CFD-DEM耦合模拟网式过滤器局部堵塞
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摘要
过滤器内部的流场不均导致使用时容易产生局部堵塞,堵塞分布受入口流速、颗粒粒径、流线轨迹等因素的共同影响。该文以计算流体力学-离散元法(computational fluid dynamics-discrete element method,CFD-DEM)耦合模拟不同流量下Y型网式过滤器内部不同粒径的沙粒运动及分布,分析过滤器内部流态对沙粒运动分布的影响并通过试验加以证明。结果表明,滤网两侧的压差占总压差的77%。网面流量呈阶梯分布,最大流量位于出口侧滤网上端,最低流量位于进口侧滤网中心,前者是后者的5.9倍;对于通过滤网的颗粒,入口流速越高,颗粒通过点越集中;对于拦截颗粒,当粒径接近孔径时,颗粒稳定附着在滤网,增加入口流速使颗粒向侧面滤网聚积并产生局部堵塞,粒径远大于孔径时,颗粒在内腔中不停运动,难以稳定附着在滤网;降低入口流速将提高颗粒分布的均匀程度,延长过滤器高效段时间,减少冲洗难度。
Due to low cost and long operational life span, screen filter is widely used in chemical industry, pharmaceutical engineering, and agricultural irrigation. In order to study the motion and spatial distribution of particles in the filter and reduce the harm of local clogging,in this paper we simulated the particles' motion under different flow rates and diameters by the method of CFD-DEM, and analyzed the effects on the particles' spatial distribution caused by flow rate and particle size. The correctness of theoretical analysis and the validity of methods were verified in experimental filtration with both clean water and muddy water under different inlet pressure. According to the velocity vector distribution and streamlines, there is a jet-flow and backflow, causing the uneven flow field in the filter. The uneven flow field in screen filter leads to local clogging whose distribution is influenced by flow rate, particle size, streamlines and etc. Pressure and velocity distribution directly reflects the resistance characteristics of mesh which results in 77 percentage of total pressure drop. The charts about the flow rate on different mesh sections, with stepped distribution characteristics, show that flux differences are obvious on account of filter shells. The lowest flow rate is located in the middle of screen close to inlet while the highest in the upper of screen close to outlet, and the former is as high as 5.9 times that of the latter. Therefore, it is necessary to optimize the filter shell for better performance. Particles' motion and distribution shows sieve effect of mesh on the movement and distribution of sediment. Although particles which can pass through the screen will not attach themselves to the mesh surface, they will aggravate clogging when the porous medium forms on mesh surface. The higher the flow rate is, the more concentrative the particles pass through the screen and the more serious the local clogging is. For the clogged particles which are the essential factor of clogging on mesh surface, bigger ratios of filter pore size to particle size cause the particles cycling in the housing, while the smaller firmly adhere to mesh surface and are more heavily agglomerated on the mesh with the rise of flow rate. So the smaller particles can lead more serious clogging and higher pressure drop than the bigger one under the same mass. The motion of both passing particles and smaller clogging particles is closely related to streamlines and surface velocity on mesh. Along streamline, particles can easily adhere to mesh surface or pass through mesh pore in lower surface velocity. When particles move with a high-velocity or the flow field speed up by the increase of inlet velocity, the kinetic energy of particles increase and the collision becomes more frequent. This decreases the possibility through the screen and weakens particles' stability. Particles prefer to adhere to the mesh in low velocity, but rarely adhere to the mesh where the streamline does not skim over regardless of the surface velocity. When the overall velocity rises, a great deal of particles amass on the section lying on end of streamlines because of the lower velocity. In most cases, adopting high inlet velocity can increase the work efficiency, but when the ratios of filter pore size to particle size is slightly greater than 1, high inlet velocity will sharply increase the harm of local clogging. In this situation, reducing the inlet velocity can increase the uniformity of particle distribution, enhance the auxiliary effect of filter cake, prolong the effective time and the operational life span of filter, and reduce the difficulty of flushing at the cost of efficiency loss. So, in practice, the filtering accuracy and inlet pressure of the filter should be adjusted according to the particle size of irrigation water for better perform.
