Fluid flow phenomena in microfluidic devices are generally in the laminar regime with very low Reynolds numbers (<10). As a result, the mixing rate is controlled by the rate of diffusion. Because of the limited area available in lab-on-a-chip devices, innovative methods need to be employed to achieve the desired extent of fluid mixing. These include winding serpentine channels and complex multiplexing structures to provide increased residence time as well as added mixing due to bend-induced vortices. These systems, as well as active mixing based devices such as the bubble pump (shown below) can be easily modeled and optimized using CFD-ACE+.