Experimental Detection of Particle Structures Detachment from a Stretchable Single Fiber during Multiple Consecutive Stretching Cycles

The deposited particulate material within a fibrous filter affects the pressure drop which develops through three different stages. The implementation of a time-adjustable matrix is intended to cause detachment of particle structures from fibers within the upstream layers at low flow velocities. The deposited particle structures are transported further within the filter and clear up void space for an extension of filter service life. As in previous studies observed fiber stretching initiate cracks and following detachment of particle structures with a simultaneously applied airflow. For complete detachment of the particle structure, five consecutive stretching cycles are performed in this study. The elongation velocity, the flow velocity and the particle loading are varied. Using an image analysis technique and a laser-light measurement technique simultaneously, the cumulative fraction of detached particle structures and the size of detached particle structures are determined. A high initial particle loading on the fiber induces early detachment of larger structures from the fiber. The size of detached structures is increased by the increase of the elongation velocity. The mean value remains almost constant whether the elongation velocity or superficial velocity are increased. For small initial structures on the fiber, a decrease in superficial velocity causes detachment of larger particle fragments

A novel method to investigate detachment of particulate structures from an elastic single fiber at low gas flow velocities

The detachment of particle structures from a stiff single fiber exposed to an airflow has been investigated by (Jankowska et al., 2000; Larsen, 1958; Löffler, 1972; Przekop et al., 2004; Qian et al., 1997; Zoller et al., 2020). In order to detach particle piles from a stiff single fiber, airflow velocities above 1.2 m/s are required. While these values are well above typical operational parameter for depth filters, a shift toward lower velocities for detachment would offer both up-and downside for filter operation. One possible application for controlled structure detachment from a filter fiber at lower velocities would be a shift of separated particulate structures from the upper layers of depth filter into lower regions. The result would be additional void space from particle deposition. Currently there is no knowledge available, if fiber stretching could enable such detachment of particle structure fragments at an operation airflow velocity below 1 m/s. It is assumed that fiber stretching might introduce shear and tensile stress to the particulate structures. That may lead to first cracks and promote final detachment. This study examines the behavior of particle structure fragments on an elastic single fiber for the first time. The fiber is loaded with a compact particle structure in a loading chamber. Glass spheres served as inert particulate material. A new customized fiber-mounting device was designed for the stretching procedure of 22 mm (55%) length. In first experiments, the fiber was stretched without an airflow. Stretching at an elongation rate of 0.4 mm/s caused re-arrangement, crack formation and rotation of the fiber. No detachment of particle structure fragments is observed. If the fiber is stretched and exposed to an airflow at 0.8 m/s, particles structure fragments re-arranged and subsequently detached. In further experiments at an elongation rate of 1.2 mm/s, intensive detachment is observed at an increase of superficial airflow velocity from 0.4 m/s to 0.8 m/s. In total, this reveals that fiber stretching enables detachment of particle structure fragments from a single fiber exposed to an airflow at superficial velocities below 1 m/s. The potential application of elastic fibers in a filter system will have the aim to delay increasing filter backpressure. This effect could be caused by the transport of particulate matter towards areas of lower loading further downstream while maintaining a high level of separation efficiency at operational filtration velocities

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

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