速度稳定波动阶段;4)气泡低速稳定运动阶段。随着进气孔径的增大气泡在上述4个阶段的稳定性增加;随着水流量的增加,第二和第三阶段的区域将会向靠近x=0 mm处缩小。其中气泡的碎化过程主要是在第二阶段发生的。     

低压低功率条件下两相自然循环特性试验研究

相比于陆基核电厂,船用核动力装置的非能动安全系统运行压力较低,运行功率变化频繁,在两相自然循环条件下,非能动安全系统内的流动更加复杂多变。为了研究两相自然循环在低压、低功率条件下的循环特性,基于比例分析方法搭建了两相自然循环的原理试验台架,研究了低压条件下功率和初始液位高度对自然循环特性的影响。结果表明,在低压条件下,系统稳定运行后的压力、流量等均受初始液位高度和功率的影响。当功率为50 kW时,初始液位越高,系统稳定后的压力越大,但是流量相差较小;初始液位一定时,功率在40%满功率～100%满功率内,随着功率的增大,系统稳定后的压力也逐渐增大。这为试验台架后续两相自然循环的研究提供了方向,也为船用核动力装置非能动安全系统研究提供了参考。     

蒸汽发生器蒸汽限流器设计改进与试验验证

介绍了压水堆核电站蒸汽发生器蒸汽限流器的一种改进设计。在保持相同喉部总流通面积的条件下,通过试验证明,改进后的19个文丘里管的蒸汽限流器结构的压力损失比传统的7个文丘里管的明显减小,并验证了蒸汽限流器的压力损失计算方法。     

Structure design on improving injection performance for venturi scrubber working in self-priming mode

The venturi scrubber working in self-priming mode is one of the most efficient gas cleaning devices to remove the radioactive particles and gases from gaseous stream during severe accident in nuclear power plant. This paper focus on improving injection performance in a split type self-priming venturi scrubber, the static pressure distributions at gas and liquid channels in the scrubber are studied emphatically, the experimental results indicate that pressure at the center of nozzle exit is lower than at the wall, and the variation laws in radial are different with increasing gas velocity. When the average gas velocity at throat U_avg = 64.3 m/s, the static pressure difference between center and wall is 2.1 KPa; with the increase of gas velocity, pressure at centre and wall reduce gradually and the pressure difference become significantly, when the average gas velocity U_avg = 225.8 m/s, pressure at the center is lower 23.2 KPa than at the wall, relative deviation is about 45.6%. However, when U_avg ≥ 230 m/s, the static pressure is not continue to decrease but reverse to recover with increasing gas velocity, and recovery rate at the wall is greater than at the center. The condition before the transition point (U_avg < 230 m/s) is defined as velocity dominate area, in this area, pressure will always decrease with increasing gas velocity; the condition after the point (U_avg ≥ 230 m/s) is defined as resistance dominate area, while pressure in this area will reverse to recover, the venturi scrubber design should be ensured in velocity dominate area. The injection performance of self-priming venturi scrubber is closely relate to pressure distribution characteristics at nozzle exit, in condition of no injection or injecting air, pressure at liquid channel is consistent with the pressure at the wall of nozzle exit, which is higher than the average static pressure; when injecting water, an additional pressure increment will generate at liquid channel duo to the momentum exchange between gas and liquid, and lead to the effective pressure difference for injection reduce further. On this occasion, the influence of liquid channel area and resistance coefficient on injection performance become important, increase liquid channel area is effective for improving injection flow rate.     

Experimental research on aerosols collection performance of self-priming venturi scrubber in FCVS

The self-priming venturi scrubber is the key component of filtered containment venting system to removal radioactive products during severe accident in nuclear power plant. In this paper, the collection performance of aerosols in the venturi scrubber is researched with experiment. The results indicate that the retention performance is closely related to the operating conditions and structures, and this relation is more closely for the removal of particle size under 0.5 μm. The retention efficiency in a venturi scrubber increase with improving of both gas velocity and injection flow rate, and the influence of gas velocity on efficiency is more effective at low injection flow rate. The venturi scrubber with a long throat length or small diffuser angle performs excellent retention performance for small size aerosols. In condition of gas velocity higher as U_avg = 200 m/s and the sufficient injection flow rate, the retention efficiency maintains upon 99% for the aerosol that size range from 0.1 μm to 10 μm. The pressure loss of the venturi scrubber increase slightly with extending the length of throat, and also with reducing diffuser angles. The removal efficiency is usually at the expense of the energy loss, while the higher aerosol retention efficiency corresponds to bigger pressure loss.     

