大压降管路节流特性分析及孔板优化设计
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摘要
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。
The orifice plate throttling pipeline with large pressure drop suffers damages from high frequency vibration caused by cavitation and low frequency vibration caused by high flow velocity.Aim at solving the vibration phenomenon of typical throttling pipeline with large pressure drop in KBA system of nuclear power plant,the key hydraulic characteristics such as pressure drop,flow velocity,streamline and eddy current were simulated and analyzed for single-stage orifice plate throttling pipeline based on CFD method.The negative pressure area was found in the downstream of the orifice plate,which means cavitation occurred,and eddy current was formed due to the large local velocity caused by the orifice plate jet.Then,the throttling performance of multi-stage concentric orifice plate was evaluated by means of blockage pressure drop method.The cavitation damage was found to be relieved greatly but not eliminated espe-cially in the last stage orifice plate.The expanding type five-stage orifice plate was designed according to pressure drop stage-decreasing principle,with which the possibility of cavitation was eliminated but large pressure drop resulted in large flow velocity at the downstream of the first orifice plate.Multi-stage eccentric orifice plate was designed considering cavitation characteristics and velocity distribution,which can not only eliminate the harm of cavitation,but also reduce the low frequency vibration caused by large flow velocity furthest.By increasing the spacing of the orifice plates,the throttling capacity of the upstream plates can be increased and the cavitation margin of the downstream plates can be improved.As a result,multi-stage eccentric orifice plate can be recommended as an optimized design scheme for the vibration control of the orifice plate pipeline with large pressure drop.
The orifice plate throttling pipeline with large pressure drop suffers damages from high frequency vibration caused by cavitation and low frequency vibration caused by high flow velocity.Aim at solving the vibration phenomenon of typical throttling pipeline with large pressure drop in KBA system of nuclear power plant,the key hydraulic characteristics such as pressure drop,flow velocity,streamline and eddy current were simulated and analyzed for single-stage orifice plate throttling pipeline based on CFD method.The negative pressure area was found in the downstream of the orifice plate,which means cavitation occurred,and eddy current was formed due to the large local velocity caused by the orifice plate jet.Then,the throttling performance of multi-stage concentric orifice plate was evaluated by means of blockage pressure drop method.The cavitation damage was found to be relieved greatly but not eliminated espe-cially in the last stage orifice plate.The expanding type five-stage orifice plate was designed according to pressure drop stage-decreasing principle,with which the possibility of cavitation was eliminated but large pressure drop resulted in large flow velocity at the downstream of the first orifice plate.Multi-stage eccentric orifice plate was designed considering cavitation characteristics and velocity distribution,which can not only eliminate the harm of cavitation,but also reduce the low frequency vibration caused by large flow velocity furthest.By increasing the spacing of the orifice plates,the throttling capacity of the upstream plates can be increased and the cavitation margin of the downstream plates can be improved.As a result,multi-stage eccentric orifice plate can be recommended as an optimized design scheme for the vibration control of the orifice plate pipeline with large pressure drop.
引文
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[3]杨元龙,郑文.船用大压降给水管道多级孔板设计及节流特性研究[J].船海工程,2015,44(3):164-168.YANG Yuanlong,ZHENG Wen.Design of the multistage orifice plate and throttle characteristics for marine feed pipe with large pressure drop[J].Ship&Ocean Engineering,2015,44(3):164-168(in Chinese).
[4]何超,赖姜,颜军明,等.孔板汽蚀诱发管道振动问题研究[J].核动力工程,2016,37(S2):65-69.HE Chao,LAI Jiang,YAN Junming,et al.Research on vibration issue due to pipe orifice cavitation[J].Nuclear Power Engineering,2016,37(S2):65-69(in Chinese).
[5]陈娟.节流孔板在发电厂的应用[J].广东电力,2004,17(4):46-48.CHEN Juan.Applying throttle orifice to power plants[J].Guangdong Electric Power,2004,17(4):46-48(in Chinese).
[6]张宝峰.多级节流孔板的设计计算[J].西北电力技术,2005,33(5):27-28.
[7]电力工业部东北电力设计院.DL/T 5054—1996火力发电厂汽水管道设计技术规[S].北京:中国电力出版社,1996.