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On-line Access: 2022-10-20

Received: 2022-03-24

Revision Accepted: 2022-06-29

Crosschecked: 2022-10-21

Cited: 0

Clicked: 197

Citations:  Bibtex RefMan EndNote GB/T7714

 ORCID:

Jin-yuan Qian

https://orcid.org/0000-0002-5438-0833

Zhi-jiang Jin

https://orcid.org/0000-0002-8063-709X

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Journal of Zhejiang University SCIENCE A 2022 Vol.23 No.10 P.783-794

http://doi.org/10.1631/jzus.A2200159


Effect of droplet superficial velocity on mixing efficiency in a microchannel


Author(s):  Jin-yuan QIAN, Lei ZHAO, Xiao-juan LI, Wen-qing LI, Zhi-jiang JIN

Affiliation(s):  Institute of Process Equipment, College of Energy Engineering, Zhejiang University, Hangzhou 310027, China; more

Corresponding email(s):   jzj@zju.edu.cn

Key Words:  Droplet characteristics, Mixing efficiency, Inner circulation, Droplet superficial velocity


Jin-yuan QIAN, Lei ZHAO, Xiao-juan LI, Wen-qing LI, Zhi-jiang JIN. Effect of droplet superficial velocity on mixing efficiency in a microchannel[J]. Journal of Zhejiang University Science A, 2022, 23(10): 783-794.

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publisher="Zhejiang University Press & Springer",
doi="10.1631/jzus.A2200159"
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T1 - Effect of droplet superficial velocity on mixing efficiency in a microchannel
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DOI - 10.1631/jzus.A2200159


Abstract: 
In this study, droplet characteristics including droplet length and formation time, and mixing efficiency in droplets were investigated via the volume of fluid (VOF) method coupled with a user defined scalar (UDS) model. A cross-shaped junction with a square cross-section was designed and used for droplet formation. An initial arrangement which differed from that of a conventional operation was adopted. Results show that when the droplet superficial velocity is constant, the exchange between the dispersed phase velocity and the continuous phase velocity has a marginal effect on the droplet formation time. However, the exchange has a great effect on droplet length. These findings provide a valuable guide for future operation of droplet formation. In addition, the results show that the mixing efficiency in the droplet forming stage can be classified into time-dominated and length-dominated regimes according to the droplet superficial velocity. When a droplet flows in a microchannel, a higher droplet superficial velocity increases mixing efficiency due to the faster inner circulation and shorter droplet length.

微通道内液滴表面流速对混合效率的影响分析

作者:钱锦远1,2,赵磊1,李晓娟1,李文庆1,金志江1
机构:1浙江大学,能源工程学院,化工机械研究所,中国杭州,310027;2浙江大学,流体动力与机电系统国家重点实验室,中国杭州,310027
目的:液滴表面流速是决定液滴混合性能的重要参数,可影响微流控系统中不同界面的更新频率和总传输时间。本文旨在建立具有正方形截面的十字型微通道,并基于VOF方法耦合标量方程,探究液滴表面流速对液滴长度、液滴形成时间以及液滴混合效率的影响机制,以期为微流控系统的进一步优化设计提供依据。
创新点:1.设计了具有正方形截面的十字型微通道用于液滴形成,改变了分散相和连续相的注入方式;2.建立数值模型,自定义标量方程,实现了混合过程的可视化,并利用无量纲数定量分析了不同液滴表面流速下液滴长度、形成时间以及混合效率等液滴特性。
方法:1.建立具有正方形截面的十字型微通道数值计算模型,验证数值方法的准确性(图3);2.自定义标量方程,调加标量至分散相中,实现混合过程的可视化分析,并以分散相液滴内标量的浓度变化作为混合效率的评价指标;3.改变液滴表面流速,并采用无量纲数定量分析液滴表面流速对液滴长度(图5)、液滴形成时间(图6)以及液滴混合效率(图10)的影响机制。
结论:1.液滴表面流速的增加可导致液滴长度和液滴形成时间减少;恒定液滴表面流速下,液滴长度随分散相分率的增加而增加,分散相和连续相的速度相互交换,液滴生成频率几乎不变;分散相体积分率越小,液滴混合效率越好。2.液滴在微通道内流动时,液滴内部产生内循环;内循环可分为主循环和次循环:主循环由液滴和壁面相互作用产生,而次循环由液滴和连续相流体相互作用产生。3.液滴混合效率可分为时间主导和长度主导两个阶段,且这两个阶段中液滴表面流速对混合效率的影响规律相反。

关键词:液滴特性;混合效率;内循环;液滴表面流速

Darkslateblue:Affiliate; Royal Blue:Author; Turquoise:Article

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