Simulation study on the effect of hydro-active patches in passive micromixer geometry for fluid flow and mixing

The study of steady and unsteady microflows plays an important role in micromixing applications. In this paper, Computational Fluid Dynamics (CFD) simulations using OpenFOAM have been carried out to investigate mixing efficiency and flow characteristics with rectangular geometry of three different wall conditions. The geometries of the microchannels were rectangular with the dimensions of 4000 μ length, 1000 μ depth and 1000 μ width. The first channel does not have a hydro-active patch along the length of the channel. In the second channel, hydro-active patches of 1000 μ are placed symmetrically on the top and bottom along the length of the microchannel. In the third channel, hydro-active patches of 1000 μ are placed asymmetrically on the top and bottom along the length of the microchannel. A three-dimensional (3D) model was created for three geometries and simulations were performed to investigate the mixing effect for mixing two different fluids. The developed mathematical model was based on modified wall surface boundary conditions with an unsteady state of the flow field. The effect of introducing hydro-active patches in the form of symmetric boundary conditions led to a reduction in micromixer length approximately by a factor of three. The enhancement in the mixing efficiency in shorter lengths is due to surface modification, which significantly affects the unsteady behaviour of the flow field. In symmetric and asymmetric geometries with hydro-active patches, swirling vortexes were developed providing good mixing results.