摘要
安装于核电站二回路的主给水调节阀通过控制给水流量来调节蒸汽发生器内的水位高度,因此主给水调节阀的流动特性影响着核电站的运行安全与效率。首先,提出了无量纲的节流窗口周向布置不平衡度δ,进行主给水调节阀节流窗口周向设计;其次,利用经网格无关性与流量实验验证的数值模拟方法分析了阀内流场的速度和压力分布特性;最后,探讨了节流窗口周向布置不平衡度对阀芯不平衡力矩和阀门流量系数的影响。结果表明:阀芯底部不均匀的压力分布会对阀芯产生不平衡力矩,增大阀芯与套筒之间的摩擦力,进而加剧阀芯与套筒之间的磨损,可能引发阀芯动作卡滞并使阀芯和套筒的工作寿命缩短;当阀门开度小于40%时,调整节流窗口周向布置方式对阀芯不平衡力矩的影响较小;当阀门开度大于40%时,通过调整节流窗口周向布置方式可以有效改变阀芯不平衡力矩;在相同条件下,通过将节流窗口周向布置不平衡度从0增大至0.5,可使阀芯不平衡力矩最大值减小22.10%,而阀门流量系数仅减小2.74%。研究结果有助于主给水调节阀及类似阀门的设计及优化。
随着世界能源需求逐年稳步增长和全球环境持续恶化,以核电为代表的清洁能源愈发引起普遍关
在核电站中,一回路内的载热工质不断将反应堆产生的热量传入蒸汽发生器,二回路内的给水在蒸汽发生器中持续吸收热量而蒸发,并最终推动汽轮机发
近些年来,在“以国代进”的背景下,我国相关阀门生产企业和研究院所针对主给水调节阀开展了技术攻关。宋
核电厂相关技术人员也根据实践经验,对主给水调节阀的设计和制造提出了指导意见。例如,针对主给水调节阀在手动操作状态下出现超调和滞后现象,并引发流量波动的问题,周广
针对阀门及类阀设备的研究,也为主给水调节阀的设计提供了参考。崔宝玲
虽然目前对主给水调节阀尤其是对基于流通能力的节流窗口的设计已有一定的研究,但是对节流窗口设计对阀门流动特性的影响的研究还不够深入,未能从保持阀门流通能力不变而改善其流动特性的角度对主给水调节阀进行优化设计。因此,本文基于数值模拟方法探讨了节流窗口周向设计对主给水调节阀流动特性的影响。提出了无量纲的节流窗口周向布置不平衡度,并讨论其对阀芯不平衡力矩和阀门流量系数的影响,以期为主给水调节阀及其他类似阀门的设计与优化提供一定的参考。
主给水调节阀的结构如

图1 主给水调节阀结构
Fig.1 Structure of MFWRV
主给水调节阀套筒的展开图如

图2 主给水调节阀套筒的展开图
Fig.2 Expanded view of MFWRV sleeve
在节流窗口周向非平衡布置的套筒中,各节流窗口顶部边长为:
(1) |
式中:tl′为非平衡布置后各节流窗口顶部边长;tavg = (t1+ t2 +t3)/3,为节流窗口顶部边长平均值;δ为节流窗口周向布置不平衡度,在本文中取δ ∈[0.5,0.5]。
以140
(2) |
(3) |
(4) |
(5) |
(6) |
(7) |
(8) |
(9) |
(10) |
(11) |
式中:u为流体的速度,m/s;ρ为流体的密度,kg/
采用六面体网格对流域进行离散化,如
(12) |
式中:Q为给水体积流量;Δp为阀前后压差;ρ0为15

图3 流域的离散模型
Fig.3 Discrete model of flow region
基于GCI (grid convergence index method,网格收敛指数)方
此外,进行通径为DN550的主给水调节阀的流量实验,以对数值模拟结果的准确性进行验证。主给水调节阀流量实验的装置如

图4 主给水调节阀流量实验的装置
Fig.4 Device for MFWRV flow test

图5 主给水调节阀流量仿真结果与实验结果的对比
Fig.5 Comparison between simulation results and experimental results of MFWRV flow
主给水调节阀阀内流场的速度云图和流线图如

图6 主给水调节阀阀内流场的速度云图和流线图
Fig.6 Velocity nephogram and streamline diagram of flow field in MFWRV

图7 主给水调节阀阀内流场的压力云图
Fig.7 Pressure nephogram of flow field in MFWRV
由
由
由
主给水调节阀关于XOY平面对称,故阀芯底面不均匀的压力分布不会引发相对于X轴的不平衡力矩。而阀芯底面垂直于Y轴,不均匀的压力分布也不会引发相对于Y轴的不平衡力矩。因此,阀芯底面不均匀的压力分布仅会引起相对于Z轴的不平衡力矩。
阀芯不平衡力矩M的计算公式如下:
(13) |
式中:pm为第m个节点的压力;Dzm为第m个节点到Z轴的距离;n为节点数。
节流窗口周向布置不平衡度对阀芯不平衡力矩的影响如

图8 节流窗口周向布置不平衡度对阀芯不平衡力的影响
Fig.8 Influence of unbalance degree of circumferential arrangement of throttling window on unbalance force of valve core
当δ=0,0.5时,不同阀门开度下阀芯不平衡力矩的变化如

图9 不同阀门开度下阀芯不平衡力矩的变化
Fig.9 Variation of unbalance torque imposed on valve core under different valve opening
节流窗口周向布置不平衡度对100%阀门开度时流量系数的影响如
当δ=0,0.5时,不同阀门开度下流量系数的变化如

图10 不同阀门开度下流量系数的变化
Fig.10 Variation of flow coefficient under different valve opening
基于常见的节流窗口周向平衡布置的套筒,通过调整各节流窗口顶部边长,将节流窗口在套筒周向进行非平衡布置,并提出了节流窗口周向布置不平衡度δ,进而通过数值模拟方法定量探讨了节流窗口周向布置方式对主给水调节阀流动特性的影响。数值模拟方法的有效性通过主给水调节阀流量实验进行了验证。
通过分析得出如下主要结论:阀芯底部不均匀的压力分布会对阀芯产生不平衡力矩,使阀芯产生倾覆趋势并增大阀芯与套筒之间的摩擦力,进而加剧阀芯与套筒之间的磨损,可能引发主给水调节阀阀芯动作卡滞,并使阀芯和套筒的工作寿命缩短;当阀门开度小于40%时,调整节流窗口周向布置方式对阀芯不平衡力矩的影响较小;当阀门开度大于40%时,通过调整节流窗口周向布置方式可以有效改变阀芯不平衡力矩;在相同条件下,通过将节流窗口周向布置不平衡度从0增大至0.5,可使最大阀芯不平衡力矩减小22.10%,而阀门流量系数仅减小2.74%。
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