R. Mandic, J. Meyer, A. Dittler

Separation and Purification Technology, 2024, 130274, https://doi.org/10.1016/j.seppur.2024.130274 (open access)

Coalescence filters are highly effective for separating sub-micron oil mist particles from gas streams. In the past, the development of these filters has focused on understanding the propagation of oil within the filter and investigating the operational parameters and material properties of the coalescing material. This review examines studies on oil mist filtration, with a particular emphasis on drainage and entrainment processes. The analysis of single fiber-droplet interactions provides essential insights into droplet motion and detachment dynamics within fiber-liquid systems, considering forces such as gravity, drag, surface tension, and inertia, as well as factors like wettability and fiber orientation. The drainage behavior is regarded through internal and rear-side drainage mechanisms in porous material. Internal drainage mechanisms are examined by analyzing material properties and operational settings to understand the underlying processes. This includes examining internal pathways and flow dynamics within porous structures or composite materials. Rear-side drainage mechanisms are assessed by evaluating drainage on larger surfaces of porous material, focusing on the interaction between the liquid and the material system. Key factors include the thickness and distribution of the liquid film, the drainage rate influenced by saturation levels, and the impact of support structures and drainage layers. Entrainment mechanisms are considered based on factors influencing how droplets become entrained, emphasizing three primary mechanisms: gas flow over liquid surfaces, droplet detachment from fibers, and bubble bursting. This includes describing the forces and conditions affecting droplet and bubble dynamics. The entrainment in oil mist filtration investigations is characterized as well as the methods for measuring a wide range of entrained droplet sizes, including in-situ and offline techniques. This comprehensive review aims to compare various examination methods and their findings while identifying unresolved research questions in the field of oil mist filtration.