An overview of the concepts of passive and active mixing in micro mixers

This paper provides an overview of micro structured mixer devices and their mixing principles for miscible liquids (and gases). The explanation of common mixing element designs, mixing characterization techniques, and application areas are all included. The mixing principles used may be split into two categories: passive and active mixing, which depend on either pumping energy or the supply of additional external energy to accomplish mixing. Devices and methods such as Y- and T-type flow-mixers, multi-laminating-, split-and-recombine-, chaotic-, jet colliding-, recirculation flow-mixers, and others are addressed in terms of passive mixing. Time-pulsing flow caused by a periodic shift in pumping energy or electrical fields, acoustic fluid shaking, ultrasound, electro wetting-based droplet shaking, micro stirrers, and other methods may all be used to achieve active mixing.