Abstract
Chaotic mixing in three different types of curved-rectangular channels flow has been studied experimentally and numerically. Two walls of the channel (inner and top walls) rotate around the center of curvature and a pressure gradient are imposed in the direction toward the exit of the channel. This flow is a kind of Taylor-Dean flow. There are two parameters dominating the flow, the Dean number De (∝ the pressure gradient or the Reynolds number) and the Taylor number Tr (∝ the angular velocity of the wall rotation). In this paper, we analyze the physical mechanism of chaotic mixing in the Taylor-Dean flow by comparing experimental results and numerical ones. We produced three micromixer models of the curved channel, several centimeters long, with rectangular cross-section of a few millimeters side. The secondary flow is measured using laser induced fluorescence (LIF) method to examine secondary flow characteristics. Also we performed three-dimensional numerical simulations with the open source CFD solver, OpenFOAM, for the same configuration as the experimental system to study the mechanism of chaotic mixing. It is found that good mixing performance is obtained in the case of De ≤ 0.1 Tr, and it becomes more remarkable when the aspect ratio tends to large. And it is found that the mixing efficiency changes according to the aspect ratio and inflow condition.
Highlights
Great attention has been paid to the development of a micro-chemical-analysis device called the micro total analysis systems in the field of engineering
We performed three-dimensional numerical simulations with the open source CFD solver, OpenFOAM, for the same configuration as the experimental system to study the mechanism of chaotic mixing
Though in the paper by Hayamizu et al [14], it was shown that entanglement of path lines is important for Lagrangian chaos in a curved channel, the present paper may add additional information of the importance of vertical structures on the enhancement of mixing. We studied both experimentally and numerically the effect of varying the aspect ratio of the channel cross section on enhancement of mixing
Summary
Great attention has been paid to the development of a micro-chemical-analysis device called the micro total analysis systems (μTAS) in the field of engineering. The flow is in the very low Reynolds number region because of the microsize of the channel, where mechanical mixing by turbulence cannot be expected without a special artifice. A micromixer is needed to mix low-Reynolds-number flows efficiently. Stroock et al [1] studied a micromixer generating secondary flows in a channel by carving a ditch into the channel wall surface. Sato et al [2] made a micromixer that generates stronger secondary flows by carving ditches into the three wall surfaces of the channel. It has been shown that these methods are effective when the flow velocity is fast, the pressure loss becomes a serious problem in this case
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