【作者】 林莹；

【导师】 王正东； 于新海；

【作者基本信息】 华东理工大学 ， 化工过程机械， 2011， 博士

【摘要】 新兴的微化工机械系统(MCMS)以其快速的传质传热能力、模块化的紧凑结构倍受关注,但是由宏观向微观世界过渡存在的许多问题极大地限制了微尺度传递理论的完整建立。随着特征尺度的微小化,无论是与特征尺寸成高次方比例关系的惯性力、电磁力等,还是与特征尺寸成低次方比例关系的粘性力、弹性力、表面张力、静电力等都可能导致微观传递现象的显著不同,对这类尺度效应的研究是完善微尺度传递理论的关键。高空间分辨率、高精度的微流体非接触测量技术是开展以上研究的关键。为此,本文提出了基于共焦显微拉曼光谱的微流体温度场和浓度场高精度测量方法,研究了微流体单相对流传热及微流体液液扩散；基于微流体的强化混合特点,研制了两种混沌对流机制共同作用的高效微混合器。本文主要工作及获得成果如下：(1)基于共焦显微拉曼光谱微流体测量的激光热效应研究采用共焦显微拉曼进行微流体测量时,若使用金相镜头,激光穿透芯片上表面聚焦到微通道内液体样品时发生折射、导致焦点变形,严重地降低了空间分辨率,特别是深度分辨率。实验发现,若使用硅基芯片,当变形的焦点覆盖了微通道底面时,以硅材料形成的通道底表面便大量吸收可见光波长的激光的能量,出现激光热效应,产生温升。本文首次通过实验和流体动力学数值模拟(CFD)对拉曼测量过程中的激光热效应进行系统研究。通过数值模拟,正交分析考察了11个影响因素的敏感性,发现表面功率和光照区域直径对温升影响最为显著；通过实验,发现表面功率对该效应的影响极为显著,但简单降低表面功率并不是解决激光热效应的根本方法；最后,关联主要影响因素,建立了用于计算微流体拉曼测量时激光热效应造成的最大局部温升的关联式。(2)基于拉曼温度测量的对流传热条件下微通道壁面轴向导热影响的研究建立了基于共焦显微拉曼光谱的微尺度水温测量方法,搭建了微流体单相对流传热实验系统。将实验与CFD研究相结合,深入研究了微尺度下轴向导热问题的影响。发现轴向导热的存在使得在通道入口处壁面热通量最大、液温和壁温均呈非线性发展；局部出现液温高于壁温的情况,使得热量反向由流体传递给固体,导致局部Nu数曲线出现奇点,奇点位置随着雷诺数的增大往出口处移动;入口效应与轴向导热的共同作用使得Nu数随着Re数的增大而增大。(3)基于拉曼浓度测量的微流体液液扩散系数测量及扩散界面控制通过CFD优化了微通道截面结构设计,减小了由于分辨率下降导致的微流体浓度测量误差。制作了Y型微通道,提出添加铝薄膜消除激光热效应的有效方法。建立了基于拉曼浓度测量的不同温度下液液扩散系数的测量方法。相比传统扩散系数测量方法,该方法可实现多个温度下扩散系数的连续测量,更为方便、高效、准确。开发了试差控制程序,基于微流体拉曼浓度测量,建立了层流流体扩散界面的控制方法,实现了物性未知的微流体扩散界面的准确控制。(4)由两种混沌对流机制共同作用的高效微混合器研制针对微化工机械系统的需求,研制了由两种混沌对流机制共同作用的不锈钢微混合器。它具有方波形结构和周期性排布的方槽。经CFD计算发现,方波形结构产生层流反复循环机制、周期方槽产生流动扭曲机制。方槽设置在紧接着方波形转角的位置能够产生相对高的混合效率,仅带来微弱的压降上升。低雷诺数下流动扭曲机制占主导地位,随着雷诺数的增大层流反复循环机制贡献逐渐加大,并与前一机制共同作用、强化混合。采用一种快速平行竞争反应定量评价其性能,发现该微混合器的最佳工作范围是雷诺数约30-220,在这范围内在保证高混合效率时、压降小能耗低。相比几个商业微混合器,该混合器易制造、可以低成本进行批量生产,且不锈钢基体能适用于许多恶劣环境,如高温、高压、强腐蚀等。更多还原