Due to low cost and long operational life span, screen filter is widely used in chemical industry, pharmaceutical engineering, and agricultural irrigation. In order to study the motion and spatial distribution of particles in the filter and reduce the harm of local clogging,in this paper we simulated the particles' motion under different flow rates and diameters by the method of CFD-DEM, and analyzed the effects on the particles' spatial distribution caused by flow rate and particle size. The correctness of theoretical analysis and the validity of methods were verified in experimental filtration with both clean water and muddy water under different inlet pressure. According to the velocity vector distribution and streamlines, there is a jet-flow and backflow, causing the uneven flow field in the filter. The uneven flow field in screen filter leads to local clogging whose distribution is influenced by flow rate, particle size, streamlines and etc. Pressure and velocity distribution directly reflects the resistance characteristics of mesh which results in 77 percentage of total pressure drop. The charts about the flow rate on different mesh sections, with stepped distribution characteristics, show that flux differences are obvious on account of filter shells. The lowest flow rate is located in the middle of screen close to inlet while the highest in the upper of screen close to outlet, and the former is as high as 5.9 times that of the latter. Therefore, it is necessary to optimize the filter shell for better performance. Particles' motion and distribution shows sieve effect of mesh on the movement and distribution of sediment. Although particles which can pass through the screen will not attach themselves to the mesh surface, they will aggravate clogging when the porous medium forms on mesh surface. The higher the flow rate is, the more concentrative the particles pass through the screen and the more serious the local clogging is. For the clogged particles which are the essential factor of clogging on mesh surface, bigger ratios of filter pore size to particle size cause the particles cycling in the housing, while the smaller firmly adhere to mesh surface and are more heavily agglomerated on the mesh with the rise of flow rate. So the smaller particles can lead more serious clogging and higher pressure drop than the bigger one under the same mass. The motion of both passing particles and smaller clogging particles is closely related to streamlines and surface velocity on mesh. Along streamline, particles can easily adhere to mesh surface or pass through mesh pore in lower surface velocity. When particles move with a high-velocity or the flow field speed up by the increase of inlet velocity, the kinetic energy of particles increase and the collision becomes more frequent. This decreases the possibility through the screen and weakens particles' stability. Particles prefer to adhere to the mesh in low velocity, but rarely adhere to the mesh where the streamline does not skim over regardless of the surface velocity. When the overall velocity rises, a great deal of particles amass on the section lying on end of streamlines because of the lower velocity. In most cases, adopting high inlet velocity can increase the work efficiency, but when the ratios of filter pore size to particle size is slightly greater than 1, high inlet velocity will sharply increase the harm of local clogging. In this situation, reducing the inlet velocity can increase the uniformity of particle distribution, enhance the auxiliary effect of filter cake, prolong the effective time and the operational life span of filter, and reduce the difficulty of flushing at the cost of efficiency loss. So, in practice, the filtering accuracy and inlet pressure of the filter should be adjusted according to the particle size of irrigation water for better perform.
引文
[1]Zong Quanli,Zheng Tiegang,Liu Huanfang,et al.Development of head loss equations for self-cleaning screen filters in drip irrigation systems using dimensional analysis[J].Biosystems Engineering,2015,133:116-127.
[2]Puig-bargués J,Barragán J,Cartagena F R,et al.Development of equations for calculating the head loss in effluent filtration in micro-irrigation systems using dimensional analysis[J].Biosystems Engineering,2005,92(3):383-390
[3]Duranros M,Arbat G,Barragán J,et al.Assessment of head loss equations developed with dimensional analysis for micro irrigation filters using effluents[J].Biosystems Engineering,2010,106(4):521-526.
