声场驱动气泡增强微流体混合的数值模拟

doi:10.16085/j.issn.1000-6613.2019-0460

摘要/Abstract

摘要：

微流体研究中，由于雷诺数较低，流体呈层流流动，流体混合主要依靠分子扩散，混合时间长，效率低，故流体混合成为亟待解决的问题。声场激振气泡可以有效促进流体混合，已经引起了广泛关注。本文模拟研究了声场作用下气泡振动对流体混合的影响，探索了微尺度流体在声场激振下的流动特性，分析了微通道高度、入口速度、气泡间距及布置方式对流体混合的影响。结果发现，微通道高度较低时，气泡振动可以更好地促进流体混合；入口速度较小时，流体在气泡附近滞留时间较长，混合较为均匀；气泡半径较大时，旋涡扰动增强，混合效率提高；两个气泡的混合效果优于单个气泡，而气泡间距对混合效率基本无影响；微通道高度较低时，气泡同侧布置和异侧布置对流体的混合效果相接近，随着微通道高度的升高，两种布置方式对混合效果的差异逐渐显现，异侧布置具有更好的混合效果。

关键词: 气泡, 振动, 微流体, 混合

Abstract:

Laminar flow is dominant in a microfluidic channel because of the low Reynolds number, so it is difficult to mix the fluids in the microchannel quickly and effectively. To solve this problem, a fast and homogenized mixing application through the use of a bubble-based microfluidic structure actuated by acoustic was reported. The effect of acoustically actuated bubbles on fluid mixing was studied. The flow characteristic of micro-scale fluid under surface acoustic waves was explored. The flow situation and mixing efficiency of different microchannel heights, inlet flow rate, bubble distance and arrangement were analyzed. The results showed that the fluid pressure change caused by bubble under acoustic actuation would have better mixing in fluids when the microchannel height is low. When the inlet flow rate is small, the time that the fluid is disturbed near the bubble will be longer, the mixing efficiency could be higher. When the inlet flow rate increases, shorter time is needed for fluid to flow through the microchannel, the two fluids change flow direction only near the bubble, and no mixing occurs. When the bubble radius is large, the vortex disturbance is enhanced and the mixing efficiency is improved. The mixing effect of two bubbles on the fluid is much greater than that of one single bubble, and the distance between the bubbles has no effect on the mixing efficiency. When the height of the microchannel is low, the mixing efficiencies of the two bubbles on the same side and different side are closed. As the height of the microchannel increases, the difference of the mixing effect between the two arrangements gradually appears. Better mixing were achieved with bubbles arranged on the different sides of the microchannel.

Key words: bubble, oscillation, microfluidics, mixing

中图分类号:

董帅,耿朋飞,纪祥勇,李春曦. 声场驱动气泡增强微流体混合的数值模拟[J]. 化工进展, 2019, 38(12): 5271-5278.

Shuai DONG,Pengfei GENG,Xiangyong JI,Chunxi LI. Numerical simulation of microfluidic mixing enhancement via acoustically actuated bubbles[J]. Chemical Industry and Engineering Progress, 2019, 38(12): 5271-5278.

图/表 15

图1 模型几何结构

图2 二维平面下气泡流计算的极坐标图示（假设在x-y平面内，x=rcosθ，y=rsinθ）

表1 物理参数表

参数	数值大小
气泡半径a/μm	10,20,30,40
振幅强度ε	0.05
动力黏度μ/Pa·s	9×10^-4
频率f/Hz	20000
溶液密度ρ/kg·m^-3	1000
扩散系数D_c/m²·s^-1	1×10^-11

图4 网格无关性验证

图5 s=0.035，流体流动瞬态混合特性

图6 不同高度下的流体流动混合特性

表2 不同高度下的流体混合效率

H/μm	混合效率/%
120	69.10
160	62.25
200	57.97
240	53.05

图7 不同s下的流体混合特性

表3 不同s下的入口速度和混合效率

s	u_p/mm·s^-1	混合效率/%
0.17	1.6	7.89
0.05	0.47	42.82
0.035	0.33	69.10
0.015	0.14	91.85

图8 不同气泡半径下的流体流动混合特性

表4 不同气泡半径下的流体混合效率

a/μm	混合效率/%
10	22.33
20	62.80
30	69.10
40	76.03

图9 不同气泡间距下的流体流动混合特性

表5 不同气泡间距的混合效率

气泡间的距离/μm	混合效率/%
0	69.10
100	96.37
200	95.89
400	96.62

图10 不同高度下两种气泡布置方式的流体混合特性

表6 不同高度下两种气泡布置方式的混合效率

气泡布置方式	H=120μm	H=180μm	H=240μm
同侧	94.34%	84.22%	69.36%
异侧	96.62%	88.83%	75.46%

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