非牛顿流体中气泡形成过程中的流体力学及传质特性

Dispersion of bubbles in a non-Newtonian fluid plays an important role in chemical industry, petrochemical industry, mineral processing, etc. The formation of a bubble and the mass transfer process during the formation stage decide the primitive bubble size, initial mixing and mass transfer condition in the system, which contribute significantly to the interfacial transport phenomena. Previous experiments and theoretical analysis based on force balance and dimensional analysis couldn't present the detailed hydrodynamics characteristics and mass transfer mechanism. In this project, the unsteady mass transfer during bubble formation in a non-Newtonian fluid will be formulated and numerically simulated by solving the flow and mass transfer equations coupled with a level set equation for capturing the interface. Combining numerical simulation and experimental approach, we will examine the effect of flow direction of the continuous phase, ratio of flow rate between gas and liquid, orifice diameter, non-Newtonian solution concentration on the hydrodynamics and mass transfer during bubble formation, and have an insight into the variation of bubble shape and size as well as the mass transfer mechanism during bubble formation. Hereafter, we expect the results of this project provide theoretical basis and reference for the development, design and optimization of gas-liquid contact equipments.

气-液非牛顿流体体系普遍存在于化工、石化和冶金等领域中，气泡的良好分散对于提高气液传递性能具有重要的作用。气泡的形成过程及该阶段的传质决定了气泡的初始大小、气液混合及传质的初始条件，在气液传质过程中占首要地位。以往的实验和理论分析难以揭示气泡形成过程中微观的流体力学特性和传质机理。本项目拟建立气泡形成过程中传质的数值模拟方法，通过数值模拟和实验相结合的手段，研究连续相的流向、气液流速比、孔口直径和安装方向、非牛顿流体浓度对气泡形成过程和形成阶段传质的影响规律，以明确外部操作条件和非牛顿流体的流变性对气泡生成过程的流体力学特性的影响，进而阐明气泡的形状和体积的变化机理，提供生成的初始气泡的流体力学特征和相应的传质速率的预测计算方法，为气液接触设备的开发、设计及优化提供理论依据和重要参考。

气泡的形成过程及该阶段的传质决定了气/液两相流动和传质的初始状态。本项目针对非牛顿流体中气泡生成动力学及传质研究的缺乏，在非牛顿流体中变体积气泡的数值模拟、气泡生成及传质的实验测试、气泡生成流体力学特性与传质规律方面取得了较大进展，具体如下：.(1) 发展了非牛顿流体中变体积气泡传质的数值模拟方法。针对数值模拟方法中气泡体积损失的问题，以level-set方法捕捉界面，在质量校正方法中同时考虑气泡溶解和气体流入的影响；建立了非牛顿流体中变体积气泡传质的数值模拟方法，采用semi-Lagrangian格式描述界面区的传质提高了传质计算的准确性。对于变体积气泡的数值模拟结果与文献及实验符合较好。.(2) 搭建了非牛顿流体中气泡形成过程中气液传质测试的实验装置，实现静止及运动连续相中气泡生成过程动态变化及传质的测试。显微摄相机拍摄气泡瞬时形状，根据气泡体积变化计算传质系数，粒子示踪流速仪获得实时流场，可耦合测试气泡生成动态变化及传质特性。.(3) 通过数值模拟和实验相结合，研究了连续相流向、气液流速比、孔口直径和安装方向、非牛顿流体浓度对气泡形成过程和传质的影响，获得了流体力学特性对传质的影响规律，建立了传质系数与反应器结构的定量关系，为气/液传质设备的科学设计提供依据。