Power-Law Fluid Droplet Dynamic Behaviors in T-Junction Micro-Channels With the Lattice Boltzmann Method
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摘要: 采用格子Boltzmann方法(LBM)研究了T型微通道内幂律流体液滴运动行为及其流型相图.主要研究了液滴幂律指数n对液滴破裂时颈部厚度、前端运动距离等形变特性以及流型相图的影响.数值结果表明,幂律流体液滴在T型微通道内存在阻塞破裂、隧道破裂以及不破裂三种流型.在阻塞破裂过程中,液滴颈部厚度随时间逐渐减小,且n越大,液滴颈部厚度随时间减小得越慢.同时液滴前端运动距离随时间线性增加,且随液滴幂律指数n增加,液滴破裂时前端运动距离越长.在隧道破裂过程中,液滴颈部厚度也随时间逐渐减小,与阻塞破裂相似,n越大液滴颈部厚度减小得越慢.与阻塞破裂相比,液滴隧道破裂时对应的临界颈部厚度有所增加,且液滴前端运动距离随时间先快速增加,然后再缓慢增加,隧道宽度随时间近似呈对数增长.此外,液滴未破裂时液滴颈部厚度以及液滴前端运动距离出现波动现象.液滴的幂律指数n越大,液滴越容易破裂,但越不容易达到阻塞破裂.根据数值模拟结果得到了各流型相图之间幂函数形式临界分界线的拟合公式,该拟合公式可以预测不同流型.Abstract: The dynamic behavior of a power-law fluid droplet passing through a T-junction micro-channel and phase diagrams of droplet flow patterns were studied with the lattice Boltzmann method. The effects of power-law exponent n on the droplet deformation characteristics including the neck thickness, the droplet motion distance and phase diagrams of droplet flow patterns were addressed. The numerical results show that, there exist 3 flow patterns for power-law droplets in T-junction micro-channels, i.e., breakup with obstruction, breakup with a tunnel and non-breakup. In the case of breakup with obstruction, the droplet neck thickness decreases with time during the evolution process, and the decrease rate drops with n.At the same time, the droplet tip motion distance increases linearly with time during the evolution process, and the distance also increases with n.In the case of breakup with a tunnel, the droplet neck thickness decreases with time, and the decrease rate drops with n.However, the droplet tip motion distance increases rapidly at first and then slowly, the droplet-wall gap width grows approximately logarithmically with time. Furthermore, the fluctuations of both the droplet neck thickness and the droplet tip motion distance occur in the non-breakup pattern of the droplet. Moreover, it is easier to break up a droplet with a larger value of power-law index n,while it is hard to reach the breakup with obstruction in this case. Eventually, several phase diagrams with power-law correlations for droplet flow patterns were obtained. The fitting functions can be used to describe the critical boundary lines between different flow patterns.
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Key words:
- power-law 2-phase fluid /
- T-junction micro-channel /
- droplet breakup /
- micro-fluidic
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