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

• Applicants: Dr. Lars Büttner; Dr. Gregory Lecrivain, Ph.D.
• Subject Area: Fluid Mechanics ; Measurement Systems
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 459505672

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.

• DFG Programme: Research Grants
• Co-Investigators: Professor Dr.-Ing. Jürgen W. Czarske; Professor Dr.-Ing. Uwe Hampel