流动聚焦微流体通道中液滴形成过程中界面的流动特性--对滴落和喷射状态的数值分析

IF 2.3 3区 工程技术 Q2 MECHANICS
Emil Grigorov, Jordan A. Denev, Boris Kirov, Vassil Galabov
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引用次数: 0

摘要

这项工作旨在更详细地阐明微流体设备中两种不相溶流体界面的共轭物理现象。分析中考虑了流动聚焦装置中出现的两种典型状态--滴流和喷射。通过精细数值网格上的并行数值模拟,进行了动态(固定点或拉格朗日跟踪点的随时间变化的分析)和局部(沿界面的线,在固定的时间实例)分析。分析结果包括液滴形成过程中的各种压力和切向应力及其平衡,并特别关注了液滴释放的时刻和位置。研究发现,滴态的特点是由于表面张力({\Δp}}_{\upsigma } \text{and}\)和跨界面的拉普拉斯压力({\Δp}}_{\text{Lapl}}\)引起的压降的局部平衡。只有在液滴捏合前的最后时刻,前一种压力才占主导地位。与此相反,在喷射状态下,液滴形成的整个过程中,张力导致的压力明显占主导地位。冯-米塞斯准则提出的剪切应力比表面张力压力和拉普拉斯压力低几倍(喷射状态)甚至一个数量级(滴落状态)。在这两种情况下,当界面曲率 κ 发生局部符号变化时,中心线轴上的压力都会出现明显的局部最大值。在喷射系统中,中心线压力的下游导数是沿喷射轴线变化的第一个参数,这表明该系统开始出现不稳定性,随后是喷射半径的波浪式变化。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Flow characteristics at the interface during droplet formation in a flow-focusing microfluidic channel—numerical analysis of dripping and jetting regimes

Flow characteristics at the interface during droplet formation in a flow-focusing microfluidic channel—numerical analysis of dripping and jetting regimes

This work has the purpose to elucidate in deeper detail the conjugated physical phenomena at the interface between two immiscible fluids in microfluidic devices. The two typical regimes—dripping and jetting—emerging in flow-focusing devices are considered for the analysis. Dynamic (time-dependent analysis of fixed or Lagrangian-tracked points) and local (lines along the interface, at a fixed time instance) analyses have been conducted from a parallel numerical simulation on a fine numerical grid. The results comprise various pressures and tangential stresses and their balance during the droplet formation process with special attention paid to the moments and locations of the droplet release. It was found that the dripping regime is characterized by the local balance of the pressure drop due to surface tension \({ {\Delta p}}_{\upsigma } \text{and}\) the Laplace pressure \({ {\Delta p}}_{\text{Lapl}}\) across the interface. Only at the last moments before the droplet pinch-off does the former pressure dominate. In contrast, in the jetting regime, there is a clear domination of the pressure due to tension during the whole process of droplet formation. Shear stresses, presented by the von Mises criterion, are several times (jetting regime) or even an order of magnitude (dripping regime) lower than the surface tension pressure and the Laplace pressure. In both regimes, when the interface curvature κ changes locally its sign, the pressure at the centerline axis shows a clear local maximum. For the jetting regime, the downstream derivative of this centerline pressure is the first parameter that changes along the jet axis—thus indicating the onset of instabilities for this regime—and it is then followed by a wavelike change of the radius of the jet.

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来源期刊
Acta Mechanica
Acta Mechanica 物理-力学
CiteScore
4.30
自引率
14.80%
发文量
292
审稿时长
6.9 months
期刊介绍: Since 1965, the international journal Acta Mechanica has been among the leading journals in the field of theoretical and applied mechanics. In addition to the classical fields such as elasticity, plasticity, vibrations, rigid body dynamics, hydrodynamics, and gasdynamics, it also gives special attention to recently developed areas such as non-Newtonian fluid dynamics, micro/nano mechanics, smart materials and structures, and issues at the interface of mechanics and materials. The journal further publishes papers in such related fields as rheology, thermodynamics, and electromagnetic interactions with fluids and solids. In addition, articles in applied mathematics dealing with significant mechanics problems are also welcome.
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