Data figure calculations from New regimes of dispersion in microfluidics as mediated by travelling temperature waves

We unveil new regimes of dispersion in miniaturized fluidic devices, by considering fluid flow triggered by a travelling temperature wave. When a temperature wave travels along a channel wall, it alters the density and viscosity of the adjacent fluid periodically. Successive expansion–contraction of the fluid volume through a spatio-temporally evolving viscosity field generates a net fluidic current. Based on the temporal evolution of the axial dispersion coefficient, new regimes of dispersion—such as a short-time ‘oscillating regime’ and a large-time ‘stable regime’—have been identified, which are absent in traditionally addressed flows through miniaturized fluidic devices. Our analysis reveals that the oscillation of axial dispersion persists until the variance of species concentration becomes equal to half of the square of the wavelength of the thermal wave. The time period of oscillation in the dispersion coefficient turns out to be a unique function of the thermal wavelength and net flow velocity induced by thermoviscous pumping. The results of this study are likely to contribute towards the improvement of microscale systems that are subjected to periodic temperature variations, including microreactors and DNA amplification devices.

本研究针对由行进温度波（travelling temperature wave）触发的流体流动，揭示了微型流体装置中全新的扩散态。当温度波沿通道壁传播时，会周期性改变邻近流体的密度与粘度；流体体积在时空演化的粘度场中持续经历膨胀与收缩过程，由此产生净流体流。基于轴向扩散系数（axial dispersion coefficient）的时间演化特性，本研究识别出两类此前在传统微型流体流动研究中未被观测到的全新扩散态：短时振荡态与长时稳态。分析结果表明，轴向扩散的振荡现象将持续至物质浓度方差等于热波波长平方的一半时为止。扩散系数的振荡周期是热波波长与热粘性泵送（thermoviscous pumping）诱导的净流速的独有函数。本研究成果有望助力受周期性温度变化影响的微尺度系统（包括微反应器（microreactors）与DNA扩增装置（DNA amplification devices））的性能优化。