[4]王忠义,任翱宇,王纪达,等.管道过滤器流场数值模拟与实验[J].华中科技大学学报:自然科学版,2015,16(1):75-79.Wang Zhongyi,Ren Aoyu,Wang Jida,et al.Numerical simulation and experimental of the pipe filter flow field[J].Journal of Huazhong University of Science and Technology:Nature Science Edition,2015,16(1):75-79.(in Chinese with English abstract)
[5]宗全利,郑铁刚,刘焕芳,等.滴灌自清洗网式过滤器全流场数值模拟与分析[J].农业工程学报,2013,29(16):57-65.Zong Quanli,Zheng Tiegang,Liu Huanfang,et al.Numerical simulation and analysis on whole flow field for drip self-cleaning screen filter[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2013,29(16):57-65.(in Chinese with English abstract)
[6]肖新棉,董文楚,潘林,等.叠片式砂过滤器水力特性模拟计算[J].农业工程学报,2008,24(8):1-5.Xiao Xinmian,Dong Wenchu,Pan Lin,et al.Computational simulation of hydraulic characteristics for laminated sand filter[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2008,24(8):1-5.(in Chinese with English abstract)
[7]喻黎明,谭弘,邹小艳,等.基于CFD-DEM耦合的迷宫流道水沙运动数值模拟[J].农业机械学报,2016,47(8):65-71.Yu Liming,Tan Hong,Zou Xiaoyan,et al.Numerical simulation of water and sediment flow in labyrinth channel based on coupled CFD-DEM[J].Transactions of the Chinese Society for Agricultural Machinery,2016,47(8):65-71.(in Chinese with English abstract)
[8]Chu Kaiwei,Chen Jiang,Wang Bo,et al.Understand solids loading effects in a dense medium cyclone:effect of particle size by a CFD-DEM method[J].Powder Technology,2017,320:594-609.
[9]喻黎明,徐洲,杨具瑞,等.基于CFD-DEM耦合的网式过滤器水沙运动数值模拟[J].农业机械学报,2018,49(3):303-308.Yu Liming,Xu Zhou,Yang Jurui,et al.Numerical simulation of water and sediment movement in screen filter based on coupled CFD-DEM[J].Transactions of the Chinese Society for Agricultural Machinery,2018,49(3):303-308.(in Chinese with English abstract)
[10]胡国明.颗粒系统的离散元素法分析仿真:离散元素法的工业应用与EDEM软件简介[M].武汉:武汉理工大学出版社,2010.
[11]王福军.计算流体动力学分析-CFD软件原理与应用[M].北京:清华大学出版社,2004.
[12]喻黎明,邹小艳,谭弘,等.基于CFD-DEM耦合的水力旋流器水沙运动三维数值模拟[J].农业机械学报,2016,47(1):126-132.Yu Liming,Zou Xiaoyan,Tan Hong,et al.3D numerical simulation of water and sediment flow in hydrocyclone based on coupled CFD-DEM[J].Transactions of the Chinese Society for Agricultural Machinery,2016,47(1):126-132.(in Chinese with English abstract)
[13]Qiu Chaoliu,Wu Chuanyu.A hybrid DEM/CFD approach for solid-liquid flows[J].Journal of Hydrodynamics,2014,26(1):19-25.
[14]Chu Kaiwei,Wang Bo,Yu Aibing,et al.CFD-DEMmodelling of multiphase flow in dense medium cyclones[J].Powder Technology,2009,193(3):235-247
[15]陶洪飞,朱玲玲,马英杰,等.网式过滤器的计算模型选择及内部流场分析[J].节水灌溉,2016,28(10):83-87.Tao Hongfei,Zhu Lingling,Ma Yingjie,et al.Calculation model selection and internal flow field analysis of screen filter[J].Water Saving Irrigation,2016,28(10):83-87.(in Chinese with English abstract)
[16]樊建中,桑吉梅,张永忠,等.铝基复合材料增强体颗粒分布均匀性的研究[J].金属学报,1998,34(11):1199-1204.Fan Jianzhong,Sang Jimei,Zhang Yongzhong,et al.The spatial distribution of reinforcements in aluminium matrix composites[J].Acta Metall Sin,1998,34(11):1199-1204.(in Chinese with English abstract)
[17]王凯,李秀峰,王跃社,等.液固两相流中固体颗粒对弯管冲蚀破坏的位置预测[J].工程热物理学报,2014,35(4):691-694.Wang Kai,Li Xiufeng,Wang Yueshe,et al.Numerical prediction of the maximum erosion location in liquid-solid two-phase flow of the elbow[J].Journal of Engineering Thermophysics 2014,35(4):691-694.(in Chinese with English abstract)
[18]刘飞,刘焕芳,宗全利,等.自清洗网式过滤器水头损失和排污时间研究[J].农业机械学报,2013,44(5):127-134.Liu Fei,Liu Huanfang,Zong Quanli,et al.Experiment on head loss and discharge time of self-cleaning screen filter[J].Transactions of the Chinese Society for Agricultural Machinery,2013,44(5):127-134.(in Chinese with English abstract)
[19]Zeier K R,Hills D J.Trickle irrigation screen filter performance as affected by sand size and concentration[J].Transactions of the ASAE,1988,30(3):735-739.
