Improvement of the mixing quality of low Reynolds number flows in micro-dimensional devices is essential. This paper investigates the optimization of the effective parameters and their effects on the mixing quality in a two-dimensional active micromixer. The micromixer mixes fluids with different concentrations entering into a microchannel from different inlets by means of four microelectrodes placed on the walls of a mixing chamber. A time-dependent electric field is applied, and the resulting electroosmotic force perturbs the parallel streamlines in the otherwise highly ordered laminar flow. The governing equations are numerically solved using the finite element-based COMSOL Multiphysics (Version 5.2a) software. The electroosmotic actuated active micromixer was numerically studied for various values of inlet velocity, phase lag, frequency, and voltage amplitude. Once the optimum values of the effective parameters are obtained for the original micromixer, they are applied to the micromixers having different obstacle shape inside the mixing chamber. The results showed that the mixing quality strongly depends on the inlet velocity of the fluids, the electrodes phase lag, the frequency, and the voltage amplitude. In addition, the mixing quality does not depend on obstacle shape when the optimum values of these parameters were used.
Droplet splitting as a significant feature of droplet-based microfluidic systems has been widely employed in biotechnology, biomedical engineering, tissue engineering, and it has been preferred over continuous flow systems. In the present paper, two-dimensional numerical simulations have been done to examine the asymmetrical droplet splitting process. The two-phase level set method (LSM) has been predicted to analyze the mechanism of droplet formation and droplet splitting in immiscible liquid/liquid two-phase flow in the branched T-junction microchannel. Governing equations on flow field have been discretized and solved using finite element-based COMSOL Multiphysics software (version 5.3a). Obtained numerical results were validated by experimental data reported in the literature which show acceptable agreement. The model was developed to simulate the mechanism of droplet splitting at the branched T-junction microchannel. This study provides a passive technique to asymmetrically split up microdroplets at the downstream T-junctions. The results show that outlet branches’ pressure gradient affects the droplet splitting. Specifically, it has been shown that the splitting ratio increases by increasing the length ratio, and equal droplet splitting can be achieved where the ratio is LL/ Lu = 1. We have used two outlet branches having the same width but different lengths to create the required pressure gradient. As the length ratio of the outlet branches increases, the diameter ratio increases as well.
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