Numerical and experimental investigation of filtration, coalescence and transport behavior in liquid-gas separation with special reference to mechanical vibration excitation

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Coalescing filters are well-established elements used for droplet separation. The mechanisms and their dependence on operating parameters, material parameters and other factors, such as the geometric arrangement of the filter elements, lead to complex interrelationships that must be considered in the design of a coalescing filter with respect to overall separation efficiency and pressure drop.In past and current research projects, some influences on the separation behavior of such filters could already be investigated. In particular, the working group Gas-Partikel-Systeme at the Karlsruhe Institute of Technology investigated various aspects of operating conditions, structural properties of the medium (wettability, media thickness, porosities, porosity distributions) in oil mist filtration. As with this work, in the literature filter elements have always been considered as a static element. However, from mechanisms already observed, it is clear that vibration can significantly influence the mechanisms or process steps of filtration. The filtration of droplets from the gas phase is divided into several process steps. These include the impact of the droplets on the fiber, the formation of fluid films, and the draining or detachment of the droplets along the filter element. In the process of draining, the liquid phase is transported along the filter element, and in the process of detaching, re-entrainment into the gas phase takes place. The present application aims to systematically investigate the effects of (periodically) excited filter elements on the separation of droplets, their coalescence behavior as well as detachment behavior starting from the micro level. Numerical and experimental investigations will be combined. Starting with the observation of a single droplet on a vibrating single fiber, the investigations will be extended to two interacting droplets and a mist-generated droplet chain on a vibrating single fiber.The aim of the studies is to describe the motion behavior of a droplet and the associated run-off/detachment behavior under different excitations, fiber properties and droplet sizes. In addition, the same studies are extended under the aspect of coalescence of two or more droplets.Findings on excited coalescing filters can make a significant contribution to the optimization of pressure drop characteristics and separation behavior. For this purpose, the extension to the meso and macro level is planned in a second project phase.