1 Copyright © 2008 by ASME Proceeding of MNHT2008 Micro/Nanoscale Heat Transfer International Conference January 6-9, 2008, Tainan, Taiwan MNHT2008-52178 Numerical Simulation of Fluid Mixing in the Ribbed Microchannels V. Esfahanian School of mechanical engineering University of Tehran, Iran evahid@ut.ac.ir F. Kowsary School of mechanical engineering University of Tehran, Iran fkowsari@ut.ac.ir M. Rezaei Barmi School of mechanical engineering University of Tehran, Iran mrezaeibarmi@ut.ac.ir N. Noroozi School of mechanical engineering University of Tehran, Iran nadernoroozi@ut.ac.ir ABSTRACT Micromixers have received much interest as essential part of microfluidic devices. Therefore, enhancement of mixing quality has gained a lot of attention in recent years. In the present study, improvement of mixing quality for two different miscible liquids is considered in passive micromixers. Numerical approach is based on a second order finite volume Jameson scheme in order to solve two dimensional incompressible Navier-Stocks and mass transport equations by implementing artificial compressibility. Mixing quality is influenced by Reynolds and Schmitt numbers as well as size and location of the ribs. Diffusion mechanism has the main role for mixing in micro scale fluid flows; therefore, increasing Peclet number leads to extend mixing time. In order to enhance mixing quality, ribs are used in different locations through the microchannel which cause more instability in the fluid flow and leads to a better mixing. The Reynolds number is constant while the Schmitt number is in the range of 10 to 100. However, in order to laminar fluid flow, ribs just have an influence near itself and faraway, mixing mechanism return to earlier state. Therefore, in low Reynolds numbers they have no effective influence. When Reynolds number increase, flow instability that is created by different ribs leads to a better mixing. INTRODUCTION The importance of microfluidic and nanofluidic devices has increased in the recent years. In order to complicate and costly construction of devices in the small scales, need to modeling and simulation of phenomena before construction is appeared necessary. Microfluidic devices have diverse parts which do special task. Micromixers play a significant role in micro chemical processing and are employed in a multitude of tasks, including blending, emulsification and suspension, as well as for chemical reaction and also in combination with integrated heat exchangers. Due to the small dimensions of the microchannels, the flow is mostly laminar and mixing is therefore limited by molecular diffusion. Some biological analysis requires to be completely mixed before the reaction has carried out considerably; therefore, simulation and optimization of micromixer with minimum mixing time or length before construction is necessitated. Due to the relatively young age of microreactor engineering, common design rules for micromixers have not yet been developed. However, one can see that apart from their minute size, microreactors are just continuous laminar flow reactors, which suggests that design approaches for mixing in microchannels could be dealt with in a similar manner to that of laminar mixing in macro scale pipe flow. In the laminar flow, the streamlines are parallel and there is no convective mixing in the radial or tangential directions. Thus in order to disturb the flow and facilitate mixing in laminar pipeline flow, in-line devices or static mixers is inserted into the microchannel. The design of micromixers, which are comparatively similar devices at a much smaller scale, can be looked at in the same manner, whereby the aim is to provide sufficient spatial and temporal mixing as fast as possible. Over the past few years, several studies using different types of micromixers have been performed with the focus on characterizing the micromixer performance using various experimental techniques, such as fluorescent microscopy and special chemical reactions, as well as computational fluid dynamic simulations to draw species trajectories [1-7]. In the present work, numerical simulation of fluid mixing in the two dimensional micromixers using finite volume Jameson scheme is investigated. Therefore, two dimensional Navier- Stocks equations are solved by applying artificial