A novel method to investigate detachment of particulate structures from an elastic single fiber at low gas flow velocities
L. Poggemann, J. Meyer, A. Dittler
Journal of Aerosol Science, 2021, 156, 105785, https://doi.org/10.1016/j.jaerosci.2021.105785 (open access)
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 ma- terial. 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 main- taining a high level of separation efficiency at operational filtration velocities.