Fundamental Expansion of the Jump & Channel Model for Predicting Droplet Separation in Coalescence Filters

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Gas-carried, submicron oil droplets (so called oil mists) usually occur as an undesirable by product, for instance in oil-lubricated screw compressors. For various reasons (environmental legislation, long-term maintenance of components), solutions are being developed to reduce these oil emissions. A common and efficient method to separate these droplets from the gas flow is the use of coalesce filters made of micro glass fiber. Regarding wettable filter media, most of the arriving airborne oil droplets are separated on the first fiber layers of the first filter layer, the coalescence region. There, as oil loading increases, the coalescence of small droplets into larger structures occurs, until oil channels in the millimeter range were formed. The resulting channels transport the oil in the direction of the airflow. This applies to both oleophilic and oleophobic media. At a sufficiently high oil loading, an oil film forms on the filter upstream or downstream side (depending on the wetting properties of the media). The main emphasis of this proposal is to fundamentally clarify the contributions of different regions (coalescence, channel, and film regions) of a coalescence filter to the overall penetration for an increased oil loading. Structural parameters of the filter, such as fiber diameter and wettability, as well as operational parameters like filter face velocity, will be varied. By manufacturing filter materials ourselves, these regions can be studied separately and their contributions to overall penetration can be quantified. At the end of the project, a theoretical model describing the penetration contributions of the coalescence region (for oleophilic media), as well as the film and channel regions, will be available as a function of filter face velocity, saturation, two selected fiber diameters, and for wettable and non-wettable filter media.