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本文采用格子Boltzmann方法模拟了液滴在分叉微通道中的迁移过程，主要分析壁面润湿性、毛细数、出口流量比对液滴动力学行为的影响机制.结果表明：当毛细数足够大时，液滴在支通道的迁移行为与壁面润湿性密切相关，对疏水壁面，液滴在主通道发生破裂生成两个子液滴，子液滴完全悬浮在支通道中并流向出口.而对亲水壁面，液滴首先同样破裂成两个子液滴，不同于疏水情形，子液滴紧接着发生二次破裂，导致部分二次子液滴黏附在固体表面上，另一部分流向出口；当毛细数足够小时，液滴则滞留在分叉口处，不发生破裂.最后，还发现通过调节出口流量比可以使液滴发生非对称破裂或者不破裂完全从流速较大的支通道流出.
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关键词:
- 格子Boltzmann方法 /
- 液滴 /
- 微通道
The droplet dynamic in a bifurcating micro-channel, as one of the basic multiphase problems, is frequently encountered in the fields of science and engineering. Due to its great relevance to many important applications and also its fascinating physical phenomena, it has attracted the increasing attention in the past decades. However, this problem is still not fully understood since it is very complicated:the droplet behaviors may be influenced by several physical factors. To clearly elucidate the physics governing droplet dynamics in a bifurcating micro-channel, a detailed numerical study on this problem is conducted. The present investigation is based on our recently developed phase-field-based lattice Boltzmann multiphase model, in which one distribution function is used to solve the Cahn-Hilliard equation, and the other is adopted to solve the Navier-Stokes equations. In this paper, we mainly focus on the effects of the surface wettability, capillary number and outlet flux ratio on the droplet dynamics, and the volume of the generated daughter droplet is also presented. The numerical results show that when the capillary number is large enough, the droplet behaviors depend critically on surface wettability. For the nonwetting case, the main droplet breaks up into two daughter droplets, which then completely suspend in the branched channels and flow towards the outlet. While for the wetting case, the main droplet also breaks up into two daughter droplets at first, and then different behaviors can be observed. The daughter droplet undergoes a secondary breakup, which results in part of droplet adhering to the wall, and the remaining flowing to the outlet. The volume of the generated daughter droplet is also measured, and it is shown that it increases linearly with contact angle increasing. When the capillary number is small enough, the droplet remains at the bifurcating position, which does not break up. Finally, we also find that the outlet flux ratio affects the rupture mechanism of the droplet. When the outlet flux ratio is 1, the droplet is split into two identical daughter droplets. When the outlet flux ratio increases, an asymmetric rupture resulting in the generation of two different daughter droplets, will be observed. However, if the outlet flux ratio is larger enough, the droplet does not breakup, and flows into the branched channel where the fluid velocity is larger. Here we define a critical outlet flux ratio, below which the droplet breakup occurs, and above which the droplet does not break up. The relationship between the capillary number and the critical outlet flux ratio is examined, and it is found that the critical outlet flux ratio increases with capillary number increasing.-
Keywords:
- lattice Boltzmann method /
- droplet /
- micro-channel
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[17] Liang H, Shi B C, Chai Z H 2016 Phys. Rev. E 93 013308
[18] Rowlinson J S, Widom B 1982 Molecular Theory of Capillarity (Oxford:Clarendon)
[19] De Gennes P G 1985 Rev. Mod. Phys. 57 827
[20] Lee T, Liu L 2010 J. Comput. Phys. 229 8045
[21] Huang J J, Huang H, Wang X 2015 Int. J. Numer. Methods Fluids 77 123
[22] Zhang T, Shi B C, Guo Z L, Chai Z H, Lu J H 2012 Phys. Rev. E 85 016701
[23] Ladd A J 1994 J. Fluid Mech. 271 285
[24] Guo Z L, Zheng C G, Shi B C 2002 Chin. Phys. 11 366
[25] Kang Q, Zhang D, Chen S 2002 Phys. Fluids 14 3203
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[1] Teh S Y, Lin R, Hung L H, Lee A P 2008 Lab on Chip 8 198
[2] Seemann R, Brinkmann M, Pfohl T, Herminghaus S 2012 Rep. Prog. Phys. 75 016601
[3] Manga M 1996 J. Fluid Mech. 315 105
[4] Link D, Anna S L, Weitz D, Stone H A 2004 Phys. Rev. Lett. 92 054503
[5] Guillot P, Colin A 2005 Phys. Rev. E 72 066301
[6] Garstecki P, Fuerstman M J, Stone H A, Whitesides G M 2006 Lab on Chip 6 437
[7] De Menech M, Garstecki P, Jousse F, Stone H A 2008 J. Fluid Mech. 595 141
[8] Christopher G F, Noharuddin N N, Taylor J A, Anna S L 2008 Phys. Rev. E 78 036317
[9] Carlson A, Do-Quang M, Amberg G 2010 Int. J. Multiphase Flow 36 397
[10] Woolfenden H, Blyth M 2011 J. Fluid Mech. 669 3
[11] Cong Z X, Zhu C Y, Fu T T, Ma Y G 2015 Sci. China:Chem. 45 34(in Chinese)[丛振霞, 朱春英, 付涛涛, 马友光2015中国科学:化学45 34]
[12] Liang H, Shi B C, Guo Z L, Chai Z H 2014 Phys. Rev. E 89 053320
[13] Guo Z L, Shu C 2013 Lattice Boltzmann Method and Its Applications in Engineering (Singapore:World Scientific) pp239-285
[14] Xu A G, Zhang G C, Li Y J, Li H 2014 Progress In Physics 34 136 (in Chinese)[许爱国, 张广财, 李英骏, 李华2014物理学进展34 136]
[15] Chai Z H, Shi B C, Guo Z L 2016 Phys. Rev. E 93 033113
[16] Liang H, Chai Z H, Shi B C, Guo Z L, Zhang T 2014 Phys. Rev. E 90 063311
[17] Liang H, Shi B C, Chai Z H 2016 Phys. Rev. E 93 013308
[18] Rowlinson J S, Widom B 1982 Molecular Theory of Capillarity (Oxford:Clarendon)
[19] De Gennes P G 1985 Rev. Mod. Phys. 57 827
[20] Lee T, Liu L 2010 J. Comput. Phys. 229 8045
[21] Huang J J, Huang H, Wang X 2015 Int. J. Numer. Methods Fluids 77 123
[22] Zhang T, Shi B C, Guo Z L, Chai Z H, Lu J H 2012 Phys. Rev. E 85 016701
[23] Ladd A J 1994 J. Fluid Mech. 271 285
[24] Guo Z L, Zheng C G, Shi B C 2002 Chin. Phys. 11 366
[25] Kang Q, Zhang D, Chen S 2002 Phys. Fluids 14 3203
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