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Alternative TitleInvestigation on gas-liquid flow charateristcs, mass transfer and mixing performance in micro-channe
Thesis Advisor杨超
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword微通道   气液两相流   阻力降   混合   传质
Abstract伴随着微电子机械系统的高速发展而出现的微流控技术,在混合、乳化和结晶等化工过程中具有广阔的应用前景。本文针对微通道反应器内气液两相体系开展了气液两相流体流动、传递特性以及混合规律的基础研究。 采用DVR(digital video record)可视化系统研究了水平放置的错流T型微通道内气液两相流动结构和流型转换规律。观察到了弹状流、弹状-环状流、环状流以及分层流现象,建立了以气液两相雷诺数之比为横坐标、液相毛细数为纵坐标的流型图绘制方法。考察了不同实验体系的液相流体物性以及通道表面浸润性对于流动过程的影响,在对流动结构以及流型转换的定性研究基础上,首次提出了包含流体物性以及通道表面浸润性影响在内的转换边界的预测模型,模型具有较好的预测精度。 在考察流动阻力降的变化规律时,发现通道表面浸润性对于微尺度下液相流动阻力降有明显的影响且液相流动的范宁摩擦因子比经典预测模型的预测值偏高。根据流动结构特点将气液两相流动区域分为分散气相以及连续气相两种情况进行研究,将通道润湿性能的影响分别引入经典的Hagen-Poiseuille方程以及离析模型,分别对上述两种情况下阻力降进行预测,新提出的修正模型具有良好的预测精度。采用溶氧法对微通道内气液两相传质过程进行研究,发现通道表面浸润性越强其内部液相体积传质系数越高,分别提出了分散气相和连续气相流动的体积传质系数的预测模型。 分别采用Micro-PIV技术和化学反应探针法对微通道内流体混合规律进行了研究,发现通道入口夹角和表面浸润性对微观混合效果均会产生影响。通道润湿性能越弱,微观混合效果越理想;而适宜的通道进样角度为90°至180°。设计开发了一种新型螺旋式微混合器,与常见的直通道微混合器相比,这种新型的混合器具有更高效的混合效果。
Other AbstractMicrofludics that is born along with Micro-Electro-Mechanical-Systems has spectacular application prospect in chemical processes such as mixing, emulsion and crystallization. Fundamental investigation of flow characteristics, mass transfer performance and mixing efficiency of gas-liquid systems in micro-channels is carried out in this dissertation. Flow patterns and flow regime transition boundaries in horizontal cross-flow T-shape micro-channels are studied. The flow patterns including slug flow, slug-annular flow, annular flow and stratified flow are captured by a DVR (digital video record) system. Novel flow maps in terms of ReG/ReL and Ca are established. Moreover, the influence of fluid property and the surface wettability of channel wall on flow characteristics are investigated. A universal model that has incorporated first time the effect of surface wettability is developed to describe the flow patterns transition boundaries. The predicted results are in good agreement with the experimental data. The research results of pressure drop show that the pressure drop in microfluidic device is closely related to the wettability of channel wall. The Fanning friction factor of liquid flow in a micro-channel is a little higher than the classic theory. For gas-liquid two-phase flows, all the flow patterns are divided into two categories: the gas phase dispersed flow (slug flow in this work) and the gas phase continuous flow. (slug-annular flow, annular flow and stratified flow in this work). A modified Hagen-Poiseuille equation and an improved separated model are developed to predict the pressure drop of gas-liquid flows of these two categories respectively. The effect of surface wettability is firstly incorporated into the present models, and the correlations fit the experimental data well. The oxygen dissolution method is used to study the mass transfer performance in micro-channels. It can be concluded that the volumetric mass transfer coefficient increases as the wettability of channel wall is enhanced. Empirical correlations of volumetric mass transfer coefficient with We and contact angle are also proposed, which show good agreement with experimental results. A simple micro-PIV system and a chemical probe method are used to explore the velocity distribution and mixing performance in micro-channels. Micromixing efficiency decreases as the wettability of channel wall is enhanced. The optimal angle of inlet intersection is between 90° to 180°. According to the mechanism of mixing processes in micro-channels, a novel spiral micro-mixer with baffles is developed. Compared to the straight and U-shape micro-mixers, the micromixing performance of the new spiral micro-mixer is much better.
Document Type学位论文
Recommended Citation
GB/T 7714
王曦. 微通道内气液流体流动、传质及混合特性的研究[D]. 中国科学院研究生院,2013.
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