流动聚焦及射流不稳定性

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doi:10.6052/1000-0992-16-026

中国科学技术大学近代力学系, 合肥 230027

详细信息

通讯作者:
司廷, 中国科学技术大学近代力学系副教授. 2000 年考入中国科学技术大学, 2004 年获得学士学位, 2009 年获得流体力学博士学位, 之后从事博士后研究工作, 2012 年引进为中国科学技术大学副教授. 曾于 2012 年及 2014—2016 年到美国俄亥俄州立大学做访问教授. 主要从事实验流体力学、界面流体力学、微纳尺度流动和生物医学工程等方面的基础和应用基础研究, 是开云棋牌官方流体力学委员会微纳尺度流动专业组成员, 中国光学学会生物医学光子学专业委员会青年委员, 国际期刊BMC Cancer分部副编辑. 目前已主持三项国家自然科学基金项目并参与国家自然科学基金创新研究群体项目和国家重大科研仪器研制项目等, 已经获国家专利 7 项, 在国际期刊发表 SCI 论文近 40 篇, 其中发表在流体力学著名期刊Journal of Fluid Mechanics和Physics of Fluids上的论文共 14 篇.E-mail:tsi@ustc.edu.cn

中图分类号:O358
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出版历程
- 收稿日期:2016-08-23
- 网络出版日期:2016-11-18
- 刊出日期:2017-02-24

Flow focusing and jet instability

Department of Modern Mechanics, University of Science and Technology of China, Hefei 230027, China

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Corresponding author:SI Ting

摘要

摘要:流动聚焦是一种有效的微细射流产生方法，其原理可以描述为从毛细管流出的流体由另一种高速运动的流体驱动，经小孔聚焦后形成稳定的锥-射流结构，射流因不稳定性破碎成单分散的液滴.自从1998年流动聚焦被提出以来，陆续发展了单轴流动聚焦、电流动聚焦、复合流动聚焦和微流控流动聚焦等毛细流动技术.这些技术稳定、易操作、没有苛刻的环境条件的要求，能够制备单分散性较好的微纳米量级的液滴、颗粒和胶囊，在科学研究和实际应用中具有重要价值.流动聚焦涉及了多尺度、多界面和多场耦合的复杂流体力学问题，其中稳定的锥形是形成稳定射流的先决条件，过程参数是影响射流界面扰动发展的关键因素，而射流不稳定性分析是揭示射流破碎的最主要理论工具.该文回顾了近二十年来不同结构流动聚焦的研究进展，概述这些技术涉及的过程控制、流动模式、尺度律和不稳定性分析等关键力学问题，总结射流不稳定性的研究方法和已取得的成果，最后展望流动聚焦的研究方向和应用前景.
- 流动聚焦/
- 射流不稳定性/
- 毛细流动/
- 界面/
- 液滴
Abstract:Flow focusing is an effective method to form thin jets. It can be characterized by the formation of a steady cone-jet configuration in the core of a focusing high-speed fluid stream, as the focused fluid is continuously supplied through a capillary needle. The jet issued from the vertex of the cone passes through an orifice, and eventually breaks up into monodisperse droplets due to flow instability. First proposed in 1998, the flow focusing principle has been adopted to develop a series of capillary flow techniques such as single flow focusing, electro-flow focusing, co-flow focusing and microfluidic flow focusing. These techniques are steady, controllable and gentle in producing monodisperse droplets, particles and capsules down to micrometer scale and below. Therefore they have great significance in science, technology and engineering applications. In flow focusing, the formation of the stable cone is the prerequisite condition to form the stable jet; the process parameters influence the perturbations deposited on the jet interface; and the growth of perturbations results in the breakup of the jet. This is a complex problem in fluid mechanics due to its multi-scale, multi-interface and multi-coupling characteristics. Jet instability analysis is the most useful tool for exploring the mechanisms of jet breakup. In this paper, we review the progress of flow focusing with different geometrical structures during recent two decades, and summarize the key mechanics problems of flow focusing including process control, flow modes, scaling laws and instability analyses. The methods and achievements in the study of jet instability are also briefly described. Finally, some future research topics and opportunities for applications are provided.
- flow focusing/
- jet instability/
- capillary flow/
- interface/
- droplet

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图 1同轴射流生成方法的例子. (a)液体射流流出液面(Hertz & Hermanrud 1983), (b)同轴电雾化(Loscertales et al. 2002), (c)同轴流动聚焦(Gañán-Calvo et al. 2007), (d)毛细管微流控流动(Utada et al. 2005)

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图 2单轴流动聚焦. (a)核心装置示意图(Martín-Banderas et al. 2005), 1-腔体(提供外部流体), 2-毛细管(输运内部流体), 3-小孔(聚焦流体), (b)流动原理示意图(Gañán-Calvo et al. 2013)

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图 3液-气界面结构的单轴流动聚焦实验结果. (a)稳定的锥-射流结构(Gañán-Calvo 1998), (b)冷冻干燥后直径约为5 μm的颗粒扫描电子显微镜图片(Martín-Banderas et al. 2005)

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图 4“气-液”界面结构实验结果. (a)稳定的锥形以及小孔外液体裹挟气泡向下游运动(Gordillo et al. 2001a), (b)收集的大量气泡(Gañán-Calvo & Gordillo 2001)

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图 5流动聚焦和电雾化相结合形成电流动聚焦(Gañán-Calvo et al. 2006b). (a)电雾化的锥-射流结构, (b)流动聚焦的锥-射流结构, (c)不同条件下电流动聚焦的锥形