Visualized measurement of extremely high-speed droplets in Venturi scrubber

Venturi scrubbers for filtered venting have been installed in nuclear power plants worldwide. Venturi scrubbers can eliminate fission products from a polluted gas by interaction through gas–liquid interfaces. Therefore, droplet diameter is important from the viewpoint of decontamination. When Venturi scrubbers are used in severe accidents, the gas flow velocity might be extremely high. In these studies, the authors did not measure droplet diameter under extremely high gas velocity conditions. In the scenarios, experimental data pertaining to droplet diameter, under the extremely high gas flow velocity, are required. Therefore, this objective is to evaluate the diameter of extremely high-speed droplets. A visualization experiment was conducted using a Venturi scrubber. The droplet diameter distribution and the Sauter mean diameter (SMD) were determined. By comparing between the experimental value of SMDs and the one evaluated using Nukiyama–Tanasawa equation, it was confirmed that the Nukiyama–Tanasawa equation can be used to evaluate SMD with good accuracy in the gas velocity range of 82–250 m/s, except the highest gas velocity conditions. Furthermore, the droplet generation mechanism in the Venturi scrubber was considered to clarify the main reason why the Nukiyama–Tanasawa equation can be used to evaluate SMD droplet diameter.     

Experimental and theoretical study of the gas-water two phase flow through a conductance multiphase Venturi meter in vertical annular (wet gas) flow

Annular gas-liquid two phase flow widely occurs in nuclear industry. Various combinations of techniques have been employed in annular gas-liquid two phase flows to measure the flow parameters (e.g. liquid film thickness, gas volume fraction and the phase flow rates). One of the most useful techniques which has proven attractive for many multiphase flow applications is the electrical conductance technique. This paper presents an advanced conductance multiphase Venturi meter (CMVM) which is capable of measuring the gas volume fractions at the inlet and the throat of the Venturi. A new model was investigated to measure the gas flow rate. This model is based on the measurement of the gas volume fractions at the inlet and the throat of the Venturi meter using a conductance technique rather than relying on prior knowledge of the mass flow quality x. We measure conductance using two ring electrodes flush with the inner surface of the Venturi throat and two ring electrodes flush with the inner surface of the Venturi inlet. The basic operation of the electrical conductance technique in a multiphase flow is that the conductance of the mixture depends on the gas volume fraction in the water. An electronic circuit was built and calibrated to give a dc voltage output which is proportional to the conductance of the mixture which can then be related to the water film thickness in annular flow (and hence to the gas volume fraction). It was inferred from the experimental results that the minimum average percentage error of the predicted gas mass flow rates (i.e. −0.0428%) can be achieved at the optimum gas discharge coefficient of 0.932.     

Dryout characteristics and flow behavior of gas-water two-phase flow through U-shaped and inverted U-shaped bends

Experimental results are presented on the flow behavior, pressure drop characteristics, and dryout characteristics by joule heating for the gas-water two-phase flow through U-shaped and inverted U-shaped tubes in vertical plane. The height of the vertical straight section of the test tube is 4100 mm, and two bend radii, 116 mm and 435 mm, are chosen for the experiments. The test tubes used are of transparent acrylic resin for the flow behavior test, and of stainless steel for the other tests, inside diameter being 18 mm for the former and 18.5 mm for the latter. Flow patterns in the vertical upflow and downflow sections are shown on the diagram of the superficial gas velocity versus liquid velocity. Further, the flow behavior in the bend section is made clear in relation to flow rates of gas and liquid. The pressure drop between inlet and outlet of the test tube for the two-phase flow is shown in comparisons with that for the single-phase flow of water. The threshold conditions of dryout in the bend section by joule heating are shown on the diagram of the superficial gas velocity versus liquid velocity. The location of the dryout in the bend section is also clarified.     

竖直窄矩形通道内弹状流中液膜特性研究

气液两相弹状流广泛存在于工程领域,弹状流中液膜特性对弹状流模型的建立具有重要意义。为此利用高速摄像系统,对竖直窄矩形通道(3.25 mm×40 mm)内弹状流中液膜进行了可视化研究。实验中发现窄矩形通道中气弹左右两侧窄边液膜厚度不等且存在波动,但其对两侧液膜速度影响较小,两侧液膜速度相等。液膜脱离厚度主要受两相流速及气弹长度影响。液膜脱离速度随液相折算速度增加而增大;在低液相流速时,随气相折算速度增加而减小;当液相流速≥1.204 m/s时,液膜不下落,液膜脱离速度随气相速度变化较小,主要受液相流速影响。     

AP1000核主泵排气过渡工况下瞬态流动特性研究

为了研究核主泵在排气过渡工况下的气液两相流瞬态流动特性,基于非均相流模型,采用CFX软件对核主泵排气过渡工况进行瞬态数值模拟,通过分析叶轮、导叶流道内的压力脉动、涡量变化及速度分布,得到了排气过渡过程的流动变化规律。研究结果表明：气液两相工况下,叶轮各流道内气相、液相的不均匀分布及两相之间的滑移作用,导致叶轮径向力产生大幅度波动;核主泵采用的扭曲型径向导叶,在进口含气率较高的工况下,其流道内易产生气泡堆积现象,使过流面积减小,产生较大的能量损失;核主泵类球形蜗壳的对称性结构,使左侧类隔舌部位出现低流速区,堵塞了部分出口流道,这也是核主泵排气过渡工况运行不稳定的重要原因。