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2023
Conference Paper
Title
Influence of material compression on the mechanical and electrostatic capturing efficiency of filter media
Abstract
One of the main design goals for filter media is a high separation performance while the pressure drop is low. During manufacturing processes such as the pleating of the filter media or during operation, the nonwoven material is locally compacted which is of importance for the above-mentioned quality characteristics. The compaction leads to a local increase of the fiber volume fraction and therefore, to a non-uniform distribution of flow resistance and filtration performance.
In this work, the influence of compression on the performance of flat filter media is examined by experiments, both for “classical” materials, for which the deposition is only based on mechanical phenomena, and electret media. To this end, an electrostatic charged media made of 100 % polypropylene (PP) is investigated. After the characterization of the media by the thickness, basis weight and airflow for a given pressure drop, properties like the solid volume fraction and flow resistivity can be deduced.
For the present media, compression levels up to 27 % are achieved using cyclic deformation. In order to avoid effects due to material relaxation, the thickness of the compacted media samples is measured over time until a steady state is reached.
Measurements of the fractional efficiency are carried out with the prepared samples under variation of the flow speed. In the case of electret media, the samples are discharged by isopropyl alcohol (IPA) treatment and the fractional efficiencies are measured again. This allows for studying the impact of the material compaction on the electrostatic contribution to the efficiency, too. The test dust used for all measurements consists of airborne sodium chloride particles with diameters ranging between 15 nm and 460 nm.
The experimental data obtained allow for a prediction of the change in filter performance with respect to deformation. In addition, the data are the basis for deposition models that consider local effects such as the degree of material compression, flow speed and deposition.
In this work, the influence of compression on the performance of flat filter media is examined by experiments, both for “classical” materials, for which the deposition is only based on mechanical phenomena, and electret media. To this end, an electrostatic charged media made of 100 % polypropylene (PP) is investigated. After the characterization of the media by the thickness, basis weight and airflow for a given pressure drop, properties like the solid volume fraction and flow resistivity can be deduced.
For the present media, compression levels up to 27 % are achieved using cyclic deformation. In order to avoid effects due to material relaxation, the thickness of the compacted media samples is measured over time until a steady state is reached.
Measurements of the fractional efficiency are carried out with the prepared samples under variation of the flow speed. In the case of electret media, the samples are discharged by isopropyl alcohol (IPA) treatment and the fractional efficiencies are measured again. This allows for studying the impact of the material compaction on the electrostatic contribution to the efficiency, too. The test dust used for all measurements consists of airborne sodium chloride particles with diameters ranging between 15 nm and 460 nm.
The experimental data obtained allow for a prediction of the change in filter performance with respect to deformation. In addition, the data are the basis for deposition models that consider local effects such as the degree of material compression, flow speed and deposition.
Author(s)