[20]Thokal R T,Raghavendra A G,Suresh N M,et al.Effect of sand particle size and concentration on performance of screen filter in trickle irrigation[J].Annals of Arid Zone,2004,43(1):65-71.
[21]徐茂云.微灌用筛网式过滤器水力性能的试验研究[J].水利学报,1992(3):54-56,64.
[22]刘焕芳,王军,胡九英,成玉彪.微灌用网式过滤器局部水头损失的试验研究[J].中国农村水利水电,2006(6):57-60.Liu Huanfang,Wang Jun,Hu Jiuying,et al.The experimental study on local head loss of screen filter in micro irrigation[J].China Rural Water and Hydropower,2006(6):57-60.(in Chinese with English abstract)
[23]宗全利,杨洪飞,刘贞姬,等.网式过滤器滤网堵塞成因分析与压降计算[J].农业机械学报,2017,48(9):215-222.Zong Quanli,Yang Hongfei,Liu Zhenji,et al.Clogging reason analysis and pressure drop calculation of screen filter[J].Transactions of the Chinese Society for Agricultural Machinery,2017,48(9):215-222.(in Chinese with English abstract)
[24]丁启圣.新型实用过滤技术[M].北京:冶金工业出版社,2011.
[25]Duran-Ros M,Puig-Bargués J,Arbat G,et al.Performance and backwashing efficiency of disc and screen filters in microirrigation systems[J].Biosystems Engineering,2009,103(1):35-42.
[26]王新坤,高世凯,夏立平,等.微灌用网式过滤器数值模拟与结构优化[J].排灌机械工程学报,2013,31(8):719-723.Wang Xinkun,Gao Shikai,Xia Liping,et al.Numerical simulation and structural optimization of screen filter in micro-irrigation[J].Journal of Drainage and Irrigation Machinery Engin,2013,31(8):719-723.(in Chinese with English abstract)
[27]Mondal S,Sharma M,Hodge R,et al.A new method for the design and selection of premium/woven sand screens[J].Spe Drilling&Completion,2012,27(3):407-416.
[28]Wu Chu-Hsiang,Sharma M,et al.A DEM-based approach for evaluating the pore throat size distribution of a filter medium[J].Powder Technology,2017,322:159-167.
[29]阿力甫江·阿不里米提,虎胆·吐马尔白,马合木江·艾合买提,等.微灌鱼雷网式过滤器全流场数值模拟[J].农业工程学报,2017,33(3):107-112.Alifujiang Abulimiti,Hudan Tumaerbai,Mulati Yusaiyin,et al.Numerical simulation on flow field of screen filter with torpedo in micro-irrigation[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2017,33(3):107-112.(in Chinese with English abstract)
[2]Puig-bargués J,Barragán J,Cartagena F R,et al.Development of equations for calculating the head loss in effluent filtration in micro-irrigation systems using dimensional analysis[J].Biosystems Engineering,2005,92(3):383-390
[3]Duranros M,Arbat G,Barragán J,et al.Assessment of head loss equations developed with dimensional analysis for micro irrigation filters using effluents[J].Biosystems Engineering,2010,106(4):521-526.
