Evaluation of electrostatic properties of electret filters for aerosol deposition

Kerner, Max; Schmidt, K.; Schumacher, Stefan; Puderbach, Vanessa; Asbach, Christof; Antonyuk, Sergiy

doi:10.1016/j.seppur.2020.116548

Cited by 42 publications

(30 citation statements)

References 25 publications

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“…The resulting filtration efficiencies at a flow velocity of 0.08 m•s −1 basically show the same shape for the filter media, but on a lower level. In our previous work [13], it was already found that both electrostatic and mechanical deposition are reduced with increasing velocity. Correspondingly, the above determined dependence on the discharging method is almost negligible.…”

Section: Resultsmentioning

confidence: 82%

“…However, it is also known that the initially high filtration efficiencies of these new electret filters can decrease significantly over operating time due to exposure to particles [7,[10][11][12][13][14][15], organic solvents [16,17], or high temperatures and/or humidity [18,19]. During this filter ageing process, the original charge decays and the filter becomes less effective in filtering particles.…”

Section: Introductionmentioning

confidence: 99%

“…3D simulations are suitable for this purpose, since the variation of parameters can be time-optimized and the micro mechanisms can be investigated in detail. In the case of electret filters, various simulation setups have recently been presented to investigate the filtration efficiency [9,13,[29][30][31][32].…”

Section: Introductionmentioning

confidence: 99%

“…Compared to the approach used from Rief [31] and Schober [32], less assumptions are required for the boundary conditions. This approach was already validated for the initial filtration efficiency at different operating conditions [13] and then extended to the abovementioned effect of filter ageing due to particle deposition [29]. The aim of this work is, therefore, also to estimate potential parameters for electret filter optimization, with respect to the charge and charge decay, by a numerical study of the particle deposition.…”

Section: Introductionmentioning

confidence: 99%

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Electret Filters—From the Influence of Discharging Methods to Optimization Potential

Kerner

Schmidt²,

Schumacher

et al. 2021

Atmosphere

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Electret filters are electrostatically charged nonwovens which are commonly used in aerosol filtration to remove fine particles from gases. It is known that the charge and thus also the filtration efficiency can degrade over time. Thus, many testing standards require to remove the charge by treatment with liquid isopropanol (IPA) or IPA-saturated air. However, the parameters influencing this discharge have not been completely clarified yet. The aim of this work was, on the one hand, to experimentally investigate the influence of the IPA treatment on different electret filters and, on the other hand, to show the optimization potential of electret filters with respect to efficiency and long-term stability by numerical simulations. The experiments revealed that the air permeability is a central influencing parameter. Small pores lead to a reduced discharge efficiency using liquid IPA, while both treatment methods are suitable for larger pores. The simulations showed that a homogeneous charge distribution within the filter depth is advantageous for the initial performance. In contrast, charge penetrating deeper in the filter medium delays the charge decay and thus increases the operating time, with the trade-off of a lower initial performance.

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Section: Resultsmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electret Filters—From the Influence of Discharging Methods to Optimization Potential

Kerner

Schmidt²,

Schumacher

et al. 2021

Atmosphere

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“…The corona charge process makes the charged ions deposited on the electret material to form surface charges [31] and trapped inside the material to form space charges [32,33]. The space charge in melt-blown PP electret air purification material mainly comes from the capture of interface traps [34].…”

Section: Relationship Between the Filtration Performance And The Heatmentioning

confidence: 99%

The Effect of Temperature and Humidity on the Filtration Performance of Electret Melt-Blown Nonwovens

