高温高压鼓泡塔中气泡群运动的实验观察与数学模拟

Bubble clustering is a heterogeneous and unstable meso-structure with the scale between single bubble and reactor. Drag force and rising velocity of the bubble cluster are quite different from those of single bubble, and difficult to be estimated. The uncertainties remarkably influence the reliability of present two phase hydrodynamic models. In addition, though industrial gas-liquid reactors are generally operated at high temperature and high pressure conditions with complex physical properties of the materials, there is a lack of experimental evidences concerning bubble motion under such severe conditions. In this project a novel mini bubble column of high temperature and high pressure with bubble visualization windows will be developed, to observe the bubble distribution and motion states at various conditions, and to detect morphological parameters and drag coefficient of the bubble or bubble cluster. Direct numerical simulation (DNS) on the meso-scale flow around bubbles will be carried out to get insight into cluster forming and flow mechanism. The obtained new bubble drag coefficient will be adopted in a novel two phase flow model to simulate the flow pattern and scale up effect of the gas-liquid reactor operated at high temperature and pressure.

气泡团聚现象（bubble clustering）是鼓泡塔中的一种非均匀不稳定的介尺度结构，气泡团的曳力和浮升速度与单个气泡有很大差别，同时也很难估算，其不确定性对两相流模型的可靠性有很大影响。特别是，工业气液反应器一般都在高温高压和复杂物系条件下操作，而目前还缺乏这种苛刻条件下的气泡实验证据。本项目拟建立一个小型高温高压气泡可视化的实验装置，观察各种条件下鼓泡塔中的气泡分布与运动状态，测定气泡或气泡团结构参数与曳力系数，进行介尺度流动的直接数值模拟以探讨气泡团的形成与流动机理，采用新的气泡曳力参数进行高温高压气液反应器的流体力学放大模拟。

气泡聚团是鼓泡塔中的一种非均匀不稳定的介尺度结构，其不确定性对两相流模型的可靠性有很大影响。本项目针对气泡团聚现象（bubble clustering）进行实验观察与数学模拟。实验观察各种条件下鼓泡塔中的气泡分布与运动状态，测定气泡或气泡团结构参数与浮升速度，进行介尺度流动的直接数值模拟确定气泡曳力参数，进行高温高压气液反应器的流体力学放大模拟。课题实施以来，开展并完成了三个方面的工作，取得了新的成果：1.设计加工了一套可用于高温高压及各种物系下的气液鼓泡塔可视化小型实验装置，带有高压视窗和高速摄影机和自编的图像处理程序软件，这是本项目有特色的一项实验技术，可用于250oC、6MPa下各种物系的气泡运动观察与拍摄。2.拍摄了数千幅图片和近百段视频，首次直观地拍摄到高温（100-250oC）、高压（0.1-6.0MP）下各种模拟体系（水、硅油、十四烷、石蜡油、空气、氦气、氮气）的气液两相流动图案，观察到特定流变性质（非牛顿流体）下的气泡聚集现象，观察到高气速下的气泡聚并-分散现象。3. 进行了气泡和气泡团绕流的数值模拟，模拟的气泡结构、大小、形状、气泡浮升速度与实验结果一致，所获得的曳力模型应用于大型鼓泡塔的两相流体力学放大模拟。基本上完成了计划内容。