Identification of Deposited Oil Structures on Thin Porous Oil Mist Filter Media Applying µ-CT Imaging Technique

Christian Straube,Achim Dittler,Jörg Meyer

doi:10.3390/separations8100193

Abstract

The identification of microscale oil structures formed from deposited oil droplets on the filter front face of a coalescence filter medium is essential to understand the initial state of the coalescence filtration process. Using µ-CT imaging and a deep learning tool for segmentation, this work presents a novel approach to visualize and identify deposited oil structures as oil droplets on fibers or oil sails between adjacent fibers of different sizes, shapes and orientations. Furthermore, the local and global porosity, saturation and fiber ratios of different fiber material of the oleophilic filter medium was compared and evaluated. Especially the local and global porosity of the filter material showed great accordance. Local and global saturation as well as the fiber ratios on local and global scale had noticeable differences which can mainly be attributed to the small field of view of the µ-CT scan (350 µm on 250 µm) or the minimal resolution of approximately 1 µm. Finally, fiber diameters of the investigated filter material were analyzed, showing a good agreement with the manufacturer’s specifications. The analytical approach to visualize and analyze the deposited oil structures was the main emphasis of this work.

Highlights

Submicron airborne oil droplets, so-called oil-mists, often occur in industrial applications as an undesired by-product, e.g., in cutting operations, crankcase ventilation or compressed gas cleaning [1]
The identification of microscale oil structures formed from deposited oil droplets on the filter front face of a coalescence filter medium is essential to understand the initial state of the coalescence filtration process
In this study, deposited oil structures on the scale of only a few micrometers on a thin porous filter material were imaged for the first time using X-ray micro tomography

Summary

Introduction

-called oil-mists, often occur in industrial applications as an undesired by-product, e.g., in cutting operations, crankcase ventilation or compressed gas cleaning [1]. The mechanisms of droplet deposition and liquid transport in the filter on the meso scale and the evolution of the pressure drop have been investigated in several publications in the past and are well described by the “Jump and Channel Model” by Kampa et al [3]. A key finding here is that filter medium is saturated in such a way that the necessary pressure drop for oil transport is built up to a level, where the resulting oil transport rate equals the loading rate of the filter In accordance with this model, arriving airborne oil droplets deposit on the first fiber layers of the filter medium and start to coalesce to form bigger droplets on the fibers. Depending on the wettability of the filter material, the formation of a thin oil film at the filter front face (non-wettable) or the filter back face (wettable) is observed [3,4,5]

Methods

Results

Conclusion