摘要
微系统是现代制造技术发展的一个重要方向,而微混合器是微系统的一个重要组成部分,得到研究者们的日益关注。为了加快我国自主设计开发高效、快速的微混合器的步伐,本文基于数值模拟技术,对不同参数下微混合器性能进行了系统研究。
基于Fluent软件平台,采用循环计算技术的策略,对不同性质流体在简单式(SCM)、交错式(SHM)与分合式(SRM)微混合器的混合性能进行了数值模拟研究。其结果表明:
1)在低雷诺数下的SCM,依靠流体的分子扩散作用实现混合,流体的扩散系数越大以及接触时间越长,其混合不均匀度越小。
2)实际刻蚀微通道的压降P与流体Re数成线性关系,与截面形状因子η成幂指数关系,即截面形状的影响比雷诺数的影响大。
3) SHM内流体的Re数对Sc数较小流体的混合不均匀度的影响较大,对Sc数较大的流体,Re数的影响作用较小。这说明与分子扩散作用相比,SHM的混沌对流作用的影响较大,当Re数增大到一定程度后,流体的混合主要由混沌对流作用决定。
4)对于SRM,流体分子扩散作用和分合扩散作用共同影响流体的混合,流体Re数对W-SRM的混合性能影响较大,而对T-SRM的影响较小。在SRM的设计中,为了提高分合式被动微混合器的混合性能,应该把分合结构设计成垂直状,使两股流体间产生压缩作用以及适当减小汇合通道的长度以保持流体的压缩混合状态。
总的来说,SHM与SRM的混合性能比SCM的混合性能要好得多;在流体Pe数小于50000的情况下,SRM的混合性能比SHM的混合性能好;而随着Pe数的继续增大,将出现SHM的混合性能优于SRM的现象。
Microsystem is one of important developing field of modern manufacture technology, and micromixer is a critical part of microsystem, which have attracted more and more attention of researches. In order to increase the speed of designing high efficiency and quick mciromixer, mixing performance of micromixer under different parameters is systematically investigated in this paper.
By Fluent, using circulating skill, mixing performance of different property fluid in simple micromixers(SCM), Staggered herringbone micromixers (SHM) and Split-Recombining micromixers(SRM) are simulated . The main conclusions show as following:
1) Mixing performance of SCM depends on molecular diffusion at low Re, the bigger diffusion coefficient of fluid and the longer fluid diffusion time is, the lower mixing nonuniform degree is.
2) Pressure drop of real microchannels by wet corrosion is linear with fluid Re and is power exponent with cross shape factorη, which means cross shape factor's effect is intenser than Re's.
3) As to SHM, the smaller Sc of fluid is, the larger influence of Re on fluidic mixing nonuniform degree is, which indicates that influence of chaotic convection is bigger than that of molecular diffusion. If Re increase up to some extent, fluid mixing will totally rely on chaotic convection.
4) As to SRM, fluid molecular diffusion and split-recombining diffusion affect fluid mixing simultaneously; Re has bigger effect on mixing performance of W-SRM compared to T-SRM. In order to improve mixing performance of split-recombine passive micromixer, the split-recombine structure should ensure the direction of two parts of fluid is vertical to each other, which makes one part of fluid hit the other one, at the same time, length of recombining channel should be decreased, which makes sure fluids have statue of hitting.
Generally, mixing performance of SHM is greater than that of SCM; when Pe≤50000, mixing performance of SRM is more excellent than that of SHM, with the Pe adding continuously, phenomenon of SHM mixing performance is more superiority than that of W-SRM.
引文
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