Abstract
In micromixer devices, laminar characteristics of the flow domain and small diffusion constants of the fluid samples that are mixed characterize the mixing process. The advection dominant flow and transport processes that develop in these devices not only create significant challenges for numerical solution of the problem, but they are also the source of numerical errors which may lead to confusing performance evaluations that are reported in the literature. In this study, the finite volume method (FVM) and finite element method (FEM) are used to characterize these errors and critical issues in numerical performance evaluations are highlighted. In this study, we used numerical methods to evaluate the mixing characteristics of a typical T-shape passive micromixer for several flow and transport parameters using both FEM and FVM, although the numerical procedures described are also equally applicable to other geometric designs as well. The outcome of the study shows that the type of stabilization technique used in FEM is very important and should be documented and reported. Otherwise, erroneous mixing performance may be reported since the added artificial diffusion may significantly affect the mixing performance in the device. Similarly, when FVM methods are used, numerical diffusion errors may become important for certain unstructured discretization techniques that are used in the idealization of the solution domain. This point needs to be also analyzed and reported when FVM is used in performance evaluation of micromixer devices. The focus of this study is not on improving the mixing performance of micromixers. Instead, we highlight the bench scale characteristics of the solutions and the mixing evaluation procedures used when FVM and FEM are employed.
Highlights
During the past two decades, numerous experimental and numerical modeling studies have been performed for the design of microfluidic devices in which various geometric designs are recommended to improve the mixing efficiency in these devices
Simulations showed that QUICK, MUSCL, and second-order upwind schemes showed oscillatory behaviors in some regions depending on the magnitude of the Reynolds number and grid size of structured prism and unstructured tetrahedral mesh types
Stable solutions were obtained for all mesh types, grid sizes, and Re scenarios using the first-order upwind scheme and the limitedLinear scheme, which is a type of total variation diminishing scheme (TVD) [14]
Summary
During the past two decades, numerous experimental and numerical modeling studies have been performed for the design of microfluidic devices in which various geometric designs are recommended to improve the mixing efficiency in these devices. Due to widespread use of microfluidic devices in diverse disciplines it is obvious that these studies will grow exponentially in the future with the main goal of improving the mixing performance. Micromixers are essential components of microfluidic systems [1] in which fluid mixing is developed in miniaturized devices. These devices are extensively used in chemical, biological, medical, and environmental applications [2,3]. Due to important advantages of passive micromixers [8,9], passive micromixers have been widely used and investigated by researchers in which improved flow, transport and mixing behavior of these devices are studied
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