Investigation of the of aerosol particle transport into liquids using an adaptive-optical measurement technique for highly-dynamic fluidic interfaces

通过移动的气液流体界面分离气溶胶颗粒是各种工业和自然应用的核心，其中突出的应用包括空气净化系统和降水清除。颗粒大小对分离率有显著影响。纳米范围内粒子的扩散主要以分子扩散为主。在这种情况下，预测模型可以准确地估计分离率。然而，当颗粒尺寸在0.1~2.5µm之间时，模型的不准确性显著增加。在这种撞击为主的区域，流体界面两侧的流动动力学和颗粒惯性之间的复杂相互作用使得开发合适的模型变得困难。最新的分离模型通常假设流体界面为球形(无论是浸没的气泡还是空气中的水滴)，从而使得模拟流体-颗粒相互作用变得相对容易。然而，这些模型不能解释由持续吸附的气溶胶引起的流体表面张力的局部变化，以及流体界面的快速变形以及相关的气液流动变化。只有在能够测量流体界面两侧的流动的情况下，才能在气溶胶分离方面取得进一步的进展。尽管测量技术不断进步，但光学测量仍然具有挑战性，因为波动的流体界面上的光折射会导致像差和严重的测量误差。为了克服这一缺点，首次提出了一种具有实时图像校正算法的自适应光学系统。在本项目中，一种包括用于像差校正的可变形膜镜的三维粒子跟踪系统将消除由于流体界面起伏引起的测量误差，该测量系统将用于测量毛细水通道中上升的气泡和暴露在湍流气流中的水滴在流体界面两侧的流动。流型将与实验和数值测量的气溶胶分离率相关联。特别是，将研究将气泡变形为非球形是否会导致更高的沉积速率，从而使颗粒分离过程更有效。这一结果将导致开发一种改进的、可靠的分离模型，该模型考虑了流体界面的变形和相关的流动变化。从长远来看，这些发现有助于开发便携式和可重复使用的无过滤分离设备，例如，可以用于有效地从废气中分离病毒或有毒颗粒。

The separation of aerosol particles by a moving gas-liquid fluidic interface is central to a wide variety of industrial and natural applications, among which stand out air purification systems and precipitation scavenging. The particle size significantly affects the separation rate. The diffusion of particles in the nanometer range is largely dominated by molecular diffusion. In this regime, predictive models accurately estimate the separation rates. Model inaccuracy increases, however, significantly when the particle size ranges from 0.1 µm to 2.5 µm. In this impaction-dominated regime, the complex interplay between the flow dynamics on both sides of the fluidic interface and the particle inertia makes it difficult to develop suitable models.State-of-the-art separation models generally assume a spherical shape of the fluidic interface (be it an immersed gas bubble or a water droplet in air), thereby making it relatively easy to simulate the fluid–particle interactions. Such models fail however to account for the local change in the fluidic surface tension caused by the continuously adsorbing aerosols and the rapid deformations of the fluidic interface along with the associated change in the gas/liquid flow. Further advances in aerosol separation can only be achieved if the flow on both sides of the fluidic interface can be measured. Despite the continuous advancement of measurement techniques, optical measurements are still challenging since the light refraction off the fluctuating fluidic interface cause aberrations and severe measurement errors. To overcome this shortcoming, an adaptive optical system equipped with a real-time image correction algorithm is suggested for the first time. In this project, a three-dimensional particle tracking system comprising a deformable membrane mirror for aberration correction will eliminate the measurement errors attributed to the fluctuating fluidic interface.This measurement system will be deployed to measure the flow on both sides of the fluidic interface of a gas bubble rising in a capillary waterchannel and of a water drop exposed to a turbulent airflow. The flow patterns will be correlated with the aerosol separation rates measured both experimentally and numerically. In particular, it will be investigated whether enforcing the bubble deformation into a non-spherical shape leads to a higher deposition rate, thereby making the particle separation process more efficient. The results will lead to the development of an improved and reliable separation model accounting for the deformation of the fluidic interface and the associated flow changes. In the longer run, the findings can contribute to development of portable and re-usable filterless separation devices, which can for instance be used to efficiently separate virus or toxic particles from flue gases.