【Abstract】 Micro-Chemo-Mechanical systems (MCMS) have attracted great attention because of their high efficiency heat and mass transfer and compactness. However, problems associated with the transition from macroscale to microscale have limited the establishment of microscale transfer theory. As the characteristic scale is miniaturized, either inertial and electromagnetic forces that are directly proportional to the high power of the size, or surface tension and viscous, elastic and electrostatic forces that are directly proportional to the low power of the size, probably lead to the significant difference of the microscale transfer phenomena. The researches on these scale effects are crucial for the improvement of the microscale transfer theory. Noninvasive measurement with high spatial resolution and high accuracy is the key to carry out those researches. In this context, a method to accurately measure the microfluid temperature and concentration fields based on confocal Raman microscope was proposed in this paper. The single-phase convective heat transfer process and the liquid diffusion were investigated. Based on the feature of the microfluid enhanced mixing, a high-efficiency micromixer employing two chaotic convective mechanisms was also developed. The main work and results of this paper are as follows:(1) Effect of laser induced heating on microfluid Raman measurementIn the microfluid measurement based on confocal Raman microscope, if metallurgic objectives are adopted, the refraction will occurr when the laser penetrates the top surface of the microchip and focuses on the liquid sample in the microchannel, leading to the focus distortion. This drastically reduces the spatial resolution, especially the depth resolution. Experiments found when the distorted focus covered the channel bottom of the silicon chip, the chip absorbed a great portion of the laser energy. This was termed laser heating effect and could result in the temperature-rise. The laser heating effect in the Raman measurement was studied for the first time in this paper. Via omputational fluid dynamics (CFD) simulations, the sensitivity of 11 factors was investigated with orthogonal analysis (OA), and the surface power and illuminated area diameter were found to have the most significant influence on the temperature-rise. The siginicant influence of the surface power on the heating effect was also observed from experiements, and simply lowering the surface power was not the efficient approach to eliminate the heating effect. Finally, a correlation to evaluate the maximum local temperature-rise in the microfluid Raman measurement was proposed.(2) Research on microchannel wall axial heat conduction under single-phase convective heat transfer condition based on Raman temperature measurementThe water temperature measurement in microscale based on the confocal Raman microscope was proposed, and the experimental system for microfluid single-phase convective heat transfer was established. The experiments were combined with CFD simulations to investigate the axial heat condution in microscale. It was found that the axial heat condution led to a maximum heat flux at the channel inlet, and the nonlinear development of fluid and wall temperatures. In some locations, the fluid temperature was even higher than the wall temperature, and heat would, therefore, transferred from fluid to the channel wall. In this case, a singular point emerged in the local Nusselt numer (Nu) curve, and would move toward the inlet as the Reynolds number (Re) was increased. The Nu increased with the increased Re, which was caused by both the entrance effect and axial heat conduction caused.(3) Microfluid liquid diffusion coefficient measurement and interface control based on Raman concentration measurementWith the optimum microchip design obtained from CFD simulations, the microfluid concentration measurement errors caused by the decreased resolution were reduced. A method for measuring the liquid diffusion coefficient at various temperatures based on the Raman concentration measurement was established. This method reallized the continuous diffusion coefficient measurement at various temperatures, and was more convenient, efficient and accurate, compared with conventional methods for diffusion coefficient measurement. Based on the Raman concentration measurement, the laminar flow fluid interface control method was proposed, using a trial-and-error control program. The accurate diffusion interface control of the micro fluids without sample property information was reallized, using this method.(4) High efficiency micromixer employing two chaotic convective mechanismsA high efficiency stainless steel micromixer employing two chaotic advective mechanisms was developed for MCMS. The micromixer featured a square-wave structure and periodic cubic grooves. CFD results revealed that the square-wave structure induced the laminar recirculation mechanism, and the periodic cubic grooves produced the flow stretching mechanism. The configuration of grooves locating right after the turns of the square-wave structure yielded the relatively higher mixing quality and minor pressure drop increase. At low Re, the flow stretching was dominant. As Re rose, the laminar recirculation contributed increasingly more and the two mechanisms became jointly influencing on the mixing so that the mixing was remarkably enhanced. A parallel competitive reaction was utilized to evaluate the performance of the proposed micromixer. The optimum Re range for its operation was 30-220. Within this range, the high mixing quality and low energy consumption could be ensured. Compared with commercial micromixers, the present micromixer was more easily-fabricated to facilitate the large-scale production. Besides, it is competent for applications with adverse circumstances, such as high temperature and pressure, and strong corrosion.更多还原