[4]王忠义,任翱宇,王纪达,等.管道过滤器流场数值模拟与实验[J].华中科技大学学报:自然科学版,2015,16(1):75-79.Wang Zhongyi,Ren Aoyu,Wang Jida,et al.Numerical simulation and experimental of the pipe filter flow field[J].Journal of Huazhong University of Science and Technology:Nature Science Edition,2015,16(1):75-79.(in Chinese with English abstract)
[5]宗全利,郑铁刚,刘焕芳,等.滴灌自清洗网式过滤器全流场数值模拟与分析[J].农业工程学报,2013,29(16):57-65.Zong Quanli,Zheng Tiegang,Liu Huanfang,et al.Numerical simulation and analysis on whole flow field for drip self-cleaning screen filter[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2013,29(16):57-65.(in Chinese with English abstract)
[6]肖新棉,董文楚,潘林,等.叠片式砂过滤器水力特性模拟计算[J].农业工程学报,2008,24(8):1-5.Xiao Xinmian,Dong Wenchu,Pan Lin,et al.Computational simulation of hydraulic characteristics for laminated sand filter[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2008,24(8):1-5.(in Chinese with English abstract)
[7]喻黎明,谭弘,邹小艳,等.基于CFD-DEM耦合的迷宫流道水沙运动数值模拟[J].农业机械学报,2016,47(8):65-71.Yu Liming,Tan Hong,Zou Xiaoyan,et al.Numerical simulation of water and sediment flow in labyrinth channel based on coupled CFD-DEM[J].Transactions of the Chinese Society for Agricultural Machinery,2016,47(8):65-71.(in Chinese with English abstract)
[8]Chu Kaiwei,Chen Jiang,Wang Bo,et al.Understand solids loading effects in a dense medium cyclone:effect of particle size by a CFD-DEM method[J].Powder Technology,2017,320:594-609.
[9]喻黎明,徐洲,杨具瑞,等.基于CFD-DEM耦合的网式过滤器水沙运动数值模拟[J].农业机械学报,2018,49(3):303-308.Yu Liming,Xu Zhou,Yang Jurui,et al.Numerical simulation of water and sediment movement in screen filter based on coupled CFD-DEM[J].Transactions of the Chinese Society for Agricultural Machinery,2018,49(3):303-308.(in Chinese with English abstract)
[10]胡国明.颗粒系统的离散元素法分析仿真:离散元素法的工业应用与EDEM软件简介[M].武汉:武汉理工大学出版社,2010.
[11]王福军.计算流体动力学分析-CFD软件原理与应用[M].北京:清华大学出版社,2004.
[12]喻黎明,邹小艳,谭弘,等.基于CFD-DEM耦合的水力旋流器水沙运动三维数值模拟[J].农业机械学报,2016,47(1):126-132.Yu Liming,Zou Xiaoyan,Tan Hong,et al.3D numerical simulation of water and sediment flow in hydrocyclone based on coupled CFD-DEM[J].Transactions of the Chinese Society for Agricultural Machinery,2016,47(1):126-132.(in Chinese with English abstract)
[13]Qiu Chaoliu,Wu Chuanyu.A hybrid DEM/CFD approach for solid-liquid flows[J].Journal of Hydrodynamics,2014,26(1):19-25.
