Oleophilic and oleophobic media combinations – Influence on oil mist filter operating performance

Abstract

For the filtration of fine mists, glass fiber nonwovens are commonly used as filter media, especially in high efficiency applications. For the filters, several layers of these media are usually wrapped around a cylindrical grid; often several types of media are combined to reduce pressure drop and entrainment and improve separation efficiency. The media in use typically differ in their structural and wetting properties. The media configuration, i.e., the sequence of individual media layers in the filters, is generally chosen based on empirical values.In this work, experimental studies with several configurations of filter media were carried out, investigating the operating behavior of the filters. Four media of different structure, two oleophilic and two oleophobic each were combined to determine combinations with beneficial operating properties. It was found that using media with coarse pore structure on the upstream side of the filters could significantly reduce pressure drop, while separation efficiency was slightly improved or hardly affected by the sequence of media. The reason for this improvement was found to be the impact of media sequence on liquid transport mechanisms in the filter media. Two mechanisms were identified to be responsible for the improvement of operating behavior: a.) The propagation of channels from coarse media into subsequent fine layers and therefore adaption of different channel structures and b.) The avoidance of a complete liquid film on the face of fine filter media.