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Simulation of Droplet-based Microfluidics Devices using a Volume of Fluid (VOF) Approach

This paper demonstrates that Computational Fluid Dynamics (CFD) simulations can be used to study important physical phenomena in Droplet-based Microfluidics Devices. The Volume of Fluid (TruVOF ® ) method in FLOW-3D ® (a general purpose CFD software) has been used to study three devices. The first example is a T-junction where a continuous flow in one channel is sheared off by a dispersion flow in the perpendicular channel. The flow patterns are closely examined and compared with experiments. The second example is a study of a co-flowing device where the formation and breakup of bubbles is simulated. The effect of viscosity on bubble formation is also analyzed. In these two examples the bubble size and frequency are related to important parameters like the width of the channel (w) and the ratio of the flow rates in the two streams (Qg/Ql). These relationships are also corroborated with experimental data. The third example is the application of the TruVOF ® method in predicting phenomena such as electrowetting and electrophoresis. The contact angle is plotted against the voltage applied across a small water droplet on a dielectric material with known properties. The results are compared with the Young-Lippmann curve. The comparisons indicate a good agreement, except at the highest voltages where experiments indicate the presence of saturation effects that limit the reduction in the apparent contact angle.