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Thesis Advisor陈家镛 ; 毛在砂
Degree Grantor中国科学院研究生院
Abstract论文从理论和实验两个方面对萃取过程中的单液滴传质规律进行了研究,将计算流体动力学的手段用于稳态运动单液滴的传质过程的研究,在正交贴体坐标系中用流函数—涡函数耦合法分别在滴内外区域对Navier-Stokes方程联立求解。并构造出有界畸变函数,使数值解的精度得以很大提高。建立了单液滴两相传质的数学模型。并以真实形状的液滴为对象。根据数值计算得出的浓度分布来计算出传质系数和萃取分数。在实验中设计加工了可基本上消除终端凝并效应的实验装置,并进行了一系列实验。研究表明:数值模拟在中低雷诺数Re < 250时可以用来对一些体系的传质系数进行预测。这为实现快捷经济的数值“实验”方法取代部分传统的实验室实验,开辟了一条新的途径。
Other AbstractBased on the previous research work, the hydrodynamics of a single drop moving steadily in an infinite immiscible fluid medium is simulated. For the free-boundary problem of a deformable drop, technical difficulty of accurate implementing the boundary conditions was generally encountered in numerical simulation. To overcome this difficulty, the technique of numerical grid generation is used to build the body-fitted orthogonal coordinate system in the domains both inside and outside the liquid drop. The robust strong constraint and weak constraint methods are adopted for this purpose. In such reference frames the Navier-Stokes equations are solved simultaneously with the stream function-vorticity (ψ-ω) formulation. The simulation shows that the Reynolds number is the main factor for the generation of wake behind a liquid drop. The higher the Reynolds number, the larger the size of the wake. The Weber number influences mainly the extent of drop deformation. The drops are deformed from a spherical shape under high We. The ratios of the viscousity and density of the drop and continuous phases play no significant effect both on the wake generation and deformation of the drop. Four parameters (Re、We、λand ζ) jointly decide the shape and wake size of the drop. A bounded-domain distortion function is developed. With this new distortion function the infinite exterior domain around the drop can be transformed into a finite but sufficiently large domain in favor of implementing boundary conditions at the far flow field, so that the precision of numerical simulation can be improved. The mathmatical model of mass transfer between a moving single drop and the continuous phase is established and the concentration field solved numerically. With this first principles-based model and direct numerical simulation, the difficulty of making hypothesis on velocity and concentration profiles in the boundary-layer theory is avoided and the reliable mass transfer coefficient and fraction of extraction are obtained with fairly good accuracy. An experimental setup with a closed-system sample collector is designed to eliminate the terminal effect of drop coalescence on the measurement of mass transfer rate. A series of experiments is conducted in three extraction systems recommended by EFCE. The experimental data are used to check the numerical simulation of mass transfer. Finally, the numerical simulation results are compared with empirical correlations, theoretical models and experimental data. It is demonstrated that numerical simulation can be used to predict the mass transfer coefficient for some systems under the condition Re < 250. Beyond this scope some future revisions must be made to take care of the factors such as unsteady motion, transient drop deformation, interfacial disturbance and so on.
Document Type学位论文
Recommended Citation
GB/T 7714
李天文. 中低雷诺数下稳态运动单液滴传质过程数值模拟及实验验证[D]. 中国科学院研究生院,1998.
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