Coalescence filters are commonly used to separate oil droplets from air streams. Nonwoven glass fiber filter media are used for applications where high efficiencies are required, for instance for compressed air preparation. The relevant mechanisms in oil mist filtration and their impact on operational behavior of the filters have received increasing attention in research over the last few years and are qualitatively well understood so far. However, the relationship between structural properties of filter media and the operating performance of coalescence filters is relatively unknown and therefore filter media are commonly chosen based on empirical values depending on the application. In this work filtration relevant media properties are described and their qualitative impact on operating performance analyzed.
To find causal relationships between media pore and fiber size distribution and fiber orientation and operating performance of the filters, various custom made nonwoven glass fiber filter media were characterized using x-ray microtomography and capillary flow porometry. These methods were evaluated regarding their suitability in identifying structural and surface properties. The qualitative impact of these properties on oil deposition and transport mechanisms in the media and therefore on the operation performance was estimated. Filtration tests were carried out to evaluate these approaches by measuring filter efficiencies and differential pressure and their respective changes during filtration.
Recent data obtained in the experiments will be presented, evaluated and discussed.