Dynamic tracking of structures in multiphase flows by ultrafast X-ray tomography and image based scanning steering

超快成像技术是分析多相流等高动态过程不可缺少的工具。后者以多种方式出现在许多技术过程中，例如在化学多相反应器中。使用数值计算格式(CFD)对多相流进行建模特别困难，因为要考虑冲量、热和质量传递的多种物理效应以及问题的多尺度。为了开发和验证多相流数值计算模型，时间和空间高分辨率测量技术是必不可少的，例如由申请人共同开发的超快X射线层析成像系统(ROFEX)。例如，鼓泡塔的尺寸很大程度上依赖于对液体和气相停留时间行为的了解。然而，关于鼓泡塔内单个气泡的跟踪研究很少，而且主要局限于气体分数较低的鼓泡塔，单个气泡不受蜂群效应的影响。利用在线测量技术同时测量真实气泡柱内的气泡结构、气泡运动和周围相分布，将有助于流体力学研究确定气泡群中的上述参数。因此，该项目的目的是推进超快X射线层析成像技术在两相流中跟踪气泡的发展。其原理是基于快速图像导向的摄影平面定位。因此，可以跟踪气泡穿过流动区域的整个过程。在它们通过的过程中，可以观察到结构的变化以及与其他气泡的相互作用(科尔斯效应、碎裂和碰撞)。此外，可以记录成像平面内的完整流动结构。为了实现动态实验，有效的测量、分析和控制技术是必不可少的。它们应该是通过与A.Kopmann(KIT)小组的跨学科合作获得的，该小组在大数据量的在线数据采集、3D图像重建和基于图像的控制方面拥有成熟的专业知识。在此基础上，应在Rofex系统上设计、开发和实施基于GPU的图像重建和图像分析算法，并结合快速数据传输解决方案。具体目标是证明在气泡塔内跟踪单个气泡群的气泡的可行性。主要的挑战在于验证数据传输的实时能力和整个数据分析链。

Ultrafast imaging techniques are indispensable tools for the analysis of highly dynamic processes such as multiphase flows. The latter occur in many technical processes, e.g. in chemical multiphase reactors, in manifold ways. Modelling of multiphase flows using numerical calculation schemes (CFD) is especially demanding because of the multitude of physical effects to be considered for impulse, heat and mass transfer along with the multiple scales of the problem. For the development and validation of models for the numerical calculation of multiphase flows temporal and spatial highresolution measurement techniques, such as the ultrafast X-ray tomography system (ROFEX), which was co-developed by the applicant, are essential. The dimensioning of bubble columns, for example, relies significantly on the knowledge about the residence time behavior of the liquid as well as the gaseous phase. However, there are only few studies on the tracking of single bubbles in bubble columns, which are furthermore mainly limited to bubble columns with low gas fractions, where the single bubbles are not affected by swarm effects. Fluid mechanic investigations for determining the above mentioned parameters within a bubble swarm would strongly benefit from an online measurement technique for simultaneous measurement of bubble structure, bubble movement and surrounding phase distribution within realistic bubble columns.Therefore, the aim of the project is the advancement of the ultrafast X-ray tomography for tracking bubbles in a two-phase flow. The principle is based on a fast image steered positioning of the to-mography plane. Thus, gas bubbles can be tracked throughout their way through the flow region. During their passage, structural changes as well as interactions with other gas bubbles (coales-cence, fragmentation, and collision) can be observed. Furthermore, the complete flow structure within the imaging plane can be recorded. For the realization of dynamic experiments, efficient measurement, analysis and controlling techniques are essential. They are supposed to be obtained by interdisciplinary cooperation with the group of A. Kopmann (KIT), which possesses proved expertise in online data acquisition of large data amounts, 3D image reconstruction and image based controlling. Based on this knowledge, GPU based image reconstruction and image analysis algorithms in combination with a fast data transfer solution should be designed, developed and implemented at the ROFEX system. Concrete aim is the demonstration of the feasibility of tracking a single bubble of a bubble swarm within a bubble column. The main challenge lies in the verification of the realtime capability of data transfer and the whole data analysis chain.