[14]Chu Kaiwei,Wang Bo,Yu Aibing,et al.CFD-DEMmodelling of multiphase flow in dense medium cyclones[J].Powder Technology,2009,193(3):235-247
[15]陶洪飞,朱玲玲,马英杰,等.网式过滤器的计算模型选择及内部流场分析[J].节水灌溉,2016,28(10):83-87.Tao Hongfei,Zhu Lingling,Ma Yingjie,et al.Calculation model selection and internal flow field analysis of screen filter[J].Water Saving Irrigation,2016,28(10):83-87.(in Chinese with English abstract)
[16]樊建中,桑吉梅,张永忠,等.铝基复合材料增强体颗粒分布均匀性的研究[J].金属学报,1998,34(11):1199-1204.Fan Jianzhong,Sang Jimei,Zhang Yongzhong,et al.The spatial distribution of reinforcements in aluminium matrix composites[J].Acta Metall Sin,1998,34(11):1199-1204.(in Chinese with English abstract)
[17]王凯,李秀峰,王跃社,等.液固两相流中固体颗粒对弯管冲蚀破坏的位置预测[J].工程热物理学报,2014,35(4):691-694.Wang Kai,Li Xiufeng,Wang Yueshe,et al.Numerical prediction of the maximum erosion location in liquid-solid two-phase flow of the elbow[J].Journal of Engineering Thermophysics 2014,35(4):691-694.(in Chinese with English abstract)
[18]刘飞,刘焕芳,宗全利,等.自清洗网式过滤器水头损失和排污时间研究[J].农业机械学报,2013,44(5):127-134.Liu Fei,Liu Huanfang,Zong Quanli,et al.Experiment on head loss and discharge time of self-cleaning screen filter[J].Transactions of the Chinese Society for Agricultural Machinery,2013,44(5):127-134.(in Chinese with English abstract)
[19]Zeier K R,Hills D J.Trickle irrigation screen filter performance as affected by sand size and concentration[J].Transactions of the ASAE,1988,30(3):735-739.
[20]Thokal R T,Raghavendra A G,Suresh N M,et al.Effect of sand particle size and concentration on performance of screen filter in trickle irrigation[J].Annals of Arid Zone,2004,43(1):65-71.
[21]徐茂云.微灌用筛网式过滤器水力性能的试验研究[J].水利学报,1992(3):54-56,64.
[22]刘焕芳,王军,胡九英,成玉彪.微灌用网式过滤器局部水头损失的试验研究[J].中国农村水利水电,2006(6):57-60.Liu Huanfang,Wang Jun,Hu Jiuying,et al.The experimental study on local head loss of screen filter in micro irrigation[J].China Rural Water and Hydropower,2006(6):57-60.(in Chinese with English abstract)
[23]宗全利,杨洪飞,刘贞姬,等.网式过滤器滤网堵塞成因分析与压降计算[J].农业机械学报,2017,48(9):215-222.Zong Quanli,Yang Hongfei,Liu Zhenji,et al.Clogging reason analysis and pressure drop calculation of screen filter[J].Transactions of the Chinese Society for Agricultural Machinery,2017,48(9):215-222.(in Chinese with English abstract)
[24]丁启圣.新型实用过滤技术[M].北京:冶金工业出版社,2011.
[25]Duran-Ros M,Puig-Bargués J,Arbat G,et al.Performance and backwashing efficiency of disc and screen filters in microirrigation systems[J].Biosystems Engineering,2009,103(1):35-42.
[26]王新坤,高世凯,夏立平,等.微灌用网式过滤器数值模拟与结构优化[J].排灌机械工程学报,2013,31(8):719-723.Wang Xinkun,Gao Shikai,Xia Liping,et al.Numerical simulation and structural optimization of screen filter in micro-irrigation[J].Journal of Drainage and Irrigation Machinery Engin,2013,31(8):719-723.(in Chinese with English abstract)
[27]Mondal S,Sharma M,Hodge R,et al.A new method for the design and selection of premium/woven sand screens[J].Spe Drilling&Completion,2012,27(3):407-416.
[28]Wu Chu-Hsiang,Sharma M,et al.A DEM-based approach for evaluating the pore throat size distribution of a filter medium[J].Powder Technology,2017,322:159-167.
[29]阿力甫江·阿不里米提,虎胆·吐马尔白,马合木江·艾合买提,等.微灌鱼雷网式过滤器全流场数值模拟[J].农业工程学报,2017,33(3):107-112.Alifujiang Abulimiti,Hudan Tumaerbai,Mulati Yusaiyin,et al.Numerical simulation on flow field of screen filter with torpedo in micro-irrigation[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2017,33(3):107-112.(in Chinese with English abstract)