气场驱动和电场驱动下的阵列流动聚焦研究

A STUDY ON MULTIPLEXED FLOW FOCUSING DRIVEN BY THE AERODYNAMIC FLOW AND ELECTRIC FIELD

翟天琪

11849101

硕士

航天工程

邓巍巍

2020-05-28

2020-07-13

哈尔滨工业大学

深圳

流动聚焦作为一种毛细流动现象，能够稳定、连续、可控、低成本地产生微纳米级液滴或者颗粒。该方法通过流场的剪切作用，将液体界面平稳拉伸，进而形成极细的射流，射流由于不稳定性自发破碎成液滴，并具有良好的单分散性。近年来，流动聚焦被广泛地应用于各个领域，展现了重要的研究和应用价值。在气驱动流动聚焦中，液体的流动一般具有良好的轴对称性。气体通过小孔时受到聚焦作用，产生压降，驱动毛细管中流出的液体形成稳定射流。但流动聚焦难以集成，产率不足。本文基于一种楔形装置与狭缝相对应的结构，分别在外加气场和电场的作用下进行了二维流动聚焦的实验研究。开展了在气驱动和电驱动两种驱动模式下阵列流动聚焦理论和实验研究。理论研究方面，建立了气体压力场和电场的理论模型，探究了两者在空间上的分布特点与各物理参数之间的关系。由此推导出了液体界面处气体压力梯度和电场强度的变化规律。实验研究方面，使用纳米脉冲激光制作了核心装置所需的具有良好润湿性的零件及狭缝。探究了激光打标机不同工作参数以及加工方法对实际加工效果的影响，并针对不同的材料和加工需求提出了可行的加工方案。为了提高核心装置的润湿性和液体在其表面和内部流动的稳定性，进行了表面微结构加工。随着楔形装置与狭缝的间距不断减少，由于瑞利-泰勒不稳定性，液体先由滴模式转变为单射流模式，并继续分裂为2个，3个以及更多的等间距射流，在达到特征间距后，液体转化为紊乱的雾化模式。推导了该情形下的色散关系，即：射流间距与气场局部压力梯度的平方根成反比。对于电驱动流动聚焦实验，推导了单液体情形下，波长与电场强度之间的色散关系，并在实验中得到了约110 μm的波长，两者拟合良好。探究了电驱动同轴锥-射流结构内部液体在射流模式和滴模式之间的转换条件。首次实现了基于瑞利-泰勒不稳定性的同轴流动聚焦线性阵列。

As a capillary flow phenomenon, flow focusing can stably and continuously produce micro/nano droplets or particles of controllable size at low cost. Through the shear action of the flow field, the liquid interface is smoothly stretched to form a very thin jet, which spontaneously breaks into droplets with good monodispersity due to fluid dynamic instability. In recent years, flow focusing has been widely used in various fields, showing important research and application value. Flow focusing of liquid in gaseous medium is typically axisymmetric and it is based on a round capillary positioned on top of a circular aperture, which restricts the gaseous flow to form a pressure drop that accelerates the liquid into a fine jet. However, the axisymmetric flow focusing configuration is difficult to scale up, limiting the production rate. This thesis reports an experimental study on the two dimensional flow focusing enabled by a wedge over a slit that provides similar gas flow restriction as well as electric field intensification.The theoretical and experimental research of linear array with flow focusing driven by gas flow field or electric field is carried out. Theoretically, the model of gas pressure field and electric field is established and the relationship between their spatial distribution and physical parameters is explored. The variation of gas pressure gradient and electric field intensity near the liquid interface is derived. Experimentally, the micromachining enabled by nanosecond pulsed laser is used to fabricate the parts with desired wetting feature and slits needed for the core devices. The effects of different machining parameters and processing methods are explored. Feasible processing schemes are proposed for different materials and processing requirements. Surface microstructures are fabricated to improve the wettability of the core device and the stability of liquid flow.As the wedge-to-slit distance is gradually reduced, the liquid dripping transforms into a single continuous jet, which then splits into two, three, and more approximately equally-spaced jets. This is essentially a consequence of Rayleigh-Taylor instability. Below a critical wedge-to-slit separation, the liquid undergoes random atomization. The complete set of phenomena is rationalized by the dispersion relation which suggests that the jet spacing is inversely proportional to the square root of local pressure gradient of the gas flow field. For the electric field driven flow focusing experiment of dispersion relation of the wavelength and the electric field of a single liquid is derived, which is supported by experimental data. The jet spacing as short as ~110 μm is achieved. The transition conditions between the jetting mode and the dropping mode of the coaxial cone-jet driven by electric filed are investigated. Finally, the linear multiplexed coaxial flow focusing based on the Rayleigh-Taylor instability has been demonstrated for the first time.

复合流动聚焦 线性阵列 多射流 波长 色散关系 激光微尺度加工

composite flow focusing linear array multi-jets wavelength dispersion relation laser micromachining

中文

联合培养

南方科技大学

翟天琪. 气场驱动和电场驱动下的阵列流动聚焦研究[D]. 深圳. 哈尔滨工业大学,2020.