基于扩散界面法的液态LBE中单个弹状气泡上升行为CFD研究
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摘要
利用扩散界面法对液态铅铋合金中弹状气泡在垂直管中的上升过程进行数值模拟研究,用来验证扩散界面法在模拟液态铅铋合金(LBE)中弹状气泡上升行为的准确性和可行性,并对模拟结果进行进一步分析,来解释弹状气泡在LBE中的上升行为。数值模拟得到不同液体流速情况下弹状气泡在上升过程中的形态和速度变化,数值模拟结果与文献中的经验关系式以及实验中的结果都吻合良好,证明了扩散界面法在模拟液态铅铋合金中弹状气泡上升行为的准确性和可行性,为液态金属和弹状气泡的两相流提供了一种新方法。对数值模拟结果进行进一步分析,发现气泡尾部形态变化较大,会在尾部两端分裂出子气泡,尾部附近流场产生旋涡,受到强烈干扰而出现湍流,对于提高换热效率起到积极作用。气泡上升对尾部区域产生影响的最远距离约80 mm,为连续气泡的注入提供了气泡间距参考值。
CFD studies were carried out on a single Taylor bubble rising behaviors in liquid lead bismuth eutectic(LBE)in a vertical tube by using diffuse-interface method,to verify the feasibility and accuracy of diffuse-interface method in simulating the Taylor bubble rising behaviors in liquid LBE. A simplified model is adopted comprising of one hemisphere connected to a cylinder for the bubble. The numerical simulation results mainly including deformation of the bubble and flow field in the wake region of the bubble are further analyzed to account for rising behaviors of the bubble. Deformation of the bubble and velocity changes during the bubble rising process with initially different liquid velocities are obtained by numerical simulation. Comparisons were made between simulative results and empirical formula of the bubble terminal velocity. Also,comparison between simulative thickness and velocity of the falling film along the bubble and the experimental data are conducted. Feasibility and accuracy of diffuse-interface method in simulating the Taylor bubble rising behaviors in liquid LBE alloy are proved by these comparisons. Thus,a new method was provided for simulating two-phase flow of Taylor bubble rising behaviors in liquid metal. Flow around the bubble nose and in the falling film are studied a lot by many researchers,but quantitative analyses of flow in the wake region are insufficient. Therefore, further investigations into simulation especially simulative results in the wake region were conducted,finding that shape of the bubble tail changed a lot,sub-bubbles would be split out at both ends of the tail,vortexes were produced in the wake region. And in the wake region the flow field was strongly disturbed and tended to be turbulent which can improve heat change efficiency during the cooling process of reactor by LBE. Influence of the rising bubble on the wake region extended as far as to 80 mm,which provided the reference value of bubble spacing for injection of continuous bubble.
CFD studies were carried out on a single Taylor bubble rising behaviors in liquid lead bismuth eutectic(LBE)in a vertical tube by using diffuse-interface method,to verify the feasibility and accuracy of diffuse-interface method in simulating the Taylor bubble rising behaviors in liquid LBE. A simplified model is adopted comprising of one hemisphere connected to a cylinder for the bubble. The numerical simulation results mainly including deformation of the bubble and flow field in the wake region of the bubble are further analyzed to account for rising behaviors of the bubble. Deformation of the bubble and velocity changes during the bubble rising process with initially different liquid velocities are obtained by numerical simulation. Comparisons were made between simulative results and empirical formula of the bubble terminal velocity. Also,comparison between simulative thickness and velocity of the falling film along the bubble and the experimental data are conducted. Feasibility and accuracy of diffuse-interface method in simulating the Taylor bubble rising behaviors in liquid LBE alloy are proved by these comparisons. Thus,a new method was provided for simulating two-phase flow of Taylor bubble rising behaviors in liquid metal. Flow around the bubble nose and in the falling film are studied a lot by many researchers,but quantitative analyses of flow in the wake region are insufficient. Therefore, further investigations into simulation especially simulative results in the wake region were conducted,finding that shape of the bubble tail changed a lot,sub-bubbles would be split out at both ends of the tail,vortexes were produced in the wake region. And in the wake region the flow field was strongly disturbed and tended to be turbulent which can improve heat change efficiency during the cooling process of reactor by LBE. Influence of the rising bubble on the wake region extended as far as to 80 mm,which provided the reference value of bubble spacing for injection of continuous bubble.
引文
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[17]Wang Y,Cai J J,Li Q.Numerical simulation of large bubble-rising behavior in nuclear reactor using diffuse interface method[J].International Journal of Energy Research,2018,42(1):276-283.
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[19]王春涛,蔡杰进.基于扩散界面法的液态铅铋合金中气泡上升行为模拟[J].原子能科学技术,2017,51(10):1834-1839.
