Experimental and numerical study of mixing behavior inside droplets in microchannels



For the practical applications of droplet-based microfluidics, we have paid special attention to the complex hydrodynamics and mixing performance inside microdroplets and the profound process intensification when forcing the droplets to move in winding channels. In this work, experimental studies using micro laser induced fluorescence (μ-LIF) technique and three-dimensional simulation based on a multiphase, multicomponents lattice Boltzmann model approach were adopted. The simulation results clearly revealed that the mixing inside the droplet is due to the convection in symmetric vortices in the two hemispheres of the droplet and the diffusion between them. They also showed the fluids inside the droplet could be reoriented due to the winding effect. Three designs of winding channels were studied, where interesting results showed the similar effect of process intensification by breaking up the flow symmetry. The revealed flow mechanism and the mixing performance inside the droplet in droplet-based microfluidics should be helpful for microdevice design and optimization. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1801–1813, 2013