磁场中离子液体-微气泡多相流体动力学研究

Ionic liquid (IL) regarded as a new absorbent and catalyst has shown remarkable technical advantages and industrial applications. However, there are not many investigations about IL-bubble multiphase fluid dynamics. For the purpose of cognizing the fluid dynamics of microbubbles in IL, the effect of various factors on the growth and motion of microbubbles in IL under the circumstance of magnetic field using a high-speed-resolution camera with magnification function, the response of bubble motion to the intensity and direction of magnetic field, the microbubble size effect and superimposed effect of magnetic field are studied in this project so that we can obtain the universal laws of microbubble motion from the scale of reactors. Based on the experimental conclusions, the fluid dynamics models including magnetic field effect are theoretically established. Then the single bubble’s expansion and detachment, single bubble motion and many bubbles’ motion are simulated using VOF, DPM and TFM model, respectively. The spatial-temporal evolution of fluid structure surrounding microbubbles are studied. The interaction mechanism among magnetic field, IL and microbubbles are revealed from the scale of the infinitesimal fluid. After the experimental and numerical studies, the fluid dynamic characteristic of IL/microbubble under the circumstance of magnetic field will be obtained. The regulatory mechanism of bubble size and gas holdup will be presented as well, which could provide scientific foundations for the design of new bubble column based on IL and magnetic field.

离子液体作为新型吸收剂和催化剂具有显著的技术优势和工业应用前景，但对离子液体-气泡多相流体动力学的研究较少。本课题围绕离子液体中微气泡的流体动力学问题，利用配有放大功能的高速摄像机，实验研究不同因素对离子液体中微气泡生长脱附迁移的影响，重点考察气泡运动对磁场强度和方向的响应行为，探索磁场叠加效应和微气泡尺寸效应，获得反应器尺度上微气泡运动的一般规律。在此基础上理论构建包括磁场作用的多相流体动力学模型，采用VOF、DPM和TFM模型，分别数值模拟单气泡生长脱附、单气泡迁移和多气泡运动行为，深入研究微气泡周围流场结构的时空演变，从流体微元尺度上揭示磁场、离子液体、微气泡间的相互作用机理。通过实验和模拟综合研究，获得磁场环境中离子液体/微气泡多相体系的流体动力学特性，提出气泡大小和气含率的调控机制，为基于离子液体和磁场调控的新型鼓泡塔设计提供科学基础。

离子液体（IL）作为新型吸收剂和催化剂具有显著的技术优势和工业应用前景，但IL 因其自身特殊离子对形式的微观结构，致使气泡运动展现出复杂流体动力学特征，常规数学模型和作用机理难以适用。虽然IL中气泡具有独特的多相流体动力学性质但截至目前专门研究IL 中气泡行为的文献较少，专门研究IL 中CO2 气泡运动行为的文献更少。本项目利用实验和模拟两种手段系统研究了离子液体气液两相流的流体力学性质。首先通过Gaussian量化计算和COSMO分子模拟获得了离子液体摩尔体积和密度的流体物性估算方法及模型，建立了相应的数据库。选定了126种离子液体，对比了其密度的计算值与实验值，偏差小于3.5%，证明了计算方法和模型的优秀预测能力。然后对于单气泡问题，通过VOF模拟建立了适合离子液体/气体体系的多相界面跟踪模型，气泡大小的模拟值与实验值吻合良好，相对偏差均小于10%。再利用物质导数为基础的拉格朗日方法，研究了不同表面力和体积力对气泡形成过程的作用机制，讨论了温度、水含量和气速对流线、涡量、速度、压力和压力梯度的影响规律，获得了气泡在离子液体特殊高粘体系中的形成、脱附以及上升规律。这非常有助于气体分布板的设计优化，为工业应用提供方法和模型支撑。最后，对于多气泡体系，以经典的Schiller-Naumann曳力模型为基础，通过引入修正函数，获得了适合于离子液体体系的欧拉/欧拉双流体模型。表观气速从0.01 m/s到0.07 m/s，气含率模拟值与实验值的相对偏差均在20%以内，且基本在10%左右，满足一般工程需要，可以用于离子液体反应器的数值优化模拟设计，解决了工业反应器模拟所亟需的数学模型问题。