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图 6同轴流动聚焦. (a)同轴流动聚焦核心装置示意图(Martín-Banderas et al. 2005), 1-外层驱动流体, 2-被驱动流体, 3-同轴锥形, (b)稳定的同轴锥形(Gañán-Calvo et al. 2007), (c)同轴液体射流(Gañán-Calvo 1998), (d)同轴射流破碎图像及制备的多核胶囊微观形貌(Martín-Banderas et al. 2005)

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图 7多轴流动聚焦. (a)三轴流动聚焦的核心装置示意图及稳定的锥-射流结构(Si et al. 2015), (b) “一包二”复合电流动聚焦核心装置示意图、稳定的锥-射流结构及制备的多核胶囊微观形貌(Si et al. 2016b)

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图 8两相流体的微流控流动聚焦. (a)油-水两相流动的二维微管道结构和不同油-水流量比下的流动模式(Anna et al. 2003), (b)气-液两相流体的二维微管道结构(Hettiarachchi et al. 2007)

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图 9三相流体的微流控流动聚焦(Vladisavljevi et al. 2013). (a)二维微管道中的三相流动聚焦结构(Nie et al. 2005), (b)二维微管道中的两级流动聚焦结构(Seo et al. 2007), (c)玻璃微毛细管中的三相流动聚焦结构(Utada et al. 2005), (d)玻璃微毛细管中的两级流动聚焦结构(Chu et al. 2007)

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图 10流动聚焦的实验系统. (a)实验平台(Gañán-Calvo et al. 2011), (b)吹气式和吸气式的实验装置(Si et al. 2015), (c)复合针头的设计(Si et al. 2015)

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图 11气驱流动聚焦中稳定锥形的界面形态(Si et al. 2015). (a)单轴流动聚焦的液-气界面, (b)同轴流动聚焦的液-液和液-气界面, (c)三轴流动聚焦的液-液(内)、液-液(外)和液-气界面

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图 12流动聚焦装置几何参数的影响. (a)单轴流动聚焦中毛细管与小孔不同轴(司廷等2008), (b)单轴流动聚焦中毛细管与小孔间距增大(司廷2009), (c)同轴流动聚焦中毛细管与小孔间距增大(李广滨2016), (d)三轴流动聚焦中毛细管与小孔间距增大(Si et al. 2015)

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图 13气驱流动聚焦中外部控制参数的影响. (a)液体流量速度Q_l增大(司廷2009); (b)气体压力差△p_g增大(司廷2009); (c)内部添加染色剂观察回流环的产生, 并与数值模拟结果对比(Gañán-Calvo et al. 2011); (d)稳定锥形的流体边界层及回流环示意图(Gañán-Calvo & Montanero 2009)

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图 14核心装置的改进. (a)将毛细管和小孔之间的距离减小形成流动模糊(Gañán-Calvo 2005); (b)将毛细管端口削成尖锐的斜角有利于微量液体聚集(Acero et al. 2013); (c)在毛细管中心插入导流棒抑制回流环的产生(Acero et al. 2012b); (d)将毛细管加工成喷管形状大大减小毛细管口直径, 可用于金属液体聚焦(Vega et al. 2013); (e)将小孔所在平板改成喷管形状有利于形成稳定的流场(Acero et al. 2012a)

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图 15电流动聚焦中高分子溶液的射流形态随电场增大的变化情况(陈晓慧等2014)

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图 16“液-气”单轴流动聚焦的流动模式及其参数域(Si et al. 2009). (a)流动模式的参数域, (b)六种流动模式的锥-射流图像: (Ⅰ)锥振动模式; (Ⅱ)锥粘连模式; (Ⅲ)螺旋射流模式; (Ⅳ)共存射流模式; (Ⅴ)轴对称射流模式; (Ⅵ)滴模式

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图 17电流动聚焦的流动模式及其参数域. (a)电场施加在锥形和射流所在区域(Li et al. 2014), (b)电压和气体压力差变化引起射流的模式转换(Li et al. 2014), (c)锥形稳定和不稳定的转换边界受电压影响(司廷等2011), (d)不同流动模式参数域受电压影响(司廷等2011)

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图 18气驱流动聚焦中射流直径的尺度律及实验验证. (a)单轴流动聚焦中射流直径随液体流量速度的变化(Si et al. 2009), (b)单轴流动聚焦中射流直径随气体压力差的变化(Si et al. 2009), (c)三轴流动聚焦中三层液体射流直径随最外层液体流量速度的变化(Si et al. 2015), (d)电流动聚焦中射流直径随气体压力差的变化以及与无电场作用下流动聚焦的尺度律进行对比(Li et al. 2014)

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图 19气驱单轴流动聚焦的锥形不稳定性. (a)锥形稳定对应的最小流量速度(Gañán-Calvo & Montanero 2009), (b)在无量纲参数We-Re空间里全局不稳定、局部不稳定和稳定射流三种模式的参数域(Vega et al. 2010)

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图 20同轴射流在Rayleigh模式下存在的可能模态(1-内流体, 2-外流体, 3-环境流体). (a) squeezing模态或paravaricose模态, (b) stretching模态或parasinuous模态, (c) transitional模态

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图 21液-气射流的简化物理模型. (a)气驱单轴流动聚焦的射流模型(Gordillo et al. 2001b), (b)气驱单轴电流动聚焦的射流模型, 包括有黏和无黏模型(Li et al. 2014)

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图 22对单轴流动聚焦的理论预测和实验结果吻合. (a)射流形貌随液体流量速度呈现规律性变化(Si et al. 2009), (b)时间不稳定性理论对界面扰动波长的预测(Si et al. 2009), (c)时空不稳定性理论对滴和射流模式转换的预测(Si et al. 2009), (d)空间不稳定性理论对轴对称和非轴对称射流模式转换的预测(Si et al. 2010)

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