Design And Numerical Simulation Of Passive Micromixers

Miniaturization is an important development direction of today’s science and technology production. With the rapid development and wide application of MEMS, microfluidic system based on micromachining technology can realize the "personalization" of analysis laboratory under the lower requirements of analyst. Micromixers and microfluidics mixing as the research focus of microfluidic system, which have been widely applied in biomedical medicine, electrical machinery, materials science, environmental health, military defense, aerospace and other fields. In the micro scale, because of low Reynolds Numbers, the microfluid in the microchannels exists in the form of laminar flow in the microchannels, which is not conducive to rapid and efficient mixing of two fluids, so the mixing index is low. Therefore, the study of efficient micromixers has currently become one hot research topic in the microfluidic field.Different from active micromixers, Passive micromixers do not need the external power input, and the mixing process is controlled by the design of complex three-dimensional structure of the microchannels. Common passive micromixers by optimizing the structures are designed to cause the chaotic convection between two or more fluids, and to increase the effective contact area between the fluid for enhancing the mixing process, which can obtain high mixing intensity of the microfluidic in the limited length for a given microchannels. This article introduces three passive microfluidic mixers, periodic twisted micromixer based on chaotic convection, high reflux passive micromixer, biomimetic network structure micromixer respectively. We have discussed a number of specific models for every microfluidic mixer, and discussed the flow and mixing of each microfluidic along their microchannel, as well as the impact of different Re numbers microchannel for mixed intensity. Simulation results show that with the T-type mixer as a comparison, the three mixers can effectively improve the mixing intensity in the range of Re that calculated. Specific results are as follows:1. In the asymmetric distortion micromixer arranges two periods channel structures, up, down, left, and right four curved respectively. The microfluidic in the main channels are successively forming shrink, expand, flip, and shrinkage structure, extension structure, and flip structure can intensify the collision imbalance of fluids that flowing into next curved channel, which expand the cross-section between the two streams and increase mixing intensity. FLUENT simulation results show that2-mixing intensity is higher than other micromixer structurals, and the length of each section of the curved channels also has certain influence on the mixing intensity, short and long curved channel are not conducive to two fluids mixing. When each section of the curved channel L=153.33μm, contact area of two fluids is the biggest, so the mixing intensity higher than other micromixer models.2. The micromixer designs symmetrical feedback channels by Coanda effect to cause reflux. The refluxes in its feedback channels lead to a longer mixing time and improve the formation of the vortexes, which then strengthen the diffusion and convection in the micromixer. The reflux rate and the mixing index of the micromixer are improved by optimizing the shape of two feedback channels and the inlet size of the mixing chamber. The performance of the proposed micromixer is examined by using the simulation software Fluent. Simulation results indicate that the reflux rate and the mixing index are only dependent on the Reynolds number for a specified micromixer. The reflux rate and the mixing index will both be improved by increasing the Reynolds number. Based on the observations with different angle parameters, a reasonable choice of the angel to achieve satisfied reflux rate and the mixing index is10°.3. According to the principles of biological tissue morphology, we design several separation and recombinant network micromixers using bionics method in the tree fractal structure. FLUENT simulation results show that the mixing index in asymmetrical circular structure is higher than that in symmetrical butterfly mixer. In the micromixers with a given finite length, two or four dislocation channels and two relative channels arranged in the double stage T-type channels of biomimetic straight achieve the substantially equal mixing index; two fluid micromixer equal; when the length and width of two dislocation channels increased2times respectively, the mixing index in all microfluidic mixers is improved.