Mixing is a process where two or more liquids or gas phase components are brought together and combined to form a uniform composition. Both turbulent and diffusive processes are typically employed to achieve the mixing action. As the scale of the process is reduced, diffusion becomes dominant. Microtechnology mixers are designed to bring together individual components for mixing with the smallest diffusional scales possible. Mixing is an important unit operation in the chemical and energy industry and can be found in combustors, microreactors, and adsorbing processes.
Micromixing technology has been developed in several different directions, but the common theme with most concepts is to rapidly bring together the constituents where a very small diffusive length scale exists for the final mixing step. Mixing in microchannel geometries has been studied in ‘‘Tee’’ sections, opposed microjets, channel flow through arrays of posts, and various interdigited designs. Mixing in converging channels and jet-in-cross-flow geometries has also been studied.
Practical micromixers have been developed and proven out using deep-etch photolithography (in silicon) where an interdigited arrangement yielded a length scale of 100 mm (distance between two streams). Note that the time for diffusional mixing is proportional to L 2 /D, where L is the distance between two mixing streams and D is the diffusion coefficient. Hence, it is important to reduce the device size to achieve rapid and complete mixing.
