Simulation of miscible diffusive mixing in microchannels

The lattice Boltzmann (LB) method is used to simulate the flow field and subsequent analyte diffusion and convection of various analytes in a Y-shaped microchannel mixer, with a channel cross-section of 250 μm × 500 μm. This required a simulation code to be implemented that couples diffusive mass transfer with hydrodynamics, thus enabling a spatially varying viscosity that depends on a local analyte concentration. Where possible the simulation results were validated with 3D MRI experimental measurements of both the analyte concentration and the flow field in the microchannel; agreement is excellent. The simulation method is also able to quantify various expected physical observations, including the variation of diffusive dispersion due to the 3D velocity profile across the microchannel (butterfly effect), and the expected scaling laws for diffusive transport. The error resulting from employing a simplified 2D representation of the 3D microchannel for simulation purposes is also explored; typically this error is less than 3% of the maximum concentration.