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[25]Dejesus J D,Ahmad W,Kawaji M.Experimental Study of Flow Structure in Vertical Slug Flow[J].Multiphase Flow,1995:105-118.
[2]Cinotti L,Gherardi G.The Pb-Bi cooled XADS status of development[J].Journal of Nuclear Materials,2002,301(1):8-14.
[3]Suzuki T,Chen X N,Rineisiski A,et al.Transient analyses for accelerator driven system PDS-XADS using the extended SIMM ER-Ⅲcode[J].Nuclear Engineering and Design,2005,235(24):2594-2611.
[4]贠军贤,沈自求.垂直管内弹状气泡上升中壁面传递的实验研究[J].高校化学工程学报,2002,16(3):275-280.
[5]Benamati G,Foletti C,Forgione,et al.Experimental study on gas-injection enhanced circulation performed with the CIRCE facility[J].Nuclear Engineering and Design,2007,237(7):768-777.
[6]陈飞.液态铅铋合金-氦气流动换热特性数值研究[D].北京:中国科学院研究生院(工程热物理研究所),2014.
[7]Boden S,Haghnegahdar M,Hampel U.Measurement of Taylor bubble shape in square channel by microfocus X-ray computed tomography for investigation of mass transfer[J].Flow Measurement and Instrumentation,2016,53:49-55.
[8]Azevedo M B D,Santos D D,Faccini J L H,et al.Experimental study of the falling film of liquid around a Taylor bubble[J].International Journal of Multiphase Flow,2016,88:133-141.
[9]Pringle C C T,Ambrose S,Azzopardi B J,et al.The existence and behavior of large diameter Taylor bubbles[J].International Journal of Multiphase Flow,2015,72:318-323.
[10]Araujo J D P,Miranda J M,Campos J B L M.CFD Study of the Hydrodynamics of Slug Flow Systems:Interaction between Consecutive Taylor Bubbles[J].International Journal of Chemical Reactor Engineering,2015,13(4):541-549.
[11]Bugg J D,Saad G A.The velocity field around a Taylor bubble rising in a stagnant viscous fluid:numerical and experimental results[J].International Journal of Multiphase Flow,2002,28(5):791-803.
[12]Li X,Tian W X,Chen R H,et al.Numerical simulation on single Taylor bubble rising in LBE using moving particle method[J].Nuclear Engineering and Design,2013,256(4):227-234.
[13]Saito Y,Mishima K,Tobita Y,et al.Velocity field measurement in gas-liquid metal two-phase flow with use of PIV and neutron radiography techniques[J].Applied Radiation and Isotopes Including Data Instrumentation and Methods for Use in Agriculture Industry and Medicine,2004,61(4):683-691.
[14]赵云淦,牛风雷,单祖华.气泡在液态铅铋合金内上升行为的数值模拟[J].原子能科学技术,2015,49(5):278-282.
[15]Wang Jifei,Wan Dechang.Numerical simulation of 3-Dwater collapse with an obstacle by FEM-leve lset method[J].Journal of Hydrodynamics,2015,27(1):112-119.
[16]王烨,蔡杰进.基于扩散界面法的较大气泡上升过程数值模拟[J].原子能科学技术,2017,51(2):269-274.
[17]Wang Y,Cai J J,Li Q.Numerical simulation of large bubble-rising behavior in nuclear reactor using diffuse interface method[J].International Journal of Energy Research,2018,42(1):276-283.
[18]Wang Y,Cai J J.Numerical investigation on bubble evolution during nucleate boiling using diffuse interface method[J].International Journal of Heat and Mass Transfer,2017,112:28-38.
[19]王春涛,蔡杰进.基于扩散界面法的液态铅铋合金中气泡上升行为模拟[J].原子能科学技术,2017,51(10):1834-1839.
[20]Yue P,Zhou C,Feng J J,et al.Phase-field simulations of interfacial dynamics in viscoelastic fluids using finite elements with adaptive meshing[J].Journal of Computational Physics,2006,219(1):47-67.
[21]Anderson D M,Mcfadden G B,Wheeler A A.Diffuse-interface methods in fluid mechanics[J].Annual Review of Fluid Mechanics,1998,30(1):139-165.
[22]Fabre J,Line A.Modeling of Two-Phase Slug Flow[J].Annual Review of Fluid Mechanics,1992,24(24):21-46.
[23]White E T and Beardome R H.The velocity of rise of single cylindrical air bubbles through liquids contained in vertical tubes[J].Chemical Engineering and Science,1962,17(5):351-361.
[24]Nicklin D J,Wilkes J O,Davidson J F.Two-phase flow in vertical tubes[J].Transactions of the Institution of Chemical Engineering,1962,40:61-68.
[25]Dejesus J D,Ahmad W,Kawaji M.Experimental Study of Flow Structure in Vertical Slug Flow[J].Multiphase Flow,1995:105-118.