Simulation of Electroosmotic and Pressure-Driven Mixed Flow of Viscoelastic Fluids in Converging-Diverging Tubes
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摘要: 电渗压力混合流已广泛应用于各种生化微流控领域中，其中黏弹性流体的弹性不稳定性不可忽视.采用黏弹性流体，对10∶1∶10的微通道缩放管中电渗压力混合驱动流动进行数值仿真.研究了不同压力和不同聚合物浓度对流体流动的影响，并分析了Newton流体与黏弹性流体在缩放管中速度分布的叠加原理.结果表明：反向压力使黏弹性流体展现出更大的不稳定性，使得入口涡流变大，压力每增大1 Pa涡流变大25 μm，而正向压力使涡流变小.较小反向压力时，入口涡流随着聚合物浓度的增大而增大，并逐渐趋于稳定.在较大反向压力下，涡流大小随着聚合物浓度的增大先升后降.Abstract: The electroosmotic and pressure-driven mixed flow was widely used in various biochemical microfluidic fields, where the elastic instability of the viscoelastic fluid cannot be ignored. A viscoelastic fluid was used to numerically simulate electroosmotic and pressure-driven mixed flow in a 10:1:10 microchannel converging-diverging tube. The effects of different pressures and different polymer concentrations on the fluid flow were studied, and the superposition principle for the velocity distributions of Newtonian fluids and viscoelastic fluids in converging-diverging tubes was analyzed. The results show that, the reverse pressure brings the viscoelastic fluid into higher instability, which makes the inlet vortex larger by 25 μm for every 1 Pa pressure increase. The positive pressure makes the eddy current smaller. For a relatively small reverse pressure, the inlet vortex increases with the polymer concentration and tends to be stable gradually. For a relatively large reverse pressure, the vortex size first increases and then decreases with the polymer concentration.
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Key words:
- non-Newtonian fluid /
- microfluidic channel /
- superposition principle /
- instability /
- electroosmotic flow
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图 3 p=0 Pa, Cp=300 ppm, E=20 V，不同时刻的流线
注 为了解释图中的颜色，读者可以参考本文的电子网页版本，后同.
Figure 3. For p=0 Pa, Cp=300 ppm, E=20 V, the streamlines at different moments
图 4 pout=3 Pa, Cp=300 ppm, E=20 V，不同时刻的流线
Figure 4. For pout=3 Pa, Cp=300 ppm, E=20 V, the streamlines at different moments
图 5 3个不同位置的速度随时间的变化
Figure 5. The change of the velocity with time at 3 different locations
图 7 Cp=300 ppm，入口处电势E=20 V，t=0.8 s时刻下的流线，pout=0 Pa，采用不同的进口压力
Figure 7. For Cp=300 ppm, entrance potential E=20 V, the streamlines at t=0.8 s, pout=0 Pa, with different inlet pressures
图 9 E=20 V, Cp=300 ppm: 涡流大小随时间大小波动和不同出口压力下涡流的平均大小
Figure 9. For E=20 V, Cp=300 ppm: the vortex current size changing with time and the vortex current sizes under different outlet pressures
图 10 E=20 V，涡流大小随聚合物浓度的变化
Figure 10. For E=20 V, the change of the vortex size with the polymer concentration
图 11 通道中点速度的离散系数
Figure 11. The dispersion coefficient of the midpoint velocity of the channel
图 12 pout=5 Pa，沿y轴的速度分布
Figure 12. The velocity distributions along the y- axis, pout=5 Pa
表 1 模型部分参数
Table 1. Numerical simulation parameters
parameter name value ρ/(kg/m3) 1 000 ηs/(Pa·s) 0.001 E0/(V/m) 20 000 ζ/mV -110 C0/(mol/m3) 0.01 T/K 300 
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