十字型微通道中非定常分散相速度下液滴生成的数值分析

Numerical Simulation of Droplet Generation in Cross-Junction Microchannel under Changing Dispersion Phase Velocities

微液滴因其独特的流体力学特性和尺寸效应,在许多领域得到了广泛的应用。在制备微液滴时常使用蠕动泵为流体提供流动推动力。实际上,当时间尺度足够小时,蠕动泵提供的推动力是呈一定周期性变化的,这对液滴的生成来说是一种周期性的扰动。为研究周期性扰动对十字型微通道内液滴生成的影响,本文基于经过验证的模型,在分散相入口流速为时间的正弦函数条件下对液滴生成情况进行了数值模拟。模拟采用流体体积(VOF)模型,以硅油为连续相、水为分散相,首先模拟了两相流体入口流速均为0.01 m×s^(-1)的工况,得到液滴生成时间为0.08 s。导入周期分别为0.04、0.08、0.12、0.16 s以及振幅分别为0.0025、0.005、0.0075、0.01的正弦函数作为分散相入口流速,模拟不同条件下液滴的尺寸和生成时间。模拟结果表明,当正弦函数周期≤0.08 s时,改变周期和振幅对液滴尺寸和生成时间的影响较小;当正弦函数周期大于0.08 s时,液滴尺寸和生成时间会呈现周期性变化。而正弦函数的振幅对液滴的生成影响不明显,只对液滴生成达到稳定状态的时间有影响。

Micro-droplets with excellent physical properties and size effects are widely used in different fields. Peristaltic pumps are often used for droplet generation. The thrust force of pumps is periodic as a periodic disturbance when the time scale is short enough. Numerical simulation based on a validated model was applied to study the periodic disturbance effects on droplet generation in a cross-junction microchannel. A volume of fluid（VOF） method was adopted with the continuous phase of silicon oil and the disperse phase of water. When the velocity of the continuous and dispersed phases is both 0.01 m×s^（-1）, the droplet generation time is 0.08 s. Sine functions with cycles of 0.04, 0.08, 0.12 and 0.16 s and amplitudes of 0.0025, 0.005, 0.0075 and0.01 were imported as the inlet velocity of the disperse phase. Droplet sizes and generation times were obtained by simulating different flow processes. The results show that when the cycle is less than 0.08 s, changes of cycle time and amplitude have few effects on droplet size and generation time. However, when the cycle time is larger than 0.08 s, droplet size and generation time change periodically. Furthermore, amplitude has few effects on droplet generation