Liu

Dai

et al. 2020

Materials

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Electret melt-blown nonwovens are widely used for air purification due to their low pressure drop and high filtration efficiency. However, the charge stability could be affected by the ambient temperature and humidity, reducing the filtration efficiency, resulting in the electret melt blown filter not providing effective protection. Herein, we used corona charge to prepare electret melt-blown nonwovens and systematically studied the effects of different temperature and humidity on the structure, morphology, filtration performance, and surface potential within 24 h. The effect of treatment temperature and humidity on pressure drop was minimal because the fiber morphology and web structure of melt-blown nonwovens were not damaged. When the treatment temperature was lower than 70 °C, the effect on the filtration efficiency of the sample was small, but when the temperature increased to 90 or 110 °C, the filtration efficiency decreased significantly with the increase of the treatment time, and the surface potential also declined similarly. In conclusion, high temperatures will lead to charge escape and reduce the electrostatic adsorption effect. Furthermore, at the same temperature, increasing relative humidity can accelerate the charge release and make the filtration efficiency drop more. After the sample was treated at 110 °C and 90% relative humidity for 24 h, the filtration efficiency decreased from 95.49% to 38.16% at a flow rate of 14.16 cm s−1, and the surface potential dropped to the lowest value of −1.01 kV. This result shows that all links of electret melt-blown filter material from raw material to final use should be avoided in high temperature and high humidity conditions to ensure the protection effect.

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Improvement of Air Filtration Performance Using Nanofibrous Membranes with a Periodic Variation in Packing Density

Liu

Shao

Wang

et al. 2021

Adv Materials Inter

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particulate matter (particle size > 10 µm), inhalable particulate matter (particle size < 10 µm), and fine particulate matter (PM 2.5 , equivalent diameter < 2.5 µm). [1] PM 2.5 particles are particularly harmful because they can be inhaled into the lungs and even enter the blood circulatory system, causing health issues. [2] PM 2.5 particles are also a good carrier of bacteria and viruses, resulting in the transmission of diseases, such as COVID-19. [3] Filtration with a filter is an effective method to remove these harmful particles and prevent the diseases from spreading.The removal mechanism of fibrous filters for these tiny particles mainly includes inertial collision, [4,5] direct interception, [6] diffusion effect, [7] gravity sedimentation, [8] and electrostatic attraction. [9] Nanofibrous filters have outstanding filtration efficiency due to the fine fiber diameters and high specific surface areas. [10] In addition, nanofibers have lower pressure drop due to the "slip effect" of their unique fiber diameter size, similar to the mean air molecule free path, reducing the airflow resistance. [11] Hence, nanofibers are widely used in air filtration, especially in air filters, [12][13][14] ventilating and air conditioning filters, [15] and masks. [16] Xia et al. [17] compared 122 nanofibrous filters with conventional heating, ventilation, and air-conditioning (HVAC) filters and showed that nanofiber filters had a higher quality factor than the conventional filters because of nanofibers' "slip effect."Considerable research has been devoted to understanding the structural parameters of nanofibers and their effect on filtration performance. For example, Wang et al. [18] studied the influence of nanofiber morphology on filtration performance. Zhang et al. [19] reported a pore size gradient combination of different nanofibrous membranes, which showed a filtration efficiency of 99.992% for 300 nm particles at a low-pressure drop. Li et al. [20] proposed a mathematical relationship between filtration efficiency and nanofibrous pore size. Bian et al. [21] established a semiempirical model to predict the influence of nanofiber diameter, membrane thickness, and packing density on the pressure drop of nanofibrous filters. Most studies have been based on nanofiber membranes with a homogenous distribution of nanofibers along the membrane.This study reports a patterned nanofibrous membrane and its novel filtration performance. The nanofibers are prepared using an electrospinning technique, and the nanofibers are collected on a commercial nonwoven fabric covering a roller collector, which is prepared using a metal sheet with a round hole array. The nanofibers collected on the metal surface have a much denser structure than those in the hole areas. As a result, the patterned nanofibrous membrane has a different filtration performance (lower pressure drop and filtration efficiency) from the uniform nanofiber membrane, prepared under the same condition but using a smooth roller collector. When two layers of this patterned nanof...

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Evaluation of electrostatic properties of electret filters for aerosol deposition

Cited by 42 publications

References 25 publications

Electret Filters—From the Influence of Discharging Methods to Optimization Potential

Electret Filters—From the Influence of Discharging Methods to Optimization Potential

The Effect of Temperature and Humidity on the Filtration Performance of Electret Melt-Blown Nonwovens

Improvement of Air Filtration Performance Using Nanofibrous Membranes with a Periodic Variation